Observations of cosmic gamma-ray bursts with the main detector of the SIGMA telescope onboard the Granat Observatory     

R. A. Burenin  O. V. Terekhov  R. A. Sunyaev  A. V. D’yachkov  G. Khavenson  B. S. Novikov  I. D. Tserenin  K. M. Sukhanov  P. Goldoni  A. Claret  A. Goldwurm  J. Paul  F. Pelaez  E. Jourdain  J. -P. Roques  G. Vedrenne 《Astronomy Letters》2000,26(7):413-422

We present the observations of cosmic gamma-ray bursts (GRBs) with the main detector of the SIGMA telescope onboard the Granat Observatory from January 1990 through September 1994. The observations were carried out in the energy range 35–1300 keV. We detected 36 GRBs and 31 high-energy solar flares during this period. No GRB fell within the main field of view; they were all recorded by the “secondary optics” of the telescope. The SIGMA telescope recorded relatively bright bursts with peak fluxes of 10^?6–10^?4 erg s^?1 cm^?2 in the 100–500-keV energy band. Stable detector background allows the long-term variability of GRB sources on a time scale of ～1000 s to be studied. The results of our search for early afterglows of GRBs are presented. The flux averaged over all bursts in the interval 100–800 s after the main event is 0.36±0.14 counts s^?(35–300 keV), suggesting that there is soft gamma-ray emission on this time scale after a considerable number of GRBs.  相似文献   

Tests for spatial isotropy of three thousand gamma-ray bursts found in BATSE archival data     

Ya. Yu. Tikhomirova  B. E. Stern 《Astronomy Letters》2000,26(10):672-678

We apply isotropy tests to our new uniform catalog of cosmic gamma-ray bursts (GRBs) (Stern and Tikhomirova 1999). The catalog contains trigger and nontrigger bursts found in 1024-ms BATSE records over seven years. Based on this catalog, we confirm isotropy of the GRB spatial distribution for a sample that surpasses previous samples in size (2934 bursts) and in achieved threshold (fluxes down to 0.1 phot. cm^?2 s^?1, which is a factor of ～2 lower than the BATSE trigger threshold). We also confirm that there is no excess of bursts toward the galaxy M 31.  相似文献   

The Spin-X wide-field X-ray monitor of the Spectrum-X-Gamma astrophysical observatory     

M. N. Pavlinsky  S. A. Grebenev  P. A. Mazov  I. A. Dekhanov  D. B. Ryvkin  R. A. Sunyaev  V. I. Surtaev  N. V. Mokrousov  A. G. Glushenko  S. I. Yampol’skii  A. D. Novikov 《Astronomy Letters》2000,26(12):779-787

The Spin-X wide-field X-ray monitor of the Spectrum-X-Gamma astrophysical observatory, which is based on the principle of a coded-aperture telescope, is designed to detect and localize cosmic gammaray-burst (GRB) sources; to survey large areas of the sky in search of new transients; and to carry out long-term observations of bright Galactic sources, including X-ray bursters. The monitor consists of two noncoaxial identical modules, Spin-X1 and Spin-X2, which together cover 6.8% of the sky. The high-apogee, four-day orbit of the Spectrum-XG satellite allows the instrument to be in observing mode more than 50% of the time. Having simulated the rate of GRB detection by Spin-X, we show that extrapolating BATSE 50–300-keV average data on the number of GRBs, their duration, and their mean energy spectrum to the X-ray energy band leads to disagreement with the observed detection rate of GRBs in the X-ray band. The number of GRBs that can be detected and localized with an accuracy r≤3′ (3σ) (the error-circle radius) by Spin-X is estimated to be ten bursts per year. We present data on the Spin-X sensitivity achievable during long-term observations of persistent and transient sources and on its sensitivity to X-ray bursts from Galactic sources in the 2–30-keV energy band.  相似文献   

Oscillation structure of gamma-ray bursts and their possible origin     

S. S. Gershtein 《Astronomy Letters》2000,26(11):730-735

It is hypothesized that thermonuclear burning of the matter from the envelope of a massive compact star accreting onto a hot neutron star produced by spherically symmetric collapse of a stellar iron core can proceed in oscillation mode (much as is the case during thermal explosions of carbon-oxygen cores in lower mass stars). Local density oscillations near the neutron-star surface can generate shock waves; in these shocks, the electron-positron plasma is stratified from the remaining matter, and shells of an expanding relativistic fireball with an oscillation time scale in cosmological gamma-ray bursts (GRBs) of ～10^?2 s are formed. It is pointed out that the GRB progenitors can be nonrotating massive Wolf-Rayet (WR) stars whose collapse, according to observational data, can proceed without any substantial envelope ejection.  相似文献   

航空伽玛射线全能谱数据分析方法的理论研究     

倪卫冲 《铀矿地质》2011,27(4):231-241

通过航空伽玛能谱测量的源项分析和测量模型建立,发现航空伽玛能谱测量谱是各种源项能谱成分的合成谱。对航空伽玛射线全能谱分析方法给出了其数学分析式,其通用式可表示为矩阵式,对于矿产勘查和核环境与核应急等不同的应用领域能表达成相应的展开式。理论研究表明,航空伽玛全谱法不需要附加的上测探测器,就可直接解决大气氡修正问题,还将具有较好的经济效益。  相似文献   

The point-spread function for airborne radiometry     

Maurice Craig 《Mathematical Geology》1993,25(8):1003-1013

Pointwise division in the Fourier domain can be used to deconvolve the effects of aircraft altitude upon gridded, two-dimensional, radiometric count data. The appropriate divisor function, expressed as a triple integral by Gunn, is developed as a convergent series suitable for its numerical evaluation. For various flying heights, graphs display in cross-section the corresponding, radially symmetric, divisor function.  相似文献   

The efficiency of different methods of observations by using Cerenkov detectors of eas with imaging cameras     

A. P. Kornienko  Yu. L. Zyskin  Yu. I. Neshpor  A. A. Stepanian 《Experimental Astronomy》1993,4(2):147-157

The detection efficiency of the atmospheric Cerenkov flashes in searching for very high energy (VHE) gamma-ray sources using the multichannel imaging cameras (MIC) are compared for various technique. Here the detection efficiency is regarded as the time needed for gamma-ray source detection with the preset flux at a certain confidence level. The shorter the time the higher the efficiency.The Monte Carlo simulation of the flashes detection process by MIC has been used for the comparison of various observational methods. The analysis has shown that the tracking of the source followed by the background tracking is the most efficient. Scanning and off-axis observations are 1.5–2.0 times less efficient.  相似文献   

Scope of high-frequency time keeping in searches for short-period gamma-ray sources     

M. L. Sapru  A. K. Tickoo  I. K. Kaul  S. K. Kaul  C. L. Bhat  R. K. Kaul  H. S. Rawat  V. K. Senecha  R. C. Rannot  H. Razdan 《Journal of Astrophysics and Astronomy》1990,11(2):141-150

This paper presents a novel technique to derive the absolute time of occurrence of an event with an accuracy of < 200 μs by adapting the HF time synchronization technique to correct for the aging rate and the frequency drift of a temperature-controlled quartz frequency standard. The propagation delay suffered by the HF time signals has been estimated by monitoring the clock error with respect to time signals from five broadcast stations located at distances in the range 500–3700 km from Gulmarg. Using simulated data, we further show the viability of this technique in permitting periodicity searches on timescales of ≥5 milliseconds in cosmic gamma-ray data An erratum to this article is available at .  相似文献   

Radial distributions of gamma-ray bursts and type Ib/c supernovae in galaxies     

D. Yu. Tsvetkov  S. I. Blinnikov  N. N. Pavlyuk 《Astronomy Letters》2001,27(7):411-415

Data on the positions of gamma-ray bursts (GRBs) in galaxies are used to construct the radial distributions of their surface density. The gradient in GRB surface density is shown to decrease sharply at a galactocentric distance equal to the effective galactic radius. In central galactic regions, the GRB density distribution agrees with the galactic surface-brightness distribution; in outer regions, the GRB density decreases more slowly than does the surface brightness. Based on improved statistics, we analyze the radial distribution of type Ib/c supernovae. We show that it differs insignificantly from the distributions of other types of supernova and exhibits a much closer similarity to the distribution of star-forming regions than do GRBs. Although the statistics for GRBs is poor, the deviation of their distribution from the distribution of active star-forming regions in nearby galaxies seems to have been firmly established. A correlation of GRBs with the distribution of dark matter in outer galactic regions is not ruled out.  相似文献   

Spectra and light curves of GRB afterglows     

A. G. Tolstov  S. I. Blinnikov 《Astronomy Letters》2003,29(6):353-360

We performed accurate numerical calculations of angle-, time-, and frequency-dependent radiative transfer for the relativistic motion of matter in gamma-ray burst (GRB) models. Our technique for solving the transfer equation, which is based on the method of characteristics, can be applied to the motion of matter with a Lorentz factor up to 1000. The effect of synchrotron self-absorption is taken into account. We computed the spectra and light curves from electrons with a power-law energy distribution in an expanding relativistic shock and compare them with available analytic estimates. The behavior of the optical afterglows from GRB 990510 and GRB 000301c is discussed qualitatively.  相似文献