Exceptionally bright optical emission from a rare and distant $γ-$ray burst
astro-ph.HE
/ Authors
Gor Oganesyan, Sergey Karpov, Martin Jelínek, Gregory Beskin, Samuele Ronchini, Biswajit Banerjee, Marica Branchesi, Jan Štrobl, Cyril Polášek, René Hudec
and 12 more authors
Eugeny Ivanov, Elena Katkova, Alexey Perkov, Anton Biryukov, Nadezhda Lyapshina, Vyacheslav Sasyuk, Martin Mašek, Petr Janeček, Jan Ebr, Jakub Juryšek, Ronan Cunniffe, Michael Prouza
/ Abstract
Long $\rm γ$-ray bursts (GRBs) are produced by the dissipation of ultra-relativistic jets launched by newly-born black holes after the collapse of massive stars. Right after the luminous and highly variable $γ$-ray emission, the multi-wavelength afterglow is released by the external dissipation of the jet in circumburst medium. We report the discovery of a very bright ($\rm \sim 10$ mag) optical emission $\rm \sim 28$ s after the explosion of the extremely luminous and energetic GRB 210619B located at redshift 1.937. Early multi-filter observations allowed us to witness the end of the shock wave propagation into the GRB ejecta. We observed the spectral transition from a bright reverse to the forward shock emission, demonstrating that the early and late GRB multi-wavelength emission is originated from a very narrow jet propagating into an unusually rarefied interstellar medium. We also find evidence of an additional component of radiation, coming from the jet wings which is able explain the uncorrelated optical/X-ray emission.