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

ATel #7233; K. Suzuki, K. Fukushima, H. Negoro (Nihon U.), S. Ueno, H. Tomida, S. Nakahira, M. Kimura, M. Ishikawa, Y. E. Nakagawa (JAXA), T. Mihara, 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.), M. Nakajima, T. Onodera, M. Fujita, F. Honda, T. Namba (Nihon U.), Y. Ueda, M. Shidatsu, T. Kawamuro, T. Hori (Kyoto U.), Y. Tsuboi, A. Kawagoe (Chuo U.), M. Yamauchi, Y. Morooka, D. Itoh (Miyazaki U.), K. Yamaoka (Nagoya U.)
on 16 Mar 2015; 15:21 UT
Credential Certification: Hitoshi Negoro (negoro@phys.cst.nihon-u.ac.jp)

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At 08:57 UT on 2015 March 16, the MAXI/GSC nova alert system triggered X-ray enhancement at the position

(R.A., Dec) = (284.170 deg, 4.727 deg) = (18 56 40, +04 43 37) (J2000)

with a statistical 90% C.L. elliptical error region with long and short radii of 0.51 deg and 0.42 deg, respectively. The roll angle of long axis from the north direction is 39.0 deg counterclockwise. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). The position is marginally consistent with that of the black hole candidate XTE J1856+053 (Marshall et al. 1996, IAUC # 6504 ) if the systematic uncertainty is included. A hard X-ray increase from this source is also recognized by the Swift/BAT transient monitor (http://swift.gsfc.nasa.gov/results/transients/weak/XTEJ1856p053/).

The 2-10 keV X-ray light curve obtained with MAXI/GSC shows that the X-ray increase has started before March 15, and that the current X-ray flux is about 15 mCrab.

XTE J1856+053 exhibited a few successive outbursts in 1996 and 2007 (Levin et al. ATel #1024), and the peak fluxes were about 100 mCrab (e.g., Sala et al. 2008, A&A 489, 1239). Thus, further increase in the X-ray flux and multiple outbursts are expected. Multi-wavelength followup observations are encouraged.

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