MAXI/GSC detects an X-ray outburst from the Galactic center region, GRO J1744-28/MAXI J1745-288

ATel #3123; F. Suwa, H. Ozawa, H. Negoro (Nihon U.), S. Nakahira (AGU), T. Mihara, M. Sugizaki, Y. E. Nakagawa, M. Serino, T. Yamamoto, T. Sootome, M. Matsuoka (RIKEN), H. Tomida, S. Ueno, M. Kohama, M. Ishikawa (JAXA), N. Kawai, M. Morii, K. Sugimori, R. Usui, T. Toizumi (Tokyo Tech), A. Yoshida, K. Yamaoka (AGU), H. Tsunemi, M. Kimura, H. Kitayama (Osaka U.), M. Nakajima (Nihon U.), Y. Ueda, N. Isobe, S. Eguchi, K. Hiroi (Kyoto U.), A. Daikyuji (Miyazaki U.), Y. Tsuboi, T. Matsumura, A. Uzawa, K. Yamazaki, (Chuo U.), report on behalf of the MAXI team
on 27 Jan 2011; 05:19 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Hitoshi Negoro (negoro@phys.cst.nihon-u.ac.jp)

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MAXI/GSC detected an X-ray outburst from the position:

(R.A., Dec) = (+266.46 deg, -28.82 deg) = (17 45 50, -28 49 12) (J2000)

with systematic uncertainty of 0.2 deg. The position is equivalent to (l, b) = (+0.12 deg, +0.02 deg).

The outburst was recognized in scan transits at least from 2011 Jan. 21 11:25 UT (MJD=55582.4757) to Jan. 22 17:58. The source flux in the 4-10 keV band was almost constant and ~200 mCrab. The source had been invisible from 2011 Jan. 19 19:43 to Jan 21 09:52 (at the time of the scan transit just before the detection) due to the occultation of the ISS solar paddles. After Jan. 22, the source has been in an undetectable area near the ISS rotation pole, and expected date to be observed with MAXI is Jan. 29.

A possible identification of this source is the bursting X-ray pulsar GRO J1744-28, 0.07deg apart from the best position. GRO 1744-28 exhibited outbursts in 1995 (Fishman et al. 1995, IAUC 6272 ) and 1996. Frequent short bursts during the outbursts and 2.14 Hz periodicity were observed (e.g., Giles et al. 1996). No apparent burst was observed during the MAXI observations. The power spectral analysis, however, shows a low-significance peak at 2.07 +/- 0.01 Hz. Since the source position is very close to the Galactic center, a possibility of a new transient can not be excluded. We tentatively name this transient MAXI J1745-288.