Luminous Fast Blue Optical Transients (LFBOTs) - the prototypical example being AT 2018cow - are a rare class of events
whose origins are poorly understood. They are characterised by rapid evolution, featureless blue spectra at early times, and
luminous X-ray and radio emission. LFBOTs thus far have been found exclusively at small projected offsets from star-forming
host galaxies. We present Hubble Space Telescope, Gemini, Chandra and Very Large Array observations of a new LFBOT,
AT 2023fhn. The Hubble Space Telescope data reveal a large offset (> 3.5 half-light radii) from the two closest galaxies, both
at redshift 𝑧 ∼ 0.24. The location of AT 2023fhn is in stark contrast with previous events, and demonstrates that LFBOTs can
occur in a range of galactic environments.
Todo mundo sabe que os raios produzidos pela Estrela da Morte em Guerra nas Estrelas não pode existir na vida real, porém no universo existem fenômenos que as vezes conseguem superar até a mais surpreendente ficção.
A galáxia Pictor A, é um desses objetos que possuem fenômenos tão espetaculares quanto aqueles exibidos no cinema. Essa galáxia localiza-se a cerca de 500 milhões de anos-luz da Terra e possui um buraco negro supermassivo no seu centro. Uma grande quantidade de energia gravitacional é lançada, à medida que o material cai em direção ao horizonte de eventos, o ponto sem volta ao redor do buraco negro. Essa energia produz um enorme jato de partículas que viajam a uma velocidade próxima da velocidade da luz no espaço intergaláctico, chamado de jato relativístico.
Para obter imagens desse jato, os cientistas usaram o Observatório de Raios-X Chandra, da NASA várias vezes durante 15 anos. Os dados do Chandra, apresentados em azul nas imagens, foram combinados com os dados obtidos em ondas de rádio a partir do Australia Telescope Compact Array, e são aparesentados em vermelho nas imagens.
Matter ejections behind the highs and lows of the transitional millisecond pu...Sérgio Sacani
Transitional millisecond pulsars are an emerging class of sources linking low-mass X-ray binaries to millisecond radio pulsars in
binary systems. These pulsars alternate between a radio pulsar state and an active low-luminosity X-ray disc state. During the active
state, these sources exhibit two distinct emission modes (high and low) that alternate unpredictably, abruptly, and incessantly. X-ray
to optical pulsations are observed only during the high mode. Knowledge of the root reason for this puzzling behaviour remains
elusive. This paper presents the results of the most extensive multi-wavelength campaign ever conducted on the transitional pulsar
prototype, PSR J1023+0038, covering from radio to X-rays. The campaign was carried out over two nights in June 2021, and involved
12 different telescopes and instruments including XMM-Newton, HST, VLT/FORS2 (in polarimetric mode), ALMA, VLA and FAST.
By modelling the broadband spectral energy distributions in both emission modes, we show that the mode switches are caused by
changes in the innermost region of the accretion disc. These changes trigger the emission of discrete mass ejections, which occur on
top of a compact jet, as testified by the detection of at least one short-duration millimetre flare with A
M82 X-2 is the first pulsating ultraluminous X-ray source discovered. The luminosity of these extreme pulsars, if
isotropic, implies an extreme mass transfer rate. An alternative is to assume a much lower mass transfer rate, but
with an apparent luminosity boosted by geometrical beaming. Only an independent measurement of the mass
transfer rate can help discriminate between these two scenarios. In this paper, we follow the orbit of the neutron star
for 7 yr, measure the decay of the orbit (P P orb orb 8 10 yr 6 1 · » - - - ), and argue that this orbital decay is driven by
extreme mass transfer of more than 150 times the mass transfer limit set by the Eddington luminosity. If this is true,
the mass available to the accretor is more than enough to justify its luminosity, with no need for beaming. This also
strongly favors models where the accretor is a highly magnetized neutron star.
The xmm newton-view_of_the_central_degrees_of_the_milk_waySérgio Sacani
Novas imagens do Observatório de Raios-X XMM-Newton da ESA revelaram alguns dos processos mais intensos que acontecem no coração da nossa Via Láctea.
As fontes brilhantes e pontuais que se destacam por toda imagem indicam os sistemas estelares binários onde uma das estrelas atingiu o final de sua vida, desenvolvendo para um objeto compacto e denso – uma estrela de nêutrons ou um buraco negro.
A região central da Via Láctea também contém jovens estrelas e aglomerados estelares e algumas dessas fontes são visíveis como pontos brancos e vermelhos brilhando na imagem, que se espalha por 1000 anos-luz.
A maior parte da ação ocorre no centro, onde nuvens difusas de gás estão sendo cavadas por ventos poderosos soprados por estrelas jovens, bem como por supernovas.
Imaging the Milky Way with Millihertz Gravitational WavesSérgio Sacani
Modern astronomers enjoy access to all-sky images across a wide range of the electromagnetic spectrum from
long-wavelength radio to high-energy gamma rays. The most prominent feature in many of these images is our
own Galaxy, with different features revealed in each wave band. Gravitational waves (GWs) have recently been
added to the astronomers’ toolkit as a nonelectromagnetic messenger. To date, all identified GW sources have been
extra-Galactic and transient. However, the Milky Way hosts a population of ultracompact binaries (UCBs), which
radiate persistent GWs in the milliHertz band that is not observable with today’s terrestrial gravitational-wave
detectors. Space-based detectors such as the Laser Interferometer Space Antenna will measure this population and
provide a census of their location, masses, and orbital properties. In this work, we will show how this data can be
used to form a false-color image of the Galaxy that represents the intensity and frequency of the gravitational
waves produced by the UCB population. Such images can be used to study the morphology of the Galaxy, identify
interesting multimessenger sources through cross-matching, and for educational and outreach purposes.
The most luminous_galaxies_discovered_by_wiseSérgio Sacani
Artigo descreve estudo feito por astrônomos e com a ajuda da sonda WISE da NASA para identificar as galáxias do tipo ELIRGs, entre elas a mais luminosa galáxia do universo, com um buraco negro gigantesco em seu interior e localizada a cerca de 12.8 bilhões de anos de distância da Terra.
The Tidal Disruption Event AT2021ehb: Evidence of Relativistic Disk Reflectio...Sérgio Sacani
We present X-ray, UV, optical, and radio observations of the nearby (≈78 Mpc) tidal disruption event
AT2021ehb/ZTF21aanxhjv during its first 430 days of evolution. AT2021ehb occurs in the nucleus of a galaxy
hosting a≈107 Me black hole (MBH inferred from host galaxy scaling relations). High-cadence Swift and Neutron
Star Interior Composition Explorer (NICER) monitoring reveals a delayed X-ray brightening. The spectrum first
undergoes a gradual soft → hard transition and then suddenly turns soft again within 3 days at δt≈272 days during
which the X-ray flux drops by a factor of 10. In the joint NICER+NuSTAR observation (δt = 264 days, harder
state), we observe a prominent nonthermal component up to 30 keV and an extremely broad emission line in the
iron K band. The bolometric luminosity of AT2021ehb reaches a maximum of -
+ 6.0 % 3.8 L 10.4
Edd when the X-ray
spectrum is the hardest. During the dramatic X-ray evolution, no radio emission is detected, the UV/optical
luminosity stays relatively constant, and the optical spectra are featureless. We propose the following
interpretations: (i) the soft → hard transition may be caused by the gradual formation of a magnetically
dominated corona; (ii) hard X-ray photons escape from the system along solid angles with low scattering optical
depth (∼a few) whereas the UV/optical emission is likely generated by reprocessing materials with much larger
column density—the system is highly aspherical; and (iii) the abrupt X-ray flux drop may be triggered by the
thermal–viscous instability in the inner accretion flow, leading to a much thinner disk.
Todo mundo sabe que os raios produzidos pela Estrela da Morte em Guerra nas Estrelas não pode existir na vida real, porém no universo existem fenômenos que as vezes conseguem superar até a mais surpreendente ficção.
A galáxia Pictor A, é um desses objetos que possuem fenômenos tão espetaculares quanto aqueles exibidos no cinema. Essa galáxia localiza-se a cerca de 500 milhões de anos-luz da Terra e possui um buraco negro supermassivo no seu centro. Uma grande quantidade de energia gravitacional é lançada, à medida que o material cai em direção ao horizonte de eventos, o ponto sem volta ao redor do buraco negro. Essa energia produz um enorme jato de partículas que viajam a uma velocidade próxima da velocidade da luz no espaço intergaláctico, chamado de jato relativístico.
Para obter imagens desse jato, os cientistas usaram o Observatório de Raios-X Chandra, da NASA várias vezes durante 15 anos. Os dados do Chandra, apresentados em azul nas imagens, foram combinados com os dados obtidos em ondas de rádio a partir do Australia Telescope Compact Array, e são aparesentados em vermelho nas imagens.
Matter ejections behind the highs and lows of the transitional millisecond pu...Sérgio Sacani
Transitional millisecond pulsars are an emerging class of sources linking low-mass X-ray binaries to millisecond radio pulsars in
binary systems. These pulsars alternate between a radio pulsar state and an active low-luminosity X-ray disc state. During the active
state, these sources exhibit two distinct emission modes (high and low) that alternate unpredictably, abruptly, and incessantly. X-ray
to optical pulsations are observed only during the high mode. Knowledge of the root reason for this puzzling behaviour remains
elusive. This paper presents the results of the most extensive multi-wavelength campaign ever conducted on the transitional pulsar
prototype, PSR J1023+0038, covering from radio to X-rays. The campaign was carried out over two nights in June 2021, and involved
12 different telescopes and instruments including XMM-Newton, HST, VLT/FORS2 (in polarimetric mode), ALMA, VLA and FAST.
By modelling the broadband spectral energy distributions in both emission modes, we show that the mode switches are caused by
changes in the innermost region of the accretion disc. These changes trigger the emission of discrete mass ejections, which occur on
top of a compact jet, as testified by the detection of at least one short-duration millimetre flare with A
M82 X-2 is the first pulsating ultraluminous X-ray source discovered. The luminosity of these extreme pulsars, if
isotropic, implies an extreme mass transfer rate. An alternative is to assume a much lower mass transfer rate, but
with an apparent luminosity boosted by geometrical beaming. Only an independent measurement of the mass
transfer rate can help discriminate between these two scenarios. In this paper, we follow the orbit of the neutron star
for 7 yr, measure the decay of the orbit (P P orb orb 8 10 yr 6 1 · » - - - ), and argue that this orbital decay is driven by
extreme mass transfer of more than 150 times the mass transfer limit set by the Eddington luminosity. If this is true,
the mass available to the accretor is more than enough to justify its luminosity, with no need for beaming. This also
strongly favors models where the accretor is a highly magnetized neutron star.
The xmm newton-view_of_the_central_degrees_of_the_milk_waySérgio Sacani
Novas imagens do Observatório de Raios-X XMM-Newton da ESA revelaram alguns dos processos mais intensos que acontecem no coração da nossa Via Láctea.
As fontes brilhantes e pontuais que se destacam por toda imagem indicam os sistemas estelares binários onde uma das estrelas atingiu o final de sua vida, desenvolvendo para um objeto compacto e denso – uma estrela de nêutrons ou um buraco negro.
A região central da Via Láctea também contém jovens estrelas e aglomerados estelares e algumas dessas fontes são visíveis como pontos brancos e vermelhos brilhando na imagem, que se espalha por 1000 anos-luz.
A maior parte da ação ocorre no centro, onde nuvens difusas de gás estão sendo cavadas por ventos poderosos soprados por estrelas jovens, bem como por supernovas.
Imaging the Milky Way with Millihertz Gravitational WavesSérgio Sacani
Modern astronomers enjoy access to all-sky images across a wide range of the electromagnetic spectrum from
long-wavelength radio to high-energy gamma rays. The most prominent feature in many of these images is our
own Galaxy, with different features revealed in each wave band. Gravitational waves (GWs) have recently been
added to the astronomers’ toolkit as a nonelectromagnetic messenger. To date, all identified GW sources have been
extra-Galactic and transient. However, the Milky Way hosts a population of ultracompact binaries (UCBs), which
radiate persistent GWs in the milliHertz band that is not observable with today’s terrestrial gravitational-wave
detectors. Space-based detectors such as the Laser Interferometer Space Antenna will measure this population and
provide a census of their location, masses, and orbital properties. In this work, we will show how this data can be
used to form a false-color image of the Galaxy that represents the intensity and frequency of the gravitational
waves produced by the UCB population. Such images can be used to study the morphology of the Galaxy, identify
interesting multimessenger sources through cross-matching, and for educational and outreach purposes.
The most luminous_galaxies_discovered_by_wiseSérgio Sacani
Artigo descreve estudo feito por astrônomos e com a ajuda da sonda WISE da NASA para identificar as galáxias do tipo ELIRGs, entre elas a mais luminosa galáxia do universo, com um buraco negro gigantesco em seu interior e localizada a cerca de 12.8 bilhões de anos de distância da Terra.
The Tidal Disruption Event AT2021ehb: Evidence of Relativistic Disk Reflectio...Sérgio Sacani
We present X-ray, UV, optical, and radio observations of the nearby (≈78 Mpc) tidal disruption event
AT2021ehb/ZTF21aanxhjv during its first 430 days of evolution. AT2021ehb occurs in the nucleus of a galaxy
hosting a≈107 Me black hole (MBH inferred from host galaxy scaling relations). High-cadence Swift and Neutron
Star Interior Composition Explorer (NICER) monitoring reveals a delayed X-ray brightening. The spectrum first
undergoes a gradual soft → hard transition and then suddenly turns soft again within 3 days at δt≈272 days during
which the X-ray flux drops by a factor of 10. In the joint NICER+NuSTAR observation (δt = 264 days, harder
state), we observe a prominent nonthermal component up to 30 keV and an extremely broad emission line in the
iron K band. The bolometric luminosity of AT2021ehb reaches a maximum of -
+ 6.0 % 3.8 L 10.4
Edd when the X-ray
spectrum is the hardest. During the dramatic X-ray evolution, no radio emission is detected, the UV/optical
luminosity stays relatively constant, and the optical spectra are featureless. We propose the following
interpretations: (i) the soft → hard transition may be caused by the gradual formation of a magnetically
dominated corona; (ii) hard X-ray photons escape from the system along solid angles with low scattering optical
depth (∼a few) whereas the UV/optical emission is likely generated by reprocessing materials with much larger
column density—the system is highly aspherical; and (iii) the abrupt X-ray flux drop may be triggered by the
thermal–viscous instability in the inner accretion flow, leading to a much thinner disk.
Spirals and clumps in V960 Mon: signs of planet formation via gravitational i...Sérgio Sacani
The formation of giant planets has traditionally been divided into two pathways: core accretion and gravitational instability. However, in recent years, gravitational instability has become less favored, primarily due
to the scarcity of observations of fragmented protoplanetary disks around young stars and low occurrence rate
of massive planets on very wide orbits. In this study, we present a SPHERE/IRDIS polarized light observation
of the young outbursting object V960 Mon. The image reveals a vast structure of intricately shaped scattered
light with several spiral arms. This finding motivated a re-analysis of archival ALMA 1.3 mm data acquired
just two years after the onset of the outburst of V960 Mon. In these data, we discover several clumps of continuum emission aligned along a spiral arm that coincides with the scattered light structure. We interpret the
localized emission as fragments formed from a spiral arm under gravitational collapse. Estimating the mass of
solids within these clumps to be of several Earth masses, we suggest this observation to be the first evidence of
gravitational instability occurring on planetary scales. This study discusses the significance of this finding for
planet formation and its potential connection with the outbursting state of V960 Mon.
The JWST Discovery of the Triply-imaged Type Ia “Supernova H0pe” and Observat...Sérgio Sacani
A Type Ia supernova (SN) at z = 1.78 was discovered in James Webb Space Telescope Near Infrared
Camera imaging of the galaxy cluster PLCK G165.7+67.0 (G165; z = 0.35). The SN is situated 1.5–
2 kpc from its host galaxy Arc 2 and appears in three different locations as a result of gravitational
lensing by G165. These data can yield a value for Hubble’s constant using time delays from this
multiply-imaged SN Ia that we call “SN H0pe.” Over the entire field we identified 21 image multiplicities,
confirmed five of them using Near-Infrared Spectrograph (NIRspec), and constructed a new
lens model that gives a total mass within 600 kpc of (2.6 ± 0.3) × 1014M⊙. The photometry uncovered
a galaxy overdensity at Arc 2’s redshift. NIRSpec confirmed six member galaxies, four of which
surround Arc 2 with relative velocity ≲900 km s−1 and projected physical extent ≲33 kpc. Arc 2
dominates the stellar mass ((5.0±0.1)×1011M⊙), which is a factor of ten higher than other members
of this compact galaxy group. These other group members have specific star formation rates (sSFR)
arXiv:2309.07326v1 [astro-ph.GA] 13 Sep 2023
2 Frye, Pascale, Pierel et al.
of 2–260 Gyr−1 derived from the Hα-line flux corrected for stellar absorption, dust extinction, and slit
losses. Another group centered on the dusty star forming galaxy Arc 1 is at z = 2.24. The total SFR
for the Arc 1 group (≳400M⊙ yr−1) translates to a supernova rate of ∼1 SNe yr−1, suggesting that
regular monitoring of this cluster may yield additional SNe.
Jet reorientation in central galaxies of clusters and groups: insights from V...Sérgio Sacani
Recent observations of galaxy clusters and groups with misalignments between their central AGN jets
and X-ray cavities, or with multiple misaligned cavities, have raised concerns about the jet – bubble
connection in cooling cores, and the processes responsible for jet realignment. To investigate the
frequency and causes of such misalignments, we construct a sample of 16 cool core galaxy clusters and
groups. Using VLBA radio data we measure the parsec-scale position angle of the jets, and compare
it with the position angle of the X-ray cavities detected in Chandra data. Using the overall sample
and selected subsets, we consistently find that there is a 30% – 38% chance to find a misalignment
larger than ∆Ψ = 45◦ when observing a cluster/group with a detected jet and at least one cavity. We
determine that projection may account for an apparently large ∆Ψ only in a fraction of objects (∼35%),
and given that gas dynamical disturbances (as sloshing) are found in both aligned and misaligned
systems, we exclude environmental perturbation as the main driver of cavity – jet misalignment.
Moreover, we find that large misalignments (up to ∼ 90◦
) are favored over smaller ones (45◦ ≤ ∆Ψ ≤
70◦
), and that the change in jet direction can occur on timescales between one and a few tens of Myr.
We conclude that misalignments are more likely related to actual reorientation of the jet axis, and we
discuss several engine-based mechanisms that may cause these dramatic changes.
A giant thin stellar stream in the Coma Galaxy ClusterSérgio Sacani
The study of dynamically cold stellar streams reveals information about the gravitational potential where they reside and provides
important constraints on the properties of dark matter. However, the intrinsic faintness of these streams makes their detection beyond
Local environments highly challenging. Here, we report the detection of an extremely faint stellar stream (µg,max = 29.5 mag arcsec−2
)
with an extraordinarily coherent and thin morphology in the Coma Galaxy Cluster. This Giant Coma Stream spans ∼510 kpc in length
and appears as a free-floating structure located at a projected distance of 0.8 Mpc from the center of Coma. We do not identify any
potential galaxy remnant or core, and the stream structure appears featureless in our data. We interpret the Giant Coma Stream as
being a recently accreted, tidally disrupting passive dwarf. Using the Illustris-TNG50 simulation, we identify a case with similar
characteristics, showing that, although rare, these types of streams are predicted to exist in Λ-CDM. Our work unveils the presence
of free-floating, extremely faint and thin stellar streams in galaxy clusters, widening the environmental context in which these objects
are found ahead of their promising future application in the study of the properties of dark matter.
Observation of Gravitational Waves from the Coalescence of a 2.5–4.5 M⊙ Compa...Sérgio Sacani
We report the observation of a coalescing compact binary with component masses 2.5–4.5 M⊙ and 1.2–2.0 M⊙ (all measurements quoted at the 90% credible level). The gravitational-wave signal GW230529 181500 was observed during the fourth observing run of the LIGO–Virgo–KAGRA detector network on 2023 May 29 by the LIGO Livingston observatory. The primary component of the source has a mass less than 5 M⊙ at 99% credibility. We cannot definitively determine from gravitational-wave data alone whether either component of the source is a neutron star or a black hole. However, given existing estimates of the maximum neutron star mass, we find the most probable interpretation of the source to be the coalescence of a neutron star with a black hole that has a mass between the most massive neutron stars and the least massive black holes observed in the Galaxy. We estimate a merger rate density of 55+127 −47 Gpc−3yr−1 for compact binary coalescences with properties similar to the source of GW230529 181500; assuming that the source is a neutron star–black hole merger, GW230529 181500-like sources constitute about 60% of the total merger rate inferred for neutron star–black hole coalescences. The discovery of this system implies an increase in the expected rate of neutron star–black hole mergers with electromagnetic counterparts and provides further evidence for compact objects existing within the purported lower mass gap.
WASP-69b’s Escaping Envelope Is Confined to a Tail Extending at Least 7 RpSérgio Sacani
Studying the escaping atmospheres of highly irradiated exoplanets is critical for understanding the physical
mechanisms that shape the demographics of close-in planets. A number of planetary outflows have been observed
as excess H/He absorption during/after transit. Such an outflow has been observed for WASP-69b by multiple
groups that disagree on the geometry and velocity structure of the outflow. Here, we report the detection of this
planet’s outflow using Keck/NIRSPEC for the first time. We observed the outflow 1.28 hr after egress until the
target set, demonstrating the outflow extends at least 5.8 × 105 km or 7.5 Rp This detection is significantly longer
than previous observations, which report an outflow extending ∼2.2 planet radii just 1 yr prior. The outflow is
blueshifted by −23 km s−1 in the planetary rest frame. We estimate a current mass-loss rate of 1 M⊕ Gyr−1
. Our
observations are most consistent with an outflow that is strongly sculpted by ram pressure from the stellar wind.
However, potential variability in the outflow could be due to time-varying interactions with the stellar wind or
differences in instrumental precision.
Hydrogen Column Density Variability in a Sample of Local Compton-Thin AGNSérgio Sacani
We present the analysis of multiepoch observations of a set of 12 variable, Compton-thin, local (z<0.1) active galactic nuclei (AGN) selected from the 100-month BAT catalog. We analyze all available X-ray data from Chandra, XMMNewton, and NuSTAR, adding up to a total of 53 individual observations. This corresponds to between 3 and 7 observations per source, probing variability timescales between a few days and ∼ 20 yr. All sources have at least one NuSTAR observation, ensuring high-energy coverage, which allows us to disentangle the line-of-sight and reflection components in the X-ray spectra. For each source, we model all available spectra simultaneously, using the physical torus models MYTorus, borus02, and UXCLUMPY. The simultaneous fitting, along with the high-energy coverage, allows us to place tight constraints on torus parameters such as the torus covering factor, inclination angle, and torus average column density. We also estimate the line-of-sight column density (NH) for each individual observation. Within the 12 sources, we detect clear line-of-sight NH variability in 5, non-variability in 5, and for 2 of them it is not possible to fully disentangle intrinsic-luminosity and NH variability. We observe large differences between the average values of line-ofsight NH (or NH of the obscurer) and the average NH of the torus (or NH of the reflector), for each source, by a factor between ∼ 2 to > 100. This behavior, which suggests a physical disconnect between the absorber and the reflector, is more extreme in sources that present NH variability. NH-variable AGN also tend to present larger obscuration and broader cloud distributions than their non-variable counterparts. We observe that large changes in obscuration only occur at long timescales, and use this to place tentative lower limits on torus cloud sizes.
EXTINCTION AND THE DIMMING OF KIC 8462852Sérgio Sacani
To test alternative hypotheses for the behavior of KIC 8462852, we obtained measurements of the star
over a wide wavelength range from the UV to the mid-infrared from October 2015 through December
2016, using Swift, Spitzer and at AstroLAB IRIS. The star faded in a manner similar to the longterm
fading seen in Kepler data about 1400 days previously. The dimming rate for the entire period
reported is 22.1 ± 9.7 milli-mag yr−1
in the Swift wavebands, with amounts of 21.0 ± 4.5 mmag in
the groundbased B measurements, 14.0 ± 4.5 mmag in V , and 13.0 ± 4.5 in R, and a rate of 5.0 ± 1.2
mmag yr−1 averaged over the two warm Spitzer bands. Although the dimming is small, it is seen at
& 3 σ by three different observatories operating from the UV to the IR. The presence of long-term
secular dimming means that previous SED models of the star based on photometric measurements
taken years apart may not be accurate. We find that stellar models with Tef f = 7000 - 7100 K and
AV ∼ 0.73 best fit the Swift data from UV to optical. These models also show no excess in the
near-simultaneous Spitzer photometry at 3.6 and 4.5 µm, although a longer wavelength excess from
a substantial debris disk is still possible (e.g., as around Fomalhaut). The wavelength dependence of
the fading favors a relatively neutral color (i.e., RV & 5, but not flat across all the bands) compared
with the extinction law for the general ISM (RV = 3.1), suggesting that the dimming arises from
circumstellar material
The first X-ray look at SMSS J114447.77-430859.3: the most luminous quasar in...Sérgio Sacani
SMSS J114447.77-430859.3 (z = 0.83) has been identified in the SkyMapper Southern Survey as the most luminous quasar in
the last ∼ 9 Gyr . In this paper, we report on the eROSITA/Spectrum–Roentgen–Gamma (SRG) observations of the source from
the eROSITA All Sky Survey, along with presenting results from recent monitoring performed using Swift, XMM-Newton, and
NuSTAR. The source shows a clear variability by factors of ∼10 and ∼2.7 overtime-scales of a year and of a few days,respectively.
When fit with an absorbed power law plus high-energy cutoff, the X-ray spectra reveal a = 2.2 ± 0.2 and Ecut = 23+26
−5 keV
. Assuming Comptonization, we estimate a coronal optical depth and electron temperature of τ = 2.5 − 5.3 (5.2 − 8) and
kT = 8 − 18 (7.5 − 14) keV , respectively, for a slab (spherical) geometry. The broadband SED is successfully modelled by
assuming either a standard accretion disc illuminated by a central X-ray source, or a thin disc with a slim disc emissivity profile.
The former model results in a black hole mass estimate of the order of 1010 M , slightly higher than prior optical estimates;
meanwhile, the latter model suggests a lower mass. Both models suggest sub-Eddington accretion when assuming a spinning
black hole, and a compact (∼ 10 rg ) X-ray corona. The measured intrinsic column density and the Eddington ratio strongly
suggest the presence of an outflow driven by radiation pressure. This is also supported by variation of absorption by an order of
magnitude over the period of ∼ 900 d .
Solving the Multimessenger Puzzle of the AGN-starburst Composite Galaxy NGC 1068Sérgio Sacani
Multiwavelength observations indicate that some starburst galaxies show a dominant nonthermal contribution from
their central region. These active galactic nuclei (AGN)-starburst composites are of special interest, as both
phenomena on their own are potential sources of highly energetic cosmic rays and associated γ-ray and neutrino
emission. In this work, a homogeneous, steady-state two-zone multimessenger model of the nonthermal emission
from the AGN corona as well as the circumnuclear starburst region is developed and subsequently applied to the
case of NGC 1068, which has recently shown some first indications of high-energy neutrino emission. Here, we
show that the entire spectrum of multimessenger data—from radio to γ-rays including the neutrino constraint—can
be described very well if both, starburst and AGN corona, are taken into account. Using only a single emission
region is not sufficient.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
More Related Content
Similar to AT2023fhn (the Finch): a Luminous Fast Blue Optical Transient at a large offset from its host galaxy
Spirals and clumps in V960 Mon: signs of planet formation via gravitational i...Sérgio Sacani
The formation of giant planets has traditionally been divided into two pathways: core accretion and gravitational instability. However, in recent years, gravitational instability has become less favored, primarily due
to the scarcity of observations of fragmented protoplanetary disks around young stars and low occurrence rate
of massive planets on very wide orbits. In this study, we present a SPHERE/IRDIS polarized light observation
of the young outbursting object V960 Mon. The image reveals a vast structure of intricately shaped scattered
light with several spiral arms. This finding motivated a re-analysis of archival ALMA 1.3 mm data acquired
just two years after the onset of the outburst of V960 Mon. In these data, we discover several clumps of continuum emission aligned along a spiral arm that coincides with the scattered light structure. We interpret the
localized emission as fragments formed from a spiral arm under gravitational collapse. Estimating the mass of
solids within these clumps to be of several Earth masses, we suggest this observation to be the first evidence of
gravitational instability occurring on planetary scales. This study discusses the significance of this finding for
planet formation and its potential connection with the outbursting state of V960 Mon.
The JWST Discovery of the Triply-imaged Type Ia “Supernova H0pe” and Observat...Sérgio Sacani
A Type Ia supernova (SN) at z = 1.78 was discovered in James Webb Space Telescope Near Infrared
Camera imaging of the galaxy cluster PLCK G165.7+67.0 (G165; z = 0.35). The SN is situated 1.5–
2 kpc from its host galaxy Arc 2 and appears in three different locations as a result of gravitational
lensing by G165. These data can yield a value for Hubble’s constant using time delays from this
multiply-imaged SN Ia that we call “SN H0pe.” Over the entire field we identified 21 image multiplicities,
confirmed five of them using Near-Infrared Spectrograph (NIRspec), and constructed a new
lens model that gives a total mass within 600 kpc of (2.6 ± 0.3) × 1014M⊙. The photometry uncovered
a galaxy overdensity at Arc 2’s redshift. NIRSpec confirmed six member galaxies, four of which
surround Arc 2 with relative velocity ≲900 km s−1 and projected physical extent ≲33 kpc. Arc 2
dominates the stellar mass ((5.0±0.1)×1011M⊙), which is a factor of ten higher than other members
of this compact galaxy group. These other group members have specific star formation rates (sSFR)
arXiv:2309.07326v1 [astro-ph.GA] 13 Sep 2023
2 Frye, Pascale, Pierel et al.
of 2–260 Gyr−1 derived from the Hα-line flux corrected for stellar absorption, dust extinction, and slit
losses. Another group centered on the dusty star forming galaxy Arc 1 is at z = 2.24. The total SFR
for the Arc 1 group (≳400M⊙ yr−1) translates to a supernova rate of ∼1 SNe yr−1, suggesting that
regular monitoring of this cluster may yield additional SNe.
Jet reorientation in central galaxies of clusters and groups: insights from V...Sérgio Sacani
Recent observations of galaxy clusters and groups with misalignments between their central AGN jets
and X-ray cavities, or with multiple misaligned cavities, have raised concerns about the jet – bubble
connection in cooling cores, and the processes responsible for jet realignment. To investigate the
frequency and causes of such misalignments, we construct a sample of 16 cool core galaxy clusters and
groups. Using VLBA radio data we measure the parsec-scale position angle of the jets, and compare
it with the position angle of the X-ray cavities detected in Chandra data. Using the overall sample
and selected subsets, we consistently find that there is a 30% – 38% chance to find a misalignment
larger than ∆Ψ = 45◦ when observing a cluster/group with a detected jet and at least one cavity. We
determine that projection may account for an apparently large ∆Ψ only in a fraction of objects (∼35%),
and given that gas dynamical disturbances (as sloshing) are found in both aligned and misaligned
systems, we exclude environmental perturbation as the main driver of cavity – jet misalignment.
Moreover, we find that large misalignments (up to ∼ 90◦
) are favored over smaller ones (45◦ ≤ ∆Ψ ≤
70◦
), and that the change in jet direction can occur on timescales between one and a few tens of Myr.
We conclude that misalignments are more likely related to actual reorientation of the jet axis, and we
discuss several engine-based mechanisms that may cause these dramatic changes.
A giant thin stellar stream in the Coma Galaxy ClusterSérgio Sacani
The study of dynamically cold stellar streams reveals information about the gravitational potential where they reside and provides
important constraints on the properties of dark matter. However, the intrinsic faintness of these streams makes their detection beyond
Local environments highly challenging. Here, we report the detection of an extremely faint stellar stream (µg,max = 29.5 mag arcsec−2
)
with an extraordinarily coherent and thin morphology in the Coma Galaxy Cluster. This Giant Coma Stream spans ∼510 kpc in length
and appears as a free-floating structure located at a projected distance of 0.8 Mpc from the center of Coma. We do not identify any
potential galaxy remnant or core, and the stream structure appears featureless in our data. We interpret the Giant Coma Stream as
being a recently accreted, tidally disrupting passive dwarf. Using the Illustris-TNG50 simulation, we identify a case with similar
characteristics, showing that, although rare, these types of streams are predicted to exist in Λ-CDM. Our work unveils the presence
of free-floating, extremely faint and thin stellar streams in galaxy clusters, widening the environmental context in which these objects
are found ahead of their promising future application in the study of the properties of dark matter.
Observation of Gravitational Waves from the Coalescence of a 2.5–4.5 M⊙ Compa...Sérgio Sacani
We report the observation of a coalescing compact binary with component masses 2.5–4.5 M⊙ and 1.2–2.0 M⊙ (all measurements quoted at the 90% credible level). The gravitational-wave signal GW230529 181500 was observed during the fourth observing run of the LIGO–Virgo–KAGRA detector network on 2023 May 29 by the LIGO Livingston observatory. The primary component of the source has a mass less than 5 M⊙ at 99% credibility. We cannot definitively determine from gravitational-wave data alone whether either component of the source is a neutron star or a black hole. However, given existing estimates of the maximum neutron star mass, we find the most probable interpretation of the source to be the coalescence of a neutron star with a black hole that has a mass between the most massive neutron stars and the least massive black holes observed in the Galaxy. We estimate a merger rate density of 55+127 −47 Gpc−3yr−1 for compact binary coalescences with properties similar to the source of GW230529 181500; assuming that the source is a neutron star–black hole merger, GW230529 181500-like sources constitute about 60% of the total merger rate inferred for neutron star–black hole coalescences. The discovery of this system implies an increase in the expected rate of neutron star–black hole mergers with electromagnetic counterparts and provides further evidence for compact objects existing within the purported lower mass gap.
WASP-69b’s Escaping Envelope Is Confined to a Tail Extending at Least 7 RpSérgio Sacani
Studying the escaping atmospheres of highly irradiated exoplanets is critical for understanding the physical
mechanisms that shape the demographics of close-in planets. A number of planetary outflows have been observed
as excess H/He absorption during/after transit. Such an outflow has been observed for WASP-69b by multiple
groups that disagree on the geometry and velocity structure of the outflow. Here, we report the detection of this
planet’s outflow using Keck/NIRSPEC for the first time. We observed the outflow 1.28 hr after egress until the
target set, demonstrating the outflow extends at least 5.8 × 105 km or 7.5 Rp This detection is significantly longer
than previous observations, which report an outflow extending ∼2.2 planet radii just 1 yr prior. The outflow is
blueshifted by −23 km s−1 in the planetary rest frame. We estimate a current mass-loss rate of 1 M⊕ Gyr−1
. Our
observations are most consistent with an outflow that is strongly sculpted by ram pressure from the stellar wind.
However, potential variability in the outflow could be due to time-varying interactions with the stellar wind or
differences in instrumental precision.
Hydrogen Column Density Variability in a Sample of Local Compton-Thin AGNSérgio Sacani
We present the analysis of multiepoch observations of a set of 12 variable, Compton-thin, local (z<0.1) active galactic nuclei (AGN) selected from the 100-month BAT catalog. We analyze all available X-ray data from Chandra, XMMNewton, and NuSTAR, adding up to a total of 53 individual observations. This corresponds to between 3 and 7 observations per source, probing variability timescales between a few days and ∼ 20 yr. All sources have at least one NuSTAR observation, ensuring high-energy coverage, which allows us to disentangle the line-of-sight and reflection components in the X-ray spectra. For each source, we model all available spectra simultaneously, using the physical torus models MYTorus, borus02, and UXCLUMPY. The simultaneous fitting, along with the high-energy coverage, allows us to place tight constraints on torus parameters such as the torus covering factor, inclination angle, and torus average column density. We also estimate the line-of-sight column density (NH) for each individual observation. Within the 12 sources, we detect clear line-of-sight NH variability in 5, non-variability in 5, and for 2 of them it is not possible to fully disentangle intrinsic-luminosity and NH variability. We observe large differences between the average values of line-ofsight NH (or NH of the obscurer) and the average NH of the torus (or NH of the reflector), for each source, by a factor between ∼ 2 to > 100. This behavior, which suggests a physical disconnect between the absorber and the reflector, is more extreme in sources that present NH variability. NH-variable AGN also tend to present larger obscuration and broader cloud distributions than their non-variable counterparts. We observe that large changes in obscuration only occur at long timescales, and use this to place tentative lower limits on torus cloud sizes.
EXTINCTION AND THE DIMMING OF KIC 8462852Sérgio Sacani
To test alternative hypotheses for the behavior of KIC 8462852, we obtained measurements of the star
over a wide wavelength range from the UV to the mid-infrared from October 2015 through December
2016, using Swift, Spitzer and at AstroLAB IRIS. The star faded in a manner similar to the longterm
fading seen in Kepler data about 1400 days previously. The dimming rate for the entire period
reported is 22.1 ± 9.7 milli-mag yr−1
in the Swift wavebands, with amounts of 21.0 ± 4.5 mmag in
the groundbased B measurements, 14.0 ± 4.5 mmag in V , and 13.0 ± 4.5 in R, and a rate of 5.0 ± 1.2
mmag yr−1 averaged over the two warm Spitzer bands. Although the dimming is small, it is seen at
& 3 σ by three different observatories operating from the UV to the IR. The presence of long-term
secular dimming means that previous SED models of the star based on photometric measurements
taken years apart may not be accurate. We find that stellar models with Tef f = 7000 - 7100 K and
AV ∼ 0.73 best fit the Swift data from UV to optical. These models also show no excess in the
near-simultaneous Spitzer photometry at 3.6 and 4.5 µm, although a longer wavelength excess from
a substantial debris disk is still possible (e.g., as around Fomalhaut). The wavelength dependence of
the fading favors a relatively neutral color (i.e., RV & 5, but not flat across all the bands) compared
with the extinction law for the general ISM (RV = 3.1), suggesting that the dimming arises from
circumstellar material
The first X-ray look at SMSS J114447.77-430859.3: the most luminous quasar in...Sérgio Sacani
SMSS J114447.77-430859.3 (z = 0.83) has been identified in the SkyMapper Southern Survey as the most luminous quasar in
the last ∼ 9 Gyr . In this paper, we report on the eROSITA/Spectrum–Roentgen–Gamma (SRG) observations of the source from
the eROSITA All Sky Survey, along with presenting results from recent monitoring performed using Swift, XMM-Newton, and
NuSTAR. The source shows a clear variability by factors of ∼10 and ∼2.7 overtime-scales of a year and of a few days,respectively.
When fit with an absorbed power law plus high-energy cutoff, the X-ray spectra reveal a = 2.2 ± 0.2 and Ecut = 23+26
−5 keV
. Assuming Comptonization, we estimate a coronal optical depth and electron temperature of τ = 2.5 − 5.3 (5.2 − 8) and
kT = 8 − 18 (7.5 − 14) keV , respectively, for a slab (spherical) geometry. The broadband SED is successfully modelled by
assuming either a standard accretion disc illuminated by a central X-ray source, or a thin disc with a slim disc emissivity profile.
The former model results in a black hole mass estimate of the order of 1010 M , slightly higher than prior optical estimates;
meanwhile, the latter model suggests a lower mass. Both models suggest sub-Eddington accretion when assuming a spinning
black hole, and a compact (∼ 10 rg ) X-ray corona. The measured intrinsic column density and the Eddington ratio strongly
suggest the presence of an outflow driven by radiation pressure. This is also supported by variation of absorption by an order of
magnitude over the period of ∼ 900 d .
Solving the Multimessenger Puzzle of the AGN-starburst Composite Galaxy NGC 1068Sérgio Sacani
Multiwavelength observations indicate that some starburst galaxies show a dominant nonthermal contribution from
their central region. These active galactic nuclei (AGN)-starburst composites are of special interest, as both
phenomena on their own are potential sources of highly energetic cosmic rays and associated γ-ray and neutrino
emission. In this work, a homogeneous, steady-state two-zone multimessenger model of the nonthermal emission
from the AGN corona as well as the circumnuclear starburst region is developed and subsequently applied to the
case of NGC 1068, which has recently shown some first indications of high-energy neutrino emission. Here, we
show that the entire spectrum of multimessenger data—from radio to γ-rays including the neutrino constraint—can
be described very well if both, starburst and AGN corona, are taken into account. Using only a single emission
region is not sufficient.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...Sérgio Sacani
Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the
atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets
receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric
composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet
transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (Porb) of 12.76 days.
The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous Porb from TESS data. We
confirmed the transit signal and Porb using ground-based photometry with MuSCAT2 and MuSCAT3, and
validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as
well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope
and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host
star is inactive, with an X-ray-to-bolometric luminosity ratio of log 5.7 L L X bol » - . Joint analysis of the light
curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 ± 0.05 R⊕,a3σ mass upper limit of
3.9 M⊕, and an equilibrium temperature of 315 ± 6 K assuming zero albedo. The transmission spectroscopy metric
(TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small
list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.
Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TES...Sérgio Sacani
We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a
bright (V = 12.6 mag, K = 7.8 mag) metal-poor M4V star only 12.162 ± 0.005 pc away from the Solar system with one of the
lowest stellar activity levels known for M-dwarfs. A planet candidate was detected by TESS based on only 3 transits in sectors
42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations
with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory,
as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of
12.76144 ± 0.00006 d and a radius of 1.0 ± 0.1 R⊕, resulting in an equilibrium temperature of ∼315 K. Gliese 12 b has excellent
future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar
compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool
stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the galaxy.
The importance of continents, oceans and plate tectonics for the evolution of...Sérgio Sacani
Within the uncertainties of involved astronomical and biological parameters, the Drake Equation
typically predicts that there should be many exoplanets in our galaxy hosting active, communicative
civilizations (ACCs). These optimistic calculations are however not supported by evidence, which is
often referred to as the Fermi Paradox. Here, we elaborate on this long-standing enigma by showing
the importance of planetary tectonic style for biological evolution. We summarize growing evidence
that a prolonged transition from Mesoproterozoic active single lid tectonics (1.6 to 1.0 Ga) to modern
plate tectonics occurred in the Neoproterozoic Era (1.0 to 0.541 Ga), which dramatically accelerated
emergence and evolution of complex species. We further suggest that both continents and oceans
are required for ACCs because early evolution of simple life must happen in water but late evolution
of advanced life capable of creating technology must happen on land. We resolve the Fermi Paradox
(1) by adding two additional terms to the Drake Equation: foc
(the fraction of habitable exoplanets
with significant continents and oceans) and fpt
(the fraction of habitable exoplanets with significant
continents and oceans that have had plate tectonics operating for at least 0.5 Ga); and (2) by
demonstrating that the product of foc
and fpt
is very small (< 0.00003–0.002). We propose that the lack
of evidence for ACCs reflects the scarcity of long-lived plate tectonics and/or continents and oceans on
exoplanets with primitive life.
A Giant Impact Origin for the First Subduction on EarthSérgio Sacani
Hadean zircons provide a potential record of Earth's earliest subduction 4.3 billion years ago. Itremains enigmatic how subduction could be initiated so soon after the presumably Moon‐forming giant impact(MGI). Earlier studies found an increase in Earth's core‐mantle boundary (CMB) temperature due to theaccumulation of the impactor's core, and our recent work shows Earth's lower mantle remains largely solid, withsome of the impactor's mantle potentially surviving as the large low‐shear velocity provinces (LLSVPs). Here,we show that a hot post‐impact CMB drives the initiation of strong mantle plumes that can induce subductioninitiation ∼200 Myr after the MGI. 2D and 3D thermomechanical computations show that a high CMBtemperature is the primary factor triggering early subduction, with enrichment of heat‐producing elements inLLSVPs as another potential factor. The models link the earliest subduction to the MGI with implications forunderstanding the diverse tectonic regimes of rocky planets.
Climate extremes likely to drive land mammal extinction during next supercont...Sérgio Sacani
Mammals have dominated Earth for approximately 55 Myr thanks to their
adaptations and resilience to warming and cooling during the Cenozoic. All
life will eventually perish in a runaway greenhouse once absorbed solar
radiation exceeds the emission of thermal radiation in several billions of
years. However, conditions rendering the Earth naturally inhospitable to
mammals may develop sooner because of long-term processes linked to
plate tectonics (short-term perturbations are not considered here). In
~250 Myr, all continents will converge to form Earth’s next supercontinent,
Pangea Ultima. A natural consequence of the creation and decay of Pangea
Ultima will be extremes in pCO2 due to changes in volcanic rifting and
outgassing. Here we show that increased pCO2, solar energy (F⨀;
approximately +2.5% W m−2 greater than today) and continentality (larger
range in temperatures away from the ocean) lead to increasing warming
hostile to mammalian life. We assess their impact on mammalian
physiological limits (dry bulb, wet bulb and Humidex heat stress indicators)
as well as a planetary habitability index. Given mammals’ continued survival,
predicted background pCO2 levels of 410–816 ppm combined with increased
F⨀ will probably lead to a climate tipping point and their mass extinction.
The results also highlight how global landmass configuration, pCO2 and F⨀
play a critical role in planetary habitability.
Constraints on Neutrino Natal Kicks from Black-Hole Binary VFTS 243Sérgio Sacani
The recently reported observation of VFTS 243 is the first example of a massive black-hole binary
system with negligible binary interaction following black-hole formation. The black-hole mass (≈10M⊙)
and near-circular orbit (e ≈ 0.02) of VFTS 243 suggest that the progenitor star experienced complete
collapse, with energy-momentum being lost predominantly through neutrinos. VFTS 243 enables us to
constrain the natal kick and neutrino-emission asymmetry during black-hole formation. At 68% confidence
level, the natal kick velocity (mass decrement) is ≲10 km=s (≲1.0M⊙), with a full probability distribution
that peaks when ≈0.3M⊙ were ejected, presumably in neutrinos, and the black hole experienced a natal
kick of 4 km=s. The neutrino-emission asymmetry is ≲4%, with best fit values of ∼0–0.2%. Such a small
neutrino natal kick accompanying black-hole formation is in agreement with theoretical predictions.
Detectability of Solar Panels as a TechnosignatureSérgio Sacani
In this work, we assess the potential detectability of solar panels made of silicon on an Earth-like
exoplanet as a potential technosignature. Silicon-based photovoltaic cells have high reflectance in the
UV-VIS and in the near-IR, within the wavelength range of a space-based flagship mission concept
like the Habitable Worlds Observatory (HWO). Assuming that only solar energy is used to provide
the 2022 human energy needs with a land cover of ∼ 2.4%, and projecting the future energy demand
assuming various growth-rate scenarios, we assess the detectability with an 8 m HWO-like telescope.
Assuming the most favorable viewing orientation, and focusing on the strong absorption edge in the
ultraviolet-to-visible (0.34 − 0.52 µm), we find that several 100s of hours of observation time is needed
to reach a SNR of 5 for an Earth-like planet around a Sun-like star at 10pc, even with a solar panel
coverage of ∼ 23% land coverage of a future Earth. We discuss the necessity of concepts like Kardeshev
Type I/II civilizations and Dyson spheres, which would aim to harness vast amounts of energy. Even
with much larger populations than today, the total energy use of human civilization would be orders of
magnitude below the threshold for causing direct thermal heating or reaching the scale of a Kardashev
Type I civilization. Any extraterrrestrial civilization that likewise achieves sustainable population
levels may also find a limit on its need to expand, which suggests that a galaxy-spanning civilization
as imagined in the Fermi paradox may not exist.
The solar dynamo begins near the surfaceSérgio Sacani
The magnetic dynamo cycle of the Sun features a distinct pattern: a propagating
region of sunspot emergence appears around 30° latitude and vanishes near the
equator every 11 years (ref. 1). Moreover, longitudinal flows called torsional oscillations
closely shadow sunspot migration, undoubtedly sharing a common cause2. Contrary
to theories suggesting deep origins of these phenomena, helioseismology pinpoints
low-latitude torsional oscillations to the outer 5–10% of the Sun, the near-surface
shear layer3,4. Within this zone, inwardly increasing differential rotation coupled with
a poloidal magnetic field strongly implicates the magneto-rotational instability5,6,
prominent in accretion-disk theory and observed in laboratory experiments7.
Together, these two facts prompt the general question: whether the solar dynamo is
possibly a near-surface instability. Here we report strong affirmative evidence in stark
contrast to traditional models8 focusing on the deeper tachocline. Simple analytic
estimates show that the near-surface magneto-rotational instability better explains
the spatiotemporal scales of the torsional oscillations and inferred subsurface
magnetic field amplitudes9. State-of-the-art numerical simulations corroborate these
estimates and reproduce hemispherical magnetic current helicity laws10. The dynamo
resulting from a well-understood near-surface phenomenon improves prospects
for accurate predictions of full magnetic cycles and space weather, affecting the
electromagnetic infrastructure of Earth.
Extensive Pollution of Uranus and Neptune’s Atmospheres by Upsweep of Icy Mat...Sérgio Sacani
In the Nice model of solar system formation, Uranus and Neptune undergo an orbital upheaval,
sweeping through a planetesimal disk. The region of the disk from which material is accreted by
the ice giants during this phase of their evolution has not previously been identified. We perform
direct N-body orbital simulations of the four giant planets to determine the amount and origin of solid
accretion during this orbital upheaval. We find that the ice giants undergo an extreme bombardment
event, with collision rates as much as ∼3 per hour assuming km-sized planetesimals, increasing the
total planet mass by up to ∼0.35%. In all cases, the initially outermost ice giant experiences the
largest total enhancement. We determine that for some plausible planetesimal properties, the resulting
atmospheric enrichment could potentially produce sufficient latent heat to alter the planetary cooling
timescale according to existing models. Our findings suggest that substantial accretion during this
phase of planetary evolution may have been sufficient to impact the atmospheric composition and
thermal evolution of the ice giants, motivating future work on the fate of deposited solid material.
Exomoons & Exorings with the Habitable Worlds Observatory I: On the Detection...Sérgio Sacani
The highest priority recommendation of the Astro2020 Decadal Survey for space-based astronomy
was the construction of an observatory capable of characterizing habitable worlds. In this paper series
we explore the detectability of and interference from exomoons and exorings serendipitously observed
with the proposed Habitable Worlds Observatory (HWO) as it seeks to characterize exoplanets, starting
in this manuscript with Earth-Moon analog mutual events. Unlike transits, which only occur in systems
viewed near edge-on, shadow (i.e., solar eclipse) and lunar eclipse mutual events occur in almost every
star-planet-moon system. The cadence of these events can vary widely from ∼yearly to multiple events
per day, as was the case in our younger Earth-Moon system. Leveraging previous space-based (EPOXI)
lightcurves of a Moon transit and performance predictions from the LUVOIR-B concept, we derive
the detectability of Moon analogs with HWO. We determine that Earth-Moon analogs are detectable
with observation of ∼2-20 mutual events for systems within 10 pc, and larger moons should remain
detectable out to 20 pc. We explore the extent to which exomoon mutual events can mimic planet
features and weather. We find that HWO wavelength coverage in the near-IR, specifically in the 1.4 µm
water band where large moons can outshine their host planet, will aid in differentiating exomoon signals
from exoplanet variability. Finally, we predict that exomoons formed through collision processes akin
to our Moon are more likely to be detected in younger systems, where shorter orbital periods and
favorable geometry enhance the probability and frequency of mutual events.
Emergent ribozyme behaviors in oxychlorine brines indicate a unique niche for...Sérgio Sacani
Mars is a particularly attractive candidate among known astronomical objects
to potentially host life. Results from space exploration missions have provided
insights into Martian geochemistry that indicate oxychlorine species, particularly perchlorate, are ubiquitous features of the Martian geochemical landscape. Perchlorate presents potential obstacles for known forms of life due to
its toxicity. However, it can also provide potential benefits, such as producing
brines by deliquescence, like those thought to exist on present-day Mars. Here
we show perchlorate brines support folding and catalysis of functional RNAs,
while inactivating representative protein enzymes. Additionally, we show
perchlorate and other oxychlorine species enable ribozyme functions,
including homeostasis-like regulatory behavior and ribozyme-catalyzed
chlorination of organic molecules. We suggest nucleic acids are uniquely wellsuited to hypersaline Martian environments. Furthermore, Martian near- or
subsurface oxychlorine brines, and brines found in potential lifeforms, could
provide a unique niche for biomolecular evolution.
Continuum emission from within the plunging region of black hole discsSérgio Sacani
The thermal continuum emission observed from accreting black holes across X-ray bands has the potential to be leveraged as a
powerful probe of the mass and spin of the central black hole. The vast majority of existing ‘continuum fitting’ models neglect
emission sourced at and within the innermost stable circular orbit (ISCO) of the black hole. Numerical simulations, however,
find non-zero emission sourced from these regions. In this work, we extend existing techniques by including the emission
sourced from within the plunging region, utilizing new analytical models that reproduce the properties of numerical accretion
simulations. We show that in general the neglected intra-ISCO emission produces a hot-and-small quasi-blackbody component,
but can also produce a weak power-law tail for more extreme parameter regions. A similar hot-and-small blackbody component
has been added in by hand in an ad hoc manner to previous analyses of X-ray binary spectra. We show that the X-ray spectrum
of MAXI J1820+070 in a soft-state outburst is extremely well described by a full Kerr black hole disc, while conventional
models that neglect intra-ISCO emission are unable to reproduce the data. We believe this represents the first robust detection of
intra-ISCO emission in the literature, and allows additional constraints to be placed on the MAXI J1820 + 070 black hole spin
which must be low a• < 0.5 to allow a detectable intra-ISCO region. Emission from within the ISCO is the dominant emission
component in the MAXI J1820 + 070 spectrum between 6 and 10 keV, highlighting the necessity of including this region. Our
continuum fitting model is made publicly available.
X-rays from a Central “Exhaust Vent” of the Galactic Center ChimneySérgio Sacani
Using deep archival observations from the Chandra X-ray Observatory, we present an analysis of
linear X-ray-emitting features located within the southern portion of the Galactic center chimney,
and oriented orthogonal to the Galactic plane, centered at coordinates l = 0.08◦
, b = −1.42◦
. The
surface brightness and hardness ratio patterns are suggestive of a cylindrical morphology which may
have been produced by a plasma outflow channel extending from the Galactic center. Our fits of the
feature’s spectra favor a complex two-component model consisting of thermal and recombining plasma
components, possibly a sign of shock compression or heating of the interstellar medium by outflowing
material. Assuming a recombining plasma scenario, we further estimate the cooling timescale of this
plasma to be on the order of a few hundred to thousands of years, leading us to speculate that a
sequence of accretion events onto the Galactic Black Hole may be a plausible quasi-continuous energy
source to sustain the observed morphology
Efficient spin-up of Earth System Models usingsequence accelerationSérgio Sacani
Marine and terrestrial biogeochemical models are key components of the Earth System Models (ESMs) used toproject future environmental changes. However, their slow adjustment time also hinders effective use of ESMsbecause of the enormous computational resources required to integrate them to a pre-industrial equilibrium. Here,a solution to this "spin-up" problem based on "sequence acceleration", is shown to accelerate equilibration of state-of-the-art marine biogeochemical models by over an order of magnitude. The technique can be applied in a "blackbox" fashion to existing models. Even under the challenging spin-up protocols used for Intergovernmental Panelon Climate Change (IPCC) simulations, this algorithm is 5 times faster. Preliminary results suggest that terrestrialmodels can be similarly accelerated, enabling a quantification of major parametric uncertainties in ESMs, improvedestimates of metrics such as climate sensitivity, and higher model resolution than currently feasible.
(May 29th, 2024) Advancements in Intravital Microscopy- Insights for Preclini...Scintica Instrumentation
Intravital microscopy (IVM) is a powerful tool utilized to study cellular behavior over time and space in vivo. Much of our understanding of cell biology has been accomplished using various in vitro and ex vivo methods; however, these studies do not necessarily reflect the natural dynamics of biological processes. Unlike traditional cell culture or fixed tissue imaging, IVM allows for the ultra-fast high-resolution imaging of cellular processes over time and space and were studied in its natural environment. Real-time visualization of biological processes in the context of an intact organism helps maintain physiological relevance and provide insights into the progression of disease, response to treatments or developmental processes.
In this webinar we give an overview of advanced applications of the IVM system in preclinical research. IVIM technology is a provider of all-in-one intravital microscopy systems and solutions optimized for in vivo imaging of live animal models at sub-micron resolution. The system’s unique features and user-friendly software enables researchers to probe fast dynamic biological processes such as immune cell tracking, cell-cell interaction as well as vascularization and tumor metastasis with exceptional detail. This webinar will also give an overview of IVM being utilized in drug development, offering a view into the intricate interaction between drugs/nanoparticles and tissues in vivo and allows for the evaluation of therapeutic intervention in a variety of tissues and organs. This interdisciplinary collaboration continues to drive the advancements of novel therapeutic strategies.
The increased availability of biomedical data, particularly in the public domain, offers the opportunity to better understand human health and to develop effective therapeutics for a wide range of unmet medical needs. However, data scientists remain stymied by the fact that data remain hard to find and to productively reuse because data and their metadata i) are wholly inaccessible, ii) are in non-standard or incompatible representations, iii) do not conform to community standards, and iv) have unclear or highly restricted terms and conditions that preclude legitimate reuse. These limitations require a rethink on data can be made machine and AI-ready - the key motivation behind the FAIR Guiding Principles. Concurrently, while recent efforts have explored the use of deep learning to fuse disparate data into predictive models for a wide range of biomedical applications, these models often fail even when the correct answer is already known, and fail to explain individual predictions in terms that data scientists can appreciate. These limitations suggest that new methods to produce practical artificial intelligence are still needed.
In this talk, I will discuss our work in (1) building an integrative knowledge infrastructure to prepare FAIR and "AI-ready" data and services along with (2) neurosymbolic AI methods to improve the quality of predictions and to generate plausible explanations. Attention is given to standards, platforms, and methods to wrangle knowledge into simple, but effective semantic and latent representations, and to make these available into standards-compliant and discoverable interfaces that can be used in model building, validation, and explanation. Our work, and those of others in the field, creates a baseline for building trustworthy and easy to deploy AI models in biomedicine.
Bio
Dr. Michel Dumontier is the Distinguished Professor of Data Science at Maastricht University, founder and executive director of the Institute of Data Science, and co-founder of the FAIR (Findable, Accessible, Interoperable and Reusable) data principles. His research explores socio-technological approaches for responsible discovery science, which includes collaborative multi-modal knowledge graphs, privacy-preserving distributed data mining, and AI methods for drug discovery and personalized medicine. His work is supported through the Dutch National Research Agenda, the Netherlands Organisation for Scientific Research, Horizon Europe, the European Open Science Cloud, the US National Institutes of Health, and a Marie-Curie Innovative Training Network. He is the editor-in-chief for the journal Data Science and is internationally recognized for his contributions in bioinformatics, biomedical informatics, and semantic technologies including ontologies and linked data.
This pdf is about the Schizophrenia.
For more details visit on YouTube; @SELF-EXPLANATORY;
https://www.youtube.com/channel/UCAiarMZDNhe1A3Rnpr_WkzA/videos
Thanks...!
Introduction:
RNA interference (RNAi) or Post-Transcriptional Gene Silencing (PTGS) is an important biological process for modulating eukaryotic gene expression.
It is highly conserved process of posttranscriptional gene silencing by which double stranded RNA (dsRNA) causes sequence-specific degradation of mRNA sequences.
dsRNA-induced gene silencing (RNAi) is reported in a wide range of eukaryotes ranging from worms, insects, mammals and plants.
This process mediates resistance to both endogenous parasitic and exogenous pathogenic nucleic acids, and regulates the expression of protein-coding genes.
What are small ncRNAs?
micro RNA (miRNA)
short interfering RNA (siRNA)
Properties of small non-coding RNA:
Involved in silencing mRNA transcripts.
Called “small” because they are usually only about 21-24 nucleotides long.
Synthesized by first cutting up longer precursor sequences (like the 61nt one that Lee discovered).
Silence an mRNA by base pairing with some sequence on the mRNA.
Discovery of siRNA?
The first small RNA:
In 1993 Rosalind Lee (Victor Ambros lab) was studying a non- coding gene in C. elegans, lin-4, that was involved in silencing of another gene, lin-14, at the appropriate time in the
development of the worm C. elegans.
Two small transcripts of lin-4 (22nt and 61nt) were found to be complementary to a sequence in the 3' UTR of lin-14.
Because lin-4 encoded no protein, she deduced that it must be these transcripts that are causing the silencing by RNA-RNA interactions.
Types of RNAi ( non coding RNA)
MiRNA
Length (23-25 nt)
Trans acting
Binds with target MRNA in mismatch
Translation inhibition
Si RNA
Length 21 nt.
Cis acting
Bind with target Mrna in perfect complementary sequence
Piwi-RNA
Length ; 25 to 36 nt.
Expressed in Germ Cells
Regulates trnasposomes activity
MECHANISM OF RNAI:
First the double-stranded RNA teams up with a protein complex named Dicer, which cuts the long RNA into short pieces.
Then another protein complex called RISC (RNA-induced silencing complex) discards one of the two RNA strands.
The RISC-docked, single-stranded RNA then pairs with the homologous mRNA and destroys it.
THE RISC COMPLEX:
RISC is large(>500kD) RNA multi- protein Binding complex which triggers MRNA degradation in response to MRNA
Unwinding of double stranded Si RNA by ATP independent Helicase
Active component of RISC is Ago proteins( ENDONUCLEASE) which cleave target MRNA.
DICER: endonuclease (RNase Family III)
Argonaute: Central Component of the RNA-Induced Silencing Complex (RISC)
One strand of the dsRNA produced by Dicer is retained in the RISC complex in association with Argonaute
ARGONAUTE PROTEIN :
1.PAZ(PIWI/Argonaute/ Zwille)- Recognition of target MRNA
2.PIWI (p-element induced wimpy Testis)- breaks Phosphodiester bond of mRNA.)RNAse H activity.
MiRNA:
The Double-stranded RNAs are naturally produced in eukaryotic cells during development, and they have a key role in regulating gene expression .
Seminar of U.V. Spectroscopy by SAMIR PANDASAMIR PANDA
Spectroscopy is a branch of science dealing the study of interaction of electromagnetic radiation with matter.
Ultraviolet-visible spectroscopy refers to absorption spectroscopy or reflect spectroscopy in the UV-VIS spectral region.
Ultraviolet-visible spectroscopy is an analytical method that can measure the amount of light received by the analyte.
2. L2 A. A. Chrimes et al.
consistent model. Circumstellar medium interactions around young
supernovae are a plausible origin for the early-time spectra and X-
ray/radio emission of some FBOTs (Pursiainen et al. 2018; Ho et al.
2023b), as well as for the optical polarisation behaviour (Maund et al.
2023). However, the peak absolute magnitude, rapid subsequent fad-
ing, high radio/X-ray luminosity and peculiar optical and radio polar-
isation of LFBOTs (Huang et al. 2019; Maund et al. 2023) require an
alternative explanation. Following AT 2018cow, a few main classes
of model emerged. These include central engines born in low-ejecta
core-collapse events, powered by black hole accretion or magnetar
spin-down (e.g. Perley et al. 2019; Margutti et al. 2019); mergers of
stellar-mass black holes and hydrogen-poor stars (e.g. Metzger 2022);
or the tidal disruption of a main sequence star (Perley et al. 2019)
or white dwarf by an intermediate mass black hole (IMBH, Kuin
et al. 2019). The former is motivated by the rapid light-curve decay
and multi-wavelength evolution which severely limits the possible
ejecta mass; the latter two also by the timescale - which is too fast
for a supermassive black hole (SMBH) tidal disruption event (TDE)
- and the weak (initially absent) hydrogen lines in the spectra. Many
of these scenarios face challenges. For example, a magnetar central
engine can power the early or late-time UV emission in AT 2018cow,
but not both (Chen et al. 2023b), while the environments of LFBOTS
thus far - at small offsets within star-forming dwarfs and spirals, and
with high circumstellar densities (Margutti et al. 2019) - favour a
short-lived, massive star progenitor over an IMBH TDE. Further in-
sight will come from similarly detailed studies of other LFBOTs, to
establish which features are common to all objects in this class, and
to understand the variety among them.
In this letter, we present multi-wavelength observations of a new
LFBOT, AT2023fhn ("the Finch"). The transient is significantly off-
set from the nearest galaxies, representing a deviation in terms of
its environment from previous LFBOTs. This letter is structured
as follows. In Section 2 we review how AT 2023fhn was discov-
ered, and present early-time X-ray and radio observations. Section 3
presents follow-up observations, including Hubble Space Telescope
(HST) imaging and Gemini spectroscopy. In Section 4 we discuss
possible interpretations, and conclusions are drawn in Section 5. We
adopt a cosmology with H0 = 69.6 km s−1 Mpc−1, Ωm = 0.29 and
ΩΛ = 0.71 (Wright 2006; Bennett et al. 2014). Uncertainties are
given as 1𝜎 unless otherwise stated, and magnitudes are quoted in
the AB system (Oke & Gunn 1982).
2 DISCOVERY AND CLASSIFICATION
2.1 Early photometry and spectra
AT 2023fhn was discovered on 10 Apr 2023 with 𝑚(𝑟) = 19.74 by
ZTF (Fremling 2023). The blue colour of 𝑔 − 𝑟 ∼ −0.47 and rapid
∼0.2 mag day−1 evolution immediately classified AT 2023fhn as an
LFBOT candidate. Ho et al. (2023a) subsequently obtained Gemini
GMOS-S spectroscopy of AT 2023fhn on 19-04-2023 (programme
GS-2023A-Q-127), finding a featureless blue spectrum. On 20 Apr
2023 they obtained a spectrum of the nearby spiral galaxy (∼5 arcsec
offset), yielding a redshift of 𝑧 ∼ 0.24. At this redshift, the earliest
ZTF 𝑔-band (12 Apr 2023) absolute magnitude is -21.5.
2.2 X-ray and radio observations
We triggered Chandra X-ray Observatory observations (PI: Chrimes;
program 24500143; Obs ID 26624), which were obtained on 25 Apr
2023 (06:58:08 – 15:46:51 UT). The faint-mode ACIS-S exposure
Table 1. VLA flux density upper-limits. These are given as 3 times the local
RMS. The third column lists the bandwidth. The final column lists limits on
the luminosity, assuming a redshift of 𝑧 = 0.238 (see Section 3.2).
Start date Freq. BW Texp Upper-limit Upper-limit
JD-2460056 GHz GHz Min. 𝜇Jy/beam 1028 erg s−1 Hz−1
0.80733 1.50 1.024 35.9 130 22.5
0.78309 3.00 2.048 30.0 35 6.0
0.76507 6.05 2.048 21.0 18 3.1
0.74688 10.00 4.096 21.1 18 3.1
0.72090 15.02 6.144 30.1 11 1.9
0.69229 21.94 8.192 28.2 17 2.9
0.66552 32.94 8.192 25.4 25 4.3
lasted 30 ks. The data were reduced and analysed with standard ciao
(v4.13, caldb v4.9.3) procedures including reprocessing, filtering
and source measurement with srcflux. Assuming a power-law with
a photon index Γ = 2 (Rivera Sandoval et al. 2018; Matthews et al.
2023), the unabsorbed source flux after correction for the Galac-
tic neutral hydrogen column density of 𝑁𝐻 = 2.4 × 1020cm−2
(Kalberla et al. 2005) is 7.6−1.8
+2.2
× 10−15 erg cm−2 s−1 (0.5-7.0 keV).
At the redshift of the spiral, this corresponds to a luminosity of
1.3−0.3
+0.4
×1042 erg s−1, comparable to other LFBOTs at the same
epoch (Rivera Sandoval et al. 2018; Margutti et al. 2019; Kuin et al.
2019; Coppejans et al. 2020; Bright et al. 2022; Yao et al. 2022;
Matthews et al. 2023).
Early radio observations (within a few weeks of discovery) pro-
duced non-detections, including a 10 GHz Northern Extended Mil-
limeter Array upper limit of 2 × 1029 erg s−1 Hz−1 on the luminosity
(Ho 2023), and upper limits from our own programme (SC240143,
PI: Chrimes) on the Karl G. Jansky Very Large Array (VLA). We
observed AT 2023fhn on 22 Apr 2023 (≈ 12 days post detection) in
standard phase-referencing mode using 3C286 as a flux density and
bandpass calibrator, with J1014+2301 and J1016+2037 as complex
gain calibrators. The observations were calibrated using the VLA
Calibration Pipeline 2022.2.0.64 in CASA version 6.4.1 with addi-
tional manual flagging. We imaged the data using the task tclean
in CASA with Briggs weighting with a robust parameter of 1. No
significant emission was detected at the source location. We pro-
vide the upper-limits in Table 1. These early-time non-detections are
consistent with the behaviour of previous LFBOTs. The transient
was subsequently detected with the VLA on 15 Jun 2023 (Ho 2023)
with luminosity 7.6 × 1028 erg s−1 Hz−1 (at 10 GHz), also similar to
other LFBOTs at the same epoch (e.g. Margutti et al. 2019; Coppe-
jans et al. 2020). The rapid evolution (timescale of a few days) and
peak optical absolute magnitude of -21.5 places AT 2023fhn firmly
within the LFBOT region of timescale/peak luminosity parameter
space (see Figures 3 and 14 of Ho et al. 2023b). Along with the hot
featureless optical spectrum, X-ray and radio detections, AT 2023fhn
is unambiguously identified as a new AT 2018cow-like LFBOT.
3 FOLLOW-UP OBSERVATIONS
3.1 Hubble Space Telescope Imaging
3.1.1 Data reduction and photometry
HST WFC3/UVIS observations were taken with the F555W and
F814W filters on 17 May 2023 (PI: Chrimes; proposal ID
17238). Three 364 s exposures with sub-pixel dithers were taken
in each filter. The F555W exposures began 09:02:23 and ended
MNRAS 000, 1–7 (2023)
3. AT2023fhn (the Finch) L3
10h08m04.4s 04.2s 04.0s 03.8s 03.6s 03.4s 03.2s
21°04'30"
27"
24"
21"
18"
Right Ascension
Declination
F555W
10h08m04.4s 04.2s 04.0s 03.8s 03.6s 03.4s 03.2s
21°04'30"
27"
24"
21"
18"
Right Ascension
F814W
Figure 1. HST images of AT 2023fhn, indicated by red pointers, and the nearby host galaxy candidates. North is up and east is left in all images. The transient
lies at a large offset from both the barred spiral to the south and the dwarf galaxy to the southeast. Smoothed and scaled 3.75×3.75 arcsec cutouts around
AT 2023fhn are shown in the inset panels. The diffuse emission northwest of the dwarf (satellite) galaxy is an alternative parent stellar population.
09:23:41 UT, the F814W exposures began 09:25:31 and ended
09:48:13 UT. The _flc images were combined using astrodriz-
zle1 (Fruchter & Hook 2002), with pix_frac = 0.8 and a final
pixel scale of 0.025 arcsec pixel−1. The transient is clearly iden-
tified in the reduced images, as shown in Figure 1. Two adja-
cent galaxies are fully resolved: a barred spiral to the south and
a dwarf/irregular to the southeast. These galaxies have Sloan Digi-
tal Sky Survey (SDSS) data release 16 (Ahumada et al. 2020) IDs
SDSS J100803.73+210422.5 and SDSS J100803.87+210425.8. We
perform photometry on AT 2023fhn with three methods. The first two
use standard photutils aperture photometry procedures in python
(Bradley et al. 2021), but the background level is calculated in two
ways. The first uses the MedianBackground estimator (using the
whole image for the estimate). The second uses an annulus around
the source (inner and outer radii of 1.5 and 4 times the aperture ra-
dius, and pixel values in the annulus clipped at ±3𝜎). For each of
these background estimations, two aperture sizes are used - 0.2 and
0.4 arcsec - with the appropriate aperture corrections for F555W and
F814W applied2. AB magnitudes are derived from the photflam
and photplam header values and the published conversion proce-
dures3. For the third method we use dolphot (v2.0, Dolphin 2000).
dolphot performs PSF photometry on each _flc image separately;
these measurements are combined to give the reported value and its
error. dolphot provides instrumental magnitudes in the Vega system,
but we instead report AB magnitudes using conversions calculated
with stsynphot (STScI Development Team 2020). Magnitude mea-
surements for each combination of filter and methodology are given
in Table 2. Smaller apertures and annulus background subtraction
results in fainter magnitudes, indicative of the presence of diffuse
emission around the transient (as can be seen in Figure 1, see insets).
1 Part of drizzlepac, http://drizzlepac.stsci.edu/
2 https://hubblesite.org/sites/www/home/
hst/instrumentation/wfc3/data-analysis/
photometric-calibration/uvis-encircled-energy
3 https://hst-docs.stsci.edu/wfc3dhb/
chapter-9-wfc3-data-analysis/9-1-photometry
Table 2. HST magnitudes 𝑚, and their uncertainties 𝛿𝑚, for AT 2023fhn.
In both filters, three photometry methods are listed - aperture photometry
with median background estimation, aperture photometry with annulus back-
ground estimation, and dolphot. For the non-dolphot measurements, two
aperture sizes (and hence enclosed energy corrections) are listed.
Filter Method Background Aperture m 𝛿m
F555W photutils Median 0.2′′ 24.31 0.02
F555W photutils Annulus 0.2′′ 24.38 0.02
F555W photutils Median 0.4′′ 24.13 0.03
F555W photutils Annulus 0.4′′ 24.30 0.02
F555W dolphot – PSF 24.57 0.01
F814W photutils Median 0.2′′ 24.17 0.03
F814W photutils Annulus 0.2′′ 24.27 0.02
F814W photutils Median 0.4′′ 23.94 0.04
F814W photutils Annulus 0.4′′ 24.11 0.03
F814W dolphot – PSF 24.45 0.07
3.1.2 Galaxy offsets and enclosed flux radii
The sky-projected spatial offset of a transient from its host is a key
piece of information for understanding its origin. Host-normalised
offsets, offsets divided by the half-light radius of the host, are widely
used in the literature (see Figure 4) as they account for the projected
extent of the host galaxy. In order to measure the offsets and host-
normalised offsets of AT 2023fhn from the two nearby galaxies, we
measure their centroids and half-light radii 𝑟50 (from Petrosian pro-
file fitting) using the python package statmorph (Rodriguez-Gomez
et al. 2019). We require objects to have at least 5 adjacent pixels,
each >1 𝜎 above the background. The resultant segmentation maps
are convolved with a uniform filter of size 10 pixels and these fil-
tered segmentation maps are used to identify objects by requiring
values > 0.5. Enclosed flux measurements are not restricted to the
galaxy-associated pixels identified with this method; flux is mea-
sured out to rmax which extends beyond the segmentation area to
the faint outer regions (further than twice then Petrosian radius, for
details see Rodriguez-Gomez et al. 2019). We note that the transient
lies outside the pixels selected as associated with the galaxy in both
cases. Segmentation maps, radial light profiles in the direction of
MNRAS 000, 1–7 (2023)
4. L4 A. A. Chrimes et al.
the transient, and statmorph Sérsic fits for the two galaxies in each
filter, are provided in the associated github repository4.
At 𝑧 = 0.238 - the redshift of the spiral (and its satellite, see Sec-
tion 3.2) - the physical scale is 3.80 kpc arcsec−1. From the centre of
the spiral, the projected offset of AT 2023fhn 𝛿𝑟 is 16.51 ± 0.09 kpc.
From the centre of the satellite, the offset is 5.35 ± 0.06 kpc (uncer-
tainties as described below). The non-parametric half-light radius r50
(enclosing 50 per cent of the flux, 𝑟50) is measured to be 4.5±0.2 kpc
in F555W for the spiral. Given the satellite’s ellipticity of 0.4 and
the orientation of AT 2023fhn, we take r50 along the semi-major
axis, which is 1.48 ± 0.10 kpc in F555W. In F814W, these values are
3.90 ± 0.13 kpc and 1.29 ± 0.10 kpc, respectively. This corresponds
to host-normalised offsets (𝑟n = 𝛿𝑟/𝑟50) of 3.7 ± 0.2 and 3.6 ± 0.2
in F555W, while in F814W, 𝑟n = 4.25 ± 0.14 and 4.1 ± 0.3 (for
the spiral and satellite respectively). The quoted offset uncertainties
are the quadrature sum of the transient positional uncertainty (given
by FWHM/(2.35×SNR), where FWHM is the full-width at half-
maximum and SNR the signal-to-noise ratio) and the uncertainty on
the galaxy centroids (𝑥c,𝑦c). The centroid uncertainties are calcu-
lated by re-sampling the input _flc image set 100 times using their
[ERR] extensions, re-drizzling each re-sampled set, and measuring
the morphological properties with statmorph on each iteration of
the re-drizzled image (see Lyman et al. 2017; Chrimes et al. 2019).
The mean and standard deviation of the resultant 𝑥c, 𝑦c and r50 distri-
butions are used, along with the AT 2023fhn positional uncertainties,
to calculate the values and their uncertainties quoted above.
3.1.3 Search for underlying and extended emission
Given the apparently isolated location of AT 2023fhn, it is prudent
to search for any underlying (extended) emission at the transient
location, such as a knot of star formation, cluster or background
galaxy. To establish whether the emission is unresolved, we first
select a reference point source in the image (the object at coor-
dinates 𝛼 = 10h08m03.13s, 𝛿 = +21d04m22.8s). Cutouts around
AT 2023fhn and the reference star are interpolated onto a pixel grid
with twice the resolution (enabling sub-pixel shifts), before subtrac-
tion of the reference image from the one containing AT 2023fhn.
The reference is scaled in peak flux and shifted in 𝑥,𝑦 to minimize
the standard deviation at the location of AT 2023fhn in the residual
image. The transient, reference and residual images are shown in
Figure 2. To determine if the residuals are consistent with a clean
point source subtraction, we perform photutils aperture photometry
(with an annulus) as described above. No significant residual flux is
detected, demonstrating that any underlying (non-transient) source
contributing significantly to the flux must be precisely co-located and
also unresolved (the physical scale at this distance is 95 pc pixel−1).
Making use of BPASS (Binary Population and Spectral Synthesis
v2.2, Eldridge et al. 2017; Stanway & Eldridge 2018) synthetic spec-
tra, we calculate the maximum mass of a stellar cluster which can
be present at the location of AT 2023fhn, without exceeding the
observed luminosity in either F555W or F814W. We find that the
maximum possible mass of an unresolved cluster rises with popula-
tion age, from 3×106M⊙ at 106 yr to ∼ 109M⊙ at 1010 yr. Therefore,
the presence of a typical stellar cluster - at any age - cannot be ruled
out. To search for extended emission, we smooth the images with a
Gaussian filter (𝜎 = 1.5) and scale them to show diffuse background
light. The inset panels of Figure 1 show cutouts of the smoothed and
scaled images. Faint emission can be seen extending northwest of
4 https://github.com/achrimes2/Finch
F555W
F814W
Figure 2. Subtraction of a reference star at the location of AT 2023fhn. The
2×2 arcsec cutouts show the transient (left), the reference star (middle) and
the residual (right), after interpolating onto a finer pixel scale and subtraction
of the shifted and vertically scaled reference star. The emission is consistent
with being a point source.
3500 4000 4500 5000 5500 6000 6500 7000 7500
0
1
2
3
4
5
F
[erg
s
1
cm
2
Å
1
]
×10 17
AT2023fhn Sky
Spectrum
BB fit
3500 4000 4500 5000 5500 6000 6500 7000 7500
Wavelength [Å]
0
1
2
3
F
[erg
s
1
cm
2
Å
1
]
×10 17
Satellite OIII
H H Spectrum
Sky
Figure 3. Upper panel: the background-subtracted spectrum of AT 2023fhn
obtained with Gemini/GMOS-S on 22/23 Apr 2023, ∼10 rest-frame days post-
discovery, and shifted into the transient rest-frame. A black-body fit returns
𝑇 = 24.8+2.4
−2.3
×103 K. Background traces are shown in grey. Lower panel: a
spectrum of the satellite galaxy. A robust detection of the H𝛼 emission line
at 𝑧 = 0.238 ± 0.004 confirms an association with the adjacent spiral.
the satellite, plausibly a tidal stream. The surface brightness near the
transient location (measured in a 1 arcsec radius around AT 2023fhn)
is 25.2 mag arcsec−2 in F555W and 24.6 mag arcsec−2 in F814W.
3.2 Gemini spectroscopy
We obtained two epochs of Gemini/GMOS-S spectroscopy on 22/23
Apr 2023 and 12 May 2023, ∼10 and ∼26 days post discovery respec-
tively (PI: Chrimes, programme GS-2023A-DD-102). The first epoch
consisted of 4×500s exposures with the R400 grating, 1 arcsec slit
width and two central wavelengths (two exposures at 520 nm and two
at 565 nm). The second epoch consisted of 4×1845s exposures with
the R400 grating, 1 arcsec slit and central wavelength 675 nm. Data
reduction was performed using the python package dragons (Labrie
et al. 2019). Associated arcs, flats and bias frames were taken as part
of the programme. Sky lines and unusable regions (e.g. due to the am-
plifier 5 failure5) are manually masked. We bin the pixels by a factor
of 6 along the wavelength axis to increase the signal-to-noise ratio,
and combine the 520 nm and 565 nm centred spectra by taking the
5 https://www.gemini.edu/node/21963
MNRAS 000, 1–7 (2023)
5. AT2023fhn (the Finch) L5
10 1 100 101
Host-normalised offset rn
0.0
0.2
0.4
0.6
0.8
1.0
Cumulative
Fraction
LGRBs
SLSNe
CCSNe
FRBs
Ca-rich SNe
SGRBs
GCs
10 1 100 101 102
Offset r [kpc]
0.0
0.2
0.4
0.6
0.8
1.0
Cumulative
Fraction
LFBOTs
LGRBs
SLSNe
CCSNe
FRBs
SNe Ia
Ca-rich SNe
SGRBs
GCs
Figure 4. The cumulative offset and host-normalised offset distributions of a variety of transients, and the offset of AT 2023fhn from the spiral (thick black
vertical lines) and its satellite (narrow vertical lines) - solid lines represent F555W, dashed lines F814W. The four previous LFBOT offsets are from Prentice
et al. (2018, the Cow), Ho et al. (2020, the Koala), Coppejans et al. (2020, CSS161010) and Yao et al. (2022, AT 2020mrf). The comparison distributions are
from Blanchard et al. (2016); Lyman et al. (2017, LGRBs), Lunnan et al. (2015); Schulze et al. (2021, SLSNe), Kelly & Kirshner (2012); Schulze et al. (2021,
CCSNe), Bhandari et al. (2022, FRBs), Wang et al. (2013, type Ia SNe), Lunnan et al. (2017); De et al. (2020, Ca-rich SNe) and Fong et al. (2022, SGRBs).
Also shown is the globular cluster (GC) offset distribution around M81 (Lomelí-Núñez et al. 2022).
mean where they overlap. We correct for Galactic extinction by adopt-
ing 𝐸(𝐵 − 𝑉) = 0.025 (Schlafly & Finkbeiner 2011), and calculate
the extinction at each wavelength with the python extinction (Bar-
bary 2016) module assuming 𝑅V = 3.1. For flux calibration, spectro-
photometric standard stars observed with the closest-matching set-up
were found in the Gemini archive. For the 525 nm data we use spectra
of EG274 (programme GS-2023A-FT-205), for the 565 nm data we
use LTT6248 (GS-2022A-Q-315) and for the 675 nm data we use
LTT1020 (GS-2022B-Q-126). The final extinction-corrected spectra
are plotted in Figure 3.
In our first epoch of spectroscopy (22/23 Apr), AT 2023fhn is
detected as shown in Figure 3. Fitting a black-body to the Galac-
tic extinction-corrected, rest-frame spectrum yields a temperature of
24.8+2.4
−2.3
×103 K (𝜒2
𝜈 = 3.66 with 282 degrees of freedom, where
uncertainties are derived from the local standard deviation of the
spectrum). This compares with a temperature of 17.5+1.2
−1.0
×103 K
derived from FORS2 photometry taken on the following night (Wise
& Perley 2023). The large 𝜒2
𝜈 is likely due to correlated, systematic
errors (e.g. from imperfect flux calibration) that have not been ac-
counted for. A power-law produces a fit of similar quality - taking
F𝜆 ∝ 𝜈2−𝛽, we find a best-fit power-law index 𝛽 = −1.24+0.06
−0.09
,
with 𝜒2
𝜈 = 3.63. Nevertheless, temperatures of ∼20 ×103 K are
comparable to AT 2018cow, which had a black-body temperature
of 19.3+0.7
−0.8
×103 K at a similar rest-frame epoch (Prentice et al.
2018). No correction for host-intrinsic extinction has been made,
however as revealed in the HST imaging, the transient appears to
be far away from any significant sources of dust, as it lies outside
the bulk of the optical light of both nearby galaxies. In the second
epoch of spectroscopy (12 May) the transient had faded sufficiently
to result in a non-detection, with an upper limit on H𝛼 emission at
its location (taking an aperture with the same radius as the seeing)
of < 1.2 × 10−16 erg s−1 cm−2. The slit was also placed on the edge
of the satellite galaxy. From the centroid and width of the H𝛼 line,
we derive a redshift 𝑧 = 0.238 ± 0.004, consistent with the spiral
redshift of ∼ 0.24 reported by Ho et al. (2023a), and backing up the
satellite interpretation for this galaxy. We have adopted 𝑧 = 0.238 for
all relevant calculations in this letter.
4 DISCUSSION
All published LFBOTS to date have occurred in star-forming dwarfs
(the Koala, CSS161010, the Camel, AT 2020mrf, Ho et al. 2020;
Coppejans et al. 2020; Perley et al. 2021; Yao et al. 2022) or spirals
(the Cow, Prentice et al. 2018; Lyman et al. 2020). AT 2023fhn also
has a star-forming host, assuming one of the spiral or dwarf (both
are strong H𝛼 emitters) is the galaxy of origin. However, in contrast
with LFBOTs so far, it lies far away from the bulk of the host light
for either choice of host galaxy. Such offsets are atypical for core-
collapse transients due to the short (10-100 Myr lifetimes) of the
progenitor stars. Figure 4 compares the physical projected offsets and
host-normalised offsets of a range of transients compiled from the
literature, including long gamma-ray bursts (LGRBs), short gamma-
ray bursts (SGRBs), superluminous supernovae (SLSNe), other core-
collapse supernovae (CCSNe), fast radio bursts (FRBs), Ca-rich and
type Ia SNe. The host offsets of four previous LFBOTs are also shown
(𝑟𝑛 values were not reported for these events). AT 2023fhn lies much
further out from its host than other LFBOTs to date. To quantify
this, we randomly draw 5 (the number of LFBOTs with host offset
measurements in Fig. 4) offsets from the Schulze et al. (2021) CCSN
distribution 104 times, and calculate the frequency with which at
least one of these lies at 5.35 (16.51) kpc or greater (for the satellite
and spiral respectively). For the satellite, this occurs in 85 per cent
of random draws, for the spiral it occurs in 13 per cent. In terms of
host-normalised offset, only ∼1 per cent of CCSNe occur at higher
offsets than AT 2023fhn. In all 4 combinations of filter and galaxy
choice, the transient lies outside the pixels selected as associated
with the galaxies, therefore (by definition) the transient will have a
fraction of light (Fruchter et al. 2006) value Flight = 0 in both filters.
This is unlikely but not unprecedented for core-collapse events; a few
per cent of CCSN have Flight = 0 (Svensson et al. 2010). Therefore,
a core-collapse origin cannot be ruled out.
If originating at a lower offset, time-of-travel arguments require
a massive star with velocity ≳50/350 km s−1 for the spiral/satellite,
assuming a long-lived 100 Myr-old progenitor (Eldridge et al. 2019)
and an origin at ∼r50. Only a small fraction of massive stars have
such high velocities (e.g. Portegies Zwart 2000; de Wit et al. 2005;
MNRAS 000, 1–7 (2023)
6. L6 A. A. Chrimes et al.
Eldridge et al. 2011; Renzo et al. 2019; Chrimes et al. 2023). The
delayed mergers of compact objects can also achieve high offsets (i.e.
SGRBs), but the luminosity, spectra and rapid evolution of LFBOTs
effectively rule out an association with even the most extreme of these
transients (e.g. Kann et al. 2011; Sarin et al. 2022). Since no spectro-
scopic redshift for the transient has been measured, we consider the
probability of a chance alignment Pchance between AT 2023fhn and
the two galaxies (following Bloom et al. 2002; Berger 2010). Pchance
is calculated using SDSS DR16 𝑟-band magnitudes for the spiral
and satellite, which are 18.94 ± 0.02 and 22.61 ± 0.14, respectively.
For the spiral we find Pchance = 0.78 per cent, and for the satellite
Pchance = 1.38 per cent. Therefore, AT 2023fhn is likely associated
with one of the two galaxies. As shown in the inset panels of Figure
1, the progenitor may have originated in a faint tidal stream or spiral
arm. Based on our early-time radio and H𝛼 upper limits (Sections
2 and 3.2), and using the star formation rate (SFR) calibrations of
Murphy et al. (2011), we derive 3 𝜎 upper limits on the underlying
SFR at the location of AT 2023fhn of ∼6 M⊙yr−1 (at 6.05 GHz, the
strongest radio constraint) and ∼0.1 M⊙yr−1 (H𝛼). The F555W (rest-
frame ∼B-band) surface brightness of 25.2 mag arcsec−2 (Sec. 3.1.3)
is among the faintest ∼2 per cent of (𝑢-band) local surface bright-
nesses for CCSNe (Kelly & Kirshner 2012). Unless the population is
extremely young, adjusting for the 𝐵-band/𝑢-band discrepancy would
give an even fainter surface brightness (due to lower flux blue-wards
of the Balmer break). An IMBH TDE explanation requires an un-
derlying cluster, since a dense stellar environment is necessary to
make encounters likely (e.g. Ye et al. 2023). As shown in Section
3.1.3, a cluster at the location of AT 2023fhn cannot be ruled out.
At 𝑧 ∼ 0.24, even the brightest and largest globular clusters (GCs)
would have optical apparent magnitudes of ∼30 - far fainter than
the source in the HST images - and angular extents too small to be
resolved (Harris 2010). Finally, we compare the offset of AT 2023fhn
from the spiral with the distribution of GCs around M81 (which has a
similar physical size and morphology), using the Sérsic distribution
of Lomelí-Núñez et al. (2022) (see also Perelmuter & Racine 1995).
The GC offsets, and distribution normalised by the F555W half-light
radius of the spiral, are shown in Figure 4. Only 0.5 per cent of GCs
occur at the offset of AT 2023fhn or higher. While unlikely based on
this statistic, the lack of strong photometric constraints mean that an
origin in a globular cluster is also not ruled out.
5 CONCLUSIONS
In this letter, we have presented HST, Gemini, Chandra and VLA
observations of AT 2023fhn, the first LFBOT to lie at a large offset
from its host galaxy. Although the location is more representative of
other transient types, given the offset, local surface brightness, limit
on star-formation and constraints on an underlying cluster, we cannot
rule out a massive star progenitor. Likewise, a tidal disruption event
in a unseen cluster cannot be ruled out. Environmental studies are
needed for a population of LFBOTs to determine if AT 2023fhn is
a significant outlier. Late-time imaging will put further constraints
on the underlying stellar population, while detailed modelling of the
spectra and multi-wavelength light-curve is needed to reveal more
about the origin of this enigmatic transient.
ACKNOWLEDGEMENTS
This work is part of the research programme Athena with project
number 184.034.002, which is (partly) financed by the Dutch Re-
search Council (NWO). This research has made use of computing
facilities provided by the Scientific Computing Research Technology
Platform of the University of Warwick. Observations analysed in this
work were taken by the NASA/ESA Hubble Space Telescope under
program 17238. This research has made use of software provided
by the Chandra X-ray Center (CXC) in the application of the CIAO
package (Fruscione et al. 2006). The National Radio Astronomy Ob-
servatory is a facility of the National Science Foundation operated
under cooperative agreement by Associated Universities, Inc. Based
on observations obtained at the international Gemini Observatory, a
program of NSF’s NOIRLab, which is managed by the Association
of Universities for Research in Astronomy (AURA) under a coopera-
tive agreement with the National Science Foundation on behalf of the
Gemini Observatory partnership. Finally, we thank the anonymous
referee for their helpful feedback on this manuscript.
DATA AVAILABILITY
The data used are available upon request. Scripts and parameter files
are available at https://github.com/achrimes2/Finch.
REFERENCES
Ahumada R., et al., 2020, ApJS, 249, 3
Barbary K., 2016, extinction v0.3.0, doi:10.5281/zenodo.804967, https:
//doi.org/10.5281/zenodo.804967
Bellm E. C., et al., 2019, PASP, 131, 018002
Bennett C. L., Larson D., Weiland J. L., Hinshaw G., 2014, ApJ, 794, 135
Berger E., 2010, ApJ, 722, 1946
Bhandari S., et al., 2022, AJ, 163, 69
Blanchard P. K., Berger E., Fong W.-f., 2016, ApJ, 817, 144
Bloemen S., et al., 2016, in Hall H. J., Gilmozzi R., Marshall H. K., eds,
Society of Photo-Optical Instrumentation Engineers (SPIE) Conference
Series Vol. 9906, Ground-based and Airborne Telescopes VI. p. 990664,
doi:10.1117/12.2232522
Bloom J. S., Kulkarni S. R., Djorgovski S. G., 2002, AJ, 123, 1111
Bradley L., et al., 2021, astropy/photutils: 1.1.0,
doi:10.5281/zenodo.4624996, https://doi.org/10.5281/zenodo.
4624996
Bright J. S., et al., 2022, ApJ, 926, 112
Chambers K. C., et al., 2016, arXiv e-prints, p. arXiv:1612.05560
Chen Y., et al., 2023a, arXiv e-prints, p. arXiv:2303.03500
Chen Y., Drout M. R., Piro A. L., Kilpatrick C. D., Foley R. J., Rojas-Bravo
C., Magee M. R., 2023b, arXiv e-prints, p. arXiv:2303.03501
Chrimes A. A., et al., 2019, MNRAS, 486, 3105
Chrimes A. A., et al., 2023, MNRAS, 522, 2029
Coppejans D. L., et al., 2020, ApJ, 895, L23
De K., et al., 2020, ApJ, 905, 58
Dolphin A. E., 2000, PASP, 112, 1383
Drout M. R., et al., 2014, ApJ, 794, 23
Eldridge J. J., Langer N., Tout C. A., 2011, MNRAS, 414, 3501
Eldridge J. J., Stanway E. R., Xiao L., McClelland L. A. S., Taylor G., Ng M.,
Greis S. M. L., Bray J. C., 2017, Publ. Astron. Soc. Australia, 34, e058
Eldridge J. J., Stanway E. R., Tang P. N., 2019, MNRAS, 482, 870
Fong W.-f., et al., 2022, ApJ, 940, 56
Fremling C., 2023, Transient Name Server Discovery Report, 2023-775, 1
Fruchter A. S., Hook R. N., 2002, PASP, 114, 144
Fruchter A. S., et al., 2006, Nature, 441, 463
Fruscione A., et al., 2006, in Silva D. R., Doxsey R. E., eds, Society of Photo-
Optical Instrumentation Engineers (SPIE) Conference Series Vol. 6270,
Society of Photo-Optical Instrumentation Engineers (SPIE) Conference
Series. p. 62701V, doi:10.1117/12.671760
Harris W. E., 2010, arXiv e-prints, p. arXiv:1012.3224
Ho A. Y. Q., 2023, Transient Name Server AstroNote, 174, 1
MNRAS 000, 1–7 (2023)
7. AT2023fhn (the Finch) L7
Ho A. Y. Q., et al., 2020, ApJ, 895, 49
Ho A. Y. Q., Perley D. A., Filippenko A. V., Zheng W., Brink T. G., Li M.,
Wang K., 2022a, Transient Name Server AstroNote, 199, 1
Ho A. Y. Q., Liu C., Chen P., Perley D., Wang K., Altunin I., 2022b, Transient
Name Server AstroNote, 275, 1
Ho A. Y. Q., et al., 2022c, ApJ, 932, 116
Ho A. Y. Q., Liu C., Andreoni I., Coughlin M., Qin Y., Perley D., 2023a,
Transient Name Server AstroNote, 93, 1
Ho A. Y. Q., et al., 2023b, ApJ, 949, 120
Huang K., et al., 2019, ApJ, 878, L25
Inkenhaag A., Jonker P. G., Levan A. J., Chrimes A. A., Mummery A., Perley
D. A., Tanvir N. R., 2023, arXiv e-prints, p. arXiv:2308.07381
Jiang J.-a., et al., 2022, ApJ, 933, L36
Kalberla P. M. W., Burton W. B., Hartmann D., Arnal E. M., Bajaja E., Morras
R., Pöppel W. G. L., 2005, A&A, 440, 775
Kann D. A., et al., 2011, ApJ, 734, 96
Kelly P. L., Kirshner R. P., 2012, ApJ, 759, 107
Kuin N. P. M., et al., 2019, MNRAS, 487, 2505
LSST Science Collaboration et al., 2009, arXiv e-prints, p. arXiv:0912.0201
Labrie K., Anderson K., Cárdenes R., Simpson C., Turner J. E. H., 2019, in
Teuben P. J., Pound M. W., Thomas B. A., Warner E. M., eds, Astro-
nomical Society of the Pacific Conference Series Vol. 523, Astronomical
Data Analysis Software and Systems XXVII. p. 321
Lomelí-Núñez L., Mayya Y. D., Rodríguez-Merino L. H., Ovando P. A.,
Rosa-González D., 2022, MNRAS, 509, 180
Lunnan R., et al., 2015, ApJ, 804, 90
Lunnan R., et al., 2017, ApJ, 836, 60
Lyman J. D., et al., 2017, MNRAS, 467, 1795
Lyman J. D., Galbany L., Sánchez S. F., Anderson J. P., Kuncarayakti H.,
Prieto J. L., 2020, MNRAS, 495, 992
Margutti R., et al., 2019, ApJ, 872, 18
Matthews D. J., et al., 2023, arXiv e-prints, p. arXiv:2306.01114
Maund J. R., et al., 2023, MNRAS, 521, 3323
Metzger B. D., 2022, ApJ, 932, 84
Murphy E. J., et al., 2011, ApJ, 737, 67
Oke J. B., Gunn J. E., 1982, PASP, 94, 586
Perelmuter J.-M., Racine R., 1995, AJ, 109, 1055
Perley D. A., et al., 2019, MNRAS, 484, 1031
Perley D. A., et al., 2021, MNRAS, 508, 5138
Perley D. A., Ho A. Y. Q., Hinds K., Jacobson-Galan W., 2023, Transient
Name Server AstroNote, 41, 1
Portegies Zwart S. F., 2000, ApJ, 544, 437
Prentice S. J., et al., 2018, ApJ, 865, L3
Pursiainen M., et al., 2018, MNRAS, 481, 894
Renzo M., et al., 2019, A&A, 624, A66
Rivera Sandoval L. E., Maccarone T. J., Corsi A., Brown P. J., Pooley D.,
Wheeler J. C., 2018, MNRAS, 480, L146
Rodriguez-Gomez V., et al., 2019, MNRAS, 483, 4140
STScI Development Team 2020, stsynphot: synphot for HST and JWST,
Astrophysics Source Code Library, record ascl:2010.003 (ascl:2010.003)
Sarin N., Omand C. M. B., Margalit B., Jones D. I., 2022, MNRAS, 516,
4949
Schlafly E. F., Finkbeiner D. P., 2011, ApJ, 737, 103
Schulze S., et al., 2021, ApJS, 255, 29
Stanway E. R., Eldridge J. J., 2018, MNRAS, 479, 75
Steeghs D., et al., 2022, MNRAS, 511, 2405
Sun N.-C., Maund J. R., Crowther P. A., Liu L.-D., 2022, MNRAS, 512, L66
Sun N.-C., Maund J. R., Shao Y., Janiak I. A., 2023, MNRAS, 519, 3785
Svensson K. M., Levan A. J., Tanvir N. R., Fruchter A. S., Strolger L. G.,
2010, MNRAS, 405, 57
Tonry J. L., et al., 2018, PASP, 130, 064505
Wang X., Wang L., Filippenko A. V., Zhang T., Zhao X., 2013, Science, 340,
170
Wise J., Perley D., 2023, Transient Name Server AstroNote, 101, 1
Wright E. L., 2006, PASP, 118, 1711
Yao Y., et al., 2022, ApJ, 934, 104
Ye C. S., Fragione G., Perna R., 2023, arXiv e-prints, p. arXiv:2303.07375
de Wit W. J., Testi L., Palla F., Zinnecker H., 2005, A&A, 437, 247
This paper has been typeset from a TEX/L
ATEX file prepared by the author.
MNRAS 000, 1–7 (2023)