主持人：刘四明教授

时间：2025年9月20日（周六）10：00

地点：犀浦校区二教2539会议室

腾讯会议号：756 683 099

题目：GRB afterglows: particle acceleration, emission, and hydrodynamic evolution

主讲人：Evgeny Derishev

Evgeny Derishev received his PhD from the Institute of Applied Physics of the Russian Academy of Science in 1999 (in the field of plasma physics and astrophysics).In 2001 -- 2002 he was a postdoc at the High Energy Astrophysics Group in the Max-Planck Institute for Nuclear Physics (Heidelberg, Germany).After that, Evgeny Derishev returned to his home Institute, where he currently has the senior researcher position.His research interests are mainly in the field of particle acceleration and radiation in astrophysical sources of high-energy photons and neutrinos (GRBs, blazars, accretion disks around compact objects),as well as physics of relativistic shocks, including both theoretical studies and numerical simulations.

Abstract

Gamma-Ray Bursts are produced by stellar explosions that channel part of their energy into ultrarelativistic jets. Plunging into curcumburst medium,these jets form relativistic shocks, whose prolonged emission is known as GRB afterglow. This emission is a combination of synchrotron and inverse Compton radiation from accelerated electrons.

At present, there are two competing scenarios of particle acceleration at relativistic shocks. The conventional scenario extrapolates well-known diffusive shock acceleration into domain of highly relativistic shock velocities and the pair-balance model is based on the converter acceleration mechanism that is specific to relativistic shocks. Despite the fact that predictions of these models are often opposite, it is not possible to discriminate between them on the basis of X-ray observations only because of large uncertainty in determination of the shock's parameters.

Recent TeV observations of Gamma-Ray Burst afterglows (GRB190114C and GRB190829A) gave an opportunity to test and compare the afterglow models with a much better precision. We show the results of spectral modelling at different times since trigger, which turn out to be consistent with the pair-balance model and are at tension with diffusive shock acceleration scenario.

Another TeV Gamma-Ray Burst, GRB221009A, has early afterglow lightcurve measured by LHAASO. Simplified hydrodynamical models are insufficient to explain all the lightcurve's details. Instead we suggest a more elaborate hydrodynamical model that well fits the measurements. It's small residuals are correlated with activity of the central engine, providing for the first time a piece of evidence for emission from the reverse shock.