A redshiftobservation time relation for gammaray bursts: evidence of a distinct subluminous population
Abstract
We show that the redshift and peak flux distributions of gammaray bursts (GRBs) have an observation time dependence that can be used to discriminate between different burst populations. We demonstrate how observation time relations can be derived from the standard integral distributions and that they can differentiate between GRB populations detected by both the Burst and Transient Source Experiment (BATSE) and Swift satellites. Using Swift data, we show that a redshiftobservation time relation (log Zlog T) is consistent with both a peak fluxobservation time relation (log Plog T) and a standard log Nlog P brightness distribution. As the method depends only on rarer smallz events, it is invariant to highz selection effects. We use the log Zlog T relation to show that subluminous GRBs are a distinct population occurring at a higher rate of the order of 150^{+ 180}_{ 90} Gpc^{ 3} yr^{ 1}. Our analysis suggests that GRB 060505  a relatively nearby GRB observed without any associated supernova  is consistent with a subluminous population of bursts. Finally, we show that our relations can be used as a consistency test for some of the proposed GRB spectral energy correlations.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 January 2013
 DOI:
 10.1093/mnras/sts020
 arXiv:
 arXiv:1206.4151
 Bibcode:
 2013MNRAS.428..167H
 Keywords:

 methods: data analysis;
 gammaray burst: general;
 supernovae: general;
 cosmology: miscellaneous;
 Astrophysics  High Energy Astrophysical Phenomena;
 Astrophysics  Cosmology and Extragalactic Astrophysics;
 General Relativity and Quantum Cosmology
 EPrint:
 Accepted by MNRAS