{
  "submitter": "Wataru Iwakiri at Chiba University <iwakiri.wataru.buz@gmail.com>",
  "subject": "GRB260616C: MAXI/GSC detection",
  "eventId": "GRB 260616C",
  "body": "W. Iwakiri (Chiba U.),M. Serino(AGU),\nH. Negoro, M. Nakajima, K. Saito, T. Yokoyama, M. Wada (Nihon U.), \nT. Mihara, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), \nT. Sakamoto, S. Sugita, Y. Kawakubo, H. Hiramatsu, A. Yoshida (AGU), \nY. Tsuboi, Y. Ishihara, H. Ogaki (Chuo U.), \nM. Shidatsu, C. Kang, M. Uenishi, T. Usuki, S. Yatsuzuka, H. Aoe (Ehime U.),\nI. Takahashi, Y. Yatsu (Science Tokyo), \nS. Nakahira, S. Ueno, H. Tomida, M. Kurihara (JAXA), \nY. Ueda, K. Fujiwara, S. Kobayashi (Kyoto U.), \nM. Yamauchi, M. Nishio, C. Hiraizumi (Miyazaki U.), \nK. Yamaoka (Nagoya U.),\nM. Sugizaki (Kanazawa U.),\nT. Kawamuro (Osaka U.), \nS. Yamada (Tohoku U),\nS. Ogawa (TUS)\nreport on behalf of the MAXI team:\n\nThe MAXI/GSC detected a bright uncatalogued X-ray transient source at 14:47 UT \non June 16 2026.\nAssuming that the source flux was constant over the transit,\nwe obtain the source position at\n(R.A., Dec) = (67.745 deg, 9.294 deg) = (04 30 58, +09 17 38) (J2000)\nwith a statistical 90% C.L. elliptical error region\nwith long and short radii of 0.39 deg and 0.3 deg, respectively.\nThe roll angle of long axis from the north direction is 22.0 deg counterclockwise.\nThere is an additional systematic uncertainty of 0.1 deg (90% containment radius).\nThe X-ray flux averaged over the scan was 148 +- 33 mCrab\n(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(66.883, 10.254) deg = (04 27 31, +10 15 14) (J2000)\n(66.471, 9.596) deg = (04 25 53, +09 35 45) (J2000)\n(68.604, 8.290) deg = (04 34 24, +08 17 23) (J2000)\n(69.019, 8.945) deg = (04 36 04, +08 56 42) (J2000) \n\nA marginal excess of about 50 mCrab may be present in the previous and next MAXI scans at 13:14 UT and 16:20 UT, respectively. However, these scans were obtained during a period of large background variations, and the significance of the excesses is currently unclear.\nThe possible presence of X-ray activity over multiple scans raises the possibility that this event is a new X-ray transient source rather than a GRB. We therefore tentatively name the source MAXI J0430+092. Multi-wavelength follow-up observations are encouraged.",
  "circularId": 44961,
  "submittedHow": "web",
  "createdOn": 1781666282442,
  "format": "text/plain"
}