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GCN Circular 17825

Subject
GRB 150518A: MAXI/GSC detection
Date
2015-05-18T23:27:34Z (9 years ago)
From
H. Negoro at Nihon U. <negoro@phys.cst.nihon-u.ac.jp>
T. Kawamuro (Kyoto U.), S. Nakahira, 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.), 
H. Negoro, M. Nakajima, K. Tanaka, T. Masumitsu (Nihon U.), 
Y. Ueda, 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 21:42:14 UT.
Assuming that the source flux was constant over the transit,
we obtain the source position at

(R.A., Dec) = (234.342 deg, 16.307 deg) = (15 37 22, +16 18 25) (J2000)

with a statistical 90% C.L. elliptical error region with long and short radii 
of 0.20 deg and 0.20 deg, respectively. The roll angle of long axis from 
the north direction is 75.0 deg counterclockwise. There is an additional 
systematic uncertainty of 0.1 deg (90% containment radius).

The X-ray flux averaged over the scan was 327 +- 49 mCrab
(4-10keV, 1 sigma error).

Without assumptions on the source constancy,we obtain a rectangular error
box for the transient source with the following corners:

(R.A., Dec) = (233.970 deg, 15.521 deg) = (15 35 52, +15 31 15) (J2000)
(R.A., Dec) = (233.627 deg, 15.744 deg) = (15 34 30, +15 44 38) (J2000)
(R.A., Dec) = (234.594 deg, 16.941 deg) = (15 38 22, +16 56 26) (J2000)
(R.A., Dec) = (234.939 deg, 16.717 deg) = (15 39 45, +16 43 01) (J2000)

There was no significant excess flux in the previous transit at 5/18 21:39 UT.
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