Intranight optical variability of blazars

Abstract

We present results of a multi‐epoch intranight optical monitoring of 11 blazars consisting of six BL Lac objects and five radio core‐dominated quasars (CDQs). These densely sampled and sensitive R‐band CCD observations, carried out from 1998 November to 2002 May during a total of 47 nights with an average of 6.5 h per night, have enabled us to detect variability amplitudes as low as ∼1 per cent on intranight time‐scales. A distinction is found for the first time between the intranight optical variability (INOV) properties of the these two classes of relativistically beamed radio‐loud active galactic nuclei (AGNs). BL Lacs are found to show a duty cycle (DC) of INOV of ∼60 per cent, in contrast to CDQs, which show a much smaller INOV DC of ∼20 per cent, the difference being attributable mainly to the weakly polarized CDQs. On longer time‐scales (i.e. between a week to a few years) variability is seen from all the CDQs and BL Lacs in our sample. The results reported here form part of our long‐term programme to understand the intranight optical variability characteristics of the four main classes of luminous AGNs, i.e. radio‐quiet quasars (RQQs) and radio lobe‐dominated quasars (LDQs), as well as CDQs and BL Lac objects.

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:…”

Intra-night optical variability of luminous radio-quiet QSOs

“…Blazars, in particular, show variation in the complete electromagnetic spectrum on all time scales ranging from minutes to years (e.g. Miller et al 1989;Quinn et al 1996;Heidt & Wagner 1996;Catanese et al 1997;Lamer & Wagner 1998;Fan & Lin 1999;Kataoka et al 1999;Peng et al 2000;Petry et al 2000;Ghosh et al 2000;Pursimo et al 2000;Fan et al 2002;Gupta et al 2002Gupta et al , 2004Gupta & Joshi 2005;Sagar et al 2004;Villata et al 2004, and references therein).…”

Intranight optical variability of radio-quiet weak emission line quasars – III

“…Thus, while making comparison with the above mentioned other AGN classes, our present estimate of INOV duty cycle for RQWLQs (∼ 5 per cent) may be treated as a lower limit. This cautionary remark is underscored by the fact that both events of INOV detection reported here (Table 4) are marked by extremely large amplitudes (ψ ∼ 30% peak-to-peak, occurring on hour-like time scale), rivaling blazars in their highly active phases (e.g, Sagar et al 2004;Gopal-Krishna et al 2011;Goyal et al 2012). Clearly, it would be very interesting to check if a factor of 2 − 3 improvement in ψ lim would reveal many more events of INOV among RQWLQs, yielding a statistically robust estimate for the duty cycle of strong INOV (ψ > 3%) for RQWLQs, which is distinctly higher than the present estimate of ∼ 5%, perhaps even approaching the high values established for blazars.…”

“…A point worth emphasizing here is that while applying the F η −test, it is specially important to use the correct rms errors on the photometric data points. It has been found that the magnitude errors returned by the routines in the data reduction softwares of DAOPHOT and IRAF, are normally underestimated by a factor η ranging between 1.3 and 1.75, as shown in various studies (e.g., Gopal-Krishna et al 1995;Garcia et al 1999;Sagar et al 2004;Stalin et al 2004b;Bachev et al 2005). Recently Goyal et al (2012) estimated the best-fit value of η to be 1.5.…”