Determining the Lorentz Factor and Viewing Angle of GRB 170817A

Abstract

GRB 170817A is a weak short gamma-ray burst (GRB) accompanied by the gravitational wave (GW) event GW170817. It is believed, that an off beaming relativistic jet, produces this weak GRB. Here we use the E p,i − E iso and Γ − E iso relations to determine the Lorentz factor Γ and the viewing angle from the edge of the jet θ • . This corresponds to the on-axis E p,i = 415 +361 −167 keV and E iso = (2.447 ergs of the GRB, which is an intrinsically weak short GRB. Interestingly, the Doppler factor and the luminosity follow a universal relation from GRBs and blazars, which indicates they may share similar radiation mechanism.

The Ep,i–Eiso correlation: type I gamma-ray bursts and the new classification method

“…Attempts of using the combination of E p , E iso , T 90,i parameters and Amati relation as classification discriminators were made in several papers (e.g. Lü et al 2010;Qin & Chen 2013;Zhang et al 2018b;Shahmoradi & Nemiroff 2015;Zou et al 2018;Pozanenko et al 2018). Below we briefly compare the several classification schemes.…”

“…Type I bursts were found to be outliers of the E p,i -E iso correlation for type II bursts, so the correlation could also be used for the classification of GRBs (e.g. Lü et al 2010;Zhang et al 2012;Qin & Chen 2013;Zhang et al 2018b;Shahmoradi & Nemiroff 2015;Zou et al 2018;Pozanenko et al 2018). More over, in Pozanenko et al (2019b) the Amati relation was used to estimate the E p,i value for the second LIGO/Virgo event S190425z connected with binary neutron star merger, which was observed in gamma-ray domain by SPI-ACS/INTEGRAL experiment.…”

Scattered Short Gamma-Ray Bursts as Electromagnetic Counterparts to Gravitational Waves and Implications of GW170817 and GRB 170817A

“…Nevertheless, the low luminosity of the prompt emission might be explained by other scenarios, such as emission from a structured jet with a wide-angle distribution (Lamb & Kobayashi 2016;Jin et al 2018;Granot et al 2017a;Xiao et al 2017;Zhang et al 2018;Burgess et al 2017b), breakout emission from a mildly-relativistic cocoon (Gottlieb et al 2018b;Pozanenko et al 2018;Piro & Kollmeier 2018) and on-axis emission from a lowluminosity sGRB population (Murguia-Berthier et al 2017a;He et al 2018;Yue et al 2018;Zou et al 2018;Lamb & Kobayashi 2018). Some of these scenarios will be tested by the future radio and X-ray observations.…”

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

“…We now know that the burst associated with GW170817 was a fairly canonical SGRB (Salafia et al, 2019), with a powerful relativistic jet that, after interacting with the merger wind, turned into a structured outflow (Lazzati et al, 2017b;Lazzati et al, 2018). Our line of sight lied somewhere between 15°and 35°a way from the jet axis, the lower value obtained by high resolution radio imaging (Mooley et al, 2018c;Ghirlanda et al, 2019), while the larger value being favored by multi-band afterglow modeling and ejecta considerations (Lazzati et al, 2018;Mandel, 2018;Zou et al, 2018). The prompt emission was powered by an energetic cocoon inflated by the interaction of the jet with the merger wind.…”