Anton B. Sanin

OBSERVATIONS OF THE PROMPT GAMMA-RAY EMISSION OF GRB 070125

The long, bright gamma-ray burst GRB 070125 was localized by the Interplanetary Network. We present light curves of the prompt gamma-ray emission as observed by Konus-Wind, RHESSI, Suzaku WAM, and Swift BAT. We detail the results of joint spectral fits with Konus and RHESSI data. The burst shows moderate hard-to-soft evolution in its multipeaked emission over a period of about 1 minute. The total burst fluence as observed by Konus is -->1.79 ? 10?4 ergs cm?2 (20 keV-10 MeV). Using the spectroscopic redshift -->z = 1.548, we find that the burst is consistent with the Amati -->Epeak,i ? Eiso correlation. Assuming a jet opening angle derived from broadband modeling of the burst afterglow, GRB 070125 is a significant outlier to the Ghirlanda -->Epeak,i ? E? correlation. Its collimation-corrected energy release, -->E? = 2.5 ? 1052 ergs, is the largest yet observed.

The Emission Time of Gamma-Ray Bursts

The concept of emission time τN is suggested as a temporal parameter which is complementary to the classical parameters of duration times T50 and T90. The emission time is defined as the time of emission of N% of the total fluence. The definition adds the time bins of high fluence in decreasing fluence rank until N% of the fluence has been reached. The emission time interval excludes low-emission intervals of bursts, and so the emission time characterizes the state of high-power emission. The distribution of this new parameter is found to be bimodal for bright bursts. The distributions of emission time τ30 and τ50, for groups based on burst intensity, are also compared.

Comparison of Redshift-known Gamma-Ray Bursts with the Main Groups of Bright BATSE Events

The small reference sample of six BATSE gamma-ray bursts with known redshifts from optical afterglows is compared with a comparison group of the 218 brightest BATSE bursts. These two groups are shown to be consistent both with respect to the distributions of the spectral peak parameter in the observers frame and also with respect to the distributions of the frame-independent cosmological invariant parameter (CIP). Using the known values of the redshifts (z) for the reference sample, the rest-frame distribution of spectral parameters is built. The deredshifted distribution of the spectral parameters of the reference sample is compared with distribution of these parameters for the comparison group after deredshifting by the factor 1/(1 + z), with z a free parameter. Requiring consistency between these two distributions produces a collective estimation of the best fitting redshifts for the comparison group z = 1.8-3.6. These values can be considered as the average cosmological redshift of the sources of the brightest BATSE bursts. The most probable value of the peak energy of the spectrum in the rest frame is 920 keV.

Rest frame properties of gamma-ray bursts

The small reference group of BATSE gamma-ray bursts with measured red-factors of optical afterglows is compared with the large comparison group of brightest BATSE bursts. These two groups are shown to be similar both in respect with distributions of measured Ep parameters in the Observer frame and also in respect with frame-independent distributions of newly implemented cosmological invariant parameters (CIP). Using the known values of red-factors Z for the reference group, the distribution of Ep(RF) is built for the rest frames of their sources. De-redshifted statistics of Ep(RF) are compared with observed distributions of Ep for the comparison group of bursts. From this comparison the collective estimation of red-shifts Z=2.5–3.5 has been performed for the group of brightest BATSE bursts.

Generic Difference Between Early and Late Stages of BATSE Gamma-Ray Bursts

The early and late stages of gamma-ray bursts are studied in a statistical analysis of the large sample of long BATSE events. The primary peak is used as the boundary between the early and late stages of emission. Significant differences are found between the stages: the early stage is shorter, it has harder emission, and it becomes a smaller fraction of the total burst duration for burst groups of decreasing intensity.

The technique of emission time estimation for BATSE GRBs

The technique of estimation of the emission time τ50, introduced as a new temporal parameter [1,2], is described.

The emission time signature of BATSE GRBs

The emission time parameter τ50 is introduced as a new temporal parameter of gamma-ray bursts.

The pure physical parameters of BATSE gamma ray bursts

The concept of Pure Physical Parameters (PPP, or P3) is presented, as the instrument-independent parameterization for the statistical search for basic physical signatures of gamma-ray bursts. The emission time of photon light curves and the peak of photon spectra of high power emission are proposed for each burst characterization, as P3 parameters for time variability and for spectral energy of gamma-rays. The P3 parameters are presented for 6 gamma-ray bursts in their rest frames with known red-shifts of optical afterglows.