Intra-night optical variability monitoring of $\gamma$-ray emitting blazars

TL;DR

This study monitored 18 blazars over 40 nights to analyze their intra-night optical variability, revealing different duty cycles across blazar subclasses and supporting the leptonic emission model.

Contribution

First comprehensive intra-night optical variability analysis of Fermi-detected blazars, correlating variability with spectral energy distribution subclasses.

Findings

Duty cycle of variability is ~11-12% overall.

LSP blazars show higher variability duty cycle (~16%) than ISP and HSP.

Variability patterns support leptonic emission models.

Abstract

We present the results obtained from our campaign to characterize the intra-night-optical variability properties of blazars detected by the {\it Fermi} Large Area Telescope. This involves R-band monitoring observations of a sample of 18 blazars, that includes five flat-spectrum radio quasars (FSRQs) and thirteen BL Lac objects (BL Lacs) covering the redshift range z = 0.085$-$1.184. Our observations, carried out using the 1.3 m J.C. Bhattacharya Telescope cover a total of 40 nights ($\sim$200 hrs) between the period 2016 December and 2020 March. We characterized variability using the power enhanced $F-$test. We found a duty cycle (DC) of the variability of about 11\% for FSRQs and 12\% for BL Lacs. Dividing the sample into different sub-classes based on the position of the synchrotron peak in their broadband spectral energy distribution (SED), we found DC of $\sim$16\%, $\sim$10\% and $\sim$7\% for low-synchrotron peaked (LSP), intermediate synchrotron peaked (ISP) and high synchrotron peaked (HSP) blazars. Such high DC of variability in LSP blazars could be understood in the context of the R-band tracing the falling part (contributed by high energy electrons) of the synchrotron component of the broadband SED. Also, the R-band tracing the rising synchrotron part (produced by low energy electrons) in the case of ISP and HSP blazars, could cause lesser variability in them. Thus, the observed high DC of variability in LSP blazars relative to ISP and HSP blazars is in accordance with the leptonic model of emission from blazar jets.