Probing the Jets of Blazars Using the Temporal Symmetry of Their Multi-Wavelength Outbursts

TL;DR

This study analyzes the symmetry of long-term and short-term blazar outbursts across multiple wavelengths, revealing insights into jet physics and particle acceleration mechanisms using observational data and the MUZORF model.

Contribution

It systematically compares the rise and decay timescales of blazar outbursts and interprets the results with the MUZORF model, providing new constraints on jet parameters.

Findings

Most long-term outbursts are symmetric, indicating crossing timescale dominance.

Short-term flares show asymmetry with varied rise and decay times.

Slower rise times suggest gradual particle acceleration.

Abstract

We compare the rise and decay timescales of $\sim$200 long-term ($\sim$weeks-months) GeV and R-band outbursts and $\sim$25 short-term ($\sim$hr-day) GeV flares in a sample of 10 blazars using light curves from the Fermi-LAT and the Yale/SMARTS monitoring project. We find that most of the long-term outbursts are symmetric, indicating that the observed variability is dominated by the crossing timescale of a disturbance, e.g., a shock. A larger fraction of short-term flares are asymmetric with an approximately equal fraction of longer and shorter decay than rise timescale. We employ the MUlti-ZOne Radiation Feedback (MUZORF) model to interpret the above results. We find that the outbursts with slow rise times indicate a gradual acceleration of the particles to GeV energy. A change in the bulk Lorentz factor of the plasma or the width of the shocked region can lead to an increase of the cooling time causing a faster rise than decay time. Parameters such as the luminosity or the distance of the broad line region (BLR) affects the cooling time strongly if a single emission mechanism, e.g., external Compton scattering of BLR photons is considered but may not if other mechanisms, e.g., synchrotron self-compton and external Compton scattering of the torus photon are included. This work carries out a systematic study of the symmetry of flares, which can be used to estimate relevant geometric and physical parameters of blazar jets in the context of the MUZORF model.