An Optically Dark GRB Observed by HETE-2: GRB 051022

Yujin E. Nakagawa , Atsumasa Yoshida (1) , Satoshi Sugita , Kaoru Tanaka (2) , Nobuyuki Ishikawa (2) , Toru Tamagawa , Motoko Suzuki (3, 4) , Yuji Shirasaki , Nobuyuki Kawai , Masaru Matsuoka , Jean-Luc Atteia (5) , Alexandre Pelangeon (6) , Roland Vanderspek , Geoffrey B. Crew , Joel S. Villasenor , Nat Butler , John P. Doty , George R. Ricker (7) , Graziella Pizzichini , Timothy Q. Donaghy , Donald Q. Lamb (8) , Carlo Graziani , Rie Sato (9) , Miki Maetou , Makoto Arimoto , Jun'Ichi Kotoku , J. Garrett Jernigan , Takanori Sakamoto , Jean-François Olive (10, 11) , Michel Boer (10, 12) , Edward E. Fenimore , Mark Galassi (13) , Stanford E. Woosley , Makoto Yamauchi , Kunio Takagishi , Isamu Hatsukade (14)

1 Chercheur indépendant
2 Department of Physics and Mathematics [Sagamihara]
3 Department of Physics
4 Botanical Garden, Graduate School of Science
5 LATT - Laboratoire Astrophysique de Toulouse-Tarbes
6 LATT - Laboratoire d'Astrophysique de l'Observatoire Midi-Pyrénées
7 CSR - Center for Space Research [Cambridge]
8 Department of Astronomy and Astrophysics [Chicago]
9 Department of Electrical Engineering
10 CESR - Centre d'étude spatiale des rayonnements
11 UMS 831 - Services communs OMP
12 OHP - Observatoire de Haute-Provence
13 LANL - Los Alamos National Laboratory
14 Faculty of Engineering

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 = (8.8-2.9+3.1) × 1022 cm-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 ? 1016cm, which could be a dusty molecular cloud.

Mots clés: gamma rays: observations; star: individual (GRB 051022); X-rays: ISM

Domaines: Cosmologie et astrophysique extra-galactique [astro-ph.CO]

Yujin E. Nakagawa, Atsumasa Yoshida, Satoshi Sugita, Kaoru Tanaka, Nobuyuki Ishikawa, et al.. An Optically Dark GRB Observed by HETE-2: GRB 051022. Publications of the Astronomical Society of Japan, 2006, 58 (4), pp.L35-L39. ⟨hal-00285518⟩