The Cosmological Population of Gamma-Ray Bursts from the Disks of Active Galactic Nuclei

TL;DR

This paper models the occurrence and detectability of gamma-ray bursts within active galactic nuclei disks, exploring how different scattering scenarios affect observable signals and their potential to probe disk structures.

Contribution

It introduces Monte Carlo simulations of GRBs in AGN disks considering scattering effects, providing new insights into their detectability and origins across different SMBH masses.

Findings

Detectable GRBs are mostly from lower redshifts and outer regions of large SMBHs.

Detection probability is 40-50% in undiffused scenarios.

Observable signals vary between gamma-ray prompt emission and X-ray afterglows depending on diffusion.

Abstract

With the discovery of gravitational waves (GWs), Active Galactic Nuclei (AGN) disks have emerged as an interesting environment for hosting a fraction of their sources. AGN disks are conducive to forming both long and short Gamma-Ray Bursts (GRBs), and their anticipated cosmological occurrence within these disks has potential to serve as an independent tool for probing and calibrating the population of stars and compact objects within them, and their contribution to the GW-detected population. In this study, we employ Monte Carlo methods in conjunction with models for GRB electromagnetic emission in extremely dense media to simulate the cosmological occurrence of both long and short GRBs within AGN disks, while also estimating their detectability across a range of wavelengths, from gamma-rays to radio. We investigate two extreme scenarios: ``undiffused", in which the radiation escapes without significant scattering (i.e. if the progenitor has excavated a funnel within the disk), and ``diffused", in which the radiation is propagated through the high-density medium, potentially scattered and absorbed. In the diffused case, we find that the majority of detectable GRBs, which are at most a few percent of the total, are likely to originate from lower redshifts, and from the outermost regions of large supermassive black hole (SMBH) masses, $\gtrsim 10^{7.5} \rm M_{\odot}$. In the undiffused case, which has a GRB detection probability $\sim 40-50\%$, we expect a similar trend, but with a considerable contribution from the intermediate regions of lower SMBH masses. Detectable emission is generally expected to be dominant in prompt $\gamma$-rays if diffusion is not dominant, and X-ray afterglow if diffusion is important; however, the nature of the dominant observable signal highly depends on the specific AGN disk model, hence making GRBs in AGN disks also potential probes of the disk structures.