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GEOTAIL observation of the SGR1806-20 Giant Flare: The first 600 ms

Toshio Terasawa·Yasuyuki Tanaka·Yasuhiro Takei·Nobuyuki Kawai·Atsumasa Yoshida·Ken'ichi Nomoto·Ichiro Yoshikawa·Yoshifumi Saito·Yasumasa Kasaba·Takeshi Takashima·Toshifumi Mukai·Hirotomo Noda·Toshio Murakami·Kyoko Watanabe·Yasushi Muraki·Takaaki Yokoyama·Masahiro Hoshino
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Abstract

On December 27, 2004, plasma particle detectors on the GEOTAIL spacecraft detected an extremely strong signal of hard X-ray photons from the giant flare of SGR1806-20, a magnetar candidate. While practically all gamma-ray detectors on any satellites were saturated during the first ~500 ms interval after the onset, one of the particle detectors on GEOTAIL was not saturated and provided unique measurements of the hard X-ray intensity and the profile for the first 600 ms interval with 5.48 ms time resolution. After ~50 ms from the initial rapid onset, the peak photon flux (integrated above ~50 keV) reached the order of 10^7 photons sec^{-1} cm^{-2}. Assuming a blackbody spectrum with kT=175 keV, we estimate the peak energy flux to be 21 erg sec^{-1} cm^{-2} and the fluence (for 0-600 ms) to be 2.4 erg cm^{-2}. The implied energy release comparable to the magnetic energy stored in a magnetar (~10^{47} erg) suggests an extremely efficient energy release mechanism.

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Toshio Terasawa, Yasuyuki Tanaka, Yasuhiro Takei, Nobuyuki Kawai, Atsumasa Yoshida, Ken'ichi Nomoto, Ichiro Yoshikawa, Yoshifumi Saito, Yasumasa Kasaba, Takeshi Takashima, Toshifumi Mukai, Hirotomo Noda, Toshio Murakami, Kyoko Watanabe, Yasushi Muraki, Takaaki Yokoyama, Masahiro Hoshino. 2005-04-18. GEOTAIL observation of the SGR1806-20 Giant Flare: The first 600 ms. https://doi.org/10.1038/nature03573

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