{
  "circularId": 39956,
  "format": "text/plain",
  "bibcode": "2025GCN.39956....1T",
  "eventId": "GRB 250331A",
  "submitter": "Yuta Kawakubo at Aoyama Gakuin University <kawakubo@phys.aoyama.ac.jp>",
  "createdOn": 1743392669587,
  "body": "K. Takagi, M. Nakajima (Nihon U.), Y. Kawakubo, M. Serino (AGU),\nH. Negoro, Y. Kudo, H. Shibui, H. Takahashi, K. Tatano, H. Nishio (Nihon U.),\nT. Mihara, S. Yamada, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN),\nT. Sakamoto, S. Sugita, H. Hiramatsu, H. Nishikawa, Y. Kondo, S. Sasao, A. Yoshida (AGU),\nY. Tsuboi, H. Sugai, N. Nagashima (Chuo U.),\nM. Shidatsu, Y. Niida, C. Kang, T. Nakamoto (Ehime U.),\nI. Takahashi, M. Niwano, N. Higuchi, Y. Yatsu (Tokyo Tech),\nS. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, S. Ogawa, M. Kurihara (JAXA),\nY. Ueda, Y. Okada, K. Fujiwara (Kyoto U.),\nM. Yamauchi, Y. Otsuki, T. Hasegawa, M. Nishio (Miyazaki U.),\nK. Yamaoka (Nagoya U.),\nM. Sugizaki (Kanazawa U.),\nW. Iwakiri (Chiba U.),\nT. Kawamuro (Osaka U.)\nreport on behalf of the MAXI team:\n\nThe MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient \nsource at 01:40:54 UT on March 31, 2025. Assuming that the source flux was constant\nover the transit, we obtain the source position at\n(R.A., Dec) = (124.987 deg, -18.636 deg) = (08 19 56, -18 38 09) (J2000)\nwith a statistical 90% C.L. elliptical error region with long and short radii of 0.25 deg\nand 0.2 deg, respectively.\nThe roll angle of long axis from the north direction is 168.0 deg counterclockwise.\nThere is an additional systematic uncertainty of 0.1 deg (90% containment radius).\nThe X-ray flux averaged over the scan was 146 +- 23 mCrab\n(4.0-10.0keV, 1 sigma error).\n\nWithout assumptions on the source constancy, we obtain a rectangular error\nbox for the transient source with the following corners:\n(124.498, -17.690) deg = (08 17 59, -17 41 24) (J2000)\n(124.178, -17.935) deg = (08 16 42, -17 56 05) (J2000)\n(125.521, -19.513) deg = (08 22 05, -19 30 46) (J2000)\n(125.843, -19.266) deg = (08 23 22, -19 15 57) (J2000)\n\nThere was no significant excess flux in the previous transit at 0:08 UT\nand in the next transit at 03:14 UT with an upper limit of 20 mCrab for each.",
  "submittedHow": "web",
  "subject": "GRB 250331A: MAXI/GSC detection"
}