[vsnet-grb-info 12725] GRB 121209A: MAXI/GSC detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  14084
SUBJECT: GRB 121209A: MAXI/GSC detection
DATE:    12/12/14 13:24:21 GMT
FROM:    Satoshi Nakahira at JAXA/MAXI  <nakahira.satoshi at jaxa.jp>

R. Sato(Kyoto U.), S. Nakahira (JAXA), M. Serino (RIKEN),
Y. Ogawa (Miyazaki U.), N. Kawai (Tokyo Tech),
H. Negoro, M. Asada (Nihon U.),
S. Ueno, H. Tomida, M. Ishikawa, K. Yamaoka, M. Kimura (JAXA),
T. Mihara, M. Sugizaki, K. Morihana, T. Yamamoto, J. Sugimoto, T. Takagi, M. Matsuoka (RIKEN),
M. Mori, R. Usui, K. Ishikawa (Tokyo Tech),
A. Yoshida, T. Sakamoto, Y. Nakano (AGU), H. Tsunemi, M. Sasaki (Osaka U.),
M. Nakajima, (Nihon U.), Y. Ueda, K. Hiroi, M. Shidatsu, T. Kawamuro (Kyoto U.),
Y. Tsuboi, M. Higa (Chuo U.)
M. Yamauchi, Y. Nishimura, T. Hanayama, K. Yoshidome (Miyazaki U.)
on behalf of the MAXI team

At 2012-12-09T21:59:11 UT, the MAXI/GSC detected an uncatalogued
X-ray transient source. Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec.) = (327.02deg, -7.69deg) = (21:48:05, -07:41:38)(J2000)

with a 90% C.L. statistical error of 0.4 deg and an additional systematic
uncertainty of 0.1 deg (90% containment radius).

The trigger time is consistent with that of GRB 121209A (Maselli et al, GCN #14045).
The Swift position lies 0.1 deg outside of the MAXI error circle.
However, assuming the position for GRB 121209A, the transit by MAXI
should have occurred from
2012/12/09T21:58:38 UT(=T0-32 s, where T0 is the Swift/BAT trigger time)
to T0+11 s, suggesting that GRB 121209A was detected near the end
of the MAXI transit, causing the small difference in the formal position.

The time interval of the significant MAXI detection was T0+0 s to T0+5 s
with 2-20 keV X-ray flux of 600+/-140 mCrab (2-20 keV).
The average spectrum is fitted by a power-law model with photon index of  0.97(-0.57/+0.62).
There was no significant excess flux at the previous transit at 17:21 UT and
at the next transit at 23:31 UT on Dec 9 with an upper limit of 20 mCrab for each.