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MAXI/GSC observation of an unexpected X-ray outburst from the Be/X-ray binary pulsar GRO J1008-57

ATel #6630; M. Nakajima (Nihon U.), T. Mihara (RIKEN), S. Ueno, H. Tomida, S. Nakahira, M. Kimura, M. Ishikawa, Y. E. Nakagawa (JAXA), M. Sugizaki, M. Morii, M. Serino, J. Sugimoto, T. Takagi, A. Yoshikawa, M. Matsuoka (RIKEN), N. Kawai, T. Yoshii, Y. Tachibana (Tokyo Tech), A. Yoshida, T. Sakamoto, Y. Kawakubo, H. Ohtsuki (AGU), H. Tsunemi, D. Uchida (Osaka U.), H. Negoro, K. Fukushima, T. Onodera, K. Suzuki, T. Namba, M. Fujita, F. Honda (Nihon U.), Y. Ueda, M. Shidatsu, T. Kawamuro, T. Hori (Kyoto U.), Y. Tsuboi, A. Kawagoe (Chuo U.), M. Yamauchi, Y. Morooka (Miyazaki U.), K. Yamaoka (Nagoya U.) report on behalf of the MAXI team:
on 28 Oct 2014; 09:57 UT
Credential Certification: Motoki Nakajima (nakajima.motoki@nihon-u.ac.jp)

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

Referred to by ATel #: 6656, 6664, 6819, 6823, 6917, 8547, 10529

The MAXI/GSC nova alert system again detected an unexpected X-ray flux increase from the Be/X-ray binary pulsar GRO J1008-57 on 2014 October 22 (MJD 56952). After the previous normal outburst reported on 2014 September 13 (MJD 56913 ; Atel#6465), the 4-10 keV source flux stayed at ~10 mCrab brightness. On October 16 (MJD 56946), the flux turned into an increase again. The daily-averaged flux in the 4-10 keV band reached 32 +- 6 mCrab on October 22 (MJD 56952), and the latest data is 75 +- 15 mCrab (MJD 56957). According to the orbital ephemeris (T_0=54416.65(MJD), Porb=249.48 d ; Kühnel et al. 2013), the trigger date is consistent with the 0.16 orbital phase. The present activity resembles the beginning of the giant outburst observed in 2012 (Atel#4561). We encouraged multi wavelength observations. The latest light curve and the image are available at the following URL:http://maxi.riken.jp/top/index.php?cid=1&jname=J1009-582