Optical microvariability of southern AGNs

Abstract

Abstract. We present results of a search for optical microvariability in a selected sample of 23 southern AGNs, which includes both radio-quiet and radio-loud objects. Microvariations were clearly detected in 60% of the radioloud sources, with amplitudes from 2.2% up to 8% within a single night. Night-to-night variability with amplitudes of ∼ 20% was also observed in the BL Lac object 0537 − 441. On the contrary, no rapid variability was detected at all in 8 radio-quiet quasars. We have used microvariability data previously reported for northern objects along with our new results for southern AGNs in order to estimate duty cycles of each class of objects from the largest possible sample.Most of the microvariability in radio-loud objects could be originating in interactions between relativistic shocks and features in the inner jets, although contributions from superluminal microlensing and accretion disk instabilities can be present in some sources. It is possible that the latter phenomenon is responsible for the microvariability observed in northern radio-quiet quasars. We suggest that the difference in the microvariability behaviour of radio and X-ray selected BL Lacs could be due to the effect of stronger magnetic fields in the latter group of objects, fields that can prevent the formation of features like density inhomogeneities and bends in the base of the jets by Kelvin-Helmholtz macroscopic instabilities.

Detection of VHE gamma-ray emission from the distant blazar 1ES 1101-232 with HESS and broadband characterisation

“…The optical emission from 1ES 1101-232 has typically varied on the timescale of months (e.g., Remillard et al 1989). Optical flares on intraday timescales have also been claimed in one observation (Romero et al 1999).…”

Multiband optical variability studies of BL Lacertae

“…To claim the variability of the source we used the most frequently used criterion introduced by Romero, Cellone, & Combi (1999), where the variability detection parameter Cavg is defined as the average of C1 and C2 with:…”

Multi-wavelength Study of Blazars Using Variability as a Tool

“…The variability parameter, C, first employed by Jang & Miller (1997) and generalized by Romero et al (1999), is defined as follows:…”

“…o assess the intra-day variability of the blazar under consideration, a C statistical test on days on which the urce was monitored for at least 1 hr was carried out. The variability parameter, C, first employed by Jang Miller (1997) and generalized by Romero et al (1999), is defined as follows: C = here and are the standard deviations of the (source -comparison star) and the (control star comparison star), respectively. A value of C > 2.576 is the criterion on which the source is classified as ariable at the 99% confidence level for the corresponding night.…”