[vsnet-grb-info 18206] GRB 160705A/MAXI J0748-149: MAXI/GSC detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  19654
SUBJECT: GRB 160705A/MAXI J0748-149: MAXI/GSC detection
DATE:    16/07/05 06:02:55 GMT
FROM:    Motoko Suzuki at RIKEN  <motoko at crab.riken.jp>

S. Oda (Kyoto U), M. Serino, W. Iwakiri (RIKEN), S. Nakahira(JAXA), H. Negoro(Nigon U.)
S. Ueno, H. Tomida, M. Ishikawa, Y. Sugawara (JAXA), 
T. Mihara, M. Sugizaki, M. Shidatsu, J. Sugimoto, T. Takagi, M. Matsuoka (RIKEN), 
N. Kawai, N. Isobe, S. Sugita, T. Yoshii, Y. Tachibana, Y. Ono, T. Fujiwara (Tokyo Tech), 
A. Yoshida, T. Sakamoto, Y. Kawakubo, Y. Kitaoka (AGU), 
H. Tsunemi, R. Shomura (Osaka U.),  M. Nakajima, K. Tanaka, T. Masumitsu, 
T. Kawase (Nihon U.), Y. Ueda, T. Kawamuro, T. Hori, A. Tanimoto (Kyoto U.), 
Y. Tsuboi, Y. Nakamura, R. Sasaki (Chuo U.), M. Yamauchi, K. Furuya (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 UT 02:30:12 on 2016 July 05.
We obtain a rectangular error box for the transient source with the following corners:
(116.602 deg, -14.589 deg) = (07 46 24, -14 35 19) (J2000)
(116.761 deg, -14.453 deg) = (07 47 02, -14 27 09) (J2000)
(117.580 deg, -15.549 deg) = (07 50 19, -15 32 55) (J2000)
(117.419 deg, -15.683 deg) = (07 49 40, -15 40 58) (J2000)
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).

The X-ray flux averaged over the scan was 631 +- 46 mCrab
(4-10keV, 1 sigma error).
There was no significant excess flux in the previous transit at 00:57 UT
and in the next transit at 04:02 UT with an upper limit of 20 mCrab for each.

Preliminary result shows that the MAXI/GSC spectrum is well fitted by a single
power-law with a photon index of 1.2 (+/- 0.3) (chi^2/d.o.f = 7.15/11) or a 
blackbody model with a temperature of 2.0 (-0.3, +0.4) keV (chi^2/d.o.f = 6.91/11). 
Since the source is located at a relatively low Galactic latitude (b ~ 5 deg) 
and the spectrum can be represented with a ~2 keV blackbody model, we can not 
exclude the possibility that this event is an X-ray burst from a Galactic source.

We tentatively name the source MAXI J0748-149.