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MAXI/GSC detection of the X-ray outbursts from Be/X-ray binary pulsars, 4U 0115+63 and GRO J1008-57

ATel #9512; M. Nakajima, T. Kawase, H. Negoro (Nihon U.), T. Mihara (RIKEN), H. Tomida, S. Ueno, S. Nakahira, M. Ishikawa, Y. Sugawara (JAXA), Y. E. Nakagawa (JAMSTEC), M. Sugizaki, M. Serino, W. Iwakiri, M. Shidatsu, J. Sugimoto, T. Takagi, M. Matsuoka (RIKEN), N. Kawai, N. Isobe, S. Sugita, T. Yoshii, Y. Tachibana, Y. Ono, T. Fujiwara, S. Harita, Y. Muraki (Tokyo Tech), A. Yoshida, T. Sakamoto, Y. Kawakubo, Y. Kitaoka (AGU), H. Tsunemi, R. Shomura (Osaka U.), K. Tanaka, T. Masumitsu (Nihon U.), Y. Ueda, T. Kawamuro, T. Hori, A. Tanimoto (Kyoto U.), Y. Tsuboi, Y. Nakamura, R. Sasaki (Chuo U.), M. Yamauchi, K. Furuya (Miyazaki U.), K. Yamaoka (Nagoya U.)
on 20 Sep 2016; 04:10 UT
Credential Certification: Motoki Nakajima (nakajima.motoki@nihon-u.ac.jp)

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

We report the onsets of X-ray outbursts from 4U 0115+63 and GRO J1008-57 triggered by the MAXI/GSC nova-alert system (Negoro et al. 2016).

The X-ray brightening of GRO J1008-57 was detected on 2016 September 17 (MJD 57648). The 4-10 keV flux of 1-day-binned data reached 0.041 +- 0.007 photons/s/cm2 (36 +- 6 mCrab) on 2016 September 19 (MJD 57650). The trigger date of the outburst onset corresponds to the orbital phase of ~0.92 which is derived with the following orbital parameters, T0=54416.65 (MJD) and Porb=249.48 d (Kühnel et al. 2013). The present onset phase and the moderate flux increase indicate that the current brightening is a normal outburst followed by the previous ones (Kretschmar et al. Atel#8547 and references therein). Swift/BAT also detects the current X-ray brightening. The 15-50 keV flux on September 17 (MJD 57648) is 0.0126 +- 0.0020 counts/s/cm2 (57 +- 9 mCrab).

The X-ray outburst from 4U 0115+63 was triggered on 2016 September 16. The current brightening started from September 16 (MJD 57647), or the orbital phase of 0.12 (Raichur et al. 2010; Porb=24.3174 d, T0=53243.038(MJD)). The 4-10 keV flux reached 0.081 +- 0.011 photons/s/cm2 (70 +- 9 mCrab) on September 19 (MJD 57650). From this source, MAXI/GSC has detected 3 consecutive outbursts synchronized with its orbital period so far (Atel#9291). Comparing with the previous outburst profiles, the onset phase and the flux increase rate are comparable with the previous ones. Thus, the current brightening would be a normal outburst. The 15-50 keV flux observed by Swift/BAT has also shown a moderate increase, and it reached 0.0092 +- 0.0013 counts/s/cm2 (42 +- 6 mCrab) on September 19 (MJD 57650).