Electromagnetic counterparts to Gravitational Wave sourcestheory.tifr.res.in/~janakee/Science_with_Subaru/Varun_Bhalerao.pdf · Varun Bhalerao | 18 Dec 2019 EMGW | Science with Subaru

Varun BhaleraoIIT Bombay

Electromagnetic counterpartsto Gravitational Wave sources

EMGW – Overview

Indian participation

Daksha

Subaru

EMGW | Science with SubaruVarun Bhalerao | 18 Dec 2019 2

Complementary informationGW

• Masses• Spins• Geometric properties» Position» Distance» Inclination angle…

EM• Precise location• Nucleosynthesis• Ejecta properties» Beaming» Mass» Velocity…

• Cosmology


Complete astrophysical picture

GW170817: GW + Gamma rays!


Credit: NASA/GSFC

Massive follow-up campaign


Credits: Pavan Hebbar, Varun Bhalerao (IITB), David Kaplan (UW Milwaukee), Mansi Kasliwal (Caltech), GROWTH collaboration

GW170817• 15 papers: 3 Science

+ 2 Nature• Photometric and

spectroscopic evolution, theoretical model (“Cocoon”), radio jet breakout and polarisation, confirmation of third peak R-process nucleosynthesis


Previously: AstroSat + GROWTH studies prove that a transient was unrelated to black hole merger GW170104

Larg

e Ind

ian Te

lesco

pes


10m SALT(South Africa)

2m HCT0.7m

0.5m, 1m, 1.3m 3.6m4m LMT planned

2.3m Vainu Bappu1m1.3m

2m IGO

0.5m 1.2m IR

GMRT

Astrosat

ORT

Gauribidanur

Cosmic fireworks: shining light on gravitational wave sources Varun Bhalerao (Physics) | [email protected]

EMGW | Science with SubaruVarun Bhalerao | 18 Dec 20198

Global Relay of Observatories Watching Transients Happen

New 0.7m, 1deg fully robotic telescope


Stepping back: a bird’s-eye view


O3a candidates

https://g

race

db.ligo

.org/sup

erev

ents/pub

lic/O

3/

New class of bursts !• GRB was very faint:

3-4 orders of magnitude lower than SGRBsnext will be fainter!

• Broadband: seen from few keV to hundreds of keV

• Missed by Swift, AstroSat, CALET…


Since the total baryonic mass of the system can only bereduced (by mass ejection), the maximum baryonic mass of themerger remnant and accretion disc is bound by MB

Initial. FromFigure 3, we can see that for the measured NS gravitationalmasses with the low-spin prior, the MS1 and SHT EOS couldnot form a BH since M MB

InitialBStatic< . Assuming that the

magnitude of the spins is small, the MS1 and SHT EOS areincompatible with BH formation. If the dimensionless spins ofthe NSs are allowed to be larger than 0.05, BH formation isonly disfavored: we find that a fraction 83% (MS1) and 84%(SHT) of the posterior distribution satisfies M MB

InitialBStatic< .

For both spin priors, we find that the H4, LS220, SFHo, andSLy EOS result in M MB

InitialBUniform> . Even when assuming a

large ejecta mass of M0.1 :, the remaining mass cannot form auniformly rotating NS. For those EOS, the merger either resultsin prompt BH formation or in a short-lived remnant, with alifetime determined by the dissipation of differential rotationand/or disk accretion.

To be compatible with scenario (ii), the lifetime of themerger remnant would have to be sufficiently long to power theGRB. We note that prompt BH formation is a dynamic processaccessible only to numerical relativity simulations. Althoughthere are parameter studies (Hotokezaka et al. 2011; Bausweinet al. 2013), they only consider equal mass binaries.Considering also the error margins of those studies, wecurrently cannot exclude prompt collapse for the H4, LS220,SFHo, and SLy EOS. Finally, we note that for the APR4 EOSonly the possibility of a stable remnant can be ruled out. Moregenerally, only EOSs with M M3.2B

Static < : are consistent withscenario (i) when assuming the low-spin prior, or withM M3.7B

Static < : for the wider spin prior. These bounds werederived from the 90% credible intervals of the MB

Initial posteriors(and these, in turn, are determined for each EOS in order toaccount for binding energy variations). These upper limits arecompatible with and complement the lower bounds on MG

Static

from the observation of the most massive known pulsar, whichhas a mass of M2.01 0.04 :( ) (Antoniadis et al. 2013). In

Section 6.5 we will discuss some model-dependent implica-tions of the lack of precursor and temporally extendedgamma-ray emission from GRB170817A on the progeni-tor NSs.

6. Gamma-ray Energetics of GRB170817Aand their Implications

Using the measured gamma-ray energy spectrum and thedistance to the host galaxy identified by the associated opticaltransient, we compare the energetics of GRB170817A to thoseof other SGRBs at known redshifts. Finding GRB170817A tobe subluminous, we discuss whether this dimness is anexpected observational bias for joint GW–GRB detections,what insight it provides regarding the geometry of the gamma-ray emitting region, what we can learn about the population ofSGRBs, update our joint detection estimates, and set limits ongamma-ray precursor and extended emission.

6.1. Isotropic Luminosity and Energetics of GRB170817A

Using the “standard” spectral information from Goldsteinet al. (2017) and the distance to the host galaxy NGC 499342.9 3.2( )Mpc, we calculate the energetics of GRB170817Ausing the standard formalisms (Bloom et al. 2001; Schaefer2007). GRBs are believed to be relativistically beamed and theiremission collimated (Rhoads 1999). Isotropic energetics areupper bounds on the true total energetics assuming the GRB isobserved within the beaming angle of the brightest part of the jet.We estimate that the isotropic energy release in gamma-raysE 3.1 0.7 10iso

46= ´( ) erg, and the isotropic peak luminos-ity, L 1.6 0.6 10iso

47= ´( ) erg s−1, in the 1 keV–10MeVenergy band. These energetics are from the source interval—i.e.,the selected time range the analysis is run over—determined inthe standard manner for GBM spectral catalog results, allowingus to compare GRB170817A to other GRBs throughout thissection. The uncertainties on the inferred isotropic energeticsvalues here include the uncertainty on the distance to the hostgalaxy. As a cross check, the isotropic luminosity is also

Figure 4. GRB170817A is a dim outlier in the distributions of Eiso and L iso, shown as a function of redshift for all GBM-detected GRBs with measured redshifts.Redshifts are taken from GRBOX (http://www.astro.caltech.edu/grbox/grbox.php) and Fong et al. (2015). Short- and long-duration GRBs are separated by thestandard T 2 s90 = threshold. For GRBs with spectra best modeled by a power law, we take this value as an upper limit, marking them with downward pointingarrows. The power law spectra lack a constraint on the curvature, which must exist, and therefore, will overestimate the total value in the extrapolated energy range.The green curve demonstrates how the (approximate) GBM detection threshold varies as a function of redshift. All quantities are calculated in the standard 1 keV–10 MeV energy band.

11

The Astrophysical Journal Letters, 848:L13 (27pp), 2017 October 20 Abbott et al.

Requirements

Order of magnitude higher sensitivity(Large area, lower noise, background rejection)

Wide spectral band(1 keV to >1 MeV)

Continuous all-sky coverage(Two satellites)


Daksha


On a le r t fo r h igh energy t rans ien ts

Daksha at a glance


Low Energy: SDDs 1-25 keV

Medium Energy: CZT20-200 keV

High Energy:Scintillator100-1000 keV

Two satellites

Daksha results – 1• Detect few hundred mergers per year» Also few on-axis GRBs per day

• Localisation: » ~10 degrees on board » ~5 degrees ground processing

• Broadband prompt spectra» Only mission to give prompt soft spectra

• Hard X-ray polarimetryEMGW | Science with SubaruVarun Bhalerao | 18 Dec 2019 16

Daksha results – 2 • Provide time and direction of burst» Lower FAR for GW searches» Lower detection statistic!

• Increase LIGO detections by 2x – 3x !

Huge discovery space


Subaru & EMGW

GW170817


Tominaga et al., 2018, Publications of the Astronomical Society of Japan, Volume 70, Issue 2, id.28

Better scheduling of observations

6 March 2017EM followup of GW sources | Varun Bhalerao 20See Rana et al., arXiv: 20161603.01689. (LIGO-P1600007) Animation by Javed Rana

Hot off the press: S191216ap• GW “MassGap” candidate (GCN 26454)• Coincident neutrino event (GCN 26463)• Subthreshold HAWC trigger (GCN 26472)» 0.3 degree localisation (1-sigma)» 266 ± 60 Mpc

• HSC: ~27 mag ⇒Mr = -10 mag


Tanaka, M., et al., Radioactively Powered Emission from Black Hole-Neutron Star Mergers

2014, The Astrophysical Journal, 780(1), 9

Subaru: possibilities•Galaxy targeting (OIR)•HSC tilingSearch

•Photometric evolution•Spectroscopic classificationVetting

•OIR photometry•SpectraStudy


Documents

Electromagnetic counterparts to Gravitational Wave sourcestheory.tifr.res.in/~janakee/Science_with_Subaru/Varun_Bhalerao.pdf · Varun Bhalerao | 18 Dec 2019 EMGW | Science with Subaru