Afterglows and Kilonovae Associated with Nearby Low-luminosity Short-duration Gamma-Ray Bursts: Application to GW170817/GRB 170817A

Abstract

Very recently, the gravitational wave (GW) event GW170817 was discovered to be associated with the short gamma-ray burst (GRB) 170817A. Multi-wavelength follow-up observations were carried out, and X-ray, optical and radio counterparts to GW170817 were detected. The observations undoubtedly indicate that GRB170817A originates from a binary neutron star (BNS) merger. However, the GRB falls into the low-luminosity class which could have a higher statistical occurrence rate and detection probability than the normal (high-luminosity) class. This implies a possibility that GRB170817A is intrinsically powerful but we are off-axis and only observe its side emission. In this paper, we provide a timely modeling of the multi-wavelength afterglow emission from this GRB and the associated kilonova signal from the merger ejecta, under the assumption of a structured jet, a two-component jet, and an intrinsically less-energetic quasi-isotropic fireball respectively. Comparing the afterglow properties with the multi-wavelength follow-up observations, we can distinguish between these three models. Furthermore, a few model parameters (e.g., the ejecta mass and velocity) can be constrained.

Late-time evolution of afterglows from off-axis neutron star mergers

“…In each case we consider the dominant component at late times: for the jets, this is the jet core and so we can ignore any structure that may be present at wider angles (see Rossi et al 2002;Granot 2005;Lamb & Kobayashi 2017;Xiao et al 2017;Kathirgamaraju et al 2018, etc). The cocoon is included as the extreme limit of any jet structure and demonstrates that even for very wide angled cocoons the late time afterglow is dominated by the core; for the choked jet-cocoon, which may have a stratified radial velocity profile (e.g.…”

Late Time Afterglow Observations Reveal a Collimated Relativistic Jet in the Ejecta of the Binary Neutron Star Merger GW170817

“…This indicated a common origin for the high-and low-frequency emission consistent with the afterglow from a relativistic blast-wave [14]. The early Xray and radio observations were consistent with a diverse arXiv:1712.03237v4 [astro-ph.HE] 11 May 2018 set of models for the origin of the blast-wave, including a top-hat jet seen off-axis [8,[15][16][17][18][19][20][21][22], a mildly relativistic, isotropic fireball [23], and a structured jet [24][25][26].…”

Short Duration Gamma-Ray Bursts and Their Outflows in Light of GW170817

“…Unfortunately, telling whether a misaligned relativistic jet is present is not easy, since all the radiation is relativistically beamed away from the line of sight. The slow but steady brightening was shown to be consistent with the presence of a jet, its energy contribution along the line of sight growing with the deceleration of the external shock (Xiao et al, 2017;De Colle et al, 2018;Finstad et al, 2018;Granot et al, 2018b;Lamb and Kobayashi, 2018;Lazzati et al, 2018;Fraija et al, 2019a;Fraija et al, 2019b;Beniamini et al, 2020b;Oganesyan et al, 2020). However, a radially stratified spherical outflow could reproduce the observations as well, albeit at the price of adding a never observed before component to the models (Li et al, 2018;Mooley et al, 2018c;Nakar and Piran, 2018;Salafia et al, 2018).…”