Quasi-Simultaneous Broadband Spectral Energy Distributions of a Sample of Fermi Blazars -- I. Correlation Results

TL;DR

This study constructs quasi-simultaneous broadband SEDs for 93 Fermi blazars, analyzing correlations among key parameters to understand jet physics and variability, and estimating Doppler factors from gamma-ray light curves.

Contribution

It provides the first comprehensive analysis of correlations in quasi-simultaneous SEDs for a large sample of Fermi blazars, revealing insights into particle acceleration and jet dynamics.

Findings

Weak relation between synchrotron peak frequency and curvature.

Confirmation of the blazar sequence in the observer's frame.

Estimation of Doppler factors for four sources using gamma-ray variability.

Abstract

Blazars' non-thermal emission shows rapid variability across all wavelengths, so spectral energy distributions (SEDs) built from quasi-simultaneous data are crucial for revealing the jets physical properties. In this work, we construct quasi-simultaneous broadband SEDs for 93 Fermi blazars (56 FSRQs, 35 BL Lacs, and 2 blazar candidates of uncertain type), fit both peaks with cubic functions to allow for potential asymmetries, and examine correlations among key parameters. Our main results are summarized as follows: (1) We find that synchrotron peak frequency and curvature are only weakly related, suggesting that charged particles are accelerated by mixed acceleration mechanism. (2) The blazar sequence is confirmed in the observer's frame through negative correlations of both the bolometic luminosity $\log L_{\rm bol}$ and the Compton dominance $\log Y$ with the synchrotron peak frequency $\log \nu_{\rm syn}^{\rm peak}$. After correcting for Doppler boosting, a weak positive correlation emerges between $\log L_{\rm bol}$ and $\log \nu_{\rm syn}^{\rm peak}$. FSRQs and BL Lacs exhibit distinct correlation patterns within the blazar sequence, indicating differences in cooling mechanisms. (3) Using variability time lags between 0.1-1 GeV and 1-300 GeV light curves, we estimate lower limits of Doppler factors for 4 sources, providing a jet-speed diagnostic anchored directly to the $\gamma$-ray emission zone.