MAXI/GSC detection of a successive X-ray outburst from the black hole candidate XTE J1856+053

ATel #7579; H. Negoro (Nihon U.), D. Itoh (Miyazaki U.), S. Ueno, H. Tomida, S. Nakahira, M. Kimura, M. Ishikawa, Y. E. Nakagawa (JAXA), T. Mihara, 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.), M. Nakajima, T. Masumitsu, K. Tanaka (Nihon U.), Y. Ueda, T. Kawamuro, T. Hori (Kyoto U.), Y. Tsuboi, S. Kanetou (Chuo U.), M. Yamauchi (Miyazaki U.), K. Yamaoka (Nagoya U.), M. Morii (ISM)
on 30 May 2015; 09:13 UT
Credential Certification: Hitoshi Negoro (negoro@phys.cst.nihon-u.ac.jp)

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At 23:18 UT on 2015 May 25, MJD 57167.9708, the MAXI/GSC nova alert system triggered the second outburst from the black hole candidate XTE J1856+053 (Marshall et al. 1996, IAU Circ. #6504). The one-day averaged 2-4 keV and 4-10 keV X-ray fluxes on May 25 were 0.016 +/- 0.008 c/s/cm² (~9 mCrab) and 0.022 +/- 0.006 c/s/cm² (~18 mCrab). Once the 2-10 keV X-ray flux decreased, but the 2-4 keV X-ray flux has increased rapidly since May 28, and reached about 0.075 +/- 0.012 c/s/cm² (~43 mCrab) on May 29. The 4-10 keV X-ray flux on May 29 was 0.023 +/- 0.007 c/s/cm² (~18 mCrab), implying that the source is entering in the soft state.

The first outburst in 2015 started around May 16, MJD 57097 (Suzuki et al. ATel # 7233, Sanna et al. ATel #7228, Rushton et al. 7338), and this outburst is brighter than the first one. Such successive outbursts were expected from past activities in 1996 and 2007 (Levine et al. ATel. #1024, Sala et al. 2007, A&A 489, 1239, also see #7233). The time interval of the onsets of the outbursts is ~70 days, which is similar to those in 2007, 60-100 days.

Followup observations are encouraged.

MAXI Public Data Product of XTE J856+053