GCN Circular 33243

S. Giarratana (University of Bologna, INAF-IRA), M. Giroletti 
(INAF-IRA), T. An (Shanghai A.O.), G. Anderson (Curtin University), P. 
Atri (ASTRON), J. S. Bright (University of Oxford), R. Fender 
(University of Oxford), G. Ghirlanda (INAF-OAB), J. K. Leung (University 
of Sydney, CSIRO), B. Marcote (JIV-ERIC), M. P��rez-Torres (IAA-CSIC), L. 
Rhodes (University of Oxford), O. S. Salafia (INAF-OAB), J. Yang (OSO)

On UT 2022 November 18 and 21 (40 and 43 days post-burst) we observed 
the radio counterpart of GRB 221009A (Dichiara et al, GCN 32632
Not found
 
 
; Veres 
et al., GCN 32636
Not found
 
 
) with the European VLBI Network (EVN) at a central 
frequency of 8.3 and 5 GHz, respectively.

 From a preliminary analysis, the source is clearly detected at both 
frequencies with >30 sigma significance. The 8.3 GHz surface brightness 
peak is ~1.3 mJ/beam. The synthesized beam is 0.9 x 0.5 mas (PA = 7.7 
deg). The 5 GHz surface brightness peak is ~1.4 mJy/beam. The 
synthesized beam is 1.7 x 0.9 mas (PA = 9.25 deg).

The source is found at a position within ~1 mas of the one previously 
reported by Atri et al., GCN 32907
Not found
 
 
 with the VLBA at 15.2 GHz. The offset 
is most likely accounted for by systematics.

All the results presented here are preliminary. Further analysis is in 
progress. We will report the final results in a forthcoming publication.

We would like to thank the directors and staff of all the EVN telescopes 
for approving, executing, and processing these out-of-session ToO 
observations.

The European VLBI Network is a joint facility of independent European, 
African, Asian, and North American radio astronomy institutes. 
Scientific results from data presented in this publication are derived 
from the following EVN project code: RG013.