# Scenarios for ultrafast gamma-ray variability in AGN

## TL;DR

This paper evaluates three models for ultrafast gamma-ray flares in AGN, finding constraints on magnetosphere scenarios and discrepancies in jet power estimates for cloud and blob models.

## Contribution

It provides a comparative analysis of three scenarios for gamma-ray variability, establishing luminosity limits and addressing jet power discrepancies.

## Key findings

- Magnetosphere scenario limited by luminosity to ~2x10^43 erg/s for 5-minute flares.
- Jet power required for cloud and blob scenarios exceeds radio-based estimates.
- Relativistic blob distribution anisotropy can reconcile jet power discrepancies.

## Abstract

We analyze three scenarios to address the challenge of ultrafast gamma-ray variability reported from active galactic nuclei. We focus on the energy requirements imposed by these scenarios: (i) external cloud in the jet, (ii) relativistic blob propagating through the jet material, and (iii) production of high-energy gamma rays in the magnetosphere gaps. We show that while the first two scenarios are not constrained by the flare luminosity, there is a robust upper limit on the luminosity of flares generated in the black hole magnetosphere. This limit depends weakly on the mass of the central black hole and is determined by the accretion disk magnetization, viewing angle, and the pair multiplicity. For the most favorable values of these parameters, the luminosity for 5-minute flares is limited by $2\times10^{43}\rm\,erg\,s^{-1}$, which excludes a black hole magnetosphere origin of the flare detected from IC310. In the scopes of scenarios (i) and (ii), the jet power, which is required to explain the IC310 flare, exceeds the jet power estimated based on the radio data. To resolve this discrepancy in the framework of the scenario (ii), it is sufficient to assume that the relativistic blobs are not distributed isotropically in the jet reference frame. A realization of scenario (i) demands that the jet power during the flare exceeds by a factor $10^2$ the power of the radio jet relevant to a timescale of $10^8$ years.