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MAXI/GSC detection of outburst onset from GRO J1008-57

ATel #7490; M. Nakajima (Nihon U.), T. Mihara (RIKEN), S. Kanetou (Chuo U.), S. Ueno, H. Tomida, S. Nakahira, M. Kimura, M. Ishikawa, Y. E. Nakagawa (JAXA), 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, K. Tanaka, T. Masumitsu (Nihon U.), Y. Ueda, T. Kawamuro, T. Hori (Kyoto U.), Y. Tsuboi (Chuo U.), M. Yamauchi, D. Itoh (Miyazaki U.), K. Yamaoka (Nagoya U.), M. Morii (ISM)
on 11 May 2015; 15:16 UT
Credential Certification: Motoki Nakajima (nakajima.motoki@nihon-u.ac.jp)

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

Referred to by ATel #: 8547

Following the quiescent state after an anomalous apastron X-ray activity (Atel #6917), the Be/X-ray binary pulsar, GRO J1008-57, has started brightening on 2015 May 09 (MJD 57151). The MAXI/GSC Nova alert system detected that the 4 day averaged source flux in 4-10 keV band exceeded the trigger level on May 10.20 (MJD 57152.20). The source flux of 6 hour binned data in 4-10 keV reached 38 +- 11 mCrab on May 9.90 (MJD 57151.90). According to the orbital parameters (T0=54416.65 (MJD) and Porb=249.48 d ; Kühnel et al. 2013 ), the onset orbital phase of this outburst is 0.93, which is consistent with those of the normal outbursts (Atel #413, #647, #1298, #1304, #1619, #1995, #2313, #2769, #3254, #3796, #3805, #4319, #5004, #5705, #6465). This means that the current brightening would be categorized as the normal outburst. The present situation is similar to that observed after the giant outburst in 2012 (Atel #5004).
The latest source flux can be checked at the following page;
http://maxi.riken.jp/top/index.php?cid=1&jname=J1009-582.