TITLE: GCN CIRCULAR NUMBER: 26638 SUBJECT: GRB 200105A: MAXI/GSC detection DATE: 20/01/06 00:53:30 GMT FROM: Satoshi Sugita at Aoyama Gakuin U. S. Sugita, M. Serino (AGU), H. Negoro, M. Nakajima, W. Maruyama, M. Aoki, K. Kobayashi, R. Takagi (Nihon U.), T. Mihara, C. Guo, Y. Zhou, T. Tamagawa, M. Matsuoka (RIKEN), T. Sakamoto, H. Nishida, A. Yoshida (AGU), Y. Tsuboi, W. Iwakiri, R. Sasaki, H. Kawai, T. Sato (Chuo U.), M. Shidatsu (Ehime U.), N. Kawai, M. Oeda, K. Shiraishi (Tokyo Tech), S. Nakahira, Y. Sugawara, S. Ueno, H. Tomida, M. Ishikawa, R. Shimomukai, M. Tominaga (JAXA), Y. Ueda, A. Tanimoto, S. Yamada, S. Ogawa, K. Setoguchi, T. Yoshitake (Kyoto U.), H. Tsunemi, T. Yoneyama, K. Asakura, S. Ide (Osaka U.), M. Yamauchi, S. Iwahori, Y. Kurihara, K. Kurogi, K. Miike (Miyazaki U.), T. Kawamuro (NAOJ), K. Yamaoka (Nagoya U.), Y. Kawakubo (LSU), M. Sugizaki (NAOC) report on behalf of the MAXI team: The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source at 21:55:28 UT on 2020 January 05. Assuming that the source flux was constant over the transit, we obtain the source position at (R.A., Dec) = (319.281 deg, -35.846 deg) = (21 17 07, -35 50 45) (J2000) with a statistical 90% C.L. elliptical error region with long and short radii of 0.11 deg and 0.1 deg, respectively. The roll angle of long axis from the north direction is 27.0 deg counterclockwise. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). Without assumptions on the source constancy, we obtain a rectangular error box for the transient source with the following corners: (318.473, -35.441) deg = (21 13 53, -35 26 27) (J2000) (318.374, -35.646) deg = (21 13 29, -35 38 45) (J2000) (320.376, -36.262) deg = (21 21 30, -36 15 43) (J2000) (320.470, -36.054) deg = (21 21 52, -36 03 14) (J2000) The X-ray flux averaged over the scan was 710 +- 50 mCrab (4.0-10.0keV, 1 sigma error). There was no significant excess flux in the previous transit at 20:42 UT with an upper limit of 20 mCrab.