G. Latini

Optical Monitoring of Gamma-Ray Loud Blazars

The observations by the Compton Gamma Ray Observatory (CGRO) have shown that highly variable and radio-loud quasars emit a significant fraction of their energy in the γ band. According to the Inverse Compton model, the γ-ray emission is due to upscattering of soft (IR-optical-UV) photons by high energy particles. Optical monitoring is thus of great value in providing information on the mechanisms that rule the production of the seed photons for the γ-ray radiation and on the γ-ray emission itself. In particular, detection of variability correlations between optical and γ-ray emissions would be a crucial test for the theoretical predictions.

Variability Characteristics of Blazar OJ 287

Blazar OJ 287 is one of the best observed extragalactic objects. It’s historical light curve goes back to 1890’s. Based on the historical behaviour Sillanpaa et al. (1988) showed that OJ 287 displays large periodic outbursts, with a period of 11.7 years. We have monitored OJ 287 intensively for two years, during the OJ-94 project. This project was created for monitoring OJ 287 during its predicted new outburst in 1994. In the data archive we have over 7000 observations on OJ 287, in the radio, infrared and optical bands. This data archive contains the best ever obtained light curves for any extragalactic object. The optical light curve shows continuous variability down to time scales of tens of minutes. The variability observed in OJ 287 can be broken down to (at least) four different categories: 1. The large outbursts that occur every 11.7 years. The last one of these happened during November 1994, almost at the predicted time. These outbursts can be due to the binary black hole model proposed by Sillanpaa et al. (1988).