How common are long Gamma-Ray Bursts in the Local Universe?

TL;DR

This study investigates the frequency of long Gamma-Ray Bursts in the local universe, finding that a small but significant fraction are nearby and estimating their local rate density based on BATSE data.

Contribution

It provides the first statistical correlation analysis between BATSE long GRBs and nearby galaxy samples, identifying a subset likely to be local GRBs and estimating their local occurrence rate.

Findings

Approximately 2 to 9 long GRBs per year are similar to known nearby bursts.

Estimated local rate density of 700 +/- 360 Gpc^{-3}yr^{-1} within 155 Mpc.

Correlation of a specific GRB sub-sample with nearby galaxies supports the existence of local long GRBs.

Abstract

The two closest Gamma-Ray Bursts so far detected (GRBs 980425 & 060218) were both under-luminous, spectrally soft, long duration bursts with smooth, single-peaked light curves. Only of the order of 100 GRBs have measured redshifts, and there are, for example, 2704 GRBs in the BATSE catalogue alone. It is therefore plausible that other nearby GRBs have been observed but not identified as relatively nearby. Here we search for statistical correlations between BATSE long duration GRBs and galaxy samples with recession velocities v <= 11,000 km/s (z = 0.0367, ~ 155 Mpc) selected from two catalogues of nearby galaxies. We also examine the correlations using burst sub-samples restricted to those with properties similar to the two known nearby bursts. Our results show correlation of the entire long GRB sample to remain consistent with zero out to the highest radii considered whereas a sub-sample selected to be low fluence, spectrally soft, with smooth single-peaked light curves (177 bursts) demonstrates increased correlation with galaxies within ~ 155 Mpc. The measured correlation (28% +/- 16% of the sample) suggests that BATSE observed between 2 and 9 long duration GRBs per year similar to, and from within similar distances to GRBs 980425 and 060218. This implies an observed local rate density (to BATSE limits) of 700 +/- 360 Gpc^{-3}yr^{-1} within 155 Mpc.