An orphan flare from a plasma blob crossing the broad-line region ?

TL;DR

This paper proposes a new model for a rapid gamma-ray flare in blazar 3C 279, attributing it to a plasma blob crossing the broad-line region and causing external Compton emission, without changes in electron injection.

Contribution

It introduces a novel two-zone emission model involving a stationary and a moving blob to explain rapid flares in blazars, emphasizing geometry and bulk motion effects.

Findings

The flare is explained by external Compton emission from a moving plasma blob.

The model accounts for rapid flux increase with minimal optical variation.

It differs from previous models by not requiring electron injection variability.

Abstract

The blazar 3C 279 is well known for its prolific emission of rapid flares. A particular event occurred on 12/20/2013, exhibiting a large flux increase with a doubling time scale of a few hours, a very hard gamma-ray spectrum, and a time-asymmetric light curve with slow decay, but no significant variations detected in the optical range. We propose a novel scenario to interpret this flare, based on two emission zones, a stationary blob and a moving plasma blob. The stationary blob, located within the BLR, accounts for the low-state emission. The moving blob decouples from the stationary zone, accelerates and crosses the BLR. The high-energy flare is attributed to the variable external Compton emission as the blob moves through the BLR, while variations in the synchrotron emission are negligible. Our interpretation differs from previous interpretations by attributing the flare to the bulk motion and geometry of the external photon fields, without invoking varying electron injection.