[vsnet-grb-info 16465] GRB 150424B: MAXI/GSC detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  17746
SUBJECT: GRB 150424B: MAXI/GSC detection
DATE:    15/04/24 10:48:10 GMT
FROM:    H. Negoro at Nihon U.  <negoro at phys.cst.nihon-u.ac.jp>

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

The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source at 
09:40:14 UT.

Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (182.759 deg, -16.212 deg) = (12 11 02, -16 12 43) (J2000) 
with a statistical 90% C.L. elliptical error region 
with long and short radii of 0.13 deg and 0.11 deg, respectively. 
The roll angle of long axis from the north direction is 23.0 deg counterclockwise. 
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).

Without assumptions on the source constancy, we obtain a rectangular error
box for the transient source with the following corners:
(182.383 deg, -15.974 deg) = (12 09 31, -15 58 27) (J2000)
(182.575 deg, -15.799 deg) = (12 10 18, -15 47 55) (J2000)
(182.974 deg, -16.261 deg) = (12 11 53, -16 15 40) (J2000)
(182.781 deg, -16.436 deg) = (12 11 07, -16 26 10) (J2000)

The X-ray flux averaged over the scan was 544 +- 53 mCrab
(4-10keV, 1 sigma error).
There was no significant excess flux in the previous transit at 08:07 UT
with an upper limit of 20 mCrab.