The emergence of diffused Gamma-Ray Burst afterglows from the disks of Active Galactic Nuclei

TL;DR

This paper models gamma-ray burst afterglows within active galactic nucleus disks, revealing how dense environments and radiation diffusion alter observable signals, aiding in understanding stellar populations and disk properties.

Contribution

It introduces a method to compute diffused GRB afterglow light curves in AGN disks, accounting for radiation diffusion and synchrotron self-absorption effects, which was not previously explored.

Findings

Radiation from radio to X-ray can be suppressed by synchrotron self-absorption.

Photon diffusion delays the emission peak, making transients appear slower and dimmer.

These transients resemble broadband AGN variability at higher frequencies.

Abstract

The disks of Active Galactic Nuclei (AGNs) have emerged as rich environments for the production and capture of stars and the compact objects that they leave behind. These stars produce long Gamma-Ray Bursts (LGRBs) at their deaths, while frequent interactions among compact objects form binary neutron stars and neutron star-black hole binaries, leading to short GRBs (SGRBs) upon their merger. Predicting the properties of these transients as they emerge from the dense environments of AGN disks is key to their proper identification and to better constrain the star and compact object population in AGN disks. Some of these transients would appear unusual because they take place in much higher densities than the interstellar medium. Others, which are the subject of this paper, would additionally be modified by radiation diffusion since they are generated within optically thick regions of the accretion disks. Here we compute the GRB afterglow light curves for diffused GRB sources for a representative variety of central black-hole masses and disk locations. We find that the radiation from radio to UV and soft X-rays can be strongly suppressed by synchrotron self-absorption in the dense medium of the AGN disk. In addition, photon diffusion can significantly delay the emergence of the emission peak, turning a beamed, fast transient into a slow, isotropic, and dimmer one. These would appear as broadband-correlated AGN variability with dominance at the higher frequencies. Their properties can constrain both the stellar populations within AGN disks as well as the disk structure.