The blob crashes into the mirror: modelling the exceptional gamma-ray flaring activity of 3C 454.3 in November 2010

TL;DR

This paper models the exceptional gamma-ray flare of 3C 454.3 in November 2010, proposing a jet-mirror cloud interaction at parsec scales as the primary mechanism, challenging traditional inside-BLR emission models.

Contribution

It introduces a novel interpretation of the 2010 flare based on jet interaction with a mirror cloud outside the BLR, explaining multifrequency observations better than inside-BLR models.

Findings

The mirror cloud interaction model explains the gamma-ray and optical/X-ray behavior.

Inside-BLR emission models face significant challenges in explaining the data.

Moderate bulk Lorentz factors (~15) can produce rapid, large-amplitude variations.

Abstract

We focus on the exceptional flaring activity of 3C 454.3 in November 2010 and we discuss a theoretical framework addressing all data in their overall evolution. For two weeks the source has shown a plateau of enhanced GeV emission preceding a sudden major flare lasting about 3 days before decaying. The gamma-ray flare onset is abrupt (about 6 hours), and is characterized by a prominent "Compton dominance" with the GeV flux exceeding the pre-flare values by a factor of 4-5, whereas the optical and X-ray fluxes increased only by a factor 2. We explore two alternatives. Case 1, with high-energy emission originating within the BLR; and Case 2, with most of it produced outside. We show that Case 1 has considerable problems in explaining the whole set of multifrequency data. Case 2, instead, leads to a consistent and interesting interpretation based on the enhanced inverse Compton radiation that is produced as the jet crashes onto a mirror cloud positioned at few parsec from the BH. This model explains the gamma-ray vs. optical/X-ray behavior of 3C 454.3, including the otherwise puzzling phenomena such as the prominent "orphan" optical flare, and the enhanced line emission with no appreciable gamma-ray counterpart that preceded the GeV flare. It also accounts for the delayed onset of the latter on top of the long plateau. Our modelling of the exceptional 3C 454.3 gamma-ray flare shows that, while emission inside the canonical BLR is problematic, major and rapid variations can be produced at parsec scales with moderate bulk Lorentz factors $\Gamma\approx 15$.