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Fluences and photon peak fluxes of the gamma-ray bursts (GRBs) detected by the Swift and RHESSI satellites are graphically compared., Comment: 2 pages, 1 figure

Several papers were written about the gamma-ray burst (GRBs) groups. Our statistical study is based on the durations and hardness ratios of the Swift and RHESSI data., Comment: 2 pages, 1 figure, 1 table

We have searched for the third, 'intermediate', subgroup of gamma-ray bursts among nearly 400 gamma-ray bursts observed by the Swift satellite. The standard chi^2 method and F-test were applied which give support for the existence of this subgroup., Comment: 5 pages, 1 figure. Published in Proceedings of the 6th INTEGRAL/BART Workshop, 26-29 March, 2009.

A sample of 427 gamma-ray bursts (GRBs), measured by the RHESSI satellite, is studied statistically to determine the number of GRB groups. Previous studies based on the BATSE Catalog and recently on the Swift data claim the existence of an intermediate GRB group, besides the long and short groups. Using only the GRB durations T90 and chi^2 or F-test, we have not found any statistically significant intermediate group. However, the maximum likelihood ratio test, one-dimensional as well as two-dimensional hardness vs. T90 plane, reveal the reality of an intermediate group. Hence, the existence of this group follows not only from the BATSE and Swift datasets, but also from the RHESSI results., Comment: 6 pages, 2 figures. Published in Proceedings of the 6th INTEGRAL/BART Workshop, 26-29 March, 2009.

A sample of 286 gamma-ray bursts, detected by Swift satellite, is studied statistically by the chi^2 test and the Student t-test, respectively. The short and long subgroups are well detected in the Swift data. But no intermediate subgroup is seen. The non-detection of this subgroup in the Swift database can be explained, once it is assumed that in the BATSE database the short and the intermediate subgroups form a common subclass., Comment: Published in 4th Heidelberg International Symposium on High Energy Gamma-Ray Astronomy, 2008

Gamma-ray bursts, detected by the Swift satellite, are separated into two samples: the bursts with and without determined redshifts. These two samples are compared by the standard Student t-test and F-test. We have compared the dispersions and the mean values of the durations, peak fluxes and fluences in order to find any differences among these two samples. No essential differences were found., Comment: Published in the Proceedings of the 4th Heidelberg International Symposium on High Energy Gamma-Ray Astronomy, 2008

A sample of 286 gamma-ray bursts (GRBs) detected by the Swift satellite and 358 GRBs detected by the RHESSI satellite are studied statistically. Previously published articles, based on the BATSE GRB Catalog, claimed the existence of an intermediate subgroup of GRBs with respect to duration. We use the statistical chi^2 test and the F-test to compare the number of GRB subgroups in our databases with the earlier BATSE results. Similarly to the BATSE database, the short and long subgroups are well detected in the Swift and RHESSI data. However, contrary to the BATSE data, we have not found a statistically significant intermediate subgroup in either Swift or RHESSI data., Comment: Published in Proceedings of the 2008 Nanjing Gamma-ray Burst Conference

A sample of almost 400 Gamma-ray bursts (GRBs) detected by the RHESSI satellite is studied statistically. We focus on GRB duration and hardness ratio and use the statistical chi^2 test and the F-test to compare the number of GRB subgroups in the RHESSI database with that of the BATSE database. Although some previous articles based on the BATSE catalog claim the existence of an intermediate GRB subgroup, besides long and short, we have not found a statistically significant intermediate subgroup in the RHESSI data., Comment: Published in Proceedings of the 4th International Meeting on High Energy Gamma-Ray Astronomy

The durations of 388 gamma-ray bursts, detected by the Swift satellite, are studied statistically in order to search for their subgroups. Then the results are compared with the results obtained earlier from the BATSE database. The standard chi^2 test is used. Similarly to the BATSE database, the short and long subgroups are well detected also in the Swift data. Also the intermediate subgroup is seen in the Swift database. The whole sample of 388 GRBs gives a support for three subgroups., Comment: 9 pages, 3 figures, accepted for publication in Astronomy and Astrophysics

A sample of 427 gamma-ray bursts (GRBs), measured by the RHESSI satellite, is studied statistically with respect to duration and hardness ratio. Standard statistical tests are used, such as $\chi^2$, F-test and the maximum likelihood ratio test, in order to compare the number of GRB groups in the RHESSI database with that of the BATSE database. 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 $\chi^2$ or F-test, we have not found any statistically significant intermediate group in the RHESSI data. However, maximum likelihood ratio test reveals a significant intermediate group. Also using the 2-dimensional hardness / $T_{90}$ plane, the maximum likelihood analysis reveals a significant intermediate group. Contrary to the BATSE database, the intermediate group in the RHESSI data-set is harder than the long one. The existence of an intermediate group follows not only from the BATSE data-set, but also from the RHESSI one., Comment: Accepted for publication in Astronomy and Astrophysics, 9 pages, 4 figures