An optically dark GRB observed by HETE-2: GRB 051022

Yujin E. Nakagawa, Atsumasa Yoshida, Satoshi Sugita, Kaoru Tanaka, Nobuyuki Ishikawa, Toru Tamagawa, Motoko Suzuki, Yuji Shirasaki, Nobuyuki Kawai, Masaru Matsuoka, Jean Luc Atteia, Alexandre Pelangeon, Roland Vanderspek, Geoffrey B. Crew, Joel S. Villasenor, Nat Butler, John P. Doty, George R. Ricker, Graziella Pizzichini, Timothy Q. DonaghyDonald Q. Lamb, Carlo Graziani, Rie Sato, Miki Maetou, Makoto Arimoto, Jun'Ichi Kotoku, J. Garrett Jernigan, Takanori Sakamoto, Jean François Olive, Michel Boer, Edward E. Fenimore, Mark Galassi, Stanford E. Woosley, Makoto Yamauchi, Kunio Takagishi, Isamu Hatsukade

Research output: Contribution to journalArticlepeer-review

12 Scopus citations


GRB 051022 was detected at 13:07:58 on 2005 October 22 UT by HETE-2. The location of GRB 051022 was determined immediately by the flight localization system. This burst contained multiple pulses, and had a rather long duration of about 190s. The detections of candidate X-ray and radio afterglows were reported, whereas no optical afterglow was found. Optical spectroscopic observations of the host galaxy revealed a redshift of z = 0.8. Using data derived by a HETE-2 observation of the prompt emission, we found absorption of NH = (8.8-29+3.1) x 1022cm -2 and visual extinction of Av = 49-16+17 mag in the host galaxy. If this is the case, no detection of any optical transient would be quite reasonable. The absorption derived by Swift XRT observations of the afterglow is fully consistent with those obtained from an early HETE-2 observation of the prompt emission. Our analysis implies an interpretation that the absorbing medium may be outside the external shock at R ∼ 10 16cm, which could be a dusty molecular cloud.

Original languageEnglish (US)
Pages (from-to)L35-L39
JournalPublications of the Astronomical Society of Japan
Issue number4
StatePublished - 2006
Externally publishedYes


  • Gamma rays: observations
  • Star: individual (GRB 051022)
  • X-rays: ISM

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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