Abstract
ABSTRACT We report the results of our observing campaign on GRB 140903A, a nearby (z = 0.351) short-duration (T 90 ∼ 0.3 s) gamma-ray burst discovered by Swift. We monitored the X-ray afterglow with Chandra up to 15 days after the burst and detected a steeper decay of the X-ray flux after t j ≈ 1 day. Continued monitoring at optical and radio wavelengths showed a similar decay in flux at nearly the same time, and we interpret it as evidence of a narrowly collimated jet. By using the standard fireball model to describe the afterglow evolution, we derive a jet opening angle θ j ≈ 5° and a collimation-corrected total energy release E ≈ 2 erg. We further discuss the nature of the GRB progenitor system. Three main lines disfavor a massive star progenitor: the properties of the prompt gamma-ray emission, the age and low star formation rate of the host galaxy, and the lack of a bright supernova. We conclude that this event likely originated from a compact binary merger.
Highlights
Gamma-ray bursts (GRBs) are produced by a highly relativistic outflow collimated into jets
The early X-ray afterglow of GRB 140903A is characterized by a period of fairly constant emission lasting ≈4 hr
One of the most popular models invokes a newborn magnetar as the power source of the GRB and its afterglow: as the magnetar spins down, it injects energy into the jet, causing a period of nearly flat emission, followed by a steeper temporal decline with slope α 2 (Zhang & Mészáros 2001)
Summary
Gamma-ray bursts (GRBs) are produced by a highly relativistic outflow collimated into jets. The angular size of the outflow is a key ingredient in determining the true energy release and the event rate. These parameters provide a crucial test for any progenitor and central engine model. The degree of collimation of short GRBs is a critical input for inferring the true rate of binary mergers, the expected detection rate of advanced LIGO and Virgo (Abadie et al 2010), and for estimating our chances to observe the electromagnetic counterpart of a GW source (Abbott et al 2016a; Troja et al 2016)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
