A comprehensive study of short bursts from SGR 1806-20 and SGR1900+14 detected by HETE-2

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, Ju N Ichi Kotoku, Makoto ArimotoGraziella Pizzichini, John P. Doty, George R. Ricker

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

40 Citations (Scopus)


Temporal and spectral studies of short bursts (≲ 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 ≳ 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 ∼ 4 and ∼ 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 30-100keV and 2-10keV 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 ≲ 700 km) emission region of a softer component (say, ∼ 4keV), which could be reprocessed X-rays by higher energy (≳ 11 keV) photons from an emission region near the stellar surface.

Original languageEnglish
Pages (from-to)653-678
Number of pages26
JournalPublications of the Astronomical Society of Japan
Issue number3
Publication statusPublished - 2007
Externally publishedYes


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

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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