Reconnection-driven State Transitions in Flat Spectrum Radio Quasars

TL;DR

This study models reconnection-driven plasmoid formation in blazar jets to explain observed skewness variations and variability patterns in FSRQ gamma-ray light curves.

Contribution

It introduces a stochastic plasmoid model that reproduces key statistical properties of blazar variability and explains skewness changes after flares.

Findings

Skewness varies systematically after large flares in FSRQs.

Simulated light curves exhibit broken-power-law PSDs similar to observations.

Entropy decreases at 3σ level, indicating increased order post-flare.

Abstract

We extend the work of Roychowdhury (2026) on skewness variations of the logarithmic flux, driven by large GeV flares in FSRQs, to a sample of 18 FSRQs. We find that they can be categorized into three groups, one where the skewness attains a persistent lower value after a large flare, one where it increases, and those where change in skewness is not significant. To provide a theoretical ground for these results, we use the statistical plasmoid model of Fermo et al. (2010) that self-consistently produces large plasmoids through merging which, when gain energy from the reconnection event and are Doppler aligned, produce large flares. We find that a downsampling of our simulation of 1500 runs to 18 statistically reproduces the observed distribution in p-values for change in skewness. We further compute the ensemble Shannon entropy of the system and the skewness, where the entropy is found to decrease at a $3\sigma$ level in both the groups where skewness either increases or decreases, as a direct evidence of increase in order in the system caused by a flare. We find that the power spectral densities of the simulated light curves are broken-power-laws, resembling a white noise+red noise broken by the typical cooling timescale in our system, in accordance with known blazar variability. We find that our results are robust to a $200-300\%$ change in several fiducial parameters of the simulation. Our stochastic simulation of plasmoids inside a blazar jet is consistent with key observable statistical properties of blazar GeV light curves.