The ultraviolet variability of the BL Lacertae object OJ 287.

Abstract

The International Ultraviolet Explorer (IUE) satellite has been used to observe the BL Lacertae object, OJ287, at 26 epochs between 1978 May and 1984 May. These observations how large and often rapid variations in both the intensity and the spectral slope of the UV continuum. In general, the changes in intensity show little or no correlation with those in spectral index. This is consistent with previous studies of the UV variability of BL Lac objects. During the early months of 1983, OJ287 underwent a violent outburst similar to that observed in 1972. A significant correlation is found between intensity and spectral index when considering only those IUE observations taken during this outburst. The correlation is in the sense that the spectrum is harder when the continuum is brighter. Correlations of this type are common in variable Seyfert galaxies. This correlation is interpreted in terms of synchrotron emission from a population of non-thermal electrons.