Outline Gravitational waves EMGW: GW170817 and results Lessons learnt Daksha Daksha: Finding High Energy Emissions from GW sources Varun Bhalerao | IIT Bombay 2
Gravitational Waves
Ripples in spacetime Credit: PhD comics Daksha: Finding High Energy Emissions from GW sources Varun Bhalerao | IIT Bombay 4
Gravitational wave detectors Daksha: Finding High Energy Emissions from GW sources Varun Bhalerao | IIT Bombay 5
Gravitational waves Credit: Teresita Ramirez / Geoffrey Lovelace / SXS Collaboration / LIGO Virgo Collaboration Daksha: Finding High Energy Emissions from GW sources Varun Bhalerao | IIT Bombay 6
s s r r a a s t l s u p n o g r n t u BH BH i t e e N r Stochastic c c A Continu… Merging GW BH NS Binaries Burst s Unknowns S u NS NS p e r n o v a e Daksha: Finding High Energy Emissions from GW sources Varun Bhalerao | IIT Bombay 7
Complementary information GW EM • Masses • Precise location • Spins • Nucleosynthesis • Geometric properties • Ejecta properties » Position » Beaming » Distance » Mass » Inclination angle… » Velocity… • Cosmology Complete astrophysical picture Daksha: Finding High Energy Emissions from GW sources Varun Bhalerao | IIT Bombay 8
Astrophysics
Where are all the heavy metals in the universe formed? What is the Equation of State of ultra-dense matter? Daksha: Finding High Energy Emissions from GW sources Varun Bhalerao | IIT Bombay 10
Nucleosynthesis By Geckzilla [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)], from Wikimedia Commons Daksha: Finding High Energy Emissions from GW sources Varun Bhalerao | IIT Bombay 11
Credit: NASA/GSFC Daksha: Finding High Energy Emissions from GW sources Varun Bhalerao | IIT Bombay 12
GW170817
GW170817 First direct detection of gravitational waves from merging binary neutron stars 40 Mpc (130 million light years) “This is a big deal…” Daksha: Finding High Energy Emissions from GW sources Varun Bhalerao | IIT Bombay 14
Observing frenzy Credits: Pavan Hebbar, Varun Bhalerao (IITB), David Kaplan (UW Milwaukee), Mansi Kasliwal (Caltech), GROWTH collaboration Daksha: Finding High Energy Emissions from GW sources Varun Bhalerao | IIT Bombay 15
Credit: LSC et al, 2017, ApJL Varun Bhalerao Thakur et al., GW190814 follow-up 16
Counterpart! GROWTH collaboration Credit: R. Hurt Kasliwal et al, 2017, Science Daksha: Finding High Energy Emissions from GW sources Varun Bhalerao | IIT Bombay 17
GW170817: GMRT W E I V E R P ACCELERATED ARTICLE PREVIEW E L C I T R A D E T A R E Daksha: Finding High Energy Emissions from GW sources Varun Bhalerao | IIT Bombay 18 L E C C A
UVOIR Lightcurve 14 −18 See also: 16 Andreoni et al. 2017 −16 Arcavi et al. 2017 18 Cowperthwaite et a. 2017 −14 Coulter et al. 2017 20 Apparent magnitude (AB) Drout et al. 2017 Absolute magnitude (AB) −12 Lipunov et al. 2017 22 Lyman et al. 2017 −10 Pian et al. 2017 24 Soares-Santos et al. 2017 −8 26 Smartt et al. 2017 −6 Tanvir et al. 2017 UVW2 +7 i,i',I +1 28 F275W +6 Utsumi et al. 2017 z,z' −0 F336W,U,u +5 −4 J −1 Villar et al. 2017 H −2 B,g' +4 30 V +3 Ks,K −3 −2 r',r +2 32 0 2 4 6 8 10 12 14 16 18 20 Time since GW170817 (days) Evans et al. 2017, Kasliwal et al. 2017c Varun Bhalerao Thakur et al., GW190814 follow-up 19
Hot source, cool source Credit: ESO/E. Pian et al./S. Smartt & ePESSTO/L. Calçada Daksha: Finding High Energy Emissions from GW sources Varun Bhalerao | IIT Bombay 20
The afterglow spectrum • Consistent with a constant slope, β =0.585±0.005 • No intrinsic absorption (only MW) • Consistent with synchrotron (p=2.17) • ! c > 1 keV (90% cl) at 260 d, ! c > 0.1 keV at 360 d. • Troja et al., 2019 (arXiv:1808.06617) Daksha: Finding High Energy Emissions from GW sources Varun Bhalerao | IIT Bombay 21
Lightcurve evolution • Slow rise, now rapid decline • Consistent with a Gaussian jet viewed off-axis • Far off-axis viewers may see more absorption Troja et al., 2019 (arXiv:1808.06617) Daksha: Finding High Energy Emissions from GW sources Varun Bhalerao | IIT Bombay 22
So, what did we learn?
1078 days, 1164 papers… 30 July 2020 Daksha: Finding High Energy Emissions from GW sources Varun Bhalerao | IIT Bombay 24
R-process 10 -6 Lanthanide 2nd peak 3rd peak 1st peak elements 10 -7 Solar r-process abundance 10 -8 10 -9 10 -10 10 -11 80 100 120 140 160 180 200 220 Atomic mass number Daksha: Finding High Energy Emissions from GW sources Varun Bhalerao | IIT Bombay 25
Equation of state • Increase the pressure. Hard EoS » Density changes a lot: “Soft” EoS » Density hardly changes: “Stiff” EoS • What was known before: » Heavy neutron stars exist è EoS is not too soft Soft EoS • What’s new: ArXiv:1805.11581 » EoS is not too hard! Daksha: Finding High Energy Emissions from GW sources Varun Bhalerao | IIT Bombay 26
O3 candidates https://gracedb.ligo.org/superevents/public/O3/ Daksha: Finding High Energy Emissions from GW sources Varun Bhalerao | IIT Bombay 27
O3 NS candidates Distance 90% area Name Type Counterpart (Mpc) (sq deg) S190425z 99% BNS 156 ± 41 7461 No 49% BNS, 13% S190426c NSBH, 24% Gap, 377 ± 100 1131 No 14% Terrestrial 42% BNS, 58% S190510g 227 ± 92 1166 No Terrestrial 2% BNS, 98% S190718y 227 ± 165 7246 No Terrestrial S190814bv 100% NSBH 267 ± 52 23 No GW170817 100% BNS 41 31 Yes Daksha: Finding High Energy Emissions from GW sources Varun Bhalerao | IIT Bombay 28
GW170817-like scaling X-ray Distance 90% area IR (10 keV- Name Type Optical (Mpc) (sq deg) (Ks) 1000 keV) S190425z 99% BNS 156 ± 41 7461 20 21 5e-8 S190426c 49% BNS 377 ± 100 1131 22 23 9e-9 S190510g 42% BNS 227 ± 92 1166 21 22 2e-8 2% BNS, 98% S190718y 227 ± 165 7246 21 22 2e-8 Terrestrial S190814bv 100% NSBH 267 ± 52 23 21 22 2e-8 Fake event 100% BNS 500 – 22 23 5e-9 GW170817 100% BNS 41 31 17 18 7e-7 Scaling from Kasliwal et al. (2017) and Abott et al 2017 (Fermi + Integral +LVC) Typical optical surveys reach ~21 mag (ZTF, PanSTARRs), ~23 DECam IR ~ 17.5 (Gattini), X-ray / Gamma ray ~ few e-7 Daksha: Finding High Energy Emissions from GW sources Varun Bhalerao | IIT Bombay 29
What’s next? Lessons from GW170817 + O3
GW170817: AstroSat Daksha: Finding High Energy Emissions from GW sources Varun Bhalerao | IIT Bombay 31
Lesson 1 Look at the entire sky at all times Daksha: Finding High Energy Emissions from GW sources Varun Bhalerao | IIT Bombay 32
GW170817 Signal is very faint 30% fainter, and it would have been missed… (LSC et al 2017, discovery paper) Daksha: Finding High Energy Emissions from GW sources Varun Bhalerao | IIT Bombay 33
New class of bursts ! • GRB was very faint: 3-4 orders of magnitude lower than SGRBs next will be fainter! • Broadband: seen = from few keV to hundreds of keV • Missed by Swift, < AstroSat, CALET… < > Daksha: Finding High Energy Emissions from GW sources Varun Bhalerao | IIT Bombay 34 � � < � = � ´ = � ´ < � � �
Lesson 2 Need 10x higher sensitivity as compared to current missions Daksha: Finding High Energy Emissions from GW sources Varun Bhalerao | IIT Bombay 35
Current missions Fermi: NASA + Europe Neil Gehrels Swift Observatory NASA Daksha: Finding High Energy Emissions from GW sources Varun Bhalerao | IIT Bombay 36
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