Abstract
There is increasing evidence of a local population of short duration gamma-ray bursts (sGRB), but it remains to be seen whether this is a separate population to higher redshift bursts. Here we choose plausible luminosity functions (LFs) for both neutron star binary mergers and giant flares from soft gamma repeaters (SGR), and combined with theoretical and observed Galactic intrinsic rates we examine whether a single progenitor model can reproduce both the overall Burst and Transient Source Experiment (BATSE) sGRB number counts and a local population, or whether a dual progenitor population is required. Though there are large uncertainties in the intrinsic rates, we find that at least a bimodal LF consisting of lower and higher luminosity populations is required to reproduce both the overall BATSE sGRB number counts and a local burst distribution. Furthermore, the best-fitting parameters of the lower luminosity population agree well with the known properties of SGR giant flares, and the predicted numbers are sufficient to account for previous estimates of the local sGRB population.
Highlights
Results from the Burst and Transient Source Experiment (BATSE) onboard the Compton Gamma-Ray Observatory showed that Gamma-ray Bursts (GRBs) divide observationally into two classes based primarily on their duration (Kouveliotou et al 1993): long GRBs have durations > 2 seconds, and short GRBs 2 seconds
The combined χ2 is dominated by the fit to the overall BATSE number counts and, as expected, all our chosen single population Luminosity Functions (LF) produce good fits to the Cmax/Cmin data leading to acceptable overall fits as measured by the combined χ2
None of the single progenitor population LFs reproduce the local burst population expected from the correlation results: for example Figure 1 shows the results from a single Schechter function LF which can be seen to produce effectively no short duration Gamma-ray Bursts (sGRB) within 300 Mpc
Summary
Results from the Burst and Transient Source Experiment (BATSE) onboard the Compton Gamma-Ray Observatory showed that Gamma-ray Bursts (GRBs) divide observationally into two classes based primarily on their duration (Kouveliotou et al 1993): long GRBs have durations > 2 seconds, and short GRBs 2 seconds. Ofek (2007) points out that the fraction cannot be less than ∼ 1% without being inconsistent with the observed Galactic SGR giant flare rate, and calculate an upper limit of 16% (95% confidence limits) based on a conservative measure of probable IPN sGRB coincidences with bright star forming galaxies within 20 Mpc. Palmer et al (2005), based again on a lack of events from the Virgo cluster, find a rate of less than 5%, though point out that the LF of SGR giant flares may extend to much larger luminosities, such as suggested by Eichler (2002). This limit is sensitive to their estimate of the completion of the galaxy sample and may be higher still
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
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
