GeV Signatures of Short Gamma-Ray Bursts in Active Galactic Nuclei

TL;DR

This paper explores gamma-ray signatures of short gamma-ray bursts within active galactic nuclei, highlighting the potential for future gamma-ray observatories to detect these signals and connect them with gravitational wave events.

Contribution

It introduces a model for gamma-ray emission from CBO mergers in AGN disks, emphasizing the dominance of EIC processes and the detectability of GeV emissions with upcoming telescopes.

Findings

EIC component dominates GeV emission near supermassive black holes.

Future CTA can detect 25-100 GeV emission up to redshift z=1.0.

Simultaneous GW and gamma-ray detection is feasible within a decade.

Abstract

The joint detection of gravitational waves and the gamma-ray counterpart of a binary neutron star merger event, GW170817, unambiguously validates the connection between short gamma-ray bursts and compact binary object (CBO) mergers. We focus on a special scenario where short gamma-ray bursts produced by CBO mergers are embedded in disks of active galactic nuclei (AGN), and we investigate the $\gamma$-ray emission produced in the internal dissipation region via synchrotron, synchrotron self-Compton and external inverse-Compton (EIC) processes. In this scenario, isotropic thermal photons from the AGN disks contribute to the EIC component. We show that a low-density cavity can be formed in the migration traps, leading to the embedded mergers producing successful GRB jets. We find that the EIC component would dominate the GeV emission for typical CBO mergers with an isotropic-equivalent luminosity of $L_{j,\rm iso}=10^{48.5}~\rm erg~s^{-1}$ which are located close to the central supermassive black hole. Considering a long-lasting jet of duration $T_{\rm dur}\sim10^2-10^3$ s, we find that the future CTA will be able to detect its $25-100$ GeV emission out to a redshift $z=1.0$. {In the optimistic case, it is possible to detect the on-axis extended emission simultaneously with GWs within one decade using MAGIC, H.E.S.S., VERITAS, CTA, and LHAASO-WCDA. Early diagnosis of prompt emissions with Fermi-GBM and HAWC can provide valuable directional information for the follow-up observations.