Multiwavelength monitoring of the BL Lacertae object PKS 2155-304. I. The IUE campaign

Daily monitoring with the IUE satellite has revealed dramatic, large-amplitude, rapid variations in the ultraviolet flux. Many smaller, rapid flares are superposed on a general doubling of the intensity. During the 5d period when sampling was roughly continuous, the rapid flaring had an apparent quasi-periodic nature. The short- and long-wavelength ultraviolet light curves are well correlated with each other, and with the optical light curve deduced from the Fine Error Sensor (FES) on IUE. The formal lag is zero, but the cross-correlation is asymmetric in the sense that the shorter wavelength emission leads the longer. The ultraviolet spectral shape varies a small but significant amount. An increase in intensity is associated with spectral hardening, but lags behind the spectral change by ~1 day. The sign of the correlation is consistent with the nonthermal acceleration processes expected in relativistic plasmas, so that the present results are consistent with relativistic jet models, which can also account for quasi-periodic flaring. In contrast, currently proposed accretion models are strongly ruled out by the observations

Duke Scholars

Author Jeffrey L. Krolik Electrical and Computer Engineering