MAXI/GSC detection of a possible X-ray flare from an RS CVn star Sigma Gem
M. Serino (RIKEN), Y. Tsuboi, A. Kawagoe (Chuo U.), S. Ueno, H. Tomida, S. Nakahira, M. Kimura, M. Ishikawa, Y. E.   Nakagawa (JAXA), T. Mihara, M. Sugizaki, M. Morii, J. Sugimoto, T. Takagi, A.   Yoshikawa, M. Matsuoka (RIKEN), N. Kawai, T. Yoshii, Y. Tachibana (Tokyo Tech), A. Yoshida, T. Sakamoto, Y. Kawakubo, H. Ohtsuki (AGU), H. Tsunemi, D. Uchida (Osaka U.), H. Negoro, M. Nakajima, K. Fukushima, T. Onodera, K. Suzuki, T. Namba,   M. Fujita, F. Honda (Nihon U.), Y. Ueda, M. Shidatsu, T. Kawamuro, T. Hori (Kyoto U.), M. Yamauchi, Y. Morooka, D. Itoh (Miyazaki U.), K. Yamaoka (Nagoya U.)
MAXI/GSC observed a possible X-ray flare from an RS CVn star Sigma Gem. The flux started to increase at 13:32:36 UT on December 12th 2014, and dimmed at 18:11:07 UT on the same day. The position of the X-ray enhancement is (115.377 deg, 29.076 deg) = (07 41 30, +29 04 33) (J2000) with a statistical 90% C.L. elliptical error region with long and short radii of 0.44 deg and 0.38 deg respectively. The roll angle of long axis from the north direction is 34.0 deg counterclockwise. The position was determined with the data obtained at three scan transits from 13:32:36 UT on December 12th to 16:45:20 UT on the same day. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). This position is consistent with that of an RS CVn star, Sigma Gem. No other source listed in the ROSAT Bright Source Catalog is in the error region. The 4-10 keV flux averaged over the three scan transits was about 57+-15 mCrab. These are corresponding to a luminosity of 2× 10 32 ergs/s for an assumed distance of 38 pc. This is the first detection of this source with MAXI/GSC.
x-ray,star,variables