- The document analyzes quasi periodic oscillations (QPOs) observed in black hole binaries MAXI J1659-152, GX 339-4, and H1743-322 using data from the Rossi X-ray Timing Explorer satellite.
- It found that H1743-322 showed a similar rms-flux relationship as previously observed in other black holes, while GX 339-4 showed a different relationship.
- More research is needed to fully understand and explain the relationships between flux, frequency, and rms observed in QPOs from black hole binaries.
3C 273 was one of the first quasars discovered in 1963. It remains one of the brightest and best studied quasars. It is located approximately 3 billion light years from Earth and radiates energy equivalent to 1014 times the luminosity of the Sun. 3C 273 plays a key role in understanding the nature of quasars as powered by accretion disks around supermassive black holes. It continues to be intensely observed across the electromagnetic spectrum to better understand the physics occurring in these energetic and distant cosmic objects.
1) The document provides a summary of a course on high-energy astrophysics that the author took. It discusses various topics covered in the course including accretion disks, pulsars, black holes, supernovae, and more.
2) The author argues that high-energy astrophysics is important for understanding the universe and requests that the provost offer a similar course at their university.
3) Key concepts in high-energy astrophysics discussed include accretion and its relation to luminosity, binary star systems, properties of neutron stars and black holes, and x-ray emissions from astrophysical phenomena like supernovae.
Radio imaging obserations_of_psr_j1023_0038_in_an_lmxb_stateSérgio Sacani
Uma estrela super densa formada depois da explosão de uma supernova está expelindo poderosos jatos de material no espaço, sugerem pesquisas recentes.
Num estudo publicado no dia 6 de Agosto de 2015, uma equipe de cientistas na Austrália e na Holanda descobriram poderosos jatos sendo expelidos de uma sistema estelar duplo conhecido como PSR J1023+0038.
Pensava-se anteriormente que os únicos objetos no universo capazes de formar jatos poderosos eram os buracos negros.
O sistema PSR J1023+0038 contém uma estrela extremamente densa que os astrônomos chamam de estrela de nêutrons, numa órbita próxima com uma estrela normal.
Ela foi identificada primeiro como uma estrela de nêutrons em 2009, mas foi somente quando a equipe de pesquisa observou a estrela com o rádio telescópio Very Large Array nos EUA em 2013 e 2014 que eles perceberam que a estrela estava produzindo jatos mais fortes do que se esperava.
Os astrônomos James Miller-Jones, do International Centre for Radio Astronomy Research (ICRAR), disse que as estrelas de nêutrons podem ser pensadas como cadáveres estelares.
“Elas são formadas quando uma estrela massiva esgota todo o seu combustível e vira uma supernova, e as partes centrais da estrela colapsam sobre sua própria gravidade”, disse ele.
“Essas coisas tem normalmente entre uma vez e meia a massa do Sol e somente entre 10 a 15 km de diâmetro, de modo que são extremamente densas”.
There are several types of ultra-compact binary star systems that orbit each other with periods of less than an hour. These systems emit gravitational waves due to their strong gravitational fields changing over time. The Laser Interferometer Space Antenna (LISA) mission aims to detect these gravitational waves. While current ground-based detectors cannot detect the waves from ultra-compact binaries, LISA may be able to do so due to observing from space. The document provides data on four example binary systems and calculates their orbital decay rates and the strain of the gravitational waves emitted.
After a supernova, a neutron star may form from the dense core. Neutron stars are extremely dense and spin rapidly, appearing as pulsars due to their intense magnetic fields and lighthouse effect. Neutron stars in binaries may become X-ray bursters or millisecond pulsars. Gamma-ray bursts are likely caused by colliding neutron stars or hypernovae. If the core is over 3 solar masses, it will collapse into a black hole requiring general relativity to describe. Anything within the event horizon of a black hole cannot escape.
A magnetar-powered X-ray transient as the aftermath of a binary neutron-star ...Sérgio Sacani
Mergers of neutron stars are known to be associated with short γ-ray
bursts1–4
. If the neutron-star equation of state is sufficiently stiff
(that is, the pressure increases sharply as the density increases), at
least some such mergers will leave behind a supramassive or even a
stable neutron star that spins rapidly with a strong magnetic field5–8
(that is, a magnetar). Such a magnetar signature may have been
observed in the form of the X-ray plateau that follows up to half
of observed short γ-ray bursts9,10. However, it has been expected
that some X-ray transients powered by binary neutron-star mergers
may not be associated with a short γ-ray burst11,12. A fast X-ray
transient (CDF-S XT1) was recently found to be associated with a
faint host galaxy, the redshift of which is unknown13. Its X-ray and
host-galaxy properties allow several possible explanations including
a short γ-ray burst seen off-axis, a low-luminosity γ-ray burst at
high redshift, or a tidal disruption event involving an intermediatemass black hole and a white dwarf13. Here we report a second X-ray
transient, CDF-S XT2, that is associated with a galaxy at redshift
z = 0.738 (ref. 14). The measured light curve is fully consistent with
the X-ray transient being powered by a millisecond magnetar. More
intriguingly, CDF-S XT2 lies in the outskirts of its star-forming host
galaxy with a moderate offset from the galaxy centre, as short γ-ray
bursts often do15,16. The estimated event-rate density of similar
X-ray transients, when corrected to the local value, is consistent
with the event-rate density of binary neutron-star mergers that is
robustly inferred from the detection of the gravitational-wave event
GW170817.
Material whose presence can be inferred from its effects on the motions of stars and galaxies, but which cannot be seen directly because it emits little or no radiation.
Explanation Of The Relationship Between The Temperature And Mass Of The Black...IOSR Journals
This thesis explains the phenomenon of the lowering of the temperature of the black hole and hence less radiation of energy from the black hole (Known from the concept of Hawking Radiation) with the increase in the mass of the black hole through the concept of gravitational waves.
3C 273 was one of the first quasars discovered in 1963. It remains one of the brightest and best studied quasars. It is located approximately 3 billion light years from Earth and radiates energy equivalent to 1014 times the luminosity of the Sun. 3C 273 plays a key role in understanding the nature of quasars as powered by accretion disks around supermassive black holes. It continues to be intensely observed across the electromagnetic spectrum to better understand the physics occurring in these energetic and distant cosmic objects.
1) The document provides a summary of a course on high-energy astrophysics that the author took. It discusses various topics covered in the course including accretion disks, pulsars, black holes, supernovae, and more.
2) The author argues that high-energy astrophysics is important for understanding the universe and requests that the provost offer a similar course at their university.
3) Key concepts in high-energy astrophysics discussed include accretion and its relation to luminosity, binary star systems, properties of neutron stars and black holes, and x-ray emissions from astrophysical phenomena like supernovae.
Radio imaging obserations_of_psr_j1023_0038_in_an_lmxb_stateSérgio Sacani
Uma estrela super densa formada depois da explosão de uma supernova está expelindo poderosos jatos de material no espaço, sugerem pesquisas recentes.
Num estudo publicado no dia 6 de Agosto de 2015, uma equipe de cientistas na Austrália e na Holanda descobriram poderosos jatos sendo expelidos de uma sistema estelar duplo conhecido como PSR J1023+0038.
Pensava-se anteriormente que os únicos objetos no universo capazes de formar jatos poderosos eram os buracos negros.
O sistema PSR J1023+0038 contém uma estrela extremamente densa que os astrônomos chamam de estrela de nêutrons, numa órbita próxima com uma estrela normal.
Ela foi identificada primeiro como uma estrela de nêutrons em 2009, mas foi somente quando a equipe de pesquisa observou a estrela com o rádio telescópio Very Large Array nos EUA em 2013 e 2014 que eles perceberam que a estrela estava produzindo jatos mais fortes do que se esperava.
Os astrônomos James Miller-Jones, do International Centre for Radio Astronomy Research (ICRAR), disse que as estrelas de nêutrons podem ser pensadas como cadáveres estelares.
“Elas são formadas quando uma estrela massiva esgota todo o seu combustível e vira uma supernova, e as partes centrais da estrela colapsam sobre sua própria gravidade”, disse ele.
“Essas coisas tem normalmente entre uma vez e meia a massa do Sol e somente entre 10 a 15 km de diâmetro, de modo que são extremamente densas”.
There are several types of ultra-compact binary star systems that orbit each other with periods of less than an hour. These systems emit gravitational waves due to their strong gravitational fields changing over time. The Laser Interferometer Space Antenna (LISA) mission aims to detect these gravitational waves. While current ground-based detectors cannot detect the waves from ultra-compact binaries, LISA may be able to do so due to observing from space. The document provides data on four example binary systems and calculates their orbital decay rates and the strain of the gravitational waves emitted.
After a supernova, a neutron star may form from the dense core. Neutron stars are extremely dense and spin rapidly, appearing as pulsars due to their intense magnetic fields and lighthouse effect. Neutron stars in binaries may become X-ray bursters or millisecond pulsars. Gamma-ray bursts are likely caused by colliding neutron stars or hypernovae. If the core is over 3 solar masses, it will collapse into a black hole requiring general relativity to describe. Anything within the event horizon of a black hole cannot escape.
A magnetar-powered X-ray transient as the aftermath of a binary neutron-star ...Sérgio Sacani
Mergers of neutron stars are known to be associated with short γ-ray
bursts1–4
. If the neutron-star equation of state is sufficiently stiff
(that is, the pressure increases sharply as the density increases), at
least some such mergers will leave behind a supramassive or even a
stable neutron star that spins rapidly with a strong magnetic field5–8
(that is, a magnetar). Such a magnetar signature may have been
observed in the form of the X-ray plateau that follows up to half
of observed short γ-ray bursts9,10. However, it has been expected
that some X-ray transients powered by binary neutron-star mergers
may not be associated with a short γ-ray burst11,12. A fast X-ray
transient (CDF-S XT1) was recently found to be associated with a
faint host galaxy, the redshift of which is unknown13. Its X-ray and
host-galaxy properties allow several possible explanations including
a short γ-ray burst seen off-axis, a low-luminosity γ-ray burst at
high redshift, or a tidal disruption event involving an intermediatemass black hole and a white dwarf13. Here we report a second X-ray
transient, CDF-S XT2, that is associated with a galaxy at redshift
z = 0.738 (ref. 14). The measured light curve is fully consistent with
the X-ray transient being powered by a millisecond magnetar. More
intriguingly, CDF-S XT2 lies in the outskirts of its star-forming host
galaxy with a moderate offset from the galaxy centre, as short γ-ray
bursts often do15,16. The estimated event-rate density of similar
X-ray transients, when corrected to the local value, is consistent
with the event-rate density of binary neutron-star mergers that is
robustly inferred from the detection of the gravitational-wave event
GW170817.
Material whose presence can be inferred from its effects on the motions of stars and galaxies, but which cannot be seen directly because it emits little or no radiation.
Explanation Of The Relationship Between The Temperature And Mass Of The Black...IOSR Journals
This thesis explains the phenomenon of the lowering of the temperature of the black hole and hence less radiation of energy from the black hole (Known from the concept of Hawking Radiation) with the increase in the mass of the black hole through the concept of gravitational waves.
Young remmants of_type_ia_supernovae_and_their_progenitors_a_study_of_snr_g19_03Sérgio Sacani
Type Ia supernovae, with their remarkably homogeneous light curves and spectra, have been used as
standardizable candles to measure the accelerating expansion of the Universe. Yet, their progenitors
remain elusive. Common explanations invoke a degenerate star (white dwarf) which explodes upon
reaching close to the Chandrasekhar limit, by either steadily accreting mass from a companion star
or violently merging with another degenerate star. We show that circumstellar interaction in young
Galactic supernova remnants can be used to distinguish between these single and double degenerate
progenitor scenarios. Here we propose a new diagnostic, the Surface Brightness Index, which can
be computed from theory and compared with Chandra and VLA observations. We use this method
to demonstrate that a double degenerate progenitor can explain the decades-long
ux rise and size
increase of the youngest known Galactic SNR G1.9+0.3. We disfavor a single degenerate scenario.
We attribute the observed properties to the interaction between a steep ejecta prole and a constant
density environment. We suggest using the upgraded VLA to detect circumstellar interaction in
the remnants of historical Type Ia supernovae in the Local Group of galaxies. This may settle the
long-standing debate over their progenitors.
Subject headings: ISM: supernova remnants | radio continuum: general | X-rays: general | bi-
naries: general | circumstellar matter | supernovae: general | ISM: individual
objects(SNR G1.9+0.3)
Inverse Compton cooling limits the brightness temperature of the radiating plasma to a maximum of
1011.5 K. Relativistic boosting can increase its observed value, but apparent brightness temperatures
much in excess of 1013 K are inaccessible using ground-based very long baseline interferometry (VLBI)
at any wavelength. We present observations of the quasar 3C 273, made with the space VLBI mission
RadioAstron on baselines up to 171,000 km, which directly reveal the presence of angular structure as
small as 26 µas (2.7 light months) and brightness temperature in excess of 1013 K. These measurements
challenge our understanding of the non-thermal continuum emission in the vicinity of supermassive
black holes and require a much higher Doppler factor than what is determined from jet apparent
kinematics.
Keywords: galaxies: active — galaxies: jets — radio continuum: galaxies — techniques: interferometric
— quasars: individual (3C 273)
This document summarizes an article that proposes an alternative explanation for dark energy and dark matter based on a modified theory of gravity. It begins by providing background on dark matter and dark energy in standard cosmology and the evidence that supports their existence. It then outlines the proposed alternative theory, which modifies Einstein's field equations by adding a function of the Ricci scalar. This introduces new curvature terms that could potentially drive accelerated expansion, providing an alternative to dark energy. The theory aims to match observations without requiring dark matter or energy, but reduces to general relativity in the solar system scale where it has been tightly tested.
EMU M.Sc. Thesis Presentation
Thesis Title: "Dark Matter; Modification of f(R) or WIMPS Miracle"
Student: Ali Övgün
Supervisor: Prof. Dr. Mustafa Halilsoy
The document discusses evidence for dark matter from astrophysical observations. It is established that dark matter is massive, cold, collisionless, and does not interact electromagnetically. However, its fundamental nature and interactions are unknown. The evidence includes missing mass observations from galaxy rotation curves, cluster dynamics, gravitational lensing as well as cosmological measurements of the cosmic microwave background and matter power spectrum. Future experiments aim to directly detect dark matter particle signatures through anomalies in cosmic ray spectra or indirect signals from early structure formation.
The characterization of_the_gamma_ray_signal_from_the_central_milk_way_a_comp...Sérgio Sacani
This document analyzes the gamma-ray signal from the central Milky Way that is consistent with emission from annihilating dark matter particles. The authors re-examine Fermi data using cuts on an event parameter to improve gamma-ray maps and more easily separate components. They find the GeV excess is robust and well-fit by a 36-51 GeV dark matter particle annihilating to bottom quarks with a cross section of 1-3×10−26 cm3/s. The signal extends over 10 degrees from the Galactic Center and is spherically symmetric, disfavoring explanations from millisecond pulsars or gas interactions.
Evidence for the_thermal_sunyaev-zeldovich_effect_associated_with_quasar_feed...Sérgio Sacani
Using a radio-quiet subsample of the Sloan Digital Sky Survey spectroscopic quasar
catalogue, spanning redshifts 0.5–3.5, we derive the mean millimetre and far-infrared
quasar spectral energy distributions (SEDs) via a stacking analysis of Atacama Cosmology
Telescope and Herschel-Spectral and Photometric Imaging REceiver data. We
constrain the form of the far-infrared emission and find 3σ–4σ evidence for the thermal
Sunyaev-Zel’dovich (SZ) effect, characteristic of a hot ionized gas component with
thermal energy (6.2 ± 1.7) × 1060 erg. This amount of thermal energy is greater than
expected assuming only hot gas in virial equilibrium with the dark matter haloes of
(1 − 5) × 1012h
−1M that these systems are expected to occupy, though the highest
quasar mass estimates found in the literature could explain a large fraction of this
energy. Our measurements are consistent with quasars depositing up to (14.5±3.3) τ
−1
8
per cent of their radiative energy into their circumgalactic environment if their typical
period of quasar activity is τ8 × 108 yr. For high quasar host masses, ∼ 1013h
−1M,
this percentage will be reduced. Furthermore, the uncertainty on this percentage is
only statistical and additional systematic uncertainties enter at the 40 per cent level.
The SEDs are dust dominated in all bands and we consider various models for dust
emission. While sufficiently complex dust models can obviate the SZ effect, the SZ
interpretation remains favoured at the 3σ–4σ level for most models.
Exocometary gas in_th_hd_181327_debris_ringSérgio Sacani
An increasing number of observations have shown that gaseous debris discs are not an
exception. However, until now we only knew of cases around A stars. Here we present the first
detection of 12CO (2-1) disc emission around an F star, HD 181327, obtained with ALMA
observations at 1.3 mm. The continuum and CO emission are resolved into an axisymmetric
disc with ring-like morphology. Using a Markov chain Monte Carlo method coupled with
radiative transfer calculations we study the dust and CO mass distribution. We find the dust is
distributed in a ring with a radius of 86:0 0:4 AU and a radial width of 23:2 1:0 AU. At
this frequency the ring radius is smaller than in the optical, revealing grain size segregation
expected due to radiation pressure. We also report on the detection of low level continuum
emission beyond the main ring out to 200 AU. We model the CO emission in the non-LTE
regime and we find that the CO is co-located with the dust, with a total CO gas mass ranging
between 1:2 10 6 M and 2:9 10 6 M, depending on the gas kinetic temperature and
collisional partners densities. The CO densities and location suggest a secondary origin, i.e.
released from icy planetesimals in the ring. We derive a CO cometary composition that is
consistent with Solar system comets. Due to the low gas densities it is unlikely that the gas is
shaping the dust distribution.
The document discusses dark matter and provides evidence for its existence from various astronomical observations. It notes that while ordinary matter makes up only about 4% of the universe, dark matter accounts for about 23%. Various properties of dark matter are described, including that it interacts gravitationally but does not emit or absorb light. Possible candidates for dark matter are discussed, including WIMPs (Weakly Interacting Massive Particles), which are favored from both astronomical data and particle physics models. The document outlines how WIMPs could have been thermally produced in the early universe to account for the observed dark matter abundance.
Evidence for reflected_lightfrom_the_most_eccentric_exoplanet_knownSérgio Sacani
Planets in highly eccentric orbits form a class of objects not seen within our Solar System. The most extreme case known amongst these objects is the planet orbiting HD 20782, with an orbital period of 597 days and an eccentricity of 0.96. Here we present new data and analysis for this system as part of the Transit Ephemeris Refinement and Monitoring Survey (TERMS). We obtained CHIRON spectra to perform an independent estimation of the fundamental stellar parameters. New radial velocities from AAT and PARAS observations during periastron passage greatly improve our knowledge of the eccentric nature of the orbit. The combined analysis of our Keplerian orbital and Hipparcos astrometry show that the inclination of the planetary orbit is > 1.22◦, ruling out stellar masses for the companion. Our long-term robotic photometry show that the star is extremely stable over long timescales. Photometric monitoring of the star during predicted transit and periastron times using MOST rule out a transit of the planet and reveal evidence of phase variations during periastron. These possible photometric phase variations may be caused by reflected light from the planet’s atmosphere and the dramatic change in star–planet separation surrounding the periastron passage.
Dark matter is an invisible form of matter that accounts for about 85% of the matter in the universe. It was first proposed in 1933 to explain unexpected motions of galaxies, and its existence and properties have since been further confirmed by various observations, though its exact nature remains unknown. Dark matter is distinct from dark energy, which is driving the accelerating expansion of the universe. Leading candidates for dark matter include WIMPs (Weakly Interacting Massive Particles) such as neutralinos and axions.
We discovered two transient events in the Kepler eld with light curves that strongly suggest they
are type II-P supernovae. Using the fast cadence of the Kepler observations we precisely estimate
the rise time to maximum for KSN2011a and KSN2011d as 10.50:4 and 13.30:4 rest-frame days
respectively. Based on ts to idealized analytic models, we nd the progenitor radius of KSN2011a
(28020 R) to be signicantly smaller than that for KSN2011d (49020 R) but both have similar
explosion energies of 2.00:3 1051 erg.
The rising light curve of KSN2011d is an excellent match to that predicted by simple models of
exploding red supergiants (RSG). However, the early rise of KSN2011a is faster than the models
predict possibly due to the supernova shockwave moving into pre-existing wind or mass-loss from the
RSG. A mass loss rate of 10 4 M yr 1 from the RSG can explain the fast rise without impacting
the optical
ux at maximum light or the shape of the post-maximum light curve.
No shock breakout emission is seen in KSN2011a, but this is likely due to the circumstellar inter-
action suspected in the fast rising light curve. The early light curve of KSN2011d does show excess
emission consistent with model predictions of a shock breakout. This is the rst optical detection of
a shock breakout from a type II-P supernova.
An elevation of 0.1 light-seconds for the optical jet base in an accreting Ga...Sérgio Sacani
Relativistic plasma jets are observed in many systems that
host accreting black holes. According to theory, coiled magnetic
fields close to the black hole accelerate and collimate the
plasma, leading to a jet being launched1–3. Isolating emission
from this acceleration and collimation zone is key to measuring
its size and understanding jet formation physics. But this
is challenging because emission from the jet base cannot
easily be disentangled from other accreting components. Here,
we show that rapid optical flux variations from an accreting
Galactic black-hole binary are delayed with respect to X-rays
radiated from close to the black hole by about 0.1 seconds, and
that this delayed signal appears together with a brightening
radio jet. The origin of these subsecond optical variations
has hitherto been controversial4–8. Not only does our work
strongly support a jet origin for the optical variations but it
also sets a characteristic elevation of ≲ 103 Schwarzschild
radii for the main inner optical emission zone above the black
hole9, constraining both internal shock10 and magnetohydrodynamic11
models. Similarities with blazars12,13 suggest that jet
structure and launching physics could potentially be unified
under mass-invariant models. Two of the best-studied jetted
black-hole binaries show very similar optical lags8,14,15, so this
size scale may be a defining feature of such systems.
This document summarizes research on determining temperatures, luminosities, and masses of the coldest known brown dwarfs. The key findings are:
1) Precise distances were measured for a sample of late-T and Y dwarfs using Spitzer Space Telescope astrometry, allowing accurate calculation of absolute fluxes, luminosities, and temperatures.
2) Y0 dwarfs were found to have temperatures of 400-450 K, significantly warmer than previous estimates, and masses of 5-20 times Jupiter's mass.
3) While having similar temperatures, Y dwarfs showed diverse spectral energy distributions, suggesting temperature alone does not determine spectra. Physical properties like gravity, clouds and chemistry also influence spectra.
1) Researchers observed 15 transits of the exoplanet GJ 1214b using the Hubble Space Telescope to measure its transmission spectrum from 1.1 to 1.7 microns.
2) The transmission spectrum was featureless, inconsistent with cloud-free atmospheres dominated by water, methane, carbon monoxide, nitrogen, or carbon dioxide.
3) The most likely explanation for the featureless spectrum is the presence of high-altitude clouds in the planet's atmosphere, which block the transmission of stellar light through the lower atmosphere.
We present long-baseline Atacama Large Millimeter/submillimeter Array (ALMA) observations of
the 870 m continuum emission from the nearest gas-rich protoplanetary disk, around TW Hya, that
trace millimeter-sized particles down to spatial scales as small as 1 AU (20 mas). These data reveal
a series of concentric ring-shaped substructures in the form of bright zones and narrow dark annuli
(1{6AU) with modest contrasts (5{30%). We associate these features with concentrations of solids
that have had their inward radial drift slowed or stopped, presumably at local gas pressure maxima.
No signicant non-axisymmetric structures are detected. Some of the observed features occur near
temperatures that may be associated with the condensation fronts of major volatile species, but the
relatively small brightness contrasts may also be a consequence of magnetized disk evolution (the
so-called zonal
ows). Other features, particularly a narrow dark annulus located only 1 AU from the
star, could indicate interactions between the disk and young planets. These data signal that ordered
substructures on AU scales can be common, fundamental factors in disk evolution, and that high
resolution microwave imaging can help characterize them during the epoch of planet formation.
Keywords: protoplanetary disks | planet-disk interactions | stars: individual (TW Hydrae)
Periodic mass extinctions_and_the_planet_x_model_reconsideredSérgio Sacani
The 27 Myr periodicity in the fossil extinction record has been con-
firmed in modern data bases dating back 500 Myr, which is twice the time
interval of the original analysis from thirty years ago. The surprising regularity
of this period has been used to reject the Nemesis model. A second
model based on the sun’s vertical galactic oscillations has been challenged
on the basis of an inconsistency in period and phasing. The third astronomical
model originally proposed to explain the periodicity is the Planet
X model in which the period is associated with the perihelion precession
of the inclined orbit of a trans-Neptunian planet. Recently, and unrelated
to mass extinctions, a trans-Neptunian super-Earth planet has been proposed
to explain the observation that the inner Oort cloud objects Sedna
and 2012VP113 have perihelia that lie near the ecliptic plane. In this
Letter we reconsider the Planet X model in light of the confluence of the
modern palaeontological and outer solar system dynamical evidence.
Key Words: astrobiology - planets and satellites - Kuiper belt:
general - comets: general
Too much pasta_for_pulsars_to_spin_downSérgio Sacani
This document summarizes a study investigating why no isolated X-ray pulsars have been observed with spin periods longer than 12 seconds. The researchers suggest this is due to a highly resistive layer in the inner crust of neutron stars, which is expected to be in a state called "nuclear pasta". Nuclear pasta has an irregular structure that increases electrical resistivity, limiting the spin-down of pulsars. Modeling the long-term magnetic field evolution incorporating a resistive nuclear pasta layer successfully reproduced the observed 12 second period limit. The results provide the first potential observational evidence for the existence of nuclear pasta in neutron star crusts.
1) The observable universe has a mass of approximately 24x10^53 kg.
2) Normal matter, including atoms, stars and galaxies, constitute only about 4% of the observable universe. The rest is dark matter (27%) and dark energy (71%).
3) Dark matter interacts gravitationally but is unseen, and helps hold galaxies together. Dark energy is causing the accelerating expansion of the universe against the force of gravity.
This document provides a summary of big-bang cosmology and the evidence supporting it. It discusses how observations of the cosmic microwave background radiation, light element abundances from big-bang nucleosynthesis, galaxy rotation curves, and type 1a supernovae provide evidence that the universe began in a hot, dense state and is undergoing expansion. It also summarizes the evidence for dark matter from various astronomical observations and outlines how weakly interacting massive particles are a leading candidate. The document concludes by discussing baryogenesis and possible mechanisms for the observed matter-antimatter asymmetry of the universe.
The Big Bang theory states that the universe began in a hot, dense state and has been expanding ever since. Key evidence includes the cosmic microwave background radiation and redshift of distant galaxies indicating an expanding universe. Dark energy and dark matter make up most of the universe and influence its expansion and structure formation. The Milky Way galaxy is a barred spiral galaxy containing over 100 billion stars located on an outer arm. Stars form constellations that change with the seasons and can be used for navigation.
A massive pulsar_in_a_compact_relativistic_binarySérgio Sacani
1) Researchers observed the pulsar PSR J0348+0432 in a compact orbit with a white dwarf companion. Timing observations yielded component masses - the pulsar has a precisely determined mass of 2.01 solar masses, among the highest yet observed.
2) Optical spectroscopy of the white dwarf companion found it has a mass of 0.172 solar masses. Analysis of the orbital parameters and component masses showed the system's orbital decay matches predictions from general relativity.
3) The high pulsar mass and compact orbit make this a sensitive laboratory for testing strong-field gravity. The observed orbital decay is consistent with general relativity, supporting its validity even in extreme gravity regimes not previously tested. This has implications
Young remmants of_type_ia_supernovae_and_their_progenitors_a_study_of_snr_g19_03Sérgio Sacani
Type Ia supernovae, with their remarkably homogeneous light curves and spectra, have been used as
standardizable candles to measure the accelerating expansion of the Universe. Yet, their progenitors
remain elusive. Common explanations invoke a degenerate star (white dwarf) which explodes upon
reaching close to the Chandrasekhar limit, by either steadily accreting mass from a companion star
or violently merging with another degenerate star. We show that circumstellar interaction in young
Galactic supernova remnants can be used to distinguish between these single and double degenerate
progenitor scenarios. Here we propose a new diagnostic, the Surface Brightness Index, which can
be computed from theory and compared with Chandra and VLA observations. We use this method
to demonstrate that a double degenerate progenitor can explain the decades-long
ux rise and size
increase of the youngest known Galactic SNR G1.9+0.3. We disfavor a single degenerate scenario.
We attribute the observed properties to the interaction between a steep ejecta prole and a constant
density environment. We suggest using the upgraded VLA to detect circumstellar interaction in
the remnants of historical Type Ia supernovae in the Local Group of galaxies. This may settle the
long-standing debate over their progenitors.
Subject headings: ISM: supernova remnants | radio continuum: general | X-rays: general | bi-
naries: general | circumstellar matter | supernovae: general | ISM: individual
objects(SNR G1.9+0.3)
Inverse Compton cooling limits the brightness temperature of the radiating plasma to a maximum of
1011.5 K. Relativistic boosting can increase its observed value, but apparent brightness temperatures
much in excess of 1013 K are inaccessible using ground-based very long baseline interferometry (VLBI)
at any wavelength. We present observations of the quasar 3C 273, made with the space VLBI mission
RadioAstron on baselines up to 171,000 km, which directly reveal the presence of angular structure as
small as 26 µas (2.7 light months) and brightness temperature in excess of 1013 K. These measurements
challenge our understanding of the non-thermal continuum emission in the vicinity of supermassive
black holes and require a much higher Doppler factor than what is determined from jet apparent
kinematics.
Keywords: galaxies: active — galaxies: jets — radio continuum: galaxies — techniques: interferometric
— quasars: individual (3C 273)
This document summarizes an article that proposes an alternative explanation for dark energy and dark matter based on a modified theory of gravity. It begins by providing background on dark matter and dark energy in standard cosmology and the evidence that supports their existence. It then outlines the proposed alternative theory, which modifies Einstein's field equations by adding a function of the Ricci scalar. This introduces new curvature terms that could potentially drive accelerated expansion, providing an alternative to dark energy. The theory aims to match observations without requiring dark matter or energy, but reduces to general relativity in the solar system scale where it has been tightly tested.
EMU M.Sc. Thesis Presentation
Thesis Title: "Dark Matter; Modification of f(R) or WIMPS Miracle"
Student: Ali Övgün
Supervisor: Prof. Dr. Mustafa Halilsoy
The document discusses evidence for dark matter from astrophysical observations. It is established that dark matter is massive, cold, collisionless, and does not interact electromagnetically. However, its fundamental nature and interactions are unknown. The evidence includes missing mass observations from galaxy rotation curves, cluster dynamics, gravitational lensing as well as cosmological measurements of the cosmic microwave background and matter power spectrum. Future experiments aim to directly detect dark matter particle signatures through anomalies in cosmic ray spectra or indirect signals from early structure formation.
The characterization of_the_gamma_ray_signal_from_the_central_milk_way_a_comp...Sérgio Sacani
This document analyzes the gamma-ray signal from the central Milky Way that is consistent with emission from annihilating dark matter particles. The authors re-examine Fermi data using cuts on an event parameter to improve gamma-ray maps and more easily separate components. They find the GeV excess is robust and well-fit by a 36-51 GeV dark matter particle annihilating to bottom quarks with a cross section of 1-3×10−26 cm3/s. The signal extends over 10 degrees from the Galactic Center and is spherically symmetric, disfavoring explanations from millisecond pulsars or gas interactions.
Evidence for the_thermal_sunyaev-zeldovich_effect_associated_with_quasar_feed...Sérgio Sacani
Using a radio-quiet subsample of the Sloan Digital Sky Survey spectroscopic quasar
catalogue, spanning redshifts 0.5–3.5, we derive the mean millimetre and far-infrared
quasar spectral energy distributions (SEDs) via a stacking analysis of Atacama Cosmology
Telescope and Herschel-Spectral and Photometric Imaging REceiver data. We
constrain the form of the far-infrared emission and find 3σ–4σ evidence for the thermal
Sunyaev-Zel’dovich (SZ) effect, characteristic of a hot ionized gas component with
thermal energy (6.2 ± 1.7) × 1060 erg. This amount of thermal energy is greater than
expected assuming only hot gas in virial equilibrium with the dark matter haloes of
(1 − 5) × 1012h
−1M that these systems are expected to occupy, though the highest
quasar mass estimates found in the literature could explain a large fraction of this
energy. Our measurements are consistent with quasars depositing up to (14.5±3.3) τ
−1
8
per cent of their radiative energy into their circumgalactic environment if their typical
period of quasar activity is τ8 × 108 yr. For high quasar host masses, ∼ 1013h
−1M,
this percentage will be reduced. Furthermore, the uncertainty on this percentage is
only statistical and additional systematic uncertainties enter at the 40 per cent level.
The SEDs are dust dominated in all bands and we consider various models for dust
emission. While sufficiently complex dust models can obviate the SZ effect, the SZ
interpretation remains favoured at the 3σ–4σ level for most models.
Exocometary gas in_th_hd_181327_debris_ringSérgio Sacani
An increasing number of observations have shown that gaseous debris discs are not an
exception. However, until now we only knew of cases around A stars. Here we present the first
detection of 12CO (2-1) disc emission around an F star, HD 181327, obtained with ALMA
observations at 1.3 mm. The continuum and CO emission are resolved into an axisymmetric
disc with ring-like morphology. Using a Markov chain Monte Carlo method coupled with
radiative transfer calculations we study the dust and CO mass distribution. We find the dust is
distributed in a ring with a radius of 86:0 0:4 AU and a radial width of 23:2 1:0 AU. At
this frequency the ring radius is smaller than in the optical, revealing grain size segregation
expected due to radiation pressure. We also report on the detection of low level continuum
emission beyond the main ring out to 200 AU. We model the CO emission in the non-LTE
regime and we find that the CO is co-located with the dust, with a total CO gas mass ranging
between 1:2 10 6 M and 2:9 10 6 M, depending on the gas kinetic temperature and
collisional partners densities. The CO densities and location suggest a secondary origin, i.e.
released from icy planetesimals in the ring. We derive a CO cometary composition that is
consistent with Solar system comets. Due to the low gas densities it is unlikely that the gas is
shaping the dust distribution.
The document discusses dark matter and provides evidence for its existence from various astronomical observations. It notes that while ordinary matter makes up only about 4% of the universe, dark matter accounts for about 23%. Various properties of dark matter are described, including that it interacts gravitationally but does not emit or absorb light. Possible candidates for dark matter are discussed, including WIMPs (Weakly Interacting Massive Particles), which are favored from both astronomical data and particle physics models. The document outlines how WIMPs could have been thermally produced in the early universe to account for the observed dark matter abundance.
Evidence for reflected_lightfrom_the_most_eccentric_exoplanet_knownSérgio Sacani
Planets in highly eccentric orbits form a class of objects not seen within our Solar System. The most extreme case known amongst these objects is the planet orbiting HD 20782, with an orbital period of 597 days and an eccentricity of 0.96. Here we present new data and analysis for this system as part of the Transit Ephemeris Refinement and Monitoring Survey (TERMS). We obtained CHIRON spectra to perform an independent estimation of the fundamental stellar parameters. New radial velocities from AAT and PARAS observations during periastron passage greatly improve our knowledge of the eccentric nature of the orbit. The combined analysis of our Keplerian orbital and Hipparcos astrometry show that the inclination of the planetary orbit is > 1.22◦, ruling out stellar masses for the companion. Our long-term robotic photometry show that the star is extremely stable over long timescales. Photometric monitoring of the star during predicted transit and periastron times using MOST rule out a transit of the planet and reveal evidence of phase variations during periastron. These possible photometric phase variations may be caused by reflected light from the planet’s atmosphere and the dramatic change in star–planet separation surrounding the periastron passage.
Dark matter is an invisible form of matter that accounts for about 85% of the matter in the universe. It was first proposed in 1933 to explain unexpected motions of galaxies, and its existence and properties have since been further confirmed by various observations, though its exact nature remains unknown. Dark matter is distinct from dark energy, which is driving the accelerating expansion of the universe. Leading candidates for dark matter include WIMPs (Weakly Interacting Massive Particles) such as neutralinos and axions.
We discovered two transient events in the Kepler eld with light curves that strongly suggest they
are type II-P supernovae. Using the fast cadence of the Kepler observations we precisely estimate
the rise time to maximum for KSN2011a and KSN2011d as 10.50:4 and 13.30:4 rest-frame days
respectively. Based on ts to idealized analytic models, we nd the progenitor radius of KSN2011a
(28020 R) to be signicantly smaller than that for KSN2011d (49020 R) but both have similar
explosion energies of 2.00:3 1051 erg.
The rising light curve of KSN2011d is an excellent match to that predicted by simple models of
exploding red supergiants (RSG). However, the early rise of KSN2011a is faster than the models
predict possibly due to the supernova shockwave moving into pre-existing wind or mass-loss from the
RSG. A mass loss rate of 10 4 M yr 1 from the RSG can explain the fast rise without impacting
the optical
ux at maximum light or the shape of the post-maximum light curve.
No shock breakout emission is seen in KSN2011a, but this is likely due to the circumstellar inter-
action suspected in the fast rising light curve. The early light curve of KSN2011d does show excess
emission consistent with model predictions of a shock breakout. This is the rst optical detection of
a shock breakout from a type II-P supernova.
An elevation of 0.1 light-seconds for the optical jet base in an accreting Ga...Sérgio Sacani
Relativistic plasma jets are observed in many systems that
host accreting black holes. According to theory, coiled magnetic
fields close to the black hole accelerate and collimate the
plasma, leading to a jet being launched1–3. Isolating emission
from this acceleration and collimation zone is key to measuring
its size and understanding jet formation physics. But this
is challenging because emission from the jet base cannot
easily be disentangled from other accreting components. Here,
we show that rapid optical flux variations from an accreting
Galactic black-hole binary are delayed with respect to X-rays
radiated from close to the black hole by about 0.1 seconds, and
that this delayed signal appears together with a brightening
radio jet. The origin of these subsecond optical variations
has hitherto been controversial4–8. Not only does our work
strongly support a jet origin for the optical variations but it
also sets a characteristic elevation of ≲ 103 Schwarzschild
radii for the main inner optical emission zone above the black
hole9, constraining both internal shock10 and magnetohydrodynamic11
models. Similarities with blazars12,13 suggest that jet
structure and launching physics could potentially be unified
under mass-invariant models. Two of the best-studied jetted
black-hole binaries show very similar optical lags8,14,15, so this
size scale may be a defining feature of such systems.
This document summarizes research on determining temperatures, luminosities, and masses of the coldest known brown dwarfs. The key findings are:
1) Precise distances were measured for a sample of late-T and Y dwarfs using Spitzer Space Telescope astrometry, allowing accurate calculation of absolute fluxes, luminosities, and temperatures.
2) Y0 dwarfs were found to have temperatures of 400-450 K, significantly warmer than previous estimates, and masses of 5-20 times Jupiter's mass.
3) While having similar temperatures, Y dwarfs showed diverse spectral energy distributions, suggesting temperature alone does not determine spectra. Physical properties like gravity, clouds and chemistry also influence spectra.
1) Researchers observed 15 transits of the exoplanet GJ 1214b using the Hubble Space Telescope to measure its transmission spectrum from 1.1 to 1.7 microns.
2) The transmission spectrum was featureless, inconsistent with cloud-free atmospheres dominated by water, methane, carbon monoxide, nitrogen, or carbon dioxide.
3) The most likely explanation for the featureless spectrum is the presence of high-altitude clouds in the planet's atmosphere, which block the transmission of stellar light through the lower atmosphere.
We present long-baseline Atacama Large Millimeter/submillimeter Array (ALMA) observations of
the 870 m continuum emission from the nearest gas-rich protoplanetary disk, around TW Hya, that
trace millimeter-sized particles down to spatial scales as small as 1 AU (20 mas). These data reveal
a series of concentric ring-shaped substructures in the form of bright zones and narrow dark annuli
(1{6AU) with modest contrasts (5{30%). We associate these features with concentrations of solids
that have had their inward radial drift slowed or stopped, presumably at local gas pressure maxima.
No signicant non-axisymmetric structures are detected. Some of the observed features occur near
temperatures that may be associated with the condensation fronts of major volatile species, but the
relatively small brightness contrasts may also be a consequence of magnetized disk evolution (the
so-called zonal
ows). Other features, particularly a narrow dark annulus located only 1 AU from the
star, could indicate interactions between the disk and young planets. These data signal that ordered
substructures on AU scales can be common, fundamental factors in disk evolution, and that high
resolution microwave imaging can help characterize them during the epoch of planet formation.
Keywords: protoplanetary disks | planet-disk interactions | stars: individual (TW Hydrae)
Periodic mass extinctions_and_the_planet_x_model_reconsideredSérgio Sacani
The 27 Myr periodicity in the fossil extinction record has been con-
firmed in modern data bases dating back 500 Myr, which is twice the time
interval of the original analysis from thirty years ago. The surprising regularity
of this period has been used to reject the Nemesis model. A second
model based on the sun’s vertical galactic oscillations has been challenged
on the basis of an inconsistency in period and phasing. The third astronomical
model originally proposed to explain the periodicity is the Planet
X model in which the period is associated with the perihelion precession
of the inclined orbit of a trans-Neptunian planet. Recently, and unrelated
to mass extinctions, a trans-Neptunian super-Earth planet has been proposed
to explain the observation that the inner Oort cloud objects Sedna
and 2012VP113 have perihelia that lie near the ecliptic plane. In this
Letter we reconsider the Planet X model in light of the confluence of the
modern palaeontological and outer solar system dynamical evidence.
Key Words: astrobiology - planets and satellites - Kuiper belt:
general - comets: general
Too much pasta_for_pulsars_to_spin_downSérgio Sacani
This document summarizes a study investigating why no isolated X-ray pulsars have been observed with spin periods longer than 12 seconds. The researchers suggest this is due to a highly resistive layer in the inner crust of neutron stars, which is expected to be in a state called "nuclear pasta". Nuclear pasta has an irregular structure that increases electrical resistivity, limiting the spin-down of pulsars. Modeling the long-term magnetic field evolution incorporating a resistive nuclear pasta layer successfully reproduced the observed 12 second period limit. The results provide the first potential observational evidence for the existence of nuclear pasta in neutron star crusts.
1) The observable universe has a mass of approximately 24x10^53 kg.
2) Normal matter, including atoms, stars and galaxies, constitute only about 4% of the observable universe. The rest is dark matter (27%) and dark energy (71%).
3) Dark matter interacts gravitationally but is unseen, and helps hold galaxies together. Dark energy is causing the accelerating expansion of the universe against the force of gravity.
This document provides a summary of big-bang cosmology and the evidence supporting it. It discusses how observations of the cosmic microwave background radiation, light element abundances from big-bang nucleosynthesis, galaxy rotation curves, and type 1a supernovae provide evidence that the universe began in a hot, dense state and is undergoing expansion. It also summarizes the evidence for dark matter from various astronomical observations and outlines how weakly interacting massive particles are a leading candidate. The document concludes by discussing baryogenesis and possible mechanisms for the observed matter-antimatter asymmetry of the universe.
The Big Bang theory states that the universe began in a hot, dense state and has been expanding ever since. Key evidence includes the cosmic microwave background radiation and redshift of distant galaxies indicating an expanding universe. Dark energy and dark matter make up most of the universe and influence its expansion and structure formation. The Milky Way galaxy is a barred spiral galaxy containing over 100 billion stars located on an outer arm. Stars form constellations that change with the seasons and can be used for navigation.
A massive pulsar_in_a_compact_relativistic_binarySérgio Sacani
1) Researchers observed the pulsar PSR J0348+0432 in a compact orbit with a white dwarf companion. Timing observations yielded component masses - the pulsar has a precisely determined mass of 2.01 solar masses, among the highest yet observed.
2) Optical spectroscopy of the white dwarf companion found it has a mass of 0.172 solar masses. Analysis of the orbital parameters and component masses showed the system's orbital decay matches predictions from general relativity.
3) The high pulsar mass and compact orbit make this a sensitive laboratory for testing strong-field gravity. The observed orbital decay is consistent with general relativity, supporting its validity even in extreme gravity regimes not previously tested. This has implications
Gravity Also Redshifts Light – the Missing Phenomenon That Could Resolve Most...ijrap
In this paper I discover that gravity also redshifts light like the velocity of its source does. When light travels towards a supermassive object, its waves (or photons) undergo continuous stretching, thereby shifting towards lower frequencies. Gravity redshifts light irrespective of whether its source is in motion or static with respect to its observer. An equation is derived for gravitational redshift, and a formula for combined redshift is presented by considering both the velocity, and gravity redshifts. Also explained is how frequencies of electromagnetic spectrum continuously downgrade as a light beam of mix frequencies passes towards a black hole. Further, a clear methodology is provided to figure out whether expansion of the universe is accelerating or decelerating, or alternatively, the universe is contracting.
Pawan Kumar Relativistic jets in tidal disruption eventsBaurzhan Alzhanov
- Fast radio bursts (FRBs) are short, intense radio pulses that last about 1 millisecond. One FRB source produced multiple outbursts over several years.
- The leading model is that FRBs originate from young, highly magnetic neutron stars called magnetars. Charged particles are accelerated by magnetic reconnection, producing coherent curvature radiation observed as FRBs.
- FRBs provide insights into neutron star physics and energetic processes in magnetar magnetospheres. Predictions include observing FRB-like bursts at higher frequencies.
This document summarizes the results of a 180 ks Chandra-LETGS observation of Mrk 509 as part of a larger multi-wavelength campaign. The observation detected several absorption features in the X-ray spectrum originating from an ionized absorber, including ions with three distinct ionization degrees. The lowest ionized component is slightly redshifted and not in pressure equilibrium with the others, likely belonging to the host galaxy's interstellar medium. The other two components are outflowing at velocities of around -200 and -455 km/s. Simultaneous HST-COS observations detected 13 UV kinematic components, and at least three can be associated with the X-ray components, providing evidence that the UV and X-
Neutron stars are the remnants of collapsed massive stars that have densities greater than atomic nuclei. They form when the core of a massive star collapses into a ball about 10-20 km in diameter. Some neutron stars spin rapidly and emit beams of electromagnetic radiation that pulse as the star rotates, known as pulsars. Evidence shows that neutron stars can have planets and exist in binary systems, pulling matter from a companion star. When the core of a collapsing star is over 3 solar masses, it will collapse into a black hole from which even light cannot escape. Black holes reveal themselves through their gravitational effects on nearby objects like binary companions. Gamma ray bursts are very bright flashes of gamma rays that come from extremely energetic explosions and are
1) Neutron stars form when the core of a massive star collapses under its own gravity after a supernova explosion. If the core is greater than 1.4 solar masses, it will continue collapsing to form a black hole.
2) Neutron stars spin rapidly, are hot, and have strong magnetic fields due to their formation in supernova explosions. Some emit beams of radiation that pulse as the star rotates, identifying them as pulsars.
3) Evidence for black holes includes observing objects over 3 solar masses, which must be black holes since nothing else could remain stable at that mass. Black holes affect spacetime so strongly that nothing, not even light, can escape from within their event horizon.
This chapter discusses atomic physics and spectra. It explains that stars with different surface temperatures emit different wavelengths of electromagnetic radiation, allowing astronomers to determine the chemical compositions of stars and interstellar clouds. Spectroscopy provides information about distant astronomical objects by analyzing their characteristic spectral lines. The temperature of a star can be estimated by examining the intensity of light across wavelengths, as hotter stars emit more radiation and peak at shorter wavelengths according to blackbody radiation laws.
The Big Bang model describes the origin and evolution of our universe. It postulates that approximately 13.8 billion years ago, the entire observable universe was only a few millimeters in size and extremely hot and dense. The universe has been expanding and cooling ever since. Evidence for the Big Bang includes the expansion of the universe, the cosmic microwave background radiation, and the relative abundance of light elements like hydrogen and helium.
The Big Bang model describes the origin and evolution of our universe. It postulates that approximately 13.8 billion years ago, the entire observable universe was only a few millimeters in size and extremely hot and dense. Since then, the universe has been expanding and cooling. Evidence for the Big Bang includes the expansion of the universe, the cosmic microwave background radiation, and the relative abundance of light elements like hydrogen and helium. The Doppler effect and redshift help astronomers measure the speeds at which distant galaxies are receding from Earth, leading to the discovery that the expansion of the universe is accelerating. Dark matter and dark energy are hypothesized to explain discrepancies in measurements of the density and expansion rate of the universe.
Gravitational waves are ripples in spacetime caused by accelerating massive objects like binary star systems and merging black holes. On February 11, 2016, the LIGO and Virgo collaborations announced the first direct observation of gravitational waves from a merging black hole system over 1 billion lightyears away. Even the strongest gravitational waves have an extremely small effect on Earth, requiring sophisticated detectors like LIGO to detect the tiny changes in length they cause.
Gravitational waves are ripples in spacetime caused by accelerating massive objects like binary star systems and merging black holes. On February 11, 2016, the LIGO and Virgo collaborations announced the first direct observation of gravitational waves from a merging black hole system over 1 billion lightyears away. Even the strongest gravitational waves have an extremely small effect on Earth, requiring sophisticated detectors like LIGO to detect the tiny changes in length they cause.
This document discusses electromagnetic radiation and spectroscopy. It begins by describing characteristics of light such as photons and their energy and momentum. It then discusses spectroscopy, which is the study of spectra to determine chemical composition. There are three main types of spectra: continuous, dark-line (absorption), and bright-line (emission). Spectroscopy is used to identify elements in stars and other celestial bodies. The document also covers the Doppler effect and how the perceived wavelength of light shifts based on whether the source is approaching or receding from the observer.
Pulsar emission amplified and resolved by plasma lensing in an eclipsing binarySérgio Sacani
Radio pulsars scintillate because their emission travels through the
ionized interstellar medium along multiple paths, which interfere
with each other. It has long been realized that, independent of their
nature, the regions responsible for the scintillation could be used
as ‘interstellar lenses’ to localize pulsar emission regions1,2
. Most
such lenses, however, resolve emission components only marginally,
limiting results to statistical inferences and detections of small
positional shifts3–5
. As lenses situated close to their source offer
better resolution, it should be easier to resolve emission regions of
pulsars located in high-density environments such as supernova
remnants6
or binaries in which the pulsar’s companion has an
ionized outflow. Here we report observations of extreme plasma
lensing in the ‘black widow’ pulsar, B1957+20, near the phase in its
9.2-hour orbit at which its emission is eclipsed by its companion’s
outflow7–9
. During the lensing events, the observed radio flux is
enhanced by factors of up to 70–80 at specific frequencies. The
strongest events clearly resolve the emission regions: they affect the
narrow main pulse and parts of the wider interpulse differently. We
show that the events arise naturally from density fluctuations in
the outer regions of the outflow, and we infer a resolution of our
lenses that is comparable to the pulsar’s radius, about 10 kilometres.
Furthermore, the distinct frequency structures imparted by the
lensing are reminiscent of what is observed for the repeating fast
radio burst FRB 121102, providing observational support for the
idea that this source is observed through, and thus at times strongly
magnified by, plasma lenses10
Relatively and Quantum Mechanics assignment 5&7Brandy Wang
1. General relativity describes large astronomical scales while quantum mechanics describes microscopic scales. When applying the theories at small scales, general relativity's smooth geometric model of space conflicts with quantum mechanics' principle of uncertainty.
2. Quantum tunneling allows particles to temporarily "borrow" energy to pass through classically forbidden areas, but does not violate energy conservation as any additional energy is given back when measured.
3. Pauli's exclusion principle states that two fermions cannot be in the same quantum state. When compressing fermions, their wavelengths shrink and momenta/energy increase, requiring more energy to further reduce separation below their wavelengths. This creates degeneracy pressure resisting compression.
New results from_an_old_friend_the_crab_nebula _and_its_pulsarSérgio Sacani
1. Recent Chandra observations of the Crab Nebula system show that the southern jet has evolved over time, with changes in position, width, and spectrum as a function of distance from the pulsar.
2. Chandra images reveal that the pulsar is not centered within the inner ring, suggesting that the ring may lie on the pulsar's axis of symmetry but at a latitude of about 5 degrees.
3. Phase-resolved spectroscopy of the pulsar with Chandra shows similarities in the variation of X-ray and gamma-ray spectral indices with pulse phase, posing a challenge to theoretical models.
4. Chandra observations were used to search for an X-ray signature of the site
Apartes de la Charla: ASTROFÍSICA RELATIVISTA – FOCUS: ASTROFÍSICA DE ONDAS G...SOCIEDAD JULIO GARAVITO
Astrofísica relativista – Focus: Astrofísica de ondas gravitacionales y agujeros negros – El caso LIGO GW150914
Por: Herman J. Mosquera Cuesta (Ph. D. en Astrofísica)
Resumen: Astrofísica relativista define el campo de investigación respecto de la estructura y evolución del Universo (y su taxonómico contenido astronómico) que incorpora la teoría de la gravedad desarrollada por Albert Einstein en 1915. La Teoría General de la Relatividad describe la interacción gravitacional entre cualquier forma de materia-energía y el espacio-tiempo mismo. En este seminario presentaré un resumen panorámico de mis contribuciones en esta área. En virtud de las más recientes observaciones realizadas por los observatorios de ondas gravitacionales LIGO en USA (The Binary Black Hole Merger GW150914), abordaré particularmente la Astrofísica de Agujeros Negros, y de Ondas de Curvatura (Radiación Gravitacional).
On my research on relativistic astrophysics – Overview: Astrophysics of black holes and gravitational waves – The case of LIGO GW150914
By: Herman J. Mosquera Cuesta (Ph. D. in Astrophysics)
Summary: Relativistic astrophysics is a major field of research on the structure and evolution of the Universe (including its astronomy taxonomical contents) which calls for the theory of gravity introduced by Albert Einstein in 1915. The General Theory of Relativity depicts the inextricable gravitational interaction between any sort of matter-energy and the space-time itself. In this seminar, I will deliver a panoramic overview around my contributions to this field of research. As a timely issue, I will focus mainly on the astrophysics of black holes and gravitational waves, as regards the most recent observations (The Binary Black Hole Merger GW150914) performed by the USA LIGO (laser interferometric gravitational-wave observatories).
Bright black holes and neutron stars beat alikeSérgio Sacani
Multi-wavelength observations of radiation from a bright
neutron-star system show signatures similar to that of a
black-hole binary, suggesting that the accretion mechanism
is the same for all such sources at high luminosities.
Similar to J. Meringa; Quasi Periodic Oscillations in Black Hole Binaries (20)
J. Meringa; Quasi Periodic Oscillations in Black Hole Binaries
1. Quasi Periodic Oscillations in Black Hole Binaries
Jeroen Meringa – 6277349
Essay Bachelor project Physics and Astronomy, extending 12 EC,
executed between 13-05-2013 and 19-07-2013.
API Institute
Faculty of Science (FNWI)
Handed in on 19-07-2013
Supervisor:
L. Heil
Second judge:
M. van der Klis
2. Abstract
In this essay, an analysis is presented of the short timescale variations in the
properties of the strong quasi periodic oscillation observed in the objects MAXI
J1659-152, GX 339-4 and H1743-322. A linear rms-flux relation is commonly seen in
the broad band noise of black hole binary systems, but when the rms-flux
dependence in a QPO was first analysed with XTE J1550-564 (L.M. Heil, S.
Vaughan, P. Uttley 2010) different correlations as well as no correlation at all had
been observed.1
In response, three more objects are analysed in this report on
timescales shorter than about 3000 seconds. We found similar behaviour in H1743-
322, while GX 339-4 showed a very different relation.
Samenvatting
Zwarte gaten zijn objecten zie zó zwaar zijn, dat hun zwaartekracht sterk genoeg is
dat zelfs licht niet meer kan ontsnapen. Soms draait er een ster om een zwart gat
heen, dat we kunnen zien omdat de ster wel licht uitzend, en om een onzichtbaar
punt heen draait. Soms valt er materiaal van de buitenste atmosfeer van de ster naar
het zwarte gat, omdat deze zo’n grote aantrekkingskracht heeft. Dit materiaal
(gaswolken) vormt dan een schijf om het zwarte gat heen voordat het naar binnen
valt. Bij het gat in de buurt beweegt het materiaal zó heftig, dat het heel heet wordt
en straling uitzend. Met een satteliet om de aarde meten we deze straling. Er zit veel
informatie in deze straling, zoals hoe snel de wolk van materiaal rond het zwarte gat
draait.
In dit onderzoek is gekeken naar dit signaal, en er is gevonden dat er iets is, een
onbekend object, dat telkens met ongeveer dezelfde snelheid (frequentie) rond het
zwarte gat draait. Als er meer licht (straling) van de schijf om het gat heen af komt,
dan zien we ook dat ons onbekende object sneller om het zwarte gat heen draait. Bij
eerdere onderzoeken is al eens gekeken naar de straling van de schijven om zwarte
gaten, en iedere keer is er een verband gevonden tussen de frequentie (hoe snel het
materiaal in de schijf om het zwarte gat heen draait) en hoe sterk het licht is dat
uitgezonden wordt. Maar in ons onbekende object is dat verband niet altijd hetzelfde.
Volgens sommige modellen kan het object een klompje met extra materiaal zijn om
het zwarte gat heen. Dit verklaart waarom er meer licht af komt, en waarom het
sneller draait als het dichter bij het midden komt, maar niet alle verbanden worden
hiermee verklaart. Meer onderzoek is dus nog nodig.
3. Index
Page 4 1 Introduction and Background
Page 4 1.1 Motivation and Introduction
Page 4 1.2 Black Hole Binary Systems
Page 5 1.3 X-ray Detection
Page 6 1.4 Light Curve and Power Spectrum
Page 7 2 Theory
Page 7 2.1 Quasi Periodic Oscillations
Page 9 2.2 RMS-Flux Relation
Page 10 2.3 Black Hole States
Page 11 2.4 Fast Fourier Transform
Page 12 2.5 Lense–Thirring precession model
Page 13 3 Observation Method and Equipment
Page 13 3.1 Rossi X-ray Timing Explorer Satellite
Page 15 3.2 The Proportional Counter Array
Page 15 3.3 Experiment Data System
Page 16 3.4 Data manipulation
Page 17 3.5 Data Analyses
Page 18 4 Results
Page 18 4.1 RMS-Flux Relation
Page 19 4.2 Central Frequency-Flux Relation
Page 21 4.3 Mean Frequency – RMS-Flux Gradient Relation
Page 22 4.4 Intercept from Linear fit of the RMS-Flux relation
Page 24 5 Discussion
Page 24 5.1 The RMS-Flux Relation Analyses
Page 25 5.2 The Central Frequency-Flux Relation
Page 25 6 Conclusion
Page 28 Attachments
4. 4
1 Introduction and Background
1.1 Motivation and Introduction
The RMS-flux relation in broad-band noise is a known and studied phenomenon.
When this rms-flux dependence was first analysed in a QPO (XTE J1550-564, L.M.
Heil, S. Vaughan, P. Uttley 2010) different correlations as well as no correlation at all
had been observed.1
This research had been conducted to see if this relation always
exists, or whether it differs per object. For that, three more objects had been
analysed (MAXI J1659-152, and H1743-322).
1.2 Black Hole Binary Systems
Black holes (BH) are difficult to detect, as they are so dense that their escape
velocity is greater than light, meaning that no information can escape from it.
Locating such object that can not be observed directly can be difficult. Indirect
methods must be used, such as looking at the effects black holes have on their
surroundings, particularly when they are part of a binary system. A binary system is
a system of two astronomical objects such as stars, brown dwarfs, black holes but
also galaxies or asteroids. If they get close enough, their gravitational interaction
causes them to orbit around a common centre of mass. In this case, we are
interested in binary systems consisting of a black hole and a star. These kind of
systems can be detected whenever a visible star can be seen orbiting a massive, but
unseen companion. This companion does not have to be a black hole per se; it might
as well be a dwarf or neutron star.
When a star with an initial mass of at least about ten times our Sun’s mass is near
the end of its lifetime and can no longer maintain nuclear fusion in its core, gravity
will cause the outer shell to collapse in upon the core. This quick collapse triggers a
supernova, and the outer material of the star is expelled outwards. What remains,
depends on the mass of the remaining core. One possibility is a neutron star. Stars
with masses less than about two to three solar masses (the Tolman-Oppenheimer-
Volkoff limit 2,3
) should remain neutron stars, and slowly radiate away their energy. If
the stellar core remaining after the supernova is heavier than that, it will collapse into
a singularity known as a black hole.
If, when a star is seen in orbit around an invisible companion, the mass of that binary
companion is bigger than three solar masses, it must therefore be a black hole.
Using Kepler’s laws of motion, the mass of the unseen companion can be calculated
from the orbital motion of the visible star. This way, Black Hole Binary (BHB)
systems can be found. The black hole Cygnus X-14
is a good example of the search
for black holes in this way. This is also the object in which the RMS-flux relation was
initially observed 20, 21, 22, 23
(see section 2.2).
5. 5
1.3 X-ray Detection
When a star system is in orbit along our line of sight, spectroscopy can be used to
detect it. The information about a spectroscopic binary system can be found in the
periodic Doppler shifting of the lines in its spectrum.30
When the visible star moves
towards us, the spectral lines are blue shifted, whereas when it’s moving away, the
lines are red shifted. From the way in how the spectral lines shift, one can get the
orbital speed, and the period can be calculated from the frequency. This information
can be used to determine the mass of the invisible companion, and identify it as a
potential black hole candidate.
Another way of detecting black holes is by looking at the X-rays that are generated
around it. These X-rays are analysed in this essay. Regular stars are not bright at all
in the X-ray spectrum, which is highly energetic radiation with wavelengths much
shorter than visible light. Since normal stars hardly emit these rays, some other
process must be causing it. If a black hole is part of a binary system, its huge
gravitational field will draw away material from the outer atmospheres of the
companion star. Due to the orbital angular momentum of the pair, the gas swirling
inwards towards the black hole will form a flat disc, called an accretion disc. The
material in the disc is accelerated to very high velocities and compressed. Friction
and turbulence will cause the material to heat up to temperatures close to 10 million
Kelvin,31
high enough to emit X-rays and gamma-rays.
Figure 1: schematic view of a black
hole binary system where gas is
flowing inwards to the black hole due
to its gravity. A disc forms around the
black hole, and turbulence will heat up
the material enough for it to emit X-
rays.
Ross Mays 2010
This scenario is not limited by black holes, as it can very well happen with neutron
stars as well, which was suspected to be the case most of the time. However,
detection methods have improved over time, and right now it is very well possible to
distinguish between black holes and neutron stars regarding X-ray emission.
6. 6
1.4 Light Curve and Power Spectrum
A satellite can record the X-ray emission by counting the incoming photons and
recording their energy and time of detection. From this data, we can see how the flux
varies over time, and the spectrum of energies.
Light Curve
Figure 2: example data
taken with the
proportional counter
array from the satellite
(see section 3.2). This
light curve shows the
number of counts
(detected photons) per
second at the indicated
time.
When a black hole accretes (material is flowing from the companion towards the BH,
forming an accretion disc) it shows variations over a wide range of different
timescales. Regarding the light curve (figure 2) this means that we see many
different variations interacting with each other. By performing a Fast Fourier
Transform (FFT; see section 2.4), power spectra can be created (see section 3.4).
These spectra tell us how well a certain sine frequency is represented in the Fast
Fourier Transform of the light curve.
Power Spectrum
Figure 3: example power
spectrum, data taken from
H1743-322. The x and y axis
are on a logarithmic scale, and
represent respectively the
power (in counts per second)
and the frequencies (in Hz).
7. 7
2 Theory
2.1 Quasi Periodic Oscillations
If at the source, there would be a strictly periodic effect, it would (in the ideal case,
after taking enough observations) show in the power spectrum as a Dirac-Delta peak
at the corresponding frequency.
Figure 4: illustrated example of
how a strictly periodic effect
would show in a power spectrum.
However, in the case of Quasi Periodic Oscillations (QPOs) there is a much broader
peak, around a central frequency. This is why the effect is called “quasi” periodic,
rather than periodic.
Figure 5: illustration of a quasi-
periodic effect. There is a
distribution around a central
frequency rather than a Dirac
peak in the power spectrum.
8. 8
As stated, accreting black holes show variations over a range of timescales. Their
power spectra includes not just QPOs and their (sub) harmonics, but also broadband
noise and band-limited noise.1
The exact reason for the observed QPOs is not yet
known, though there are models describing them (see section 2.5). QPOs are not
only observed strictly in BHBs, but in neutron stars as well. QPOs are commonly
classified in three types; type A, B and C.6, 7, 8, 9, 10
Type A and B are seen in the soft
intermediate states (see section 2.3) while type C is observed in hard states. Here,
mainly type C QPOs will be discussed, as those are the observed ones. The
frequency of these QPOs are known to be correlated with the spectral properties of
the source, disc fluxes and power law, disc inner radius, photon index and disc
temperature.11, 12
The details of the physical origin is not yet clear, although there are
models (such as the Lense-Thirring model, see section 2.5) describing them.
9. 9
2.2 RMS-Flux Relation
The different timescale variations seen in Figure 2 are the result of underlying
processes and effects taking place in the accretion disc of the source. In the outer
edges of the source, long timescale effects occur. While the outer material flow falls
inwards, more volatile interactions will cause shorter timescale effects on top of the
already existing long timescale ones. This is visible in the light curve in the form of
variations with short periods stacked on top of ones with longer periods. The waves
interact multiplicatively, so that when the mean flux is higher, the amplitude of the
short timescale variations increases.
In general, the RMS-flux relation is a simple and stable relation, connecting the RMS
amplitude of variations to the mean flux with a positive linear correlation that can be
seen over a wide range of timescales, as long as the power spectra stay similar
enough.20
This relation is characteristic to short-term variability with an (almost)
stationary power-spectral shape. Changes in the longer-term RMS might be caused
by changes in the source, evolving through different spectral states over time.
However, these are different to the RMS-flux relation which seems to be a
fundamental feature of the variability process itself.
We also see that the RMS-flux relation flattens. In terms of the light curve, this
means that the fluctuation stops getting bigger as the flux increases. A conclusion
from the original paper was that the QPO just gets to a strength where it can no
longer increase with increasing flux. A possible explanation for the difference seen in
the objects could have to do with the difference in inclination. GX 339-4 is a low-
inclination system, whereas H1743-322 has a very high inclination. Why this would
affect the relation between the central frequency and the flux in the observed
fashion, is unclear. No clear trend is seen in MAXI J1659-152. The signal-to-noise
ratio was very low, meaning that the observations had too much noise to see clear
trends. In high inclination sources there seem to be stronger QPOs than in the lower
inclination ones, so perhaps the angle at which the QPO are seen is what causes the
differences. It could be that in lower inclination sources the QPO does not get strong
enough to observe this effect, or maybe if the Lense-Thirring model is correct we
generally see a bigger occultation at high inclinations, but eventually the precessing
region gets so small that we see the more emission in the dips that we do when the
region is larger. So the amplitude of the oscillation stays over all the same even
when the emission in the peaks is higher.
For the analysis, the (sub) harmonics of the QPOs had not been analysed. They
generally show the same relations as the main peak, and should not influence the
result. They do have been fitted, as that will affect the RMS values, though the
relations should remain the same regardless.
An explanation for the RMS-flux relation found in the broad-band noise of accreting
systems is the “propagating fluctuation” model.20, 22, 23, 24
This model describes that
long timescale fluctuations in the accretion rate come from processes at large radii in
the accretion disc. This could be due to random viscosity fluctuations. While
propagating inwards, shorter timescale variations coming occurring at smaller radii 25,
26, 27
interact with the already existing longer timescale ones, until the mixed effects
become visible at the innermost regions, where the X-rays are produced. This would
explain why the X-ray emission varies over such wide timescales, and a linear RMS-
flux relation because of the multiplicative interactions of variations on all timescales.
It is not clear what this would imply for the QPO though, or how it would fit into this
model.
10. 10
2.3 Black Hole States
The observation of correlated and periodic timing and spectral behaviour led to the
introduction of the canonical states for black hole systems. The definition of those
states have changed a lot over the years,7,15,16,17
as first they were determined
mainly by luminosity, but later on spectral hardness dominated. The states used here
are based on the relative location in the Hardness-Intensity Diagram (HID) and the
properties of the power spectra. Systems go through different states and behave
differently over time. Low-mass X-ray binaries with low-mass stellar companions are
transient and go through outbursts. The spectral evolution through these outbursts
can be described by the HID. The classification based on the HID is done by looking
at the energies of the emitted X-rays, thus the energy carried by each individual
photon emitted from the BHB source. If these photons carry a lot of energy they are
indicated as hard photons. Likewise, low-energy photons are soft. This separation is
arbitrary, however usually energies ranging from 4-6 keV are considered soft, and
from 9-20 keV are hard. A state is then identified as a Hard State (HS) if the ratio
high-to-low energy photons is high, meaning that if there are relatively many hard
photons emitted at some point in time, it is in the hard state. Visa versa, a flux with
relatively many low-energy photons is in the Soft State (SS). The hard state is further
characterized with an X-ray spectrum dominated by a hard power-law and strong,
band-limited noise over a wide range of timescales in the power spectrum.18
For the
soft state, there’s a soft, disk blackbody dominated X-ray spectrum and little rapid
variability. There are also intermediate states (IMS), where both the power law as
well as disk blackbody contribute significantly to the power spectrum. In these states,
the most complex variability characteristics are shown, which includes most of the
QPOs. All three states happen over a wide range of luminosity, but the very lowest
level of luminosity occurs mostly when
the system is in quiescence.
Figure 6: a hardness-intensity diagram. It
is followed chronologically in an anti-
clockwise direction along the line, starting
at the top right in the hard state. Over
time, it evolves through intermediate
states to the soft state. At times indicated
by the jet line, jets are observed from the
black hole. This track is an example of
those followed by black hole transients in
outburst, but any persistent source can
follow parts of the track.18
The grey area is
the area of the intermediate states. This
can be split in the hard intermediate state
and the soft intermediate state.
Adapted from M. Klein-Wolt and M. van der Klis, 2007.18
11. 11
For this research, data from when the system was in a hard state had been
analysed. This occurs mostly during an outburst, when the systems were easier to
detect. In the lower hard states, the QPO mean frequency was too low for this
analysis. Often, the noise level is too high in some observations in order to be able to
clearly distinguish the QPO amongst the noise. However, the QPO is the strongest in
the high hard state, which is when it’s observed best, so focussing mainly on those
regions will not compromise the results. The QPO frequency is too low in the lower
hard state, and the QPO disappears in the low state and most of the intermediate
states. So the focus is on the hard intermediate state.
2.4 Fast Fourier Transform
In order to create a power spectrum from the light curve, a Fast Fourier Transform
must be performed. The Fourier Transform (FT) is used to convert time-varying
signals to the frequency domain. A FFT is an algorithm for calculating the Discrete
Fourier Transform (DFT) and its inverse. The FFT is used to convert time to
frequency (and the other way around) much faster than other transformations. The
FFT computes the DFT with the exact same result as when the DTF would be
evaluated from its definition directly, but the FFT performs this calculation much
quicker. The DFT is defined as:
In order to evaluate this, O(N2
) operations are required, as there are N outputs Xk,
and each of them require a sum of N terms. An FFT is any method to compute the
same result, only with O(N log(N)) operations.
The fundamental idea of the FFT is to split the Fourier Transform into smaller parts.19
For example, if there would be 2N
data points, the FT is split into 2N
/ 2 chunks, each
containing only two numbers. Proceed to FT every pair and put it back together
again. This results in much less operations, as stated before. For our computation,
this means fewer round off errors in the final result (as there were fewer steps
involved), so numerical accuracy improves by using the FFT. Further, computing
time gets greatly reduced as well.
By performing this FFT on the light curve, power spectra can be created. These
spectra tell us how well a certain sine frequency is represented in the Fast Fourier
Transform of the light curve. These power spectra have then been analysed for
QPOs.
For this research, the FFT algorithm from the IDL programming language had been
used. This is based on one in Numerical Recipes (Press et. al. 1998). For the IDL
program used, see the attachments.
12. 12
2.5 Lense–Thirring precession model
The positive flux-frequency relation observed finds a possible explanation in the
Lense–Thirring precession model. This is a general-relativistic model concerning
frame-dragging where the hot, optically thin inner flow in the region closest to the
black hole is not aligned with the accretion disc and precesses on its own. The spin
axis of the black hole is misaligned with the disc allowing this to happen.
Figure 25: schematic diagram of the considered geometry. The inner flow is indicated with
grey, and the blue vectors are the angular momentum. The inner flow precesses about the
black hole, indicated with a black angular momentum vector. The outer disc (orange/red)
remains aligned with the binary partner.
Image by 29
Adam Ingram, Chris Done and P. Chris Fragile, 2009.
The QPO can be explained using this model, by stating that there would be a spot
with cluttered material, a region of higher density in the accretion disk. More material
means more things that can send out the X-rays, thus resulting in a higher flux. As
indicated, the inner region precesses. When it faces the satellite (with the higher
density region) a higher flux will be detected. If due to the precession the geometry
faces away from the observation point (in this case, the satellite) the flux diminishes.
This would cause the oscillation in flux and result in a QPO.
In order to better understand the flux-frequency relation, the inner regions need to be
considered. Due to conservation of angular momentum, material in the disc spins
faster when it’s closer to the black hole and slower when it is further away. In the
outer regions of the disc the mass concentration contributes relatively little to the
total mass in that outer orbit, as there is much more other mass in that ring of the
flow. But as the concentration moves inwards, there is fractionally more mass at
these radii, so the inner hot flow precesses faster. Note that this will result in the
entire inner body rotating faster. The extra mass contributes more and more relative
to the total mass the closer it moves to the black hole’s most inner stable orbits. The
extra mass will result in a higher flux, because there is just more material to send
photons towards us, and because the region precesses faster, the QPO frequency
goes up as well. Recall that the inner region isn’t aligned with the rest of the disc, but
rather at an angle receding to and from us, causing the oscillation in flux. This would
explain the Frequency-flux relation: relatively more mass at a closer orbit, thus
higher flux with increasing frequency. This model doesn’t tell us anything about the
power though.
13. 13
Figure 26: illustration of the
inner regions around the black
hole. The material concentration
contributes relatively more to
the total mass in the inner
orbits, making for a higher flux
and causing the whole inner
flow to precess at higher
velocity, which in turn results in
a higher frequency observed.
3 Observation Method and Equipment
3.1 Rossi X-ray Timing Explorer Satellite
For this research, the measurements and observations of the Rossi X-ray Timing
Explorer (RXTE) have been used. The RXTE was a mission sponsored by the Office
Space Science and Applications and managed by NASA’s Goddard Space Flight
Center.5
It was launched in 1996 on a Delta II rocket. Its primary objective was to
study temporal and broad-band spectral phenomena with regard to galactic and
stellar systems having compact objects. This includes white dwarfs, black holes and
neutron stars. Its instruments span an energy range of 2-200 keV, and can study
timescales from microseconds to years. The design also facilitates multifrequency
observations.
Figure 7: animated picture of the Rossi X-
ray timing Explorer. It orbits the Earth at
an altitude of 580 km, with an orbital
period of 90 minutes and an inclination of
23 degrees.13
Image by Nasa.gov
14. 14
The satellite is equipped with three major instruments. First there’s the Proportional
Counter Array (PCA). This instrument is made from five large proportional counters
with anticoincidence features. Electronic anticoincidence is a method to lower
unwanted background events. An event that we want to study (in this case, a high-
energy interaction due to a gamma ray) occurs, and is then detected by the
electronic detector. This creates an electronic pulse, but the desired events get
mixed up with a large number of other events created by background processes, and
the detector can not distinguish between relevant events and ones created by
background. The anticoincidence feature is an arrangement of other photon
detectors to intercept the unwanted background events, producing simultaneous
pulses that can be used with fast electronics to reject the unwanted background. A
mechanical hexagonal collimator (a device that narrows the incoming beam of
photons to become more aligned in a specific direction) provides 1 degree (FWHM)
collimation (adjusted to the line of sight of the optical device). This means that
sources as faint as 1/1000 of the Crab nebula could be detected within just a few
seconds.
The second instrument is a High-Energy X-ray Timing Experiment (HEXTE). This
features a large area and low background with a 1 degree field of vision co-aligned
with the PCA field of vision. Eight phoswich detectors (detectors developed to detect
very low-intensity X-rays) are arranged in two clusters, each of which rocks on and
off the source. This, together with automatic gain control for each of the eight
detectors together, makes for a well determined background. This means that it can
take spectral measurements of a faint source at 100 keV in about 24 hours.
Last, the RXTE is equipped with an All Sky Monitor (ASM). The ASM alerts RXTE to
flares and changes of state in X-ray sources. It has three rotating Scanning Shadow
Cameras (SSC) that scan about 80% of the sky in 1.5 hours. The cameras measure
intensities of about 75 known celestial sources per day and can measure the position
of a new source with about 3` precision.
15. 15
3.2 The Proportional Counter Array
In this experiment, the data from the PCA has been used. It consists of five large
detectors, spanning a total net area of 6250 cm2
. Every detector is a bigger (about
50%) version of the HEAO-1 A2 HED (an earlier X-ray experiment) sealed detector.
These are filled with xenon gas and are capable of getting low background due to
efficient anti-coincidence schemes. These include side and rear chambers and
propane top layers. The three signal detection layers have xenon of 3,6 cm thick at a
pressure of 1 bar. As a quench gas (a gas to ensure that each pulse discharge
terminates), methane has been used. There are aluminized Mylar windows of 25 μm
on the front window, and a window separating the xenon/methane chambers. The
propane layer can also be used as a signal layer in the energy range of 1-3 keV.
Figure 8: the proportional counter array. It
measures photons with energies between 2
and 60 keV, and consists of five X-ray
detectors filled with gas. The background noise
is kept low due to anti-coincidence chambers
on four sides of the detection chamber. The
energy is calibrated with an on-board
radioactive source.
Figure by H. Bradt, M. Halverson et al.5
3.3 Experiment Data System
The PCA X-ray data is pre-analysed by the Experimental Data System (EDS) before
it sends down the data to the ground, as the telemetry bandwidth is limited.
Telemetry is the highly automated communications process by which measurements
are made and other data collected at remote or inaccessible points and transmitted
to receiving equipment for monitoring.14
The EDS bins data and analyses it
according to criteria that can be changed for each observation. It is also in control of
the ASM rotation, and processes the ASM data. Further, it is equipped with six Event
Analysers (EA) that can independently analyse the entire PCA data stream at the
same time.
16. 16
3.4 Data manipulation
After obtaining several light spectra for each observation, power spectra were
created. This is done by manipulating the spectra data taken by the satellite. The
light curves have been segmented into two-second pieces each.
Figure 9: the light curves are segmented
into pieces of two seconds.
Each of those segments has then undergone a FFT. This means that each segment
of the light curve got decomposed into sine waves and their respective strengths and
frequencies.
Figure 10: the FFT of each two second
segment is taken.
The mean counts per second value was taken for each segment, and then the
segments got binned together according to flux. If the satellite observations were
long enough to create at least four power spectra in the final output, then those
observations have been analysed.
17. 17
3.5 Data Analyses
After creating the power spectra as described in section 3.4, they have been
analysed for QPOs. In order to measure the strength of the QPO peaks, the spectra
have been fitted using a broken power law to fit the continuum, and Lorentzians to fit
the QPO peak and (sub) harmonics. A Lorentzian distribution was chosen over a
Poisson one due to the former better fitting the wings of the peak, and not because
the physical interpretation of the QPO peak would call for a Lorentzian rather.
Figure 11: the example data of H1743-322.
The continuum is fitted using a broken power
law (red), and the QPO and harmonic have
been fitted with Lorentzians (green and blue
respectively).
The strength of the QPO is then indicated by the area under the peak. To calculate
the integrated area, a custom program named ana_ascii had been used. The extra
area from the runaway to the sides of the QPO peak is neglectable, as the axes are
scaled logarithmically and the extra contribution off the sides of the X-axis is not
influencing the result. Further, for the relations that have been focussed on (Root
Mean Square (RMS)-Flux relation and how the central frequency shifts over time),
the absolute and exact strength of the peak is not as important as how trends
change over time.
The RMS of the integrated area is taken next (for the program, see Attachments)
and then plotted against the flux. This way, there is a clear view of the relation (if
any) between the flux and the strength of the QPOs.
18. 18
4 Results
4.1 RMS-Flux Relation
The relation between the RMS and the flux had been analysed for the objects MAXI
J1659-152, GX 339-4 and H1743-322 to see how they would compare to the first
time this relation had been observed in QPOs, in object XTE J1550-564.1
The
gradient of the RMS-flux relation for each observation flattened with increasing
frequency as well in XTE J1550-564.
Figure 12: RMS-Flux plot from the observations of GX 339-4.
Figure 13: RMS-Flux plot from the observations of MAXI J1659-152.
19. 19
Figure 14: RMS-Flux plot from the observations of H1743-322.
4.2 Central Frequency-Flux Relation
The relation between the central frequency of the QPO and the flux has also been
analysed.
Figure 15: central frequencies of the QPOs plotted against the flux for each observation of
object GX 339-4.
20. 20
Figure 16: central frequencies of the QPOs plotted against the flux for each observation of
object MAXI J1659-152.
Figure 17: central frequencies of the QPOs plotted against the flux for each observation of
object H1743-322.
21. 21
4.3 Mean Frequency – RMS-Flux Gradient Relation
The gradient of the RMS-flux relation had been plotted to compare it with the earlier
studied1
XTE J1550-564. The gradient was calculated with a custom IDL program
(see Attachments).
Figure 18: the gradient of the RMS-flux relation plotted against the mean QPO frequency of
the relevant observation for GX 339-4.
Figure 19: the gradient of the RMS-flux relation plotted against the mean QPO frequency of
the relevant observation for MAXI J1659-152.
22. 22
Figure 20: the gradient of the RMS-flux relation plotted against the mean QPO frequency of
the relevant observation for H1743-322.
4.4 Intercept from Linear fit of the RMS-Flux relation
The intercept of the linear fit to the RMS-flux relation had been analysed in order to
see whether it is consistent with zero in all cases or not, within error. This could tell
whether the relation is directly proportional or just shows that there is a relation. The
intercept had been calculated using a custom IDL program (see Attachments).
Figure 21: plot of the intercept values with error of GX 339-4. For this object, 9 linear plots
had been analysed, as indicated by the x-axis.
23. 23
Figure 22: plot of the intercept values with error of MAXI J1659-152. For this object, 8 linear
plots had been analysed, as indicated by the x-axis.
Figure 23: plot of the intercept values with error of H1743-322. For this object, 11 linear plots
had been analysed, as indicated by the x-axis.
24. 24
5 Discussion
5.1 The RMS-Flux Relation Analyses
In GX 339-4 we see that as the flux increases, so does the RMS. This relation
seems to be positively linear, as expected. However, in the case of H1743-322, there
are some negative relations too, as well as relations within a single observation that
don’t seem to be linear at all. This doesn’t seem to be the result of a problem with
the data nor due to a poor signal to noise ratio.
As for the mean frequency – RMS-flux gradient relation, we can see with H1743-322
that the gradient flattens (gets closer to zero) as the frequency increases. This is
consistent with what had been observed in a previous study (see 1
L.M. Heil, S.
Vaughan, P. Uttley – 2010) with object XTE J1550-564.
The QPO frequency at which the gradient of the RMS-flux relation becomes zero is
at about the same frequency for both objects as well, around 5,5 Hz. This could
mean that there is something fundamental occurring at a certain distance from the
black hole.
Figure 24: comparison of the
gradient-frequency plot of
XTE J1550-564 (by 1
L.M.
Heil, S. Vaughan, P. Uttley –
2010) and H1743-322. Not
only is the trend similar, but
so are the gradient values.
Also, at around 5,5 Hz the
gradients become zero in
both objects. This is a
remarkable similarity.
Top plot by 1 L.M. Heil, S. Vaughan, P.
Uttley – 2010.
25. 25
However, despite H1743-332 showing remarkably similar characteristics, GX 339-4
shows no obvious relation with the frequency, within errors. Apart from inclination,
there should be no real differences between the object. Maxi J1659-152 again shows
too much noise to support any sensible conclusions.
5.2 The Central Frequency-Flux Relation
In the case of H1743-322, it is very clear in some observations that as the flux
increases, so does the central frequency of the QPO. There are models such as the
Lense–Thirring precession model 28, 29
describing this phenomenon (see section
2.5). However, with object GX 339-4, the relation seems the opposite way around.
There is a negative correlation, as when the flux goes up, the central frequencies of
the QPOs decrease. Again, no trend is seen in MAXI J1659-152. The signal-to-noise
ratio was just too low.
The intercept of the linear fit to the RMS-flux relation had been analysed for
consistency with zero. This could tell whether the relation is directly proportional or
just shows that there is a relation. Nearly all points are zero within three sigma. This
would indicate that the frequency-flux relation is directly proportional.
6 Conclusion
There doesn’t always seem to be a linear RMS-flux relation in the QPO. This relation
is obeyed only in the case of H1743-322. This object is also the one showing a
positive frequency-flux correlation, and the gradients of the RMS-flux relation behave
similar (both qualitatively and quantitatively) to what was observed earlier1
in XTE
J1550-564. The flattening in the RMS-flux relation may be because the QPO just
gets to a strength where it can no longer increase with increasing flux, though this
has not been observed with all objects. The frequency-flux correlation might be
explained with the Lense–Thirring precession model. However, GX 339-4 shows
almost opposite correlations. MAXI J1659-152 had too much noise to say anything
conclusive. This is new behaviour, and further research is needed. A possible
explanation for the differences might have to do with the inclinations with which the
objects are observed. H1743-322 is a high-inclination source, while GX 339-4 is low-
inclination. Further research could include looking at objects with high inclinations
and check if they all exhibit the same behaviour, and ditto for low-inclination objects.
The power spectra can also be looked at next, to see whether they differ per
observation.
Acknowledgements
With sincere thanks to supervisor L. Heil and secondary supervisor M. van der Klis
for the guidance and constant supervision as well as for providing necessary
information regarding the project, and also for the support in completing the project.
26. 26
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