Intranight optical variability of core dominated quasars and TeV blazars

Abstract

We have investigated the intranight optical variability (INOV) of powerful flat spectrum core dominated radio quasars (CDQs) and TeV blazars to test unification models of radio-loud AGN. A sample of 15 CDQs, including both low-polarization and high-polarization objects, were observed at three sites in India on 49 nights; with data from the literature this sample was extended to 24 CDQs and 110 nights. The INOV duty cycle was about 18% for the low polarization sub-sample but about 66% for the high polarization sub-sample. Given that all these CDQs had synchrotron self-absorbed cores all should be relativistically beamed, so this difference indicates that optical polarization is more strongly linked with rapid variability than is relativistic beaming. For the first systematic attempt to characterize the INOV of TeV detected blazars we monitored 9 of them over 26 nights and have included additional data (some from our earlier studies) on 13 more for a total of 22 TeV blazars observed on 116 nights. The overall INOV duty cycle for this group is about 59%, with the LBLs distinctly more variable than the HBLs. Given that the Doppler boosting factors for TeV blazars are expected to be very high, it is somewhat surprising that no variations faster than one hour were seen for any members of the TeV sample.