Reconnection-driven State Transitions in Flat Spectrum Radio Quasars

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 does not, 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 $3σ$ 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 self-consistently reproduces key observable statistical properties of blazar GeV light curves.

Figures (10)

• Figure 1: Left panel : Figure shows the histogram of p-values obtained from the Mann Whitney U Test between the preflare and postflare skewness distributions of the eighteen FSRQs in our sample. The departure from unimodality is not statistically significant. Right panel : The corresponding common language effect size using the Mann Whitney U statistic. More clutter at $<0.5$ is evident, in expectation with the p-value histogram.
• Figure 2: Figure shows the change in median skewness $\Delta\mathbb{S}$ through the largest flare for each of our sources, colored by the corresponding p-values for the statistical significance of a skewness reduction across the flare. The distribution of $\Delta \mathbb{S}$ is smooth, between $\sim -0.5-0.75$, exhibiting the range of different physical properties of our sample.
• Figure 3: Light curves arranged in order of increasing p-value, with lightest light curves showing a statistically significant reduction in skewness and boldest light curves showing a statistically significant increase in skewness.
• Figure 4: Figure shows a simulated light curve from our model, that closely mimicks real GeV flaring blazar light curves. The rolling skewness is shown in the bottom plot of the left panel, where it is discernible by eye that the skewness has decreased after the flare and stayed at that level for some
• Figure 5: Left : A p-value histogram for the Mann Whitney U test for the decrease in skewness across the largest flare for the 1500 simulated light curves. A bimodal distribution is evident, exhibiting two types of sources where skewness either decreases (low p-value) or increases (high p-value). Right : The corresponding common language effect size of the Mann Whitney Test, showing the number of light curves as a function of the probability where a random pair of pre and postflare skewness values has the preflare value larger than the postflare.