Multi-Band Intra-Night Optical Variability of BL Lacertae

Haritma Gaur,Rumen Bachev,Evgeni Semkov,Sunay Ibryamov,Alok Gupta,Anton Strigachev,Minfeng Gu,Paul Wiita

doi:10.3390/galaxies5040094

Abstract

We monitored BL Lacertae frequently during 2014 - 2016 when it was generally in a high state. We searched for intra-day variability for 43 nights using quasi-simultaneous measurements in the B, V, R, and I bands (totaling 143 light curves); the typical sampling interval was about eight minutes. On hour-like timescales, BL Lac exhibited significant variations during 13 nights in various optical bands. Significant spectral variations are seen during most of these nights such that the optical spectrum becomes bluer when brighter. The amplitude of variability is usually greater for longer observations but is lower when BL Lac is brighter. No evidence for periodicities or characteristic variability time-scales in the light curves was found. The color variations are mildly chromatic on long timescales.

Highlights

BL Lacertae is a prototype of the blazar class at redshift z = 0.069 [1]
We used the enhanced F-test to search for genuine flux variations on these intra-day variability (IDV) time-scales, finding 19 light curve (LC) to be variable across the filter set over the course of 13 nights of observation
In our previous extensive search for IDV in BL Lac over 38 nights in the period 2010–2012, we found 50 filter LCs to be variable during 19 nights using the same enhanced F-test [19], or a DC = 44%, the B band data were usually better

Summary

Introduction

BL Lacs, along with many flat spectrum radio quasars, constitute the blazar class of active galaxies. On some occasions, BL Lacertae has shown broad Hα and Hβ emission lines in its spectrum, thereby raising the issue of it being part of its eponymous class [3]. BL Lac is classified as a low frequency peaked blazar (LBL) because of its first spectral hump peaks in the near IR/optical region, which is explained as the synchrotron emission from highly relativistic electrons within a helical jet [4]. Optical observations are helpful in studying the acceleration and cooling timescales of the electrons in the relativistic jets

Results

Discussion

Conclusion