Gamma-ray bursts

Research on the statistical properties of the temporal variability of GRBs was continued. It was shown that complex (containing many pulses) bursts have a different brightness distribution when compared with simple bursts. It is consistent with the fact that complex bursts are intrinsically brighter. This fact can have important implications for the models of GRBs. GRBs being extremely different in their temporal appearance turn out to be very similar in Fourier space. The power density spectra of long GRBs are consistent with a power-law with the index $-5/3$ close to the Kolmogorov law.

The energy spectra of GRBs and their time evolution are also analyzed. The behaviour of the instantaneous (i.e., temporally resolved) spectra are of interest as they directly reflect the physics of the underlying emission processes. Especially, the spectral evolution within individual pulses is studied. The connection between the spectral and the intensity evolution has been formulated in a compact form. It was also demonstrated in what way the instantaneous spectra are related to the generally studied time-integrated pulse spectrum. It was shown how this can be used when studying observed GRB spectra.

Many detectable GRBs escaped detection (triggering) by BATSE because of too low intensity, or, so called, dead-time intervals. Such GRBs can be found in the daily count rate records which are accumulated during the full CGRO operation. Analysing the $\sim 40$ Gb of archival data using an advanced triggering procedure about 1700 non-triggered GRBs were found which doubles the available sample of GRBs. Most importantly, the efficiency of the search was measured with a novel ``test burst'' technique. A database of non-triggered GRBs is publically available here.