Multi-Band Intra-Night Optical Variability of BL Lacertae

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.Comment: 15 pages, 5 Figures, 3 Tables; Accepted for publication in Galaxies; a special issue on Microvariability of Blazar

Radio Properties of Low Redshift Broad Line Active Galactic Nuclei Including Extended Radio Sources

We present a study of the extended radio emission in a sample of 8434 low redshift (z < 0.35) broad line active galactic nuclei (AGN) from the Sloan Digital Sky Survey (SDSS). To calculate the jet and lobe contributions to the total radio luminosity, we have taken the 846 radio core sources detected in our previous study of this sample and performed a systematic search in the Faint Images of the Radio Sky at Twenty-centimeters (FIRST) database for extended radio emission that is likely associated with the optical counterparts. We found 51 out of 846 radio core sources have extended emission (> 4" from the optical AGN) that is positively associated with the AGN, and we have identified an additional 12 AGN with extended radio emission but no detectable radio core emission. Among these 63 AGN, we found 6 giant radio galaxies (GRGs), with projected emission exceeding 750 kpc in length, and several other AGN with unusual radio morphologies also seen in higher redshift surveys. The optical spectra of many of the extended sources are similar to that of typical broad line radio galaxy spectra, having broad H$\alpha$ emission lines with boxy profiles and large M_BH. With extended emission taken into account, we find strong evidence for a bimodal distribution in the radio-loudness parameter R, where the lower radio luminosity core-only sources appear as a population separate from the extended sources, with a dividing line at log(R) $\approx 1.75$. This dividing line ensures that these are indeed the most radio-loud AGN, which may have different or extreme physical conditions in their central engines when compared to the more numerous radio quiet AGN.Comment: 25 pages, 6 figures, accepted to A

Multi-band optical variability of three TeV Blazars on Diverse Timescales

We present our optical photometric observations of three TeV blazars, PKS 1510-089, PG 1553+113 and Mrk 501 taken using two telescopes in India, one in Bulgaria, one in Greece and one in Serbia during 2012 - 2014. These observations covered a total of 95 nights with a total of 202 B filter frames, 247 images in V band, 817 in R band while 229 images were taken in the I filter. This work is focused on multi-band flux and colour variability studies of these blazars on diverse timescales which are useful in understanding the emission mechanisms. We studied the variability characteristics of above three blazars and found all to be active over our entire observational campaigns. We also searched for any correlation between the brightness of the sources and their colour indices. During the times of variability, no significant evidence for the sources to display spectral changes correlated with magnitude was found on timescales of a few months. We briefly discuss the possible physical mechanisms most likely responsible for the observed flux variability.Comment: 11 pages, 7 figures, 9 tables. Accepted for publication in MNRA