TITLE: GCN CIRCULAR NUMBER: 10596 SUBJECT: GRB 100415A: MAXI/GSC detection of a probable GRB DATE: 10/04/15 12:42:26 GMT FROM: Motoko Suzuki at RIKEN T. Sootome, T. Mihara, Y.E. Nakagawa, M. Sugizaki, M. Suzuki, T. Yamamoto (RIKEN), M. Matsuoka, K. Kawasaki, S. Ueno, H. Tomida, M. Kohama, M. Ishikawa (JAXA), N. Kawai, M. Morii, K. Sugimori (Tokyo Tech), A. Yoshida, K. Yamaoka, S. Nakahira (AGU), H. Tsunemi, M. Kimura (Osaka U.), H. Negoro, M. Nakajima H. Ozawa, F. Suwa (Nihon U.), Y. Ueda, N. Isobe, S. Eguchi, K. Hiroi (Kyoto U.), A. Daikyuji (Miyazaki U.), A. Uzawa, T. Matsumura, K. Yamazaki (Chuo U.) report on behalf of the MAXI team: At the scan transit centered at UT 2010-04-15T03:44:57, MAXI/GSC detected a short X-ray transient lasting about 23 seconds within the 50 seconds triangular transit response of MAXI/GSC.  Judging from its location and spectral hardness ratio, this transient is probably a gamma-ray burst. 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) = (+7.48 deg, -15.57 deg) = (00 29 55, -15 34 12)(J2000) (R.A., Dec) = (+6.91 deg, -15.86 deg) = (00 27 38, -15 51 36)(J2000) (R.A., Dec) = (+7.92 deg, -17.25 deg) = (00 31 41, -17 15 00)(J2000) (R.A., Dec) = (+8.49 deg, -16.96 deg) = (00 33 58, -16 57 36)(J2000) There is additional systematic uncertainty of 0.2 deg (90% containment radius). The preliminary flux (4-10 keV) of the source was at least 170 mCrab. There was no significant detection at the transit location in the previous and following orbits (92 min before or after the detection) with an upper limit of 20 mCrab. There is no known bright X-ray source at the detected position. Follow-up observations are encouraged.