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MAXI/GSC detection of a soft-to-hard state transition of the BHC Swift J1910.2-0546 / MAXI J1910-057

ATel #4273; S. Nakahira (JAXA), Y. Ueda (Kyoto U.), T. Takagi, T. Mihara, M. Sugizaki, M. Serino, T. Yamamoto, J. Sugimoto, M. Matsuoka (RIKEN), S. Ueno, H. Tomida, M. Ishikawa (JAXA), N. Kawai, M. Morii, R. Usui, K. Ishikawa, T. Yoshii (Tokyo Tech), H. Negoro, M. Nakajima, M. Asada, H. Sakakibara, N. Serita (Nihon U.), A. Yoshida (AGU), H. Tsunemi, M. Kimura (Osaka U.), K. Hiroi, M. Shidatsu, R. Sato (Kyoto U.), Y. Tsuboi, M. Higa (Chuo U.) M. Yamauchi, Y. Nishimura, T. Hanayama, K. Yoshidome (Miyazaki U.), K. Yamaoka (Waseda U.) report on behalf of the MAXI team
on 25 Jul 2012; 01:15 UT
Credential Certification: Satoshi NAKAHIRA (nakahira@crab.riken.jp)

Subjects: X-ray, Binary, Black Hole, Transient

Referred to by ATel #: 4295, 4328, 4347

We report on an ongoing soft-to-hard transition of the newly discovered X-ray transient Swift J1910.2-0546/MAXI J1910-057 (Krimm at al. #4139, Usui et al.#4140). Immediately after the discovery of the source, it entered into the soft state or intermediate/very high state (Kimura et al.#4198).
The 2-10 keV X-ray flux peaked at ∼1 Crab on MJD56088, and then decayed down to 190 mCrab on MJD56120-56125. Meanwhile the innermost disk temperature obtained from the MAXI/GSC spectra by employing a multi-color disk plus a power-law model changed from ∼0.6 keV to ∼0.45 keV. At 2012-07-24T04:29 (MJD56132.1868), the MAXI/GSC nova alert system triggered on a gradual spectral change of Swift J1910.2-0546 / MAXI J1910-057. The recent light curve of MAXI/GSC shows an increase of the 4-10 keV X-ray flux against the 2-4 keV flux. The 2-4 keV flux slightly decreased from 310 ± 16 mCrab (MJD56127.0-56130.0) to 270 ± 13 mCrab (MJD 56131.0-56132.5), while the 4-10 keV X-ray flux increased from 33 ± 8 mCrab (MJD56127.0-56130.0) to 77 ± 8 mCrab (MJD56131.0-56132.0), and then to 112 ± 12 mCrab (MJD56132.0-56132.5). We suggest that the source is entering into the hard state.
Further observations are encouraged.
The latest source flux can be checked at the following page: http://maxi.riken.jp/top/index.php?cid=1&jname=J1910-057