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MAXI/GSC detection of an unexpected brightening from Be/X-ray binary pulsar, GRO J1008-57

ATel #4561; M. Nakajima (Nihon U.), T. Mihara, M. Sugizaki (RIKEN), K. Yoshidome, M. Yamauchi, Y. Nishimura, T. Hanayama (Miyazaki U.), S. Ueno, H. Tomida, S. Nakahira, M. Ishikawa (JAXA), M. Serino, K. Morihana, T. Yamamoto, J. Sugimoto, T. Takagi, M. Matsuoka (RIKEN), N. Kawai, M. Morii, R. Usui, K. Ishikawa (Tokyo Tech), A. Yoshida, T. Sakamoto (AGU), H. Tsunemi, M. Kimura (Osaka U.), H. Negoro, M. Asada, H. Sakakibara, N. Serita (Nihon U.), Y. Ueda, K. Hiroi, M. Shidatsu, R. Sato (Kyoto U.), Y. Tsuboi, M. Higa (Chuo U.), K. Yamaoka (ISAS), report on behalf of the MAXI team:
on 9 Nov 2012; 13:00 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Motoki Nakajima (nakajima.motoki@nihon-u.ac.jp)

Subjects: Optical, X-ray, Binary, Neutron Star, Transient, Pulsar

Referred to by ATel #: 4564, 4573, 4577, 4759, 5004, 5705, 6465, 6630, 6656, 6917, 10529

MAXI Nova-search system detected an unexpected brightening from a Be/X-ray binary pulsar, GRO J1008-57. This source is currently undergoing a peculiar long outburst (Atel#4319, #4355). After the decay of the long outburst lasting for about 2 month, the flux turned into an increase again from MJD 56236 (2012-11-05). The flux reached 62 +- 7 mCrab (4-10 keV) on 2012-11-08 (MJD 56239) in 1-day bin. The latest 4-10 keV flux at 2012-11-09 03:00 UT reached 120 +- 9 mCrab in 4-hour bin. It is already as bright as the peak of the regular normal outburst at periastron. The Swift/BAT also detected the increase in 15-50 keV. According to the binary orbital parameters (Coe et al. 2007; Sootome et al. 2012), the present flare corresponds to ~0.3 orbital phase. Such a bright flare has not been recorded at this orbital phase.

The latest light curve and the image are available at the following URL:

The folded light curve by the orbital phase is available at