Optical microvariability of EGRET blazars

• Published in: Astronomy and astrophysics (Berlin) Vol. 390; no. 2; pp. 431 - 438
• Main Authors: Romero, G. E., Cellone, S. A., Combi, J. A., Andruchow, I.
• Format: Journal Article
• Language: English
• Published: EDP Sciences 01.08.2002
• Subjects: BL Lacertae objects: general; galaxies: active; galaxies: photometry; gamma-rays: observations
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361:20020743

We present results of a photometric CCD study of the incidence of microvariability in the optical emission of a sample of 20 blazars detected at gamma-ray energies by the EGRET instrument of the Compton Gamma-Ray Observatory. We have observed strong outbursts in some sources, but many others displayed no significant variability on timescales of hours. The typical minimum timescale is found to be of ~several hours, not tens of minutes as claimed by some authors. The duty cycle for optical intranight microvariations of gamma-ray blazars, as estimated from our observations, seems to be ~50%, lower than what is usually assumed. For night-to-night variations, instead, the duty cycle approaches that observed in radio-selected BL Lacs and flat-spectrum radio quasars (i.e. ~70%).