1206.0700 (Tsvi Piran et al.)

The Origin of Long, Short and Low-luminosity Gamma-Ray Bursts    [PDF]

Tsvi Piran, Omer Bromberg, Ehud Nakar, Re'em Sari

The origin of Gamma-Ray Bursts is one of the most interesting puzzles in recent astronomy. During the last decade a consensus formed that long GRBs (LGRBs) arise from the collapse of massive stars and that short GRBs (SGRBs) have a different origin, most likely neutron star mergers. A key ingredient of the Collapsar model that explains how the collapse of massive stars produces a GRB is the emergence of a relativistic jet that penetrates the stellar envelope. The condition that the emerging jet penetrates the envelope poses strong constraints on the system (Bromberg et al). Using these constraints we show that: (i) Low luminosity GRBs \llGRBs, a sub population of GRBs with a very low luminosities (and other peculiar properties: single peaked, smooth and soft) cannot be formed by Collapsars (Bromberg et al). They have a different origin (most likely a shock breakout). (ii) On the other hand regular LGRBs must be formed by Collapsars (Bromberg et al). (iii) While for BATSE the dividing duration between Collapsars and non-Collapsar is indeed at $\sim 2$ sec, the dividing duration is different for other GRBs detectors (Bromberg et al). In particular most {\it Swift} bursts longer than 0.7 sec are of a Collapsar origin. This last results requires a revision of many conclusions concerning the origin of {\it Swift} SGRBs which were based on the classical 2 sec limit.

View original: http://arxiv.org/abs/1206.0700