MAXI/GSC detection of an outburst from a black hole candidate 4U 1630-472

ATel #3830; S. Nakahira(RIKEN), H. Negoro(Nihon U.), T. Mihara, M. Sugizaki, M. Serino, T. Yamamoto, T. Sootome, M. Matsuoka (RIKEN), M. Nakajima, F. Suwa M. Asada, H. Sakakibara (Nihon U.), S. Ueno, H. Tomida, M. Kohama, M. Ishikawa (JAXA), N. Kawai, M. Morii, K. Sugimori, R. Usui, T. Toizumi, Y. Aoki, S. Song (Tokyo Tech), A. Yoshida, K. Yamaoka (AGU), H. Tsunemi, M. Kimura, H. Kitayama (Osaka U.), Y. Ueda, K. Hiroi, M. Shidatsu (Kyoto U.), Y. Tsuboi, T. Matsumura, K. Yamazaki (Chuo U.), M. Yamauchi, Y. Nishimura, T. Hanayama (Miyazaki U.) report on behalf of the MAXI team
on 28 Dec 2011; 04:02 UT
Credential Certification: Satoshi NAKAHIRA (nakahira@crab.riken.jp)

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We report on a detection of a renewed outburst from a black hole candidate 4U 1630-472 with MAXI/GSC. The source was first detected on 2011 December 17 (MJD 55912) at 35±5 mCrab (2-20 keV), and increased to 135±5 mCrab on MJD 55915 and 168±8 mCrab on MJD 55920. Then it has rapidly increased since December 26 (MJD 55921), and reached 360±10 mCrab on MJD 55922.
The spectrum until MJD 55920 is described by a heavily absorbed multi-colored disk blackboby with a powerlaw model. Along with the Suzaku observation of the 4U 1630-472 by Kubota et al. (PASJ 59, S185, 2007), under the assumption of hydrogen column density of 8 × 10²² cm^-2, distance of 10 kpc and inclination angle of 70 degree and the photon index of 2.5, the innermost temperature and the radius are obtained as 1.48 (-0.07/+0.05) keV and 24 (-2/+3) km, respectively, from the GSC spectrum between MJD 55915 and 55920. The innermost radius is consistent with the result in Kubota et al. Thus we conclude the source currently in outburst is 4U 1630-472.
The latest source flux can be checked at the following page; http://maxi.riken.jp/top/index.php?cid=1&jname=J1634-473