[vsnet-grb-info 16821] GRB 150801A: MAXI/GSC detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  18102
SUBJECT: GRB 150801A: MAXI/GSC detection
DATE:    15/08/01 13:23:23 GMT
FROM:    H. Negoro at Nihon U.  <negoro at phys.cst.nihon-u.ac.jp>

M. Ishikawa, S. Nakahira (JAXA), H. Negoro, (Nihon U.), 
S. Ueno, H. Tomida,  M. Kimura, Y. E. Nakagawa (JAXA),
T. Mihara, M. Sugizaki, M. Serino, M. Shidatsu, J. Sugimoto, T. Takagi, M. Matsuoka (RIKEN), 
N. Kawai, Y. Tachibana, T. Yoshii (Tokyo Tech), 
A. Yoshida, T. Sakamoto, Y. Kawakubo, H. Ohtsuki (AGU), 
H. Tsunemi, R. Imatani (Osaka U.), M. Nakajima, T. Masumitsu, 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 01:18:55 UT.
Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (256.013 deg, -9.523 deg) = (17 04 03, -09 31 22) (J2000) 
with a statistical 90% C.L. elliptical error region 
with long and short radii of 0.26 deg and 0.25 deg, respectively. The roll
angle of long axis from the north direction is 50.0 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:
(R.A., Dec) = (255.708 deg, -10.291 deg) = (17 02 49, -10 17 28) (J2000)
(R.A., Dec) = (255.273 deg, -9.991 deg) = (17 01 05, -09 59 28) (J2000)
(R.A., Dec) = (256.932 deg, -8.065 deg) = (17 07 43, -08 03 53) (J2000)
(R.A., Dec) = (257.356 deg, -8.376 deg) = (17 09 25, -08 22 32) (J2000)

The X-ray flux averaged over the scan was 103 +- 21 mCrab
(4-10keV, 1 sigma error).
There was no significant excess flux in the previous transit at 23:46 UT on 31 July
and in the next transit at 02:51 UT with an upper limit of 20 mCrab for each.