MAXI/GSC detection of brightening of a transient LMXB XTE J1810-189

ATel #4752; H. Negoro(Nihon U.), M. Serino, M. Sugizaki, K. Morihana, T. Yamamoto, J. Sugimoto, T. Takagi, T. Mihara, M. Matsuoka (RIKEN), S. Ueno, H. Tomida, S. Nakahira, M. Kimura, M. Ishikawa (JAXA), N. Kawai, M. Morii, R. Usui, K. Ishikawa (Tokyo Tech), A. Yoshida, T. Sakamoto, Y. Nakano (AGU), H. Tsunemi, M. Sasaki (Osaka U.), M. Nakajima, M. Asada (Nihon U.), Y. Ueda, K. Hiroi, M. Shidatsu, R. Sato, T. Kawamuro (Kyoto U.), Y. Tsuboi, M. Higa (Chuo U.) M. Yamauchi, Y. Nishimura, T. Hanayama, K. Yoshidome, Y. Ogawa (Miyazaki U.), K. Yamaoka (ISAS) report on behalf of the MAXI team
on 21 Jan 2013; 10:55 UT
Credential Certification: Motoko Suzuki (motoko@crab.riken.jp)

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MAXI/GSC detected X-ray brightening of a neutron star low mass X-ray binary XTE J1810-189. The source flux was about 40 mCrab (4-10 keV) on 2013 January 5.1 (MJD=56297.1). It indicates that the source exhibits a new outburst. The beginning of this outburst is not clear in the MAXI light curves ( http://maxi.riken.jp/top/index.php?cid=1&jname=J1810-190 ) since the source region was not observed between 2012 December 14 and 2013 January 5. The Swift/BAT light curve, however, shows a sign that the outburst started on 2012 December 10. ( http://heasarc.gsfc.nasa.gov/docs/swift/results/transients/weak/XTEJ1810-189/ ) The source was in the hard state on January 5, as its hardness ratio of the 15-50 keV flux (Swift/BAT) to the 2-20 keV (MAXI/GSC) was 0.14 Crab / 0.03 Crab = 4.7. Here we adopt 0.4 as the hardness threshold between the hard and soft states according to Asai et al. 2012 (PASJ, 64, 128).

The last outburst of this source was observed in March of 2003 (ATel #1424, #1430, #1432, #1441, #1443, #1446, #1633), and the source has remained quiescent since then. The latest light curve and image is available at
http://maxi.riken.jp/top/index.php?cid=1&jname=J1810-190