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

Abstract

This is continuation of our search for the elusive radio-quiet blazars, by carrying out a systematic programme to detect intranight optical variability (INOV) in a subset of ‘weak-line quasars’ which are designated as ‘high-confidence BL Lac candidates’ and are known to be radio-quiet. For 10 such radio-quiet weak-line quasars (RQWLQs), we present here the INOV observations taken in 16 sessions of durations ≳ 3.5 h each. Combining these data with our previously published INOV monitoring of RQWLQs in 13 sessions gives a set of INOV observations of 15 RQWLQs monitored in 29 sessions, each lasting more than 3.5 h. The 29 differential light curves, thus obtained for the 15 RQWLQs, were subjected to a statistical analysis using the F-test, and the deduced INOV characteristics of the RQWLQs are compared with those published recently for several prominent AGN classes, also using the F-test. However, since the RQWLQs are generally 1–2 mag fainter, a rigorous comparison has to wait for somewhat more sensitive INOV observations than those presented here. Based on our existing INOV observations, it seems that RQWLQs in our sample show a significantly higher INOV duty cycle than radio-quiet quasars and radio lobe-dominated quasars. Two sessions when we detected rather strong (blazar-like) INOV for RQWLQs are pointed out, and both these RQWLQs are therefore candidates for radio-quiet BL Lacs.