TITLE: GCN CIRCULAR NUMBER: 44176 SUBJECT: GRB 260401A: MAXI/GSC detection DATE: 26/04/01 14:47:29 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo@phys.aoyama.ac.jp> T. Usuki (Ehime U.), K. Fujiwara (Kyoto U.), M. Serino, Y. Kawakubo (AGU), M. Nakajima, H. Negoro, K. Takagi, H. Nishio (Nihon U.), T. Mihara, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, S. Sugita, H. Hiramatsu, Y. Kondo, D. Iijima, A. Yoshida (AGU), Y. Tsuboi, H. Sugai, N. Nagashima, Y. Ishihara (Chuo U.), M. Shidatsu, C. Kang, T. Nakamoto, M. Uenishi, S. Yatsuzuka (Ehime U.), I. Takahashi, Y. Yatsu (Science Tokyo), S. Nakahira, S. Ueno, H. Tomida, S. Ogawa, M. Kurihara (JAXA), Y. Ueda, S. Kobayashi (Kyoto U.), M. Yamauchi, M. Nishio, C. Hiraizumi (Miyazaki U.), K. Yamaoka (Nagoya U.), M. Sugizaki (Kanazawa U.), W. Iwakiri (Chiba U.), T. Kawamuro (Osaka U.), S. Yamada (Tohoku U) report on behalf of the MAXI team: The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source at 10:53:19 UT on 2026 April 1. Assuming that the source flux was constant over the transit, we obtain the source position at (R.A., Dec) = (219.942 deg, -17.349 deg) = (14 39 46, -17 20 56) (J2000) with a statistical 90% C.L. elliptical error region with long and short radii of 0.06 deg and 0.02 deg, respectively. The roll angle of long axis from the north direction is 15.0 deg counterclockwise. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). The X-ray flux averaged over the scan was 5700 +- 200 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) = (220.028, -17.391) deg = (14 40 06, -17 23 27) (J2000) (R.A., Dec) = (220.046, -17.270) deg = (14 40 11, -17 16 11) (J2000) (R.A., Dec) = (219.512, -17.198) deg = (14 38 02, -17 11 52) (J2000) (R.A., Dec) = (219.494, -17.319) deg = (14 37 58, -17 19 08) (J2000) There was no significant excess flux in the previous transit at 09:20 UT and in the next transit at 12:26 UT with an upper limit of 20 mCrab for each. This event is spatially and temporally consistent with GRB 260401A, which was also detected by Fermi/GBM (GCN #44174, #44175). View this GCN Circular online at https://gcn.nasa.gov/circulars/44176. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...