MAXI/GSC detection of brightening of a transient LMXB 4U1608-52

ATel #4478; J. Sugimoto, T. Mihara, M. Sugizaki, K. Asai, M. Matsuoka, T. Yamamoto, M. Serino (RIKEN), S. Ueno, H. Tomida, S. Nakahira, M. Ishikawa (JAXA), N. Kawai, M. Morii, R. Usui, K. Ishikawa (Tokyo Tech), A. Yoshida, T. Sakamoto (AGU), H. Tsunemi, M. Kimura (Osaka U.), H. Negoro, M. Nakajima, M. Asada, H. Sakakibara, N. Serita (Nihon U.), Y. Ueda, 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 12 Oct 2012; 10:26 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Tatehiro Mihara (mihara@crab.riken.jp)

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MAXI/GSC detected X-ray brightening of a Low Mass X-ray Binary, 4U1608-52. The source flux began to increase on 2012 October 10.7 (MJD=56210.7), and reached about 0.2 Crab (4-10 keV) on 2012 October 11.7 (MJD 56211.7). It indicates that the source exhibits a new outburst. Swift/BAT also detected the beginning of this outburst on October 11 http://swift.gsfc.nasa.gov/docs/swift/results/transients/H1608-522/
The hardness ratio of the 15-50 keV flux in Swift/BAT to the 2-20 keV in MAXI/GSC was 0.011 Crab / 0.13 Crab = 0.08 on October 11, which indicates that the source was already in the soft state. We used 0.4 for the hardness threshold between the hard and the soft state according to Asai et al. 2013 (http://arxiv.org/abs/1206.3927).
The period from the outburst onset to the hard-to-soft transition was <~ 1 day, which is classified as the Fast-type outburst. The latest light curve and image is available at
http://maxi.riken.jp/top/index.php?cid=1&jname=J1612-524