Rapid optical variability in radio-quiet QSOs

We report results of the observations at the Vainu Bappu Observatory and th e Uttar Pradesh State Observatory of eight radio-quiet quasi-stellar object s (RQQSOs) during 1996-99. This is a part of our ongoing programme to searc h for intranight optical variability in RQQSOs. Additional evidence for ver y rapid variability in three of the five optically bright and very luminous RQQSOs we had observed earlier, 1049-006, 1444+308 and 1630+377, was found . Of the three newly observed RQQSOs, the data for 0043+039 are too noisy t o allow conclusions about variability to be drawn, but 0748+294 and 0824+09 8 show strong hints of microvariability, We also present a summary of the r esults from our entire programme to date, which includes observations of 16 radio-quiet QSOs and one radio-weak QSO, and compare the general propertie s of rapid variability in radio-quiet versus radio-loud AGN as determined f rom our work and that of several other groups. Observations of this kind ar e likely to play a key role in understanding the relative contributions of accretion discs and relativistic plasma jets to rapid optical fluctuations of AGN.