TITLE: GCN CIRCULAR NUMBER: 12360 SUBJECT: MAXI/GSC detection of a short soft X-ray transient DATE: 11/09/20 09:39:23 GMT FROM: Motoko Suzuki at RIKEN M. Kohama(JAXA), T. Toizumi(Tokyo Tech), H. Negoro (Nihon U.), M. Serino(RIKEN), S. Ueno, H. Tomida, M. Ishikawa (JAXA), M. Matsuoka ,T. Mihara, M. Sugizaki, S. Nakahira, T. Yamamoto, T. Sootome (RIKEN), N. Kawai, M. Morii, K. Sugimori, R. Usui (Tokyo Tech), A. Yoshida, K. Yamaoka (AGU), H. Tsunemi, M. Kimura, H. Kitayama (Osaka U.), M. Nakajima, F. Suwa (Nihon U.), Y. Ueda, K. Hiroi, M. Shidatsu (Kyoto U.), Y. Tsuboi, T. Matsumura, K. Yamazaki (Chuo U.) report on behalf of the MAXI team: MAXI/GSC triggered at UT 2011-09-16T20:33:01 on a bright uncatalogued soft X-ray transient source. The best-fit position of the source is (R.A., Dec) = (+171.57 deg, -17.71 deg) = (11 26 16, -17 42 22)(J2000) Since the emission was detected only for a fraction of the triangular transit response, the uncertainty of its position along the scan direction is large. Without assuming the source constancy, we obtain a rectangular error box (90%C.L.) with the following corners: (R.A., Dec) = (+170.94 deg, -17.43 deg) = (11 23 45, -17 25 47)(J2000) (R.A., Dec) = (+171.14 deg, -17.18 deg) = (11 24 34, -17 10 35)(J2000) (R.A., Dec) = (+172.19 deg, -18.00 deg) = (11 28 46, -17 59 51)(J2000) (R.A., Dec) = (+171.98 deg, -18.24 deg) = (11 27 55, -18 14 37)(J2000) The preliminary flux (4-10 keV) of the source is approximately 150 mCrab. There was no significant detection at this position in the previous and the following transits (92 min before and after the detection) with an upper limit of 20 mCrab. There is no known bright source at the detected position.