Neutron star mergers and kilonovas

15 min presentation with an overview of the astrophysics of neutron star mergers and kilonovas, following the birth of multimessenger astronomy with GW170817. I discussed opportunities for wide-field optical telescopes. Talk given at the S-PLUS workshop on Sep. 28th 2018.

Speaker: Prof. Rodrigo Nemmen. Universidade de Sao Paulo.
https://rodrigonemmen.com

Credit for the slides/figures belongs to Rodrigo Nemmen, unless otherwise stated.

Transcript

1. Rodrigo Nemmen Universidade de Sao Paulo Neutron star mergers and kilonovas
2. theory observations S-PLUS opportunities Rodrigo Nemmen Universidade de Sao Paulo Neutron star mergers and kilonovas
3. Mergers of binary neutron stars: Short GRBs NS NS NS BH or Paczynski 1986; Eichler et al. 1989; Narayan et al. 1992 time
4. Mergers of binary neutron stars: Short GRBs NS NS Paczynski 1986; Eichler et al. 1989; Narayan et al. 1992 time GWs orbit decays due to GW emission
5. Mergers of binary neutron stars: Short GRBs NS NS Paczynski 1986; Eichler et al. 1989; Narayan et al. 1992 time neutron rich, magnetized accreting torus GWs orbit decays due to GW emission duration ~ ms
6. Rezzolla+2011 cf. also Ruiz+2016 Numerical relativity simulation of NS merger: Short GRB emerges naturally Rezzolla, Giacomazzo et al. 2011 Cactus/Carpet/Whisky codes (solves Einstein eqs. + ideal MHD) Initial condition: •NS binary a few orbits before its coalescence •2 NSs •each NS with M=1.5Msun •Bmax=1012 G (each star)
7. Rezzolla+2011 cf. also Ruiz+2016 gas density magnetic fields
8. Rezzolla+2011 cf. also Ruiz+2016 gas density magnetic fields Results in: • accreting BH, M = 2.91 Msun • short GRB jet, Δt = 30 ms • opening angle 30 deg • amplifies B to 1015 G • Eiso = 1049 erg
9. fallback material GRB jet (beamed) Ejecta (unbeamed)
10. fallback material GRB jet (beamed) Lattimer & Schramm 1974 produces many Earth-mass amounts of precious metals (r-process, lanthanides) Ejecta (unbeamed) radio optical X-rays γ-rays kilonova: IR optical UV
11. fallback material GRB jet (beamed) Lattimer & Schramm 1974 produces many Earth-mass amounts of precious metals (r-process, lanthanides) Ejecta (unbeamed) radio optical X-rays γ-rays kilonova: IR optical UV Short GRB multimessenger time series: GWs + light Fernandez & Metzger 2016 nandez-Metzger ARI 4 May 2016 13:30 Event Signal Phase Coalescence X-ray/radio precursor? μ Ω r-process ms magnetar? Short GRB X-ray extended emission/plateau Ye > 0.25 Ye < 0.25 Free n? Shocked ISM GW “chirp” GWs from remnant NS? Inspiral Dynamical Accretion Remnant BH ?? Blue kilonova ?? Neutron precursor (UV) Red kilonova Radio transient Seconds Milliseconds 10 ms 100 ms Minutes–hours Hours–days Days–weeks Month–years Event Signal Coalescence X-ray/radio precursor? μ Ω r-process ms magnetar? Short GRB X-ray extended emission/plateau Ye > 0.25 Ye < 0.25 Free n? Shocked ISM GW “chirp” GWs from remnant NS? NS BH NS ?? Blue kilonova ?? Neutron precursor (UV) Red kilonova Radio transient Figure 1 Phases of a neutron star (NS) merger as a function of time, showing the associated observational signatures and underlying physical phenomena. Abbreviations: BH, black hole; GRB, γ -ray burst; GW, gravitational wave; ISM, interstellar medium; n, neutron; UV, ultraviolet; Ye , electron fraction. Coalescence inset courtesy of D. Price and S. Rosswog (see also Reference 15).
12. Birth of multimessenger astronomy: GWs and EM radiation from GW170817
13. Birth of multimessenger astronomy: GWs and EM radiation from GW170817
14. Diaz+2017
15. Kilonova opportunities for GMT lighter elements (lanthanide-poor) heavier elements (lanthanide-rich) (UV) (NIR) cf. also Cowperthwaite+2017
16. Kilonova opportunities for GMT lighter elements (lanthanide-poor) heavier elements (lanthanide-rich) (UV) (NIR) cf. also Cowperthwaite+2017
17. r-process nucleosynthesis in the dynamical ejecta from NS-NS or NS-BH mergers
18. r-process nucleosynthesis in the dynamical ejecta from NS-NS or NS-BH mergers
20. Figure 2. gri light curves of the EM counterpart to GW170817, obtained with T80S on 2017 August 18. The g points have been offset by −0.4mag for clarity. Table 1 Time-series Photometry Timea Band Mag σ (mag) 1.4390 g 18.43 0.06 1.4447 g 18.51 0.04 1.4458 g 18.48 0.04 Figure 3. Top: comparison of the light curve slopes (magnitudes per day) of the transient (arrows) in gri (left, center, and right panels, respectively) relative to 885 objects in the T80S FoV with similar colors ( g r r i , 0.1 - - < ∣ ∣ ∣ ∣ ). The horizontal error bars indicate the 1s uncertainty in the values for the transient. Bottom: statistical significance of the values for the transient in gri (left, center, and right panels, respectively) relative to the comparison sample. The Astrophysical Journal Letters, 848:L29 (5pp), 2017 October 20 Díaz et al. 80S FoV with similar colors to the transient (within 0.1 mag both g − r and r i - ). We performed weighted linear fits as a nction of time on the light curves of all of the selected objects gure 2. gri light curves of the EM counterpart to GW170817, obtained with 0S on 2017 August 18. The g points have been offset by −0.4mag for rity. Table 1 Time-series Photometry mea Band Mag σ (mag) 390 g 18.43 0.06 447 g 18.51 0.04 458 g 18.48 0.04 469 g 18.62 0.04 481 r 17.93 0.02 492 r 17.97 0.02 502 r 17.94 0.02 514 i 17.74 0.03 te. Days since GW trigger. his table is available in its entirety in machine-readable form.) Figure 3. Top: comparison of the light curve slopes (magnitudes per day) of the transient (arrows) in gri (left, center, and right panels, respectively) relative to 885 objects in the T80S FoV with similar colors ( g r r i , 0.1 - - < ∣ ∣ ∣ ∣ ). The horizontal error bars indicate the 1s uncertainty in the values for the transient. Bottom: statistical significance of the values for the transient in gri (left, center, and right panels, respectively) relative to the comparison sample.
21. 10000 1042 1041 1040 8000 6000 4000 Temperature (K) Magnitude (+ offset) Luminosity (erg s–1) 0 5 10 15 0 5 10 15 12.5 15.0 17.5 20.0 22.5 25.0 27.5 30.0 32.5 35.0 on January 2, 2018 http://science.sciencemag.org/ aded from Kilpatrick+2017, Science Cowperthwaite+2017 Drout+2017, Science Rest-frame days after merger
22. 10000 1042 1041 1040 8000 6000 4000 Temperature (K) Magnitude (+ offset) Luminosity (erg s–1) 0 5 10 15 0 5 10 15 12.5 15.0 17.5 20.0 22.5 25.0 27.5 30.0 32.5 35.0 on January 2, 2018 http://science.sciencemag.org/ aded from Kilpatrick+2017, Science Cowperthwaite+2017 Drout+2017, Science Rest-frame days after merger ric light curves, in n≲1 day, then fades volution to the red . 2 exhibit similarly ter the trigger the , but it transitions r spectrum with at near 9000 Å (12). numerous absorp- n the spectra of or- s of astrophysical h at least one of the 7a: the rise time of g at ≳1 mag dayÀ1, H-band magnitudes À1:2 to þ3:6 mag featureless optical Among previously thermal continuum s is rapidly evolving these events have luminous, typically s, do not have the nd do not fade as hermal relativistic lows can produce are not expected to or just after the merger, is thought to be ob- and spectral energy distribution of a kilonova 10000 1042 1041 1040 8000 6000 erature (K) Magnitude (+ offset) Luminosity (erg s–1) 0 5 10 15 12.5 15.0 17.5 20.0 22.5 25.0 27.5 30.0 32.5 on January 2, 2018 http://science.sciencemag.org/ nloaded from Rest-frame days after merger
23. Scientific questions w/ kilonova monitoring how many heavy-elements (lanthanides) produced? how much gold in the universe is produced in NSNS mergers? signatures of NS-BH mergers? velocity and mass of ejecta?
24. LETTER doi:10.1038/nature24471 A gravitational-wave standard siren measurement of the Hubble constant The LIGO Scientific Collaboration and The Virgo Collaboration*, The 1M2H Collaboration*, The Dark Energy Camera GW-EM Collaboration and the DES Collaboration*, The DLT40 Collaboration*, The Las Cumbres Observatory Collaboration*, The VINROUGE Collaboration* & The MASTER Collaboration* On 17 August 2017, the Advanced LIGO1 and Virgo2 detectors observed the gravitational-wave event GW170817—a strong signal from the merger of a binary neutron-star system3. Less than two seconds after the merger, a γ-ray burst (GRB 170817A) was detected within a region of the sky consistent with the LIGO–Virgo-derived location of the gravitational-wave source4–6. This sky region was subsequently observed by optical astronomy facilities7, resulting in the identification8–13 of an optical transient signal within about ten arcseconds of the galaxy NGC 4993. This detection of GW170817 in both gravitational waves and electromagnetic waves represents the first ‘multi-messenger’ astronomical observation. Such observations enable GW170817 to be used as a ‘standard siren’14–18 (meaning that the absolute distance to the source can be this galaxy allow us to estimate the appropriate value of the Hubble flow velocity. Because the source is relatively nearby, the random relative motions of galaxies, known as peculiar velocities, need to be taken into account. The peculiar velocity is about 10% of the measured recessional velocity (see Methods). The original standard siren proposal14 did not rely on the unique identification of a host galaxy. By combining information from around 100 independent gravitational-wave detections, each with a set of potential host galaxies, an estimate of H0 accurate to 5% can be obtained even without the detection of any transient optical counterparts22. This is particularly relevant, because gravitational-wave networks will detect many binary black-hole mergers over the coming years23 and these are not expected to be accompanied by electromagnetic counterparts.
25. LETTER doi:10.1038/nature24471 A gravitational-wave standard siren measurement of the Hubble constant The LIGO Scientific Collaboration and The Virgo Collaboration*, The 1M2H Collaboration*, The Dark Energy Camera GW-EM Collaboration and the DES Collaboration*, The DLT40 Collaboration*, The Las Cumbres Observatory Collaboration*, The VINROUGE Collaboration* & The MASTER Collaboration* On 17 August 2017, the Advanced LIGO1 and Virgo2 detectors observed the gravitational-wave event GW170817—a strong signal from the merger of a binary neutron-star system3. Less than two seconds after the merger, a γ-ray burst (GRB 170817A) was detected within a region of the sky consistent with the LIGO–Virgo-derived location of the gravitational-wave source4–6. This sky region was subsequently observed by optical astronomy facilities7, resulting in the identification8–13 of an optical transient signal within about ten arcseconds of the galaxy NGC 4993. This detection of GW170817 in both gravitational waves and electromagnetic waves represents the first ‘multi-messenger’ astronomical observation. Such observations enable GW170817 to be used as a ‘standard siren’14–18 (meaning that the absolute distance to the source can be this galaxy allow us to estimate the appropriate value of the Hubble flow velocity. Because the source is relatively nearby, the random relative motions of galaxies, known as peculiar velocities, need to be taken into account. The peculiar velocity is about 10% of the measured recessional velocity (see Methods). The original standard siren proposal14 did not rely on the unique identification of a host galaxy. By combining information from around 100 independent gravitational-wave detections, each with a set of potential host galaxies, an estimate of H0 accurate to 5% can be obtained even without the detection of any transient optical counterparts22. This is particularly relevant, because gravitational-wave networks will detect many binary black-hole mergers over the coming years23 and these are not expected to be accompanied by electromagnetic counterparts. Distance from GW observations z from EM obs. measurements of H0
26. LETTER doi:10.1038/nature24471 A gravitational-wave standard siren measurement of the Hubble constant The LIGO Scientific Collaboration and The Virgo Collaboration*, The 1M2H Collaboration*, The Dark Energy Camera GW-EM Collaboration and the DES Collaboration*, The DLT40 Collaboration*, The Las Cumbres Observatory Collaboration*, The VINROUGE Collaboration* & The MASTER Collaboration* On 17 August 2017, the Advanced LIGO1 and Virgo2 detectors observed the gravitational-wave event GW170817—a strong signal from the merger of a binary neutron-star system3. Less than two seconds after the merger, a γ-ray burst (GRB 170817A) was detected within a region of the sky consistent with the LIGO–Virgo-derived location of the gravitational-wave source4–6. This sky region was subsequently observed by optical astronomy facilities7, resulting in the identification8–13 of an optical transient signal within about ten arcseconds of the galaxy NGC 4993. This detection of GW170817 in both gravitational waves and electromagnetic waves represents the first ‘multi-messenger’ astronomical observation. Such observations enable GW170817 to be used as a ‘standard siren’14–18 (meaning that the absolute distance to the source can be this galaxy allow us to estimate the appropriate value of the Hubble flow velocity. Because the source is relatively nearby, the random relative motions of galaxies, known as peculiar velocities, need to be taken into account. The peculiar velocity is about 10% of the measured recessional velocity (see Methods). The original standard siren proposal14 did not rely on the unique identification of a host galaxy. By combining information from around 100 independent gravitational-wave detections, each with a set of potential host galaxies, an estimate of H0 accurate to 5% can be obtained even without the detection of any transient optical counterparts22. This is particularly relevant, because gravitational-wave networks will detect many binary black-hole mergers over the coming years23 and these are not expected to be accompanied by electromagnetic counterparts. the SHoES result is just outside the 90% confidence range. It will be particularly interesting to compare these constraints to those from modelling7 of the short γ-ray burst, afterglow and optical counterpart associated with GW170817. We have presented a standard siren determination of the Hubble constant, using a combination of a distance estimate from gravita- tional-wave observations and a Hubble velocity estimate from electro- magnetic observations. Our measurement does not use a ‘distance ladder’ and makes no prior assumptions about H0 . We find = . − . + . − − H 70 0 km s Mpc 0 8 0 12 0 1 1, which is consistent with existing meas- urements20,21. This first gravitational-wave–electromagnetic multi- messenger event demonstrates the potential for cosmological inference from gravitational-wave standard sirens. We expect that additional multi-messenger binary neutron-star events will be detected in the coming years, and combining subsequent independent measurements of H0 from these future standard sirens will lead to an era of precision gravitational-wave cosmology. 2 2 2 2 2 2 2 2 3
28. there should be a wide variety of kilonova properties that are not clear from only n = 1 data point
29. there should be a wide variety of kilonova properties that are not clear from only n = 1 data point
30. there should be a wide variety of kilonova properties that are not clear from only n = 1 data point expect 1 NS-NS or NS-BH merger seen by LIGO- Virgo per month
31. there should be a wide variety of kilonova properties that are not clear from only n = 1 data point expect 1 NS-NS or NS-BH merger seen by LIGO- Virgo per month
32. there should be a wide variety of kilonova properties that are not clear from only n = 1 data point expect 1 NS-NS or NS-BH merger seen by LIGO- Virgo per month many opportunities for EM followups!
33. there should be a wide variety of kilonova properties that are not clear from only n = 1 data point expect 1 NS-NS or NS-BH merger seen by LIGO- Virgo per month many opportunities for EM followups!
34. there should be a wide variety of kilonova properties that are not clear from only n = 1 data point expect 1 NS-NS or NS-BH merger seen by LIGO- Virgo per month many opportunities for EM followups! nearby ones should be observable with S-PLUS
35. What I would like to see coverage of S-PLUS competitive with DECam dedicated workgroup for kilonova monitoring coordination with LIGO/Virgo for triggers theorists required (kilonova modeling)
36. Summary: Kilonova opportunities for S-PLUS (i) measuring kilonova light curve (ii) photometric zs → cosmology w/ GW sources (iii) afterglow (did not discuss) Rodrigo Nemmen Kilonovas: product of NS-NS or NS-BH mergers, radioactive glow from debris Produce most of the gold in the universe S-PLUS opportunities Should we organize a dedicated workgroup for these transients?
37. Github Twitter Web E-mail Bitbucket Facebook Group figshare rodrigo.nemmen@iag.usp.br rodrigonemmen.com @nemmen rsnemmen facebook.com/rodrigonemmen nemmen blackholegroup.org bit.ly/2fax2cT
38. Directors cut
41. 0 5 10 15 20 25 30 35 0 2 4 6 8 10 12 14 16 18 20 Long Short Opening angle θ j (degrees) Number Figure 18 Distributions of jet opening angles for short (blue) and long (red ) GRBs on the basis of breaks in their afterglow emission. Arrows mark lower or upper limits on the opening angles. The observations are summarized in Section 8.4. From Fong et al. (2013) and references therein. . Downloaded from www.annualreviews.org s on 06/05/14. For personal use only. Berger 2014 ARAA
42. Van Eerten 2018
43. slide: optical opportunities for GMT afterglow measurements what they can teach us Log Optical Flux -> Log Time -> Most GRB Have Optical Afterglows Prompt X/-ray light curves bright (wide field instruments), highly variable, inhomogeneous shapes LGRB typically ~ 40-100 s OPT AG MEASUREMENTS COMMON - Hundreds observed, dozens per year. (Flares ignored here) Physics well understood to be interaction of a jet with ISM. [Early or prompt phase not measured for most GRBs] Covino et al.: The prompt and the afterglow of GRB 060908 5 10-6 10-5 10-4 10-3 10-2 10-1 100 101 102 101 102 103 104 105 106 107 108 Flux (mJy) Time from burst (s) 1 keV U (x 100) B (x 30) V (x 10) R (x 3) I (x 1) Z (x 0.4) White (x 0.4) J (x 0.06) H (x 0.035) K (x 0.02) Covimo+2010 5.1. The picture since Swift Fig. 3. An overview of the various issues raised by GRB afterglow observations from 2004+, in particular those by Swift XRT. Since the launch of Swift, a complex picture of X-ray and optical afterglows has emerged. To some extent, this picture can be described in terms of a canonical long GRB afterglow light curve189–191 (see also Fig. 3, expanded from an illustration in Ref. 192), although analysis of the Swift XRT sample shows that ‘canonical’ should be taken with a grain of salt193, 194 and that the measured temporal slopes of the light curves span a wide range. After an initial flaring behaviour presumably connected to the prompt emission, the light curve drops steeply until it reaches a plateau value. The light curve then maintains this value for longer than was Eerten 2018
44. Slide: Xue-Feng Wu
45. GRB optical jet breaks Liang+2008