DOI

https://doi.org/10.48717/s29w-se25

Project

RG010

Title

e-EVN: rsm05, ep118a, rg010a

Abstract

We propose to observe the radio counterpart of GRB190829A, the third closest long GRB ever with measured distance. The gamma-ray emission, detected up to the TeV range, is accompanied by a bright optical, NIR and radio afterglow. Located only at 350 Mpc, this is a rare but exquisite opportunity to study the emission mechanism, the progenitor nature, its environment and the structure/orientation of its jet. For GW/GRB170817, high resolution radio observations uniquely and successfully measured the source size and its proper motion. The jet structure and its orientation can be constrained by monitoring the source. These observations will allow us to constrain the kinetic energy of the jet which is a key parameter for the interpretation of the origin of the very high energy (TeV) emission, detected only recently in another GRB (190114C). On 29 August 2019, the Fermi/GBM and Swift/BAT reported a detection of a long-duration GRB 190829A. It is attractive for several reasons: (1) The redshift of GRB 190829A is 0.0785, making it one of the closest GRBs observed to date, offering rare opportunity for multi-band follow-up observations; (2) It was detected by H.E.S.S above 5 sigma. It is the second GRB afterglow with TeV energies been detected above 3sigma and is also 5.4 times closer than first TeV-detected GRB 190114C. The radio emission is detected by NOEMA with 6.3 mJy at 90 GHz three days after the burst. We request EVN observations to resolve the compact source structure and probe the expansion speed at 5 GHz.