{
  "circularId": 41602,
  "eventId": "GRB 250830B",
  "submittedHow": "web",
  "createdOn": 1756532242503,
  "format": "text/plain",
  "submitter": "Hitoshi Negoro at Nihon University/MAXI team <negoro.hitoshi@nihon-u.ac.jp>",
  "subject": "GRB 250830B: MAXI/GSC detection",
  "bibcode": "2025GCN.41602....1U",
  "body": "T. Usuki (Ehime U.), H. Negoro, M. Nakajima, K. Takagi, H. Takahashi, H. Nishio  (Nihon U.),\nT. Mihara, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, M. Serino, S. Sugita, \nY. Kawakubo, H. Hiramatsu, Y. Kondo, A. Yoshida (AGU), Y. Tsuboi, H. Sugai, N. Nagashima, \nY. Ishihara (Chuo U.), M. Shidatsu, C. Kang, T. Nakamoto (Ehime U.), I. Takahashi, \nY. Yatsu (Science Tokyo), S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, S. Ogawa, M. Kurihara (JAXA), Y. Ueda, K. Fujiwara (Kyoto U.), M. Yamauchi, M. Nishio, C. Hiraizumi (Miyazaki U.), \nK. Yamaoka (Nagoya U.), M. Sugizaki (Kanazawa U.), W. Iwakiri (Chiba U.), T. Kawamuro (Osaka U.), \nS. Yamada (Tohoku U),report on behalf of the MAXI team:\n\nThe MAXI/GSC nova alert system triggered on a bright uncatalogued X-ray transient source \nat 03:56:44 UT on August 30, 2025. Assuming that the source flux was constant over the transit,\nwe obtain the source position at\n(R.A., Dec) = (105.209 deg, -64.628 deg) = (07 00 50, -64 37 40) (J2000)\nwith a 90% C.L. statistical error of 0.33 deg and an additional systematic uncertainty of \n0.1 deg (90% containment radius).\nThe X-ray flux averaged over the scan was 225 +- 36 mCrab (4.0-10.0keV, 1 sigma error).\nWithout assumptions on the source constancy, we obtain a rectangular error\nbox for the transient source with the following corners:\n(R.A., Dec) = (105.751, -63.592) deg = (07 03 00, -63 35 31) (J2000)\n(R.A., Dec) = (104.300, -63.666) deg = (06 57 11, -63 39 57) (J2000)\n(R.A., Dec) = (104.713, -65.344) deg = (06 58 51, -65 20 38) (J2000)\n(R.A., Dec) = (106.255, -65.266) deg = (07 05 01, -65 15 57) (J2000)\nThere was no significant excess flux in the previous transit at 02:23 UT \nand in the next transit at 05:30 UT with an upper limit of 20 mCrab for each.\n\nWe requested Swift/XRT followup observation. "
}