A lower occurrence rate of bright X-ray flares in SN-GRBs than z < 1 GRBs: evidence of energy partitions?. Issue 3 (18th May 2018) - Mu, Hui-Jun
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 per cent) than in Sample II (35.6 per cent). In addition, if dim X-ray fluctuations are included as flares, then 16.7 per cent of Sample I and 55.6 per cent 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.