Correlated Radio and Optical Variations in a Sample of AGN. A Simultaneous Radio-Optical Flare in BL Lacertae

摘要

The document contains 2 papers. In the first paper, the authors have studied fluxvariations in the optical and at radio wavelengths of a sample of extragalactic sources. Even though similar analyses have been done earlier, this is the first extensive study of connections between long-term optical and high radio frequency (from 22 GHz up to 230 GHz) variability in a large sample (22 sources) of AGN. In 10 out of the 22 sources, the authors found a clear radio-optical correlation, and in as many as 6 sources the optical and high frequency radio variability was simultaneous. In the second paper, an outburst of BL Lacertae was observed in the optical and at 22 and 37 GHz. The flare peaked at all frequencies within one week. Previous correlation analyses have demonstrated that radio variations in BL Lacertae are time delayed by as much as a few years. It is suggested that this, the first clear case of a truly simultaneous radio-optical flare, indicates the existence of at least two kinds of optical events.