MAXI/GSC detects a quasi-regular outburst and a possible soft state transition in H 1743-322

ATel #3842; H. Negoro (Nihon U.), N. Kawai (Tokyo Tech), S. Nakahira, T. Mihara, M. Sugizaki, M. Serino, T. Yamamoto, T. Sootome, M. Matsuoka (RIKEN), S. Ueno, H. Tomida, M. Kohama, M. Ishikawa (JAXA), 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.), M. Nakajima, F. Suwa, M. Asada, H. Sakakibara (Nihon 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 1 Jan 2012; 14:15 UT
Credential Certification: Hitoshi Negoro (negoro@phys.cst.nihon-u.ac.jp)

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MAXI/GSC detected renewed activity from the Galactic black hole candidate H 1743-322 on December 22, 2011 (MJD 55917) with a flux of 29±8 mCrab in the 4-10 keV band. The source was slightly visible in an image on December 19, but solar X-rays and invisible areas of detectors did not allow us to confirm the source activity until December 22. The 2-20 keV flux has increased since December 22, and the spectrum became soft on December 31. One-day averaged 2-4 keV and 4-10 keV fluxes changed from 20±6 mCrab and 42±6 mCrab, respectively, on December 30 to 41±7 mCrab and 51±6 mCrab on December 31, implying that the source made a transition to a soft state.

This is the 4th renewed outburst that MAXI detected since August 2009, and the outbursts almost regularly take place at intervals of 7-8 months. The last outburst started on 2011 April 6 (Kuulers et al. ATel #3263. also see #3267, #3277, #3280). H 1743-322 is one of the two black hole candidates exhibiting quasi-regular outbursts. The other is 4U 1630-472, currently in outburst (Nakarira et al. ATel #3830), showing about 1.8 yr quasi-periodicity.

From the previous outburst profiles, it is expected that the 2-10 keV flux will rapidly increase and double in a few days. Note that the data are obtained only with the detectors with high voltages lowered to 1550 V, which are not well calibrated, so that the data are not publicly available, yet. The data will be soon available at the site http://maxi.riken.jp/top/index.php?cid=1&jname=J1746-322 .

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