Intra-night optical variability of luminous radio-quiet QSOs

We report the detection of intra-night variability in some radio-quiet quasi-stellar objects (RQQSOs) and one lobe-dominated radio-loud quasi-stellar object (LDQ). To study intra-night variability, we carried out photometric monitoring of seven RQQSOs and one LDQ in Johnson V-passband using 1.2 m optical/IR telescope at Gurushikhar, Mount Abu, India. Observations were made in nine nights during the first half of the year 2000; seven RQQSOs: 0748+291, 0945+438, 1017+280, 1029+329, 1101+319, 1225+317, 1252+020 and one LDQ: 1103-006 were observed. RQQSOs 0748+291, 1225+317 and LDQ 1103-006 have shown intra-night variations. In the case of 1017+280 (RQQSO) there is indication of intra-night variation on one night where as the observations on another night do not convincingly show the existence of intra-night variability. RQQSOs 0945+438, 1029+329, 1101+319 and 1252+020 have not shown any intra-night variations. We compiled intra-night variability data for radio-loud and radio-quiet AGNs from the literature for statistical analysis. It is found that some radio-quiet AGNs show intra-night variations with the maximum amplitude of variation being about 10%. On the other hand blazars at times show intra-night flux variability up to 100%. In the case of radio-loud AGNs (excluding blazars), the maximum amplitude of intra-night variation lies between the variability amplitude of radio-quiet AGNs and blazars i.e. the flux variation is close to 50%. The results indicate that the energy generation mechanism and the environment around the central engine in different classes of AGNs may be similar, if not identical. The standard model for radio-loud AGNs, where shocks are propagating down relativistic jets or models based on disturbances in accretion disks can also explain the micro-variability in RQQSOs.