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GCN Circular 34735

Detection of self-absorbed radio emission from GRB 230812B with the JVLA + uGMRT
2023-09-19T03:00:15Z (8 months ago)
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Poonam Chandra (NRAO), Tomas Ahumada (UMD), Varun Bhalerao (IITB), Gaurav Waratkar (IITB), Gokul Srinivasaragavan (UMD), Suchindram Dasgupta (Rutgers), Mansi Kasliwal (Caltech), Shreya Anand (Caltech), Viswajit Swain (IITB), David Kaplan (UWM),  Harsh Kumar (IITB) and Daniel Perley (LJMU) report on behalf of a larger collaboration:

We observed GRB 230812B (Fermi GBM Team, GCN Circ. 34386) with Karl G. Jansky Very Large Array on Sep 2, 2023 during 18:24:52 - 19:53:33 UT (proposal # 23B-292) in X (8-12 GHz), C (4-8 GHz) and S (2-4 GHz) bands and with the upgraded Giant Metrewave Radio Telescope (uGMRT)  on Sep 17, 2023, 11:30:00 UT (proposal # DDT C305)  in band 5 (1000-1450 MHz). We detect the GRB in the three  observed JVLA bands with S, C, X bands flux densities to be  30.6+/-11.2, 49.2+/-7.9 uJy and 28.2+/-10.1 uJy, respectively. The GRB is not detected in the uGMRT band 5 with a 3-sigma upper limit of ~40 uJy, consistent with the results of Mohnani et al., (GCN Circ. 34727). This indicates that the GRB is in the optically thin regime at  C band and higher frequencies, however, it is self-absorbed at lower frequencies, i.e. JVLA S band and the uGMRT band 5.

We thank the VLA and GMRT staff for carrying out the observations. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.  GMRT is run by the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research. More observations are planned. 

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