{
  "bibcode": "2021GCN.30094....1S",
  "body": "Y. Sugawara (JAXA), H. Negoro, M. Nakajima, K. Kobayashi, K. Asakura, K. Seino (Nihon U.),\nT. Mihara, T. Tamagawa, M. Matsuoka (RIKEN),\nT. Sakamoto, M. Serino, S. Sugita, K. Komachi, A. Yoshida (AGU),\nY. Tsuboi, W. Iwakiri, H. Kawai, Y. Okamoto, S. Kitakoga (Chuo U.),\nM. Shidatsu (Ehime U.),\nN. Kawai, M. Niwano, R. Hosokawa (Tokyo Tech),\nS. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, M. Tominaga, T. Nagatsuka (JAXA),\nY. Ueda, S. Yamada, S. Ogawa, K. Setoguchi, T. Yoshitake, Y. Goto, R. Uematsu (Kyoto U.),\nH. Tsunemi (Osaka U.),\nM. Yamauchi, Y. Nonaka, T. Sato, R. Hatsuda, R. Fukuoka (Miyazaki U.), T. Kawamuro (UDP/NAOJ),\nK. Yamaoka (Nagoya U.),\nY. Kawakubo (LSU),\nM. Sugizaki (NAOC) report on behalf of the MAXI team:\n\nThe MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source \nat 22:51:37 UT on 2021 May 28.\nAssuming that the source flux was constant over the transit,\nwe obtain the source position at\n(R.A., Dec) = (239.539 deg, 5.983 deg) = (15 58 09, +05 58 58) (J2000)\nwith a statistical 90% C.L. elliptical error region\nwith long and short radii of 0.26 deg and 0.22 deg, respectively.\nThe roll angle of long axis from the north direction is 133.0 deg counterclockwise.\nThere is an additional systematic uncertainty of 0.1 deg (90% containment radius).\nWithout assumptions on the source constancy, we obtain a rectangular error\nbox for the transient source with the following corners:\n(238.974, 6.826) deg = (15 55 53, +06 49 33) (J2000)\n(238.661, 6.518) deg = (15 54 38, +06 31 04) (J2000)\n(240.060, 5.113) deg = (16 00 14, +05 06 46) (J2000)\n(240.373, 5.421) deg = (16 01 29, +05 25 15) (J2000)\nThe X-ray flux averaged over the scan was 170 +- 28 mCrab (4.0-10.0keV, 1 sigma error).\nThere was no significant excess flux in the previous transit at 21:18 UT\nand in the next transit at 00:24 on May 29 UT with an upper limit of 20 mCrab for each.",
  "circularId": 30094,
  "createdOn": 1622248707000,
  "email": "serino@phys.aoyama.ac.jp",
  "subject": "GRB 210528B: MAXI/GSC detection",
  "submitter": "Motoko Serino at Aoyama Gakuin U.  <serino@phys.aoyama.ac.jp>",
  "eventId": "GRB 210528B"
}