# Meeting the Challenge from Bright and Fast Gamma-Ray Flares of 3C 279

## TL;DR

This paper presents a model explaining rapid, bright gamma-ray flares in blazar 3C 279 through a clumpy jet structure with plasmoids, involving synchrotron emission, reflection, and inverse Compton scattering, matching observed flare characteristics.

## Contribution

The model introduces a novel plasmoid-based jet structure with a moving mirror mechanism to explain fast gamma-ray flares without significant optical-UV counterparts.

## Key findings

- Reproduces minute-scale gamma-ray flares at ~10^{18} cm from black hole
- Achieves high Compton dominance factors up to 100
- Predicts minimal optical-X-ray variability during gamma-ray flares

## Abstract

Bright and fast gamma-ray flares with hard spectra have been recently detected from the blazar 3C 279, with apparent GeV luminosities up to $10^{49}$ erg/s. The source is observed to flicker on timescales of minutes with no comparable optical-UV counterparts. Such observations challenge current models of high-energy emissions from 3C 279 and similar blazar sources that are dominated by relativistic jets along our line of sight with bulk Lorentz factors up to $ \Gamma \sim 20$ launched by supermassive black holes. We compute and discuss a model based on a clumpy jet comprising strings of compact plasmoids as indicated by radio observations. We follow the path of the synchrotron radiations emitted in the optical - UV bands by relativistic electrons accelerated around the plasmoids to isotropic Lorentz factors $\gamma \sim 1000$. These primary emissions are partly reflected back by a leading member in the string that acts as a moving mirror for the approaching companions. Around the plasmoids, shrinking \emph{gap} transient overdensities of seed photons build up. These are upscattered into the GeV range by inverse Compton interactions with the relativistic electrons accelerated in situ. We show that such a combined process produces bright gamma-ray flares with minor optical to X-ray enhancements. Main features of our model include: bright gamma-ray flares with risetimes as short as a few minutes, occurring at distances of order $10^{18} $ cm from the central black hole; Compton dominance at GeV energies by factors up to some $10^2$; little reabsorption from local photon-photon interactions.