The effects of Time-Variable Absorption due to Gamma-Ray Bursts In Active Galactic Nuclei Accretion Disks

TL;DR

This study models how gamma-ray bursts in active galactic nuclei disks cause time-variable absorption, revealing spectral signatures that can identify burst environments and inform on disk structure and AGN variability.

Contribution

It introduces a radiation transfer simulation coupling metal and dust evolution to analyze time-dependent absorption in GRBs within AGN disks, a novel approach.

Findings

Spectral evolution expected for supermassive black holes between 10^5 and 5×10^7 solar masses (long GRBs).

Spectral evolution expected for black holes between 10^4 and 10^7 solar masses (short GRBs).

Potential to identify GRBs in AGN disks through spectral signatures.

Abstract

Both long and short gamma-ray bursts (GRBs) are expected to occur in the dense environments of active galactic nuclei (AGN) accretion disks. As these bursts propagate through the disks they live in, they photoionize the medium causing time-dependent opacity that results in transients with unique spectral evolution. In this paper we use a line-of-sight radiation transfer code coupling metal and dust evolution to simulate the time-dependent absorption that occurs in the case of both long and short GRBs. Through these simulations, we investigate the parameter space in which dense environments leave a potentially observable imprint on the bursts. Our numerical investigation reveals that time dependent spectral evolution is expected for central supermassive black hole masses between $10^5$ and $5 \times 10^7$ solar masses in the case of long GRBs, and between $10^4$ and $10^7$ solar masses in the case of short GRBs. Our findings can lead to the identification of bursts exploding in AGN disk environments through their unique spectral evolution coupled with a central location. In addition, the study of the time-dependent evolution would allow for studying the disk structure, once the identification with an AGN has been established. Finally, our findings lead to insight into whether GRBs contribute to the AGN emission, and which kind, thus helping to answer the question of whether GRBs can be the cause of some of the as-of-yet unexplained AGN time variability.