Optical microvariability of EGRET blazars

G. E. ROMERO; S. A. CELLONE; J. A. COMBI; I. ANDRUCHOW

ASTRONOMY AND ASTROPHYSICS

EDP Sciences

Lugar: Les Ulis Cedex A; Año: 2002 vol. 390 p. 431 - 438

0004-6361

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%). Based on observations made at the Complejo Astronómico El Leoncito, which is operated under agreement between CONICET and the National Universities of La Plata, Córdoba, and San Juan. Table \ref{t_stars} is only available in electronic form at http://www.edpsciences.org