GCN Circular 33831

Y. Umeki (Miyazaki U.), M. Serino (AGU), Y. Kawakubo (LSU), H. Negoro, M. Nakajima, K. Kobayashi, M. Tanaka, Y. Soejima, Y. Kudo (Nihon U.), T. Mihara, T. Kawamuro, S. Yamada, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, S. Sugita, H. Hiramatsu, H. Nishikawa, A. Yoshida (AGU), Y. Tsuboi, S. Urabe, S. Nawa, N. Nemoto (Chuo U.), M. Shidatsu (Ehime U.), I. Takahashi, M. Niwano, S. Sato, N. Higuchi, Y. Yatsu (Tokyo Tech), S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, S. Ogawa, T. Kurihara (JAXA), Y. Ueda, K. Setoguchi, T. Yoshitake, Y. Nakatani (Kyoto U.), M. Yamauchi, Y. Hagiwara, Y. Otsuki (Miyazaki U.), K. Yamaoka (Nagoya U.), M. Sugizaki (NAOC), W. Iwakiri (Chiba U.) report on behalf of the MAXI team: The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source at 05:03:24 UT on 20 May 2023. Assuming that the source flux was constant over the transit, we obtain the source position at (R.A., Dec) = (142.422 deg, 1.524 deg) = (09 29 41, +01 31 26) (J2000) with a statistical 90% C.L. elliptical error region with long and short radii of 0.04 deg and 0.03 deg, respectively. The roll angle of long axis from the north direction is 90.0 deg counterclockwise. Without assumptions on the source constancy, we obtain a rectangular error box for the transient source with the following corners: (142.239, 1.362) deg = (09 28 57, +01 21 43) (J2000) (142.281, 1.327) deg = (09 29 07, +01 19 37) (J2000) (142.576, 1.677) deg = (09 30 18, +01 40 37) (J2000) (142.535, 1.712) deg = (09 30 08, +01 42 43) (J2000) There is an additional systematic uncertainty of 0.1 deg (90% containment radius). The X-ray flux averaged over the scan was 1405 +- 69 mCrab (4.0-10.0keV, 1 sigma error). There was no significant excess flux in the previous transit at 03:30 UT with an upper limit of 20 mCrab.