Waves on the lake: the astrophysics behind gravitational waves May 28 – June 1, 2018

1. Como Lake School, 1st June 2018
Elena Pian
INAF - Astrophysics and Space
Science Observatory, Bologna
Electromagnetic
counterparts of
Gravitational Waves

2. Setting multi-messenger
astronomy in context:
Search and follow-up of
electromagnetic counterparts of
cosmic sources of:
1) Neutrinos
2) cosmic rays
3) GWs

3. Cosmic neutrino spectrum

4. Solar neutrinos
Proton-proton reaction chain (simplest
version):
This process is responsible for radiation
production in stars smaller than 1.3 solar
masses

5. Core-collapse supernova neutrinos
Electron capture (or inverse beta decay):
This process is responsible for neutronization of
massive stellar cores undergoing gravitational
collapse (neutron star remnant formation)

6. SN1987A (LMC, 50 kpc)
The neutrino detectors
IMB (USA), Kamiokande
(Japan) and Baksan
(Russia) detected a
handful of neutrinos
each, a few hours
before light detection
from SN1987A (I.
Shelton 1987, IAU Circ.
4316)
Color-composite of
SN1987A nowadays:
visible (HST, green),
radio (red, ALMA), X-
rays (purple, Chandra) 2”

7. Super Kamiokande experiment for MeV neutrino detection

8. Electron capture (p + e-  n + nu_e)
and beta+ decay (p  n + e+ + nu_e)
Are also responsible for supernova light
emission, dominated by the decay chain:
56Ni  56Co  56Fe
The emitted neutrino flux is normally way
too weak to be detected

9. Light curves of various types of supernovae
In general, LCs follow radioactive
exponential decay of 56-Cobalt

10. Periodic table of elements
https://en.wikipedia.org/wiki/R-process
Lanthanides: Z = 57-71

11. ICECUBE South Pole neutrino observatory
Esperimento per rivelare i cosiddetti “ultra-high-energy neutrinos” (Energia > 1 TeV)
https://icecube.wisc.edu
Colonne di fotomoltiplicatori

12. Hadronic processes (particle cascades) in relativistic
jetted sources can produce UHE neutrinos.
Only promising case so far of association between UHE
neutrino and cosmic source:
BL Lac object TXS0506+056 (z = 0.33, Paiano et al. 2018)
IceCube detected a PeV event on 22 Sep 2017 (Kopper
& Blaufuss 2017) from a sky area that is compatible
with variable multi-wavelength emission
Ultra-high energy neutrinos (>1 TeV)

13. ~200 sources
(M82, NGC253)
http://tevcat.uchicago.eduTeV Sky interactive
map
TXS0506+056,
MAGIC

14. Cosmic rays: Victor Hess
1883-1964
1911-1913: Hess accomplishes first baloon flights
To measure extraterretrial “radiation”
Nobel Prize 1936,
with Carl David
Anderson

15. Pierre Auger Observatory
for cosmic rays
Argentinian territory area covered by PAO
Typical detector
Pierre Victor Auger (1899-1993)

16. Spectrum of Cosmic Rays
Kotera & Olinto 2011

17. Relationship between magnetic field and Larmor radius
Kotera & Olinto 2011
RL = E / ZeB

18. Hypothesis that supernova remnants
(SNR) are good CR accelerator
candidates.
Are SNRs good “Pevatrons”?
In order to be so, they must accelerate
both nucleons and electrons, to
account for predominance of
nucleonic CR component

19. X-ray spectrum of NE rim is non-
thermal (featureless power-law). X-ray
synchrotron emission implies electron
energies of ~100 TeV
Supernova remnants: SN1006 (2 kpc, Type Ia SN)
ASCA, 0.4-8 keV
Koyama et al. 1995
TeV observation with CANGAROO
N(E)~ E-2
Photon energy:
Chandra

20. Y. Fukui, MIAPP 2018
Shock velocity ~ 10000 km/s

21. Aharonian et al. 2007
2’ = 2 pc
SNR RX J1713.7-3946 (uncertain SN explosion type)
HESS observation: sum of 2004 and 2005 data
(ASCA contours in black )
High-resolution millimetric observations have revealed interstellar CO molecular gas
interacting with the SNR. A molecular cloud of ∼200 solar masses is associated with
the X-ray and TeV peak, providing strong evidence for proton acceleration (electrons
suffer too severe synchrotron and Inverse Compton losses to survive and fill the
molecular cloud volume).

22. Giuliani et al. 2011
SNR W44 with AGILE-GRID
1.1 x 0.75 deg2
AGILE-GRID map
VLA, 324 MHz
age ~20000 yr
Distance ~3 kpc
Neutral pion decay signature 
hadronic process
Neutral pion
decay
Bremsstrahlung
Synchrotron
IC

23. K. Fang, MIAPP 2018
Pulsars:

24. A double neutron star merger is expected to produce:
1) a GW signal at ~1-1000 Hz (nearly isotropic)
2) a short GRB (highly directional and anisotropic)
3) r-process nucleosynthesis (nearly isotropic)
Lattimer & Schramm 1974; Eichler et al. 1989; Li & Paczynski 1998

25. Hulse & Taylor 1975; Taylor & Weisberg 1982
NP 1993 to Hulse & Taylor
PSR1913+16
Orbital period = 7.75 hr
Binary PSR J0737-3039:
merger time of ~85 Myr
Binary compact star systems with merger times less than the age of the Universe
Orbital period
decay caused
by GW
radiation:
-> merger time
of ~300 Myr
2003, Nat, 426, 531

27. Search for GW170817 optical counterpart:
GW error regions and Swope 1m pointings
Coulter et al. 2017

28. Comparison of Swope discovery image with archival HST image
Coulter et al. 2017
(AT2017gfo)

29. Optical and near-infrared light curves of GW170817 / AT2017gfo
Villar et al. 2018 , and references therein

30. Host of GW170817: Lenticular galaxy NGC 4993 (40 Mpc)
Levan et al. 2017
MUSE contours
in [N II] line
10”

31. ESO VLT X-Shooter spectral sequence of kilonova GW170817
Pian et al. 2017; Smartt et al. 2017
purely thermal spectrum
(T = 5000 K).
Initial expansion
speed of ~0.2c
Broad absorption lines
indicate material at high
speed (0.1-0.2c)

32. Receding photosphere: P-Cygni profile of absorption lines

33. Supernova spectral evolution: the photosphere (τ ~ 1)
recedes with time (SN1998bw, 35 Mpc)
Patat et al. 2001
Si II -> 6355 Å

34. Typical spectra of Stripped-envelope core-collapse SNe
Pian & Mazzali 2017
Si II
He I
O I
Fe II
Hα

35. Geometry of 3-component model for kilonova
Tanaka et al. 2017, PASJ
(v ~ 0.2c)
(v ~ 0.05c)
(v ~ 0.05c)

36. Geometry of 3-component
model for kilonova and
resulting spectra
Mej ~ 0.03
Tanaka et al. 2017, Utsumi et al. 2017
(v ~ 0.2c)
(v ~ 0.05c)
(v ~ 0.05c)

37. Element abundances at 1 day after merger
Tanaka et al. 2017, PASJ
solar
actinideslanthanides
Ye = np / (np + nn)

38. Kilonova 3-component model for AT2017gfo
1.5 days
Dynamical ejecta, lanthanide-rich (Ye = 0.1-0.4)
Wind, mixed (Ye = 0.25)
Wind, lanthanide-free (Ye = 0.3)
v ~ 0.2c
v ~ 0.05c
v ~ 0.05c

39. Kilonova 3-component model for AT2017gfo:
ejecta mass is 0.03-0.05 solar masses

40. An example of a _good_ spectral fit (SN2004eo)
Mazzali et al. 2008

41. AT2017gfo evolves much more rapidly than any supernova
Arcavi et al. 2017

42. Magellan spectral sequence of kilonova GW170817
Shappee et al. 2017
spectra at < 1 day
indicate temperature
of ~10000 K

43. gamma-ray bursts are brief flashes of radiation at 100-1000 keV. They are
Produced by non-thermal processes in a relativistic plasma, most probably
propagating in a jet. Their progenitors are core-collapse supernovae (long GRBs) and
compact star mergers (short GRBs)
relativistic jet

44. Hardness-Duration Classification
of GRBs
50 - 300 keV flux
10 - 50 keV flux
H =
Short/Hard
Long/Soft
Kouveliotou+1993; von Kienlin+2014
long
short

45. Cumulative distribution of projected offsets of various
explosions with respect to their host centers
Berger 2014
GRB050724
(z = 0.258)

46. Short GRB130603B
(z = 0.356)
Kilonova:
Ejection of r-process material
from a NS merger (0.01-0.1 Mo)
(Barnes & Kasen 2013)
MH ≈ -15
MR ≈ -13
Tanvir et al. 2013;
Berger et al. 2013
MJ = -15.35

47. GW170817 and
GRB170817A
The short GRB170817A
lags GW signal by 1.7s:
is this timescale related
to the engine or to the
plasma outflow? First of
all it tells us that GW
and light propagation
speeds differ by less
than 1 part in e15
Epeak ~200 keV (GBM)
Abbott et al. 2017;
Savchenko et al. 2017;
Fermi Collaboration 2017

48. Energy output of GRBs
Courtesy: L. Amati

49. Multiwavelength light curves of AT2017gfo
within ~3 weeks of BNS merger
Troja et al. 2017

50. They peak earlier than ~100 s, unlike in
GRB170817A, where no X-ray flux was
detected for 10 days
D’Avanzo et al. 2014
Van Eerten &
MacFadyen 2011
X-ray light curves of short GRB afterglows
normalized to Eiso
“top-hat” jet

51. Geometry of GW/GRB/kilonova system Troja et al. 2017

52. Jet morphology
Abbott et al. 2017

53. GRB170817A: multiwavelength LCs and emission models.
A structured off-axis jet or a quasi-isotropic outflow are preferred
Xie, Zrake, MacFadyen 2018
Narrow engine Wide engine
Kilonova Kilonova
Uniform jet

54. Typical angular sizes of GW error boxes in the era of
Simultaneous LIGO Hanford, Livingstone, Virgo and INDIGO
R. Weiss, CfA, Feb 2018

55. Conclusions on multi-messenger astrophysics (1)
Multi-messenger astrophysics started ~100 years ago, when the search for
cosmic rays started. Evidence that SNRs are PeVatrons has built up, but
origin of highest energy cosmic rays is still unknown.
Neutrino astronomy has spearheaded multi-messenger astrophysics: MeV
neutrinos from the Sun and from SN1987A and UHE neutrinos from (jetted?)
sources.
While GWs from binary stellar BH mergers should not produce any EM
signal, binary neutron star mergers produce kilonova -> first direct proof that
neutron star mergers are r-process factories.

56. Conclusions on multi-messenger astrophysics (2)
The preliminary models require more than one kilonova component, with
different proportions of species (lanthanide-rich vs lanthanide-free). The
ejecta are about 0.03-0.05 solar masses.
More realistic atomic models and opacities are necessary to use with density
structure profiles, nuclear reaction networks and radiative transport codes.
Fundamental problem of NS Equation of State can be addressed with joint
gravitational and electromagnetic information (see A. Perego’s talk;
dynamical ejecta should be larger for smaller radii of the NSs, i.e. for softer
EoS, and for asymmetric NS masses; larger remnant mass implies lower
ejecta).
O3 (starting Jan 2019) expectations are based on Abbott et al. (2017)
predicted rate:

57. THESEUS
https://www.isdc.unige.ch/theseus/
medium-size mission (M5) within the
Cosmic Vision Programme, selected
by ESA on 2017 May 7 to enter an
assessment phase study
4 Soft X-ray Imager (SXI, 0.3 – 6 keV),
~1sr FOV, location accuracy < 1-2’
0.7m InfraRed Telescope (IRT, 0.7 – 1.8 μm)
10’x10’ FOV, fast response, imaging and
spectroscopy capabilities
X-Gamma rays Imaging Spectrometer
(XGIS, 2 keV – 20 MeV),
coded-mask
cameras based on
Si diodes coupled
with CsI crystal
scintillator,
~1.5sr FOV, location
accuracy of ~5’ in
2-30 keV