MAXI/GSC detection of an X-ray enhancement possibly from a variable star HD 347929/1RXS J180724.2+194217
ATel #5075; H. Negoro, T. Onodera (Nihon U), Y. Ogawa (Miyazaki U.), M. Serino (RIKEN), S. Ueno, H. Tomida, S. Nakahira, M. Kimura, M. Ishikawa, Y. Nakagawa (JAXA), T. Mihara, M. Sugizaki, M. Morii, T. Yamamoto, J. Sugimoto, T. Takagi, M. Matsuoka (RIKEN), N. Kawai, R. Usui, K. Ishikawa, T. Yoshii (Tokyo Tech), A. Yoshida, T. Sakamoto, Y. Nakano, Y. Kawakubo (AGU), H. Tsunemi, M. Sasaki (Osaka U.), M. Nakajima, K. Fukushima, K. Suzuki (Nihon U.), Y. Ueda, M. Shidatsu, T. Kawamuro (Kyoto U.), Y. Tsuboi, M. Higa (Chuo U.), M. Yamauchi, K. Yoshidome, H. Yamada (Miyazaki U.), K. Yamaoka (Nagoya U.) report on behalf of the MAXI team
on 20 May 2013; 14:00 UT
Credential Certification: Hitoshi Negoro (negoro@phys.cst.nihon-u.ac.jp)
Subjects: X-ray, Star, Transient, Variables
On May 20, 2013, MAXI/GSC detected an X-ray enhancement from the position at (R.A., Dec.) = (271.75 deg, 19.65 deg) = (18 07 0, +19 38 60) (J2000) with a 90% C.L. statistical error of 0.3 deg and an additional systematic uncertainty of 0.1 deg (90% containment radius), if a constant source flux is assumed.
The enhanced emission has been recognized since the scan transit at 08:52 on May 19, 2013 (UT). At previous scan transits, the region was in an undetectable area of the detectors for about 1 day. Thus, the start time of this event is uncertain, but a linear extrapolation of the observed gradual increase in X-ray flux suggests that its started around the beginning of May 19.
The average 4-10 keV flux during eight scan transits from 11:58 to 22:48 on May 19 was 30+- 5 mCrab, and that of the following three scan transits up to 03:26 on May 20 was 22+-7 mCrab.
The source position is consistent with that of a variable star HD 347929 (1RXS J180724.2+194217), apart from the best position by 6.6 arcmin, and a similar X-ray flux was observed from the source with MAXI/GSC on June 27, 2010 (Usui et al. ATel #2700, also see Keanna et al. ATel #2701). However, a possibility of a new X-ray transient cannot be excluded. We tentatively name the source MAXI J1807+196.
Followup observations are encouraged.
