Subsequent Nonthermal Emission Due to the Kilonova Ejecta in GW170817

Abstract

The ejected material at the binary neutron star merger GW 170817 was confirmed as a kilonova by UV, optical, and IR observations. This event provides a unique opportunity to investigate the particle acceleration at a mildly relativistic shock propagating in the circumbinary medium. In this paper, we simulate the nonthermal emission from electrons accelerated by the shock induced by the kilonova ejecta with a time-dependent method. The initial velocity and mass of the ejecta in the simulations are obtained from the kilonova observations in GW 170817. If the ambient density is high enough (≥ 10 −2 cm −3 ), radio, optical/IR, and X-ray signals will be detected in a few years, though the off-axis short gamma-ray burst models, accounting for the X-ray/radio counterpart detected at ∼ 10 days after the merger, implies low ambient density. We also demonstrate that the additional low-mass (∼ 10 −5 M ⊙ ) component with a velocity of 0.5c-0.8c can reproduce the early X-ray/radio counterpart. This alternative model allows a favorably high density to detect the nonthermal emission due to the kilonova ejecta. Even for a low ambient density such as ∼ 10 −3 cm −3 , depending on the microscopic parameters for the electron acceleration, we can expect a growth of radio flux of ∼ 0.1 mJy in a few years.

Search for GeV Gamma-Ray Counterparts of Gravitational Wave Events by CALET

“…The rising X-ray and radio afterglow light curves as far as ∼100 days (Mooley et al 2017;Ruan et al 2017) are also difficult to explain with an off-axis afterglow model with a simple top-hat jet (or they may suggest a structured jet). GRB 170817A may belong to another population of gamma-ray transient phenomena other than the short GRB as proposed by Bromberg et al (2018), Gottlieb Asano & To (2018). In such cases, the expected gamma-ray flux in the GeV range is not constrained by the previous short GRB observations.…”

Prompt emission from the counter jet of a short gamma-ray burst

“…However, in our case, the off-axis afterglow peaks at a later time, so that the emission is very weak in the very early epoch (10 2−3 s). The early afterglows caused by macronova ejecta are also dim [84]. Another is the optical counterpart of the temporally extended emission associated with sGRBs [e.g., 40].…”

Dark Count Rate Degradation in CMOS SPADs Exposed to X-Rays and Neutrons

“…GRB 170817A may belong to another population of gamma-ray transient phenomena other than the short GRB as proposed by Bromberg et al (2017), Gottlieb et al (2017), Kasliwal al. (2017), Murguia-Berthier et al (2017, and Asano & To (2018). In such cases, the expected gamma-ray flux in the GeV range is not constrained by the previous short GRB observations.…”