Intranight optical variability of BL Lacs, radio-quiet quasars and radio-loud quasars

Abstract

We report monitoring observations of 20 high‐luminosity active galactic nuclei (AGN), 12 of which are radio‐quiet quasars (RQQs). Intranight optical variability (INOV) was detected for 13 of the 20 objects, including 5 RQQs. The variations are distinctly stronger and more frequent for blazars than for the other AGN classes. By combining these data with results obtained earlier in our programme, we have formed an enlarged sample consisting of 9 BL Lacs, 19 RQQs and 11 lobe‐dominated radio‐loud quasars (RLQs). The moderate level of rapid optical variability found for both RQQs and radio lobe‐dominated quasars (LDQs) argues against a direct link between INOV and radio loudness. We supplemented the present observations of 3 BL Lacs with additional data from the literature. In this extended sample of 12 well observed BL Lacs, stronger INOV is found for the EGRET detected subset.

Multi-color optical variability of the TeV blazar Mrk 501 in the low-state

“…For any time lag k, the value of a(i+k) was calculated by linear interpolation between the two adjacent data points. In a similar fashion SF was calculated for a large number of IDV light curves (Sagar et al 2004, Stalin et al 2005). The behavior of the first order SF have the following types:…”

The optical variability of steep-spectrum radio quasars in the SDSS stripe 82 region

“…While the observational data cannot exclude accretion disk flares as the source of the intranight optical variability in radio-quiet quasars and LDQs, it does not preclude a substantial contribution from blazar-like relativistically beamed emission. As suggested by Stalin et al (2005), the radio-quiet quasars may also eject relativistic jets. However, their jets are probably quenched while crossing the innermost micro-arcsecond scale, possibly through heavy inverse Compton losses in the vicinity of the central engine (e.g., Gopal-Krishna et al 2003).…”

“…Both the long-term or short-term variabilities of radio-quiet AGNs have also been explored (e.g., Stalin et al 2004Stalin et al , 2005Gupta & Joshi 2005;Ai et al 2010). The accretion disk instabilities might explain the optical microvariability of radio quiet AGNs (e.g., Gopal-Krishna et al 1995; see also Gopal-Krishna et al 2003, for alternative scenario).…”

“…However, the variations in SSRQs might still be caused by a mixture of a jet and accretion disk, since they are powerful radio emitters. The optical variations of SSRQs have been poorly studied, and few explanations have been presented (e.g., Stalin et al 2004Stalin et al , 2005. While the color variations and/or spectral variations of blazars have been extensively investigated (e.g., Ghisellini et al 1997;Fan et al 1998;Massaro et al 1998;Ghosh et al 2000;Clements & Carini 2001;Raiteri et al 2001;Villata et al 2002;Vagnetti et al 2003;Wu et al 2005Wu et al , 2007Gu et al 2006;Rani et al 2010;Gu & Ai 2011), it has not been the case for SSRQs.…”

On the Photometric Error Calibration for the Differential Light Curves of Point-like Active Galactic Nuclei

“…Results of this ongoing study have been reported in a series of publications and in the Ph.D. theses of C. S. Stalin (2003) and Arti (Goyal et al 2012 and references therein; Stalin et al 2005 and references therein). Optical intra-night monitoring data from other optical observatories in India, such as the 2-m Himalayan Chandra Telescope (HCT) and the 2.4m Vainu Bappu Telescope (VBT) of IIA, the 1.2m telescope at the Gurushikhar observatory of PRL and the 2-m IUCAA Girawali Observatory (IGO) telescope of IUCAA were also obtained to augment the data taken with the 1-m ST. Nearly always, just one target AGN was monitored on a given night.…”