Nakagawa 2007 SGR1806-20 SGR1900+14的系统研究

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astro-ph/0701701 [abs, ps, pdf, other] :

Title: A Comprehensive Study of Short Bursts from SGR 1806-20 and SGR 1900+14 Detected by HETE-2
Authors: Yujin E. Nakagawa, Atsumasa Yoshida, Kevin Hurley, Jean-Luc Atteia, Miki Maetou, Toru Tamagawa, Motoko Suzuki, Tohru Yamazaki, Kaoru Tanaka, Nobuyuki Kawai, Yuji Shirasaki, Alexandre Pelangeon, Masaru Matsuoka, Roland Vanderspek, Geoff B. Crew, Joel S. Villasenor, Rie Sato, Satoshi Sugita, Jun'ichi Kotoku, Makoto Arimoto, Graziella Pizzichini, John P. Doty, George R. Ricker
Comments: 48 pages, 14 figures, submitted to publication in PASJ

We present the results of temporal and spectral studies of the short burst (less than a few hundred milliseconds) from the soft gamma repeaters (SGRs) 1806-20 and 1900+14 using the HETE-2 samples. In five years from 2001 to 2005, HETE-2 detected 50 bursts which were localized to SGR 1806-20 and 5 bursts which were localized to SGR 1900+14. Especially SGR 1806-20 was active in 2004, and HETE-2 localized 33 bursts in that year. The cumulative number-intensity distribution of SGR 1806-20 in 2004 is well described by a power law model with an index of -1.1+/-0.6. It is consistent with previous studies but burst data taken in other years clearly give a steeper distribution. This may suggest that more energetic bursts could occur more frequently in periods of greater activity. A power law cumulative number-intensity distribution is also known for earthquakes and solar flares. It may imply analogous triggering mechanisms. Although spectral evolution during bursts with a time scale of > 20 ms is not common in the HETE-2 sample, spectral softening due to the very rapid (<> 11 keV) photons from an emission region near the stellar surface.