Nature of Intra-night Optical Variability of BL Lacertae

TL;DR

This study presents extensive multi-band intra-night optical monitoring of BL Lacertae from 2010 to 2012, revealing significant hour-like variability, spectral changes, and flux-dependent amplitude variations, with no evidence of periodicity.

Contribution

It provides detailed multi-band intra-night variability analysis of BL Lacertae, highlighting flux-dependent amplitude, spectral behavior, and absence of characteristic timescales, expanding understanding of jet emission processes.

Findings

Significant intra-night variability on hour-like timescales in 19 nights.

Optical spectrum becomes flatter with increasing flux.

Variability amplitude is higher at higher frequencies and decreases with increasing flux.

Abstract

We present the results of extensive multi-band intra-night optical monitoring of BL Lacertae during 2010--2012. BL Lacertae was very active in this period and showed intense variability in almost all wavelengths. We extensively observed it for a total for 38 nights; on 26 of them observations were done quasi-simultaneously in B, V, R and I bands (totaling 113 light curves), with an average sampling interval of around 8 minutes. BL Lacertae showed significant variations on hour-like timescales in a total of 19 nights in different optical bands. We did not find any evidence for periodicities or characteristic variability time-scales in the light curves. The intranight variability amplitude is generally greater at higher frequencies and decreases as the source flux increases. We found spectral variations in BL Lacertae in the sense that the optical spectrum becomes flatter as the flux increases but in several flaring states deviates from the linear trend suggesting different jet components contributing to the emission at different times.