Abstract Details

Name: Sreelakshmi P. Chakyar
Affiliation: IIST, Thiruvananthapuram
Conference ID: ASI2020_530
Title : The Effect of Viewing Angle in Gamma Ray Burst Properties
Authors and Co-Authors : Sreelakshmi P. Chakyar and Resmi Lekshmi
Abstract Type : Oral
Abstract Category : Extragalactic Astronomy
Abstract : The first Binary Neutron Star (NS) merger, GW170817, and associated electromagnetic counterparts have established the association of short duration Gamma-Ray Bursts (GRBs) and NS mergers. Due to relativistic beaming, classical short GRB population triggered in gamma-rays has to mostly consist of jets directed towards the observer. However, GW associated GRBs will mostly be mis-aligned jets, providing an unprecedented opportunity for in-depth study of off-axis GRBs. Motivated by this, we are investigating how duration and hardness of GRB prompt emission vary with observer's viewing angle. For our initial calculations we consider a uniform top-hat model for the GRB jet. We find that spectral hardness of the prompt pulse decreases with viewing angle. Our analysis shows that relativistic effects can cause an increase in the total duration of the prompt pulse for an off-axis observer. However, the same effects will also quench the pulse amplitude. This has the potential to reduces the effective duration of the pulse observable above the given detector threshold. Ultimately, while GRB becomes less luminous and softer for an off-axis observer, whether it will become shorter or longer depends on its apparent brightness and detector sensitivity.  Based on our analysis we attempt to predict the properties of GRB170817A had it been observed along the jet axis like the standard short GRB population.