A lower occurrence rate of bright X-ray flares in SN-GRBs than $z<1$ GRBs: evidence of energy partitions?

TL;DR

This study compares the occurrence of bright X-ray flares in low-redshift gamma-ray bursts with and without supernovae, suggesting energy partitioning influences flare activity and revealing fewer flares in SN-associated GRBs.

Contribution

It provides the first comparative analysis of X-ray flare occurrence rates between SN-GRBs and non-SN GRBs at low redshift, proposing energy partitioning as a key factor.

Findings

Lower bright X-ray flare occurrence in SN-GRBs (11.1%) compared to non-SN GRBs (35.6%)

Most bright X-ray flares are likely related to central engine reactivity

Energy partitioning may explain the discrepancy in flare occurrence rates

Abstract

The occurrence rates of bright X-ray flares in z<1 gamma-ray bursts (GRBs) with or without observed supernovae (SNe) association were compared. Our Sample I: the z<1 long GRBs (LGRBs) with SNe association (SN-GRBs) and with early Swift/X-Ray Telescope (XRT) observations, consists of 18 GRBs, among which only two GRBs have bright X-ray flares. Our Sample II: for comparison, all the z<1 LGRBs without observed SNe association and with early Swift/XRT observations, consists of 45 GRBs, among which 16 GRBs present bright X-ray flares. Thus, the study indicates a lower occurrence rate of bright X-ray flares in Sample I (11.1%) than in Sample II (35.6%). In addition, if dim X-ray fluctuations are included as flares, then 16.7% of Sample I and 55.6% of Sample II are found to have flares, again showing the discrepancy between these two samples. We examined the physical origin of these bright X-ray flares and found that most of them are probably related to the central engine reactivity. To understand the discrepancy, we propose that such a lower occurrence rate of flares in the SN-GRB sample may hint at an energy partition among the GRB, SNe, and X-ray flares under a saturated energy budget of massive star explosion.