Abstract
Recent years have seen a growing sample of TeV emission detections in gamma-ray burst afterglows, as well as an increasing role for structured jets in afterglow modelling. Using a kinetic approach, we show that the structure of an afterglow jet impacts its TeV emission, with jets where the energy falls off more sharply with angle showing a decrease in Inverse Compton (IC) peak flux relative to synchrotron peak flux. We use a modified version of the code katu, to which we have added adiabatic expansion and a fully self-consistent treatment of IC cooling both for the electron and photon populations. We compare our results to the semi-analytical code afterglowpy, finding a good agreement with our model except at early times off axis where the effects of baryon loading are important. We compare electron cooling in the cases where there is no IC cooling, Thomson cooling and an inclusion of Klein-Nishina effects, finding that the spectra can only be distinguished if the Compton potential is significantly increased. The smooth and gradual transition of our KN cooling also leads to a disparity in the cooling between our results and semi-analytical solutions based on asymptotic limits. Finally, we combine best fit parameters from afterglowpy to reproduce the light curves of GRB 170817A in our model. For our choice of parameters, we find that GRB 170817 would not have been detected in the TeV domain if seen on-axis, even by the upcoming Cherenkov Telescope Array Observatory.
Original language | English |
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Number of pages | 20 |
Journal | Monthly Notices of the Royal Astronomical Society |
Early online date | 21 Jan 2025 |
DOIs | |
Publication status | E-pub ahead of print - 21 Jan 2025 |
Data Availability Statement
No new data was generated or analysed in support of this research.Acknowledgements
JPH would like to thank Geoff Ryan, for helpful discussions on implementing the flux calculations in this work, as well as providing advice on how to compare the Katu and afterglowpy shell models. JPH also thanks Clement Pellouín and Tanmoy Laskar for additional discussion.Funding
HJvE, PS and SK acknowledge support by the Science and Technology Facilities Council (STFC) through grant ST/X001067/1, and JPH through grant ST/W507301/1. HJvE further acknowledges support by the European Union Horizon 2020 programme under the AHEAD2020 project (grant agreement number 871158). This work used the Isambard 2 UK National Tier-2 HPC Service (http://gw4.ac.uk/isambard/) operated by GW4 and the UK Met Office, and funded by EPSRC (EP/T022078/1).
Funders | Funder number |
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Engineering and Physical Sciences Research Council | EP/T022078/1 |
Keywords
- gamma-ray bursts
- radiation mechanisms: non-thermal
- software: simulations
- astroparticle physics
- Relativistic processes