Intranight optical monitoring of optically selected bright quasars

Abstract

As part of an ongoing programme to search for intranight optical variations, we report results for six radio-quiet and one radio-moderate, but all optically bright and luminous, quasi-stellar objects (QSOs), using the 2.34-m Vainu Bappu Telescope. Moderately strong evidence is found for the microvariability of the radio-quiet QSOs 0946+301 and 1444+408 and weaker evidence is found for the QSO 0117+213. We also draw attention to a few `spikes' (on time-scales of <=10 min) seen in the optical output of the radio-quiet QSOs 0117+213, 0946+301 and 1630+377. Additional observations of these and other QSOs could provide a powerful means of discriminating among the various theoretical mechanisms proposed for the energy source and, in particular, the origin of optical microvariability in active galactic nuclei (AGN). Finally, by comparing the present observations with those made by us ~1 yr earlier, long-term variability (5 to 15 per cent) is detected for four of the QSOs in our sample.