GCN Circular 32949
Subject
GRB 221009A: Japanese VLBI Network observation
Date
2022-11-19T04:37:23Z (a year ago)
From
Kotaro Niinuma at Yamaguchi University <niinuma@yamaguchi-u.ac.jp>
=========================================================================
K. Niinuma (Yamaguchi Univ.), Y. Yonekura (Ibaraki Univ.), K. Fujisawa,
K. Motogi (Yamaguchi Univ.), and W. Iwakiri (Chiba Univ.)
We carried out the very long baseline interferometry (VLBI) observations
of GRB221009A/Swift J1913.1+1946 (Dichiara et al. GCN 32632, ATel 15650)
at 9:00 - 10:15 UT on October 11, at 8:00 - 9:15 on October 25 and 26,
2022 (1.82 days, 15.78 days, and 16.78 days after the Fermi-GBM trigger
(Veres et al. GCN 32632), respectively).
The observation was performed in both C-band (center frequency of 6856
MHz with a bandwidth of 512 MHz) and X-band (center frequency of 8448
MHz with a bandwidth of 512 MHz), simultaneously by single baseline
interferometry consisting of Yamaguchi-34m radio telescope operated by
Yamaguchi University and Hitachi-32m radio telescope operated by Ibaraki
University. Both telescopes recorded only left-circular polarization.
This array is a part of the Japanese VLBI Network and the baseline
length is of 873 km.
GRB221009A/Swift J1913.1+1946 was successfully detected on October 11,
and its VLBI flux densities were 13+/���3 mJy at 6.86 GHz and of 11+/-3
mJy at 8.45 GHz. On the other hand, it was not detected on October 25
and 26, and the 5-sigma upper limits of VLBI flux density were 3mJy at
both 6.86GHz and 8.45GHz. The bright quasar J1905+1943 was also observed
to determine the VLBI flux density of GRB221009A/Swift J1913.1+1946. The
radio emission from the very compact component detected by our VLBI
observation showed slightly steep spectrum in radio band on 1.82 days
after the Fermi-GBM trigger.
=========================================================================
--
NIINUMA Kotaro
Graduate School of Sciences and Technology for Innovation,
Yamaguchi Univ., Yoshida 1677-1, Yamaguchi 753-8512, Japan
Phone: +81-(0)83-933-5759
E-mail:niinuma@yamaguchi-u.ac.jp
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