{
  "bibcode": "2022GCN.32949....1N",
  "body": "=========================================================================\n\nK. Niinuma (Yamaguchi Univ.), Y. Yonekura (Ibaraki Univ.), K. Fujisawa, \nK. Motogi (Yamaguchi Univ.), and W. Iwakiri (Chiba Univ.)\n\nWe carried out the very long baseline interferometry (VLBI) observations \nof GRB221009A/Swift J1913.1+1946 (Dichiara et al. GCN 32632, ATel 15650) \nat 9:00 - 10:15 UT on October 11, at 8:00 - 9:15 on October 25 and 26, \n2022 (1.82 days, 15.78 days, and 16.78 days after the Fermi-GBM trigger \n(Veres et al. GCN 32632), respectively).\n\nThe observation was performed in both C-band (center frequency of 6856 \nMHz with a bandwidth of 512 MHz) and X-band (center frequency of 8448 \nMHz with a bandwidth of 512 MHz), simultaneously by single baseline \ninterferometry consisting of Yamaguchi-34m radio telescope operated by \nYamaguchi University and Hitachi-32m radio telescope operated by Ibaraki \nUniversity. Both telescopes recorded only left-circular polarization. \nThis array is a part of the Japanese VLBI Network and the baseline \nlength is of 873 km.\n\nGRB221009A/Swift J1913.1+1946 was successfully detected on October 11, \nand its VLBI flux densities were 13+/���3 mJy at 6.86 GHz and of 11+/-3 \nmJy at 8.45 GHz. On the other hand, it was not detected on October 25 \nand 26, and the 5-sigma upper limits of VLBI flux density were 3mJy at \nboth 6.86GHz and 8.45GHz. The bright quasar J1905+1943 was also observed \nto determine the VLBI flux density of GRB221009A/Swift J1913.1+1946. The \nradio emission from the very compact component detected by our VLBI \nobservation showed slightly steep spectrum in radio band on 1.82 days \nafter the Fermi-GBM trigger.\n\n=========================================================================\n\n\n\n-- \nNIINUMA Kotaro\nGraduate School of Sciences and Technology for Innovation,\nYamaguchi Univ., Yoshida 1677-1, Yamaguchi 753-8512, Japan\nPhone: +81-(0)83-933-5759\nE-mail:niinuma@yamaguchi-u.ac.jp\n\n������ ���������\n��������������������� ���������������������\n���753-8512 ������������������������������������������",
  "circularId": 32949,
  "createdOn": 1668832643000,
  "email": "niinuma@yamaguchi-u.ac.jp",
  "subject": "GRB 221009A: Japanese VLBI Network observation",
  "submitter": "Kotaro Niinuma at Yamaguchi University  <niinuma@yamaguchi-u.ac.jp>",
  "eventId": "GRB 221009A"
}