Statistics of the Optical Variations of a Large Sample of Quasars

Abstract

SYSTEMATIC monitoring of the optical variations of large samples of quasars has been somewhat limited, because of the extensive telescope time that is required. Penston and Cannon¹ have reported the results of a 2 year study of a group of twenty-four quasars whose photographic magnitudes m_pg were brighter than 17. About 20% of this sample showed “violent” variations (which they designated as “OVV”) of a magnitude or more on a time scale of days or weeks, and there seemed to be good correlation between such activity and a flat radio spectrum. A group of thirty quasars monitored by Peach² included no cases of violent optical activity, the common form of variation being a fluctuation of a few tenths of a magnitude on a time scale of several months. Peach was unable to establish a correlation between such moderate optical activity and other observable parameters including the radio spectral index. In 1969 Hunter and Lü³ reported that about 20% of a sample of fourteen quasars had shown short-term outbursts of 0.7 mag. or more.