Intra night optical variability in optically selected QSOs

Abstract

We report results from a continuing programme to search for intranight optical variability in one radio-moderate and six radio-quiet (but all optically bright and luminous) quasi-stellar objects, using the 2.34-m Vainu Bappu Telescope. Our data clearly show microvariability for the radio-moderate QSO, 0838+359, and provide strong indications of microvariability for two of the radio-quiet QSOs, 0946+301 and 1049-006, and possibly also for a third, 1206+459. Additional observations of these and other QSOs could provide a powerful means of discriminating among various theoretical mechanisms proposed for the energy source and, in particular, the origin of optical microvariability in active galactic nuclei. These apparent detections of microvariability in radio-quiet QSOs seem to favour models where flares on accretion discs are responsible for the microvariability.