Search for gamma-ray burst classes with the RHESSI satellite

Abstract

Aims. We study a sample of 427 gamma-ray bursts (GRBs), measured by the RHESSI satellite, statistically with respect to duration and hardness ratio. Methods. Standard statistical tests were used, such as χ 2 , F-test, and the maximum likelihood ratio test, to compare the number of GRB groups in the RHESSI database with that of the BATSE database. Results. Previous studies based on the BATSE Catalog claim the existence of an intermediate GRB group, besides the long and short groups. Using only the GRB duration T 90 as information and χ 2 or F-test, we do not find any statistically significant intermediate group in the RHESSI data. However, maximum likelihood ratio test reveals a significant intermediate group. Using the 2-dimensional hardness/T 90 plane, the maximum likelihood analysis also reveals a significant intermediate group. In contrast to the BATSE database, the intermediate group in the RHESSI data set is harder than the long one. Conclusions. The existence of an intermediate group follows not only from the BATSE data set, but also from the RHESSI one.

ON THE SPECTRAL LAGS AND PEAK COUNTS OF THE GAMMA-RAY BURSTS DETECTED BY THERHESSISATELLITE

“…Concerning this third reason, the mean duration of the intermediate group appears to vary according to the database in which it is found. For the Swift data Huja et al 2009) the mean duration is ∼12 s, which resembles the durations of the long GRBs, but for the RHESSI and BATSE data Mukherjee et al 1998;Horváth et al 2006;Rípa et al 2009) this mean is far below 10 s.…”

Gamma-Ray Burst Prompt Correlations

“…Later, Lu et al [177], with the results of time-resolved spectral analysis, computed the peak -tot relation for 51 LGRBs and 11 bright SGRBs observed with Fermi/GBM. For each GRB, they fitted a simple power law function.…”

“…The first afterglow observation (for GRB970228) was due to the BeppoSAX satellite [44,45]. Another class, besides SGRBs and LGRBs, that is, intermediate in duration, was proposed to be present in univariate duration distributions [46][47][48][49][50][51], as well as in higher dimensional parameter spaces [51][52][53][54][55][56]. On the other hand, this elusive intermediate class might be a statistical feature that can be explained by modeling the duration distribution with skewed distributions, instead of the commonly applied standard Gaussians [57][58][59][60][61].…”

What is the Astrophysical Meaning of the Intermediate Subgroup of GRBs

“…There are at least two different groups, 'short/hard' and 'long/soft' [1,2,3,4,5,6,7,8]. A possibility of the existence of further groups has been intensively studied using various statistical techniques [9,10,11,12,13,14,15,16,17,18,19,20,21,22]. It has been postulated that there might be a third group of GRBs with intermediate durations.…”