Optical Microvariability in Radio-quiet Quasars

Abstract

We report the results of a study of optical microvariability in radio-quiet and radio-intermediate quasars. Observations were obtained on a total of seven objects: five radio-quiet quasars and two radio-intermediate quasars. No micro-variability was detected in either the radio-quiet or radio-intermediate objects in our sample, despite intensive monitoring for several consecutive nights. In one object, PG 1257+346, evidence for interday variability was detected. We examined a sample of 117 radio-quiet objects found in the literature that have been studied for microvariability. This sample is discussed in terms of classification, redshift distribution, R (the ratio of the radio [5 GHz] flux to the optical [4400 8] flux), optical magnitude, luminosity, and observing strategy. Objects with 10 > R > 1 were found to show a higher instance of microvariability than those with R < 1. This suggests that R ¼ 1 is the appropriate cutoff between radio-loud and radio-quiet objects. A preference for low-redshift objects to display microvariability more often than higher redshift objects is seen; however, this is explainable via selection effects. We find a dependence in detection probability on observation length similar to that seen in radio-loud objects.