  Classification of gamma-ray bursts (GRBs) into groups has been intensively
studied by various statistical tests in previous years. It has been suggested
that there was a distinct group of GRBs, beyond the long and short ones, with
intermediate durations. However, such a group is not securely confirmed yet.
Strangely, concerning the spectral hardness, the observations from the Swift
and RHESSI satellites give different results. For the Swift/BAT database it is
found that the intermediate-duration bursts might well be related to so-called
X-ray flashes (XRFs). On the other hand, for the RHESSI dataset the
intermediate-duration bursts seem to be spectrally too hard to be given by
XRFs. The connection of the intermediate-duration bursts and XRFs for the BATSE
database is not clear as well. The purpose of this article is to check the
relation between XRFs and GRBs for the BATSE and RHESSI databases,
respectively. We use an empirical definition of XRFs introduced by other
authors earlier. For the RHESSI database we also use a transformation between
the detected counts and the fluences based on the simulated detector response
function. The purpose is to compare the hardnesses of GRBs with the definition
of XRFs. There is a 1.3-4.2 % fraction of XRFs in the whole BATSE database. The
vast majority of the BATSE short bursts are not XRFs because only 0.7-5.7 % of
the short bursts can be given by XRFs. However, there is a large uncertainty in
the fraction of XRFs among the intermediate-duration bursts. The fraction of
1-85 % of the BATSE intermediate-duration bursts can be related to XRFs. For
the long bursts this fraction is between 1.0 % and 3.4 %. The uncertainties in
these fractions are large, however it can be claimed that all BATSE
intermediate-duration bursts cannot be given by XRFs. At least 79 % of RHESSI
short bursts, at least 53 % of RHESSI intermediate-duration bursts, and at
least...

High Energy Astrophysical Phenomena