Repeated injections of energy in the first 600 ms of the giant flare of SGR 1806-20.
The massive flare of 27 December 2004 from the soft gamma-ray repeater SGR 1806-20, a possible magnetar, saturated almost all gamma-ray detectors, meaning that the profile of the pulse was poorly characterized. An accurate profile is essential to determine physically what was happening at the source. Here we report the unsaturated gamma-ray profile for the first 600 ms of the flare, with a time resolution of 5.48 ms. The peak of the profile (of the order of 10(7) photons cm(-2) s(-1)) was reached approximately 50 ms after the onset of the flare, and was then followed by a gradual decrease with superposed oscillatory modulations possibly representing repeated energy injections with approximately 60-ms intervals. The implied total energy is comparable to the stored magnetic energy in a magnetar (approximately 10(47) erg) based on the dipole magnetic field intensity (approximately 10(15) G), suggesting either that the energy release mechanism was extremely efficient or that the interior magnetic field is much stronger than the external dipole field.
Terasawa
Toshio
T
Department of Earth and Planetary Science, University of Tokyo, Tokyo 113-0033, Japan. terasawa@eps.s.u-tokyo.ac.jp
Tanaka
Yasuyuki T
YT
Takei
Yasuhiro
Y
Kawai
Nobuyuki
N
Yoshida
Atsumasa
A
Nomoto
Ken'ichi
K
Yoshikawa
Ichiro
I
Saito
Yoshifumi
Y
Kasaba
Yasumasa
Y
Takashima
Takeshi
T
Mukai
Toshifumi
T
Noda
Hirotomo
H
Murakami
Toshio
T
Watanabe
Kyoko
K
Muraki
Yasushi
Y
Yokoyama
Takaaki
T
Hoshino
Masahiro
M