Property Studies of "Loner" Flares of Gamma-Ray Blazars

TL;DR

This study identifies and analyzes 24 gamma-ray blazar flares, characterizing their durations, spectral changes, and potential physical origins, providing insights into the nature of these rare, isolated flaring events.

Contribution

It is the first detailed analysis of loner gamma-ray flares in blazars, revealing their durations, spectral behaviors, and possible physical mechanisms.

Findings

Flares last between 4-25 days.

Most flares show harder spectra during the event.

Longer, harder flares may originate from jet processes.

Abstract

We search through $\gamma$-ray data obtained with the Large Area Telescope (LAT) onboard the Fermi Gamma-Ray Space Telescope and find 24 blazars (or candidates) that have a single clear flare event in their 9.5 year long-term light curves. We define these events as loner flares since each flare stands out significantly above the relatively stable, low-flux light curve. We analyze the LAT data in detail for these 24 sources. The flares in ten of them are primarily due to a single sharp peak, for which we study by fitting with two different analytic functions. The time durations thus determined for the sharp peaks are in a range of 4-25 days. The $\gamma$-ray spectra of the 24 blazar sources can be described with a power-law or a log-parabola function. We obtain their spectral properties in the flaring and quiescent states, and find that in the flares 16 of the sources have harder emission and three have softer emission while the other five keep the same emission. We discuss a possible correlation between the differences in photon index in the quiescent and flaring states and photon indices in quiescence. In addition, the sharp peak flares seem to have a tendency of having long time durations and hard emission, possibly related to their physical origin in a blazar jet. Studies of more similar flares will help establish these possible features.