Mathematics – Probability
Scientific paper
Jun 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...445..731s&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 445, no. 2, p. 731-735
Mathematics
Probability
3
Bremsstrahlung, Energy Spectra, Gamma Ray Bursts, Ginga Satellite, Mathematical Models, Nonthermal Radiation, Probability Density Functions, Proportional Counters, Satellite-Borne Instruments, Spectrum Analysis, Time Functions
Scientific paper
We report the detection of an unusual high-energy transient by the gamma-ray burst detectors onboard the satellite Ginga. This event was much softer than classical gamma-ray bursts, with a spectrum that peaks between 16 and 18 keV and decreases both above and below the peak. A thermal bremsstrahlung fit to the 20 - 400 keV emission gives a characteristic temperature of approximately equal 24 keV; much softer (cooler) than the greater than 100 keV temperatures characteristic of the classical gamma-ray bursts, but similar to that of the soft gamma-ray repeaters (SGRs). The spectrum above the peak is similar to that of type 1 X-ray bursts; however, the peak energy is higher by about a factor of 5, well above the Eddington limit. We have established with high confidence that the spectrum rolls over below 15 keV. Spectral models which include photoelectric absorption from neutral matter with column densities of approximately equal to 1024/sq cm give acceptable fits to the low-energy rollover, as does a power-law fit with an index alpha is approximately equal to -2.5. Power-law models with indices greater than -1.5 are strongly rejected by the data (a Rayleigh-Jeans spectrum has index -1.0). The time history of the event is simple, with a rise time of approximately equal 0.7 s followed by an exponential decay with a 3 s time scale, similar to those seen from type 1 X-ray bursts as well as some classical gamma-ray bursts, but somewhat unusual for a SGR.
Fenimore Edward E.
Murakami Tadayoshi
Strohmayer Tod E.
Yoshida Akio
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