Diversity of Kilonova Light Curves

Abstract

We perform radiative transfer simulations for kilonova in various situations, including the cases of prompt collapse to a black hole from neutron-star mergers, high-velocity ejecta possibly accelerated by magnetars, and a black hole-neutron star merger. Our calculations are done employing ejecta profiles predicted by numerical-relativity simulations and a new line list for all the r-process elements. We found that (i) the optical emission for binary neutron stars promptly collapsing to a black hole would be fainter by 1-2 mag than that found in GW170817, while the infrared emission could be as bright as that in GW170817 if the post-merger ejecta is as massive as ≈ 0.01 M ; (ii) the kilonova would be brighter than that observed in GW170817 for the case that the ejecta is highly accelerated by the electromagnetic energy injection from the remnant, but it would decline rapidly and the magnitude would become fainter than in GW170817 within a few days; (iii) the optical emission from a black hole-neutron star merger ejecta could be as bright as that observed in GW170817 for the case that sufficiently large amount of matter is ejected ( 0.02 M ), while the infrared brightness would be brighter by 1-2 mag at the same time. We show that the difference in the ejecta properties would be imprinted in the differences in the peak brightness and time of peak. This indicates that we may be able to infer the type of the central engine for kilonovae by observation of the peak in the multiple band.

Searching for electromagnetic counterparts to gravitational-wave merger events with the prototype Gravitational-Wave Optical Transient Observer (GOTO-4)

“…In the optical frequencies at which GOTO-4 observes, this KN may in fact be fainter than an AT2017gfo analogue, unless a significant (≥ 0.02M ) amount of matter is ejected (e.g. Kawaguchi et al 2020;Zhu et al 2020). However, for a larger ejecta mass, this signal may in fact be brighter instead.…”

“…The KN signature from an NSBH merger is expected to be different to those produced by a BNS (Kawaguchi et al 2016;Tanaka et al 2018; Barbieri et al 2019) -typically predicted to be brighter in the infrared (e.g. Metzger 2017; Kawaguchi et al 2020), although see Foucart et al (2019). There is also some evidence to suggest that NSBH mergers may be distinguishable in the observed sGRB population (e.g.…”

Optical follow-up of the neutron star–black hole mergers S200105ae and S200115j

“…The best limiting magnitudes correspond to absolute magnitudes −16 mag for both events, with typical observations ranging from M∼ −16.5 mag to M∼ −17.5 mag. AT2017gfo 12 , the optical counterpart to GW170817, peaked at M∼ −16 mag, and KNe from NSBH models are typically brighter than those from BNSs [13][14][15] , indicating that our observations are in the magnitude range required for detection.…”

“…We also find that deep iand z-band exposures contribute significantly towards constraining a larger portion of the M ej -θ obs and binary parameter-space (see Extended Data Figure 8). Literature on kilonova models 15,21 have predicted kilonovae from NSBH mergers to be brighter in the iand z-bands compared to gand r-bands. The same reddened emission is evident in our models (see Extended Data Figure 5 and Extended Data Figure 6), and is demonstrated by our re-analysis of the DECam upper limits on S190814bv.…”

Neutron Star Extreme Matter Observatory: A kilohertz-band gravitational-wave detector in the global network

“…The joint electromagnetic and gravitational-wave detection of GW170817-like events with the addition of a NEMO will enable significant further insight into gamma-ray burst physics. For example, the delay time between the collapse and the prompt emission will drive studies into the jet-launching mechanism (e.g., Zhang 2019;Beniamini et al 2020) that is currently ill-understood (Zhang 2018), and the existence and lifetime of the remnant will reveal the impact of neutrino radiation on heavy-element formation through the rapid neutroncapture process in kilonovae (Metzger & Fernández 2014;Martin et al 2015;Fernández et al 2019;Kawaguchi, Shibata, & Tanaka 2020).…”