TITLE: GCN CIRCULAR NUMBER: 39038 SUBJECT: GRB 250126A: MAXI/GSC detection DATE: 25/01/26 12:11:19 GMT FROM: Hitoshi Negoro at Nihon University/MAXI team negoro.hitoshi@nihon-u.ac.jp
Y. Okada (Kyoto U.), H. Negoro (Nihon U.), Y. Kawakubo (AGU), M. Nakajima, Y. Kudo, H. Shibui, K. Takagi, H. Takahashi, K. Tatano, H. Nishio (Nihon U.), T. Mihara, S. Yamada, S. Wang, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, M. Serino, S. Sugita, H. Hiramatsu, H. Nishikawa, Y. Kondo, S. Sasao, A. Yoshida (AGU), Y. Tsuboi, H. Sugai, N. Nagashima (Chuo U.), M. Shidatsu, Y. Niida (Ehime U.), I. Takahashi, M. Niwano, N. Higuchi, Y. Yatsu (Tokyo Tech), S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, S. Ogawa, M. Kurihara (JAXA), Y. Ueda, K. Fujiwara (Kyoto U.), M. Yamauchi, Y. Otsuki, T. Hasegawa, M. Nishio (Miyazaki U.), K. Yamaoka (Nagoya U.), M. Sugizaki (Kanazawa U.), W. Iwakiri (Chiba U.), T. Kawamuro (Osaka U.), report on behalf of the MAXI team:
The MAXI/GSC nova alert system triggered on a bright uncatalogued X-ray transient source, probably GRB 250126A (GCN Circ. 39035, 39036), at 05:01:45 UT on January 26, 2025. Assuming that the source flux was constant over the transit, we obtain the source position at (R.A., Dec) = (337.621 deg, -14.383 deg) = (22 30 29, -14 22 58) (J2000) with a statistical 90% C.L. elliptical error region with long and short radii of 0.32 deg and 0.23 deg, respectively. The roll angle of the long axis from the north direction is 50.0 deg counterclockwise. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). The X-ray flux averaged over the scan was 148 +- 29 mCrab (4.0-10.0keV, 1 sigma error). Without assumptions on the source constancy, we obtain a rectangular error box for the transient source with the following corners: (R.A., Dec) = (337.049, -14.721) deg = (22 28 11, -14 43 15) (J2000) (R.A., Dec) = (337.415, -14.977) deg = (22 29 39, -14 58 37) (J2000) (R.A., Dec) = (338.598, -13.378) deg = (22 34 23, -13 22 40) (J2000) (R.A., Dec) = (338.233, -13.124) deg = (22 32 55, -13 07 26) (J2000) There was no significant excess flux in the previous transit at 03:29 UT and in the next transit at 06:34 UT with an upper limit of 20 mCrab for each.
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