MAXI/GSC detection of the onset of the X-ray outburst from Be/X-ray binary pulsar A 0535+26

ATel #8977; W. Iwakiri, M. Serino, T. Takagi, T. Mihara (RIKEN), M. Nakajima (Nihon U.), S. Ueno, H. Tomida, S. Nakahira, M. Ishikawa, Y. E. Nakagawa (JAXA), M. Sugizaki, M. Shidatsu, J. Sugimoto, M. Sudo, M. Matsuoka (RIKEN), N. Kawai, N. Isobe, S. Sugita, T. Yoshii, Y. Tachibana, Y. Ono, T. Fujiwara (Tokyo Tech), A. Yoshida, T. Sakamoto, Y. Kawakubo, Y. Kitaoka (AGU), H. Tsunemi, R. Shomura (Osaka U.), H. Negoro, K. Tanaka, T. Masumitsu (Nihon U.), Y. Ueda, T. Kawamuro, T. Hori, A. Tanimoto (Kyoto U.), Y. Tsuboi, R. Sasaki, Y. Nakamura (Chuo U.), M. Yamauchi, D. Itoh, K. Furuya (Miyazaki U.), K. Yamaoka (Nagoya U.), M. Morii (ISM)
on 22 Apr 2016; 16:08 UT
Credential Certification: Motoki Nakajima (nakajima.motoki@nihon-u.ac.jp)

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The MAXI/GSC nova alert system detected an X-ray flux increase from the Be X-ray binary pulsar A 535+262 on 2016 April 21 (MJD 57499) in the 1-day bin light curve. According to the orbital ephemeris (T₀=44943.5(MJD), P_orb=111.0 d ; Giovannelli et al. 2013), the trigger date corresponds to the orbital phase of 0.11. Comparing with the onset phase of the last outburst (Atel#7015), that of the present outburst is delayed by 0.06. On the basis of the MAXI on-demand analysis, the daily-averaged X-ray flux in the 4-10 keV band reached to 0.024 +- 0.005 photons/s/cm² (19 +- 4 mCrab) on MJD 57499. On the other hand, the Swift/BAT hard X-ray transient monitor does not detect any significant flux till MJD 57499. In general, a bright outburst exhibit a rapid flux increase in the hard band (e.g. Atel#2324). Thus the observed fluxes indicate that this outburst do not develop into giant one. The latest light curve can be checked at the following page;
http://maxi.riken.jp/top/index.php?cid=1&jname=J0538+263