A comprehensive study of short bursts from SGR 1806-20 and SGR 1900+14 detected by HETE-2

作者：Nakagawa Yujin E^*; Yoshida Atsumasa; Hurley Kevin; Atteia Jean Luc; Maetou Miki; Tamagawa Toru; Suzuki Motoko; Yamazaki Tohru; Tanaka Kaoru; Kawai Nobuyuki; Shirasaki Yuji; Pelangeon Alexandre; Matsuoka Masaru; Vanderspek Roland; Crew Geoff B; Villasenor Joel S; Sato Rie; Sugita Satoshi; Kotoku Jun'ichi; Arimoto Makoto; Pizzichini Graziella; Doty John P; Ricker George R

来源：Publications of the Astronomical Society of Japan, 2007, 59(3): 653-678.

• gamma rays : observations
• stars pulsars : individual(SGR 1806-20, SGR 1900+14)
• X-rays : stars

Temporal and spectral studies of short bursts (less than or similar to a few hundred milliseconds) are presented for the soft gamma repeaters (SGRs) 1806-20 and 1900+14 using the HETE-2 samples. In five years from 2001 to 2005, HETE-2 localized 50 bursts from SGR 1806-20 and 5 bursts from SGR 1900+14. The cumulative number-intensity distribution of SGR 1806-20 in the active year 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. From the data, the spectral evolution during bursts with a time scale of greater than or similar to 20 ms does not seem to be common in the HETE-2 sample. The spectra of all short bursts are well reproduced by a two blackbody function with temperatures of similar to 4 and similar to 11 keV. From a timing analysis to the SGR 1806-20 data, a time lag of 2.2 +/- 0.4 ms is found between the 30-100 keV and 2-10 keV radiation bands. This may imply (1) a very rapid spectral softening and energy reinjection, (2) diffused (elongated) emission plasma along the magnetic field lines in pseudo-equilibrium with multi-temperatures, or (3) a separate (located at less than or similar to 700 km) emission region of a softer component (say, similar to 4 keV), which could be reprocessed X-rays by higher energy (greater than or similar to 11 keV) photons from an emission region near the stellar surface.

• 出版日期2007
• 单位中国科学院国家天文台