[vsnet-grb-info 16287] GRB 150311A: MAXI/GSC possible afterglow detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  17568
SUBJECT: GRB 150311A: MAXI/GSC possible afterglow detection
DATE:    15/03/12 05:16:34 GMT
FROM:    Motoko Suzuki at RIKEN  <motoko at crab.riken.jp>

M. Morii (RIKEN), H. Negoro (Nihon U.), M. Serino (RIKEN),
S. Ueno, H. Tomida, S. Nakahira, M. Kimura, M. Ishikawa, Y. E. Nakagawa (JAXA),
T. Mihara, M. Sugizaki, J. Sugimoto, T. Takagi, A. Yoshikawa, M. Matsuoka (RIKEN),
N. Kawai, T. Yoshii, Y. Tachibana (Tokyo Tech),
A. Yoshida, T. Sakamoto, Y. Kawakubo, H. Ohtsuki (AGU),
H. Tsunemi, D. Uchida (Osaka U.),
M. Nakajima, K. Fukushima, T. Onodera, K. Suzuki, T. Namba, M. Fujita, F. Honda (Nihon U.),
Y. Ueda, M. Shidatsu, T. Kawamuro, T. Hori (Kyoto U.),
Y. Tsuboi, A. Kawagoe (Chuo U.),
M. Yamauchi, Y. Morooka, D. Itoh (Miyazaki U.),
K. Yamaoka (Nagoya U.)
report on behalf of the MAXI team:

The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source at 2015-03-11T16:18:16 UT .
Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (235.099 deg, -15.809 deg) = (15 40 23, -15 48 32) (J2000)
with a statistical 90% C.L. elliptical error region
with long and short radii of 0.27 deg and 0.26 deg, respectively.
The roll angle of long axis from the north direction is 79.0 deg counterclockwise.
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).
The X-ray flux averaged over the scan was 93 +- 20 mCrab
(4-10keV, 1 sigma error).
There was no significant excess flux in the previous transit at UT 14:45
and in the next transit at 17:50 UT with an upper limit of 20 mCrab for each.

According to GCN IPN_RAW Notices, The Konus-Wind instrument triggered at
16:16:24.88, which is 111s before the MAXI trigger.
Therefore MAXI might have observed the afterglow of GRB 150311A triggered by
Konus-Wind, while the position of this burst is not known.