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Neutron Star Merger Afterglows: Population Prospects for the Gravitational Wave Era
R. Duque, F. Daigne & R. Mochkovitch
March. 26th 2019 –
New Era of Multi-Messenger Astrophysics,Groningen, The Netherlands
On August 17th 2017…
2
• Confirmed NS-NS mergers as progenitors for short GRBs• Inauguration of the era of multi-messenger
astronomy with GW• Other fundamental (astro-)physics: GR, NS EOS,
Hubble constant measurement, r-process nucleosynthesis, etc.
Afterglows and kilonovae:What should we expect for O3?
Vill
aret
al.
2018
Abbot
t et
al.
2017b
Moo
ley
et a
l. 2018
Context
3
• Which kilonovae and afterglows to expect and what will they look like?• How will they help to study the environments of NS binaries?• What insight will they bring on the origin of the jet structure?• What will they tell us on GRBs and their dissipation mechanisms?
O3 is coming (April 2019)àMore GW with afterglow
and kilonova!
Afterglow, kilonova= great wealth of information!
ü Localizationü External medium densityü Jet kinetic energyü Jet geometryü Viewing angleü Magnetic fieldü And more!
Ghir
landa
et a
l. 2018
Gravitational wave
Θv
Kinetic energy E
external densitynext
1540+3200 BNS/Gpc3/yr (Abbott+2018)-1220
GW h
orizo
n
Afterglow
Detection depends on D, Θv
… and GW horizon
O3: 380 MpcDesign: 430 Mpc
Detection depends on D, Θv , E, next, … and radio sensitivity
VLA: 15 µJy @ 3GHzSKA1-Mid: 3 µJy
Population model with ingredients: D, Θv , E, next , …+ Detection criterionà Deduce GW+AG observed population of mergers
Method
Kilonova
Detection depends on D, Θv
… and Vis.-IR follow-up depth
D
5
Population model distributions:
Energy Density
intrinsic populationGW+Radio observed
intrinsic populationGW+Radio observed
Reference model:Ø Energy: BPL, break energy 2.1052 erg, slopes +0.5 and -2 (Ghirlanda et al. 2016)
Ø Density: Log-normal centered on 10-3 cm-3
selection bias towards larger energy and density
Log(
d
)
(Detectable) Event rates for NS-NS
Detector conf. #GW #(GW+AG) #(GW+KN)
O3 + VLA 9 2
Design + VLA 21 4
Design + SKA 21 6
700 MpcHorizon + SKA
92 20
6
• In general: 10-20% events have detectable AG (depending on energy distribution)
• Large deviation from this = constraints on population!
Uncertainties: +200% (intrinsic rate from LIGO-Virgo O2/O3)+ uncertainty on population model-73%
GW+GRB ~ 1-10% (O3) (Beniamini et al. 2018)
?
100%
Can we detectall detectable
events?
� Most events seen off axis!
� Mean angle ~20-30°
7
0 20 40 60 80
✓v (deg)
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.035
dN/d
✓ v
Joint (O3+VLA)
GW only
All events
RD
, Dai
gne,
Moc
hko
vitc
h(in p
rep.)
+ Other distributions:distance, peak flux, proper motion, …
Properties of joint events: viewing angle
0 20 40 60 80
✓v (deg)
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.035
dN/d
✓ v
Joint (O3+VLA)
GW only
All events
Properties of joint events: viewing angle
� Most events seen off axis!
� Mean angle ~20-30°
� New insight on GRB physics
à Jet geometry? Origin of lateral structure?
à GRB dissipation mechanisms (thermal tail?)
8
170817
RD
, Dai
gne,
Moc
hko
vitc
h(in p
rep.)
+ Other distributions:distance, peak flux, proper motion, …
Merger medium density (low)
Formation medium density (high)
10�2 10�1 100
fHD
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
f HDp(
f HD|N
HD,N
TO
T)
HD/Tot = 0/10
HD/Tot = 1/10
HD/Tot = 3/10
9
Binaries in high density media
Ben
iam
ini,
RD
, Moc
hko
vitc
h, D
aign
e(in p
rep.)
Observation of 3 high-density out of 10 à log(fHD) = - 1 ± 0.6High density ⬄ Large viewing angle
� NS binaries with high eccentricity or efficient common envelope phase merge in high density media after short delay time (Beniamini+2016)
� Mergers occurring in dense media produce brighter AG and are more likely detected (F ~ n4/5)
à Tight constraints on binary environment from only a few events
0 20 40 60 80
✓v/deg
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.035
0.040
dN/d
✓ v
Joint, n = 1 cm�3
Joint, n = 10�3 cm�3
Ben
iam
ini,
RD
, Moc
hko
vitc
h, D
aign
e(in p
rep.)
?
intrinsic fraction
obs. fraction of HD events
0/101/103/10
Expectations for kilonovae
10
Moc
hko
vitc
h, R
D, D
aign
e, Z
itou
ni(
in p
rep.)
b filterr filter
170817
• Vis.-IR signal depends on viewing angle because of ejecta contrasts
For O3:ü Magnitude OK a prioriü Volume to explore potentially
100x larger than for 170817ü Contrast with host galaxy
Lanthanide-poorBlue (low !)
Lanthanide-richRed (high !)
For O3…
Moves with increasing GW horizon(more weak events)
à Finding the OT challenging!KN model and population details in poster: Prospects for KN signals in the GW era
Conclusion� Afterglows and KN are important to understand the local and
viewing conditions of NS-NS mergers
� O3 is coming: several NS-NS GW events, a few with afterglow, all with detectable KN
� Actual fraction of AG/GW will constrain population of NS-NS merger population (jet parameters, external density, etc.)
� Most events are seen off-axis, allowing to probe the jet geometry and emission therein
� High-density mergers will allow to study fast-merging binaries. Only a few events are necessary to constrain this particular binary NS evolution channel.
� What to expect from NS-BH mergers?
11
Interpretation tools for observations of GRBs in the multi-messenger context:① Modeling of EM counterparts of CO fusions: sGRBs and
afterglows Context: observations by LIGO–Virgo (~2019)
② Modeling of the general population of GRBs and afterglows
Context: present and future observations:Swift, Fermi, INTEGRAL, SVOM
Long runLi
nk p
op. c
oale
scen
ce
—po
p. s
GRB
Determining viewing angle and density from multi-messenger observations
13
10 15 20 25 30 35 40 45
✓v/deg
10�5
10�4
10�3
10�2
n/c
m�
3
KNAG
AG
VLBI
GW
14
• Distinguish NS-NS and BH-NS?• Nature of final object? Link with ring-
down signal?• Systematic
fusion/GW/sGRB/kilonova/afterglow association?
• GW/GRB delay?
1: GRBs & CO fusions
2: General population of GRBs
Rates: (Wei, Cordier et al. 2017a):• SVOM: 60-70 yr-1
• Swift, Fermi, INTEGRAL: ~100 yr-1
• Radiative processes in GRB (shocks/magnetic reconnection)?
• Ejecta magnetization?• Other afterglow observables
(polarization, imaging)?
Wei
, Cor
die
r et
al.
2017a
Gamma-ray bursts
Duration
Longs (ccSNe):• > 2s• Soft• High SFR galaxies
Short (compact object mergers):• < 2s• Hard• Early-type galaxies
Light curves:• Strong variability• Shape diversity• Variation time-scale diversity
15
Pac
iesa
s et
al.
1996
Pac
iesa
s et
al.
1996
Gamma-ray burstslog(R/m)
compact central engine
radiation: photosphere + IC?
dissipation:• shocks?• reconnection?
radiation:synchrotron
prompt phase (X-ray, gamma) afterglow (X, UV, O, IR, Radio)
afterglow:• deceleration• jet opening• synchrotron
16