Multi-Band Intra-Night Optical Variability of BL Lacertae
Haritma Gaur,
Alok C. Gupta,
Rumen Bachev,
Anton Strigachev,
Evgeni Semkov,
Paul J. Wiita,
Minfeng Gu,
Sunay Ibryamov
Affiliations
Haritma Gaur
Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, China
Alok C. Gupta
Aryabhatta Research Institute of Observational Sciences (ARIES), Manora Peak, Nainital 263002, India
Rumen Bachev
Institute of Astronomy and National Astronomical Observatory, Bulgarian Academy of Sciences, 72 Tsarigradsko Shosse Blvd., 1784 Sofia, Bulgaria
Anton Strigachev
Institute of Astronomy and National Astronomical Observatory, Bulgarian Academy of Sciences, 72 Tsarigradsko Shosse Blvd., 1784 Sofia, Bulgaria
Evgeni Semkov
Institute of Astronomy and National Astronomical Observatory, Bulgarian Academy of Sciences, 72 Tsarigradsko Shosse Blvd., 1784 Sofia, Bulgaria
Paul J. Wiita
Department of Physics, The College of New Jersey, P.O. Box 7718, Ewing, NJ 08628-0718, USA
Minfeng Gu
Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, China
Sunay Ibryamov
Department of Theoretical and Applied Physics, Faculty of Natural Sciences, University of Shumen, 115, Universitetska Str., 9712 Shumen, Bulgaria
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.
