Multiwavelength monitoring of the BL Lacertae object PKS 2155-304. IV. Multiwavelength analysis

For pt.III see ibid., vol.438, no.1, p.108-19 (1995). Simultaneous X-ray, ultraviolet, optical, infrared, and radio monitoring data were used to test and constrain models of continuum emission from the BL Lac object PKS 2155-304. Intensively sampled ultraviolet and soft X-ray light curves showed a clear temporal correlation, with the X-rays leading the ultraviolet by 2-3 hr. This lag was found to be significantly different from zero after an exhaustive comparison of four different techniques for measuring temporal correlations. Variations in the ultraviolet through optical wave bands were also all strongly correlated, with no measurable lag down to limiting timescales of ≲1-2 hr. This strong correlation extends to the near-infrared, but the less intensive sampling precludes measurement of any lag beyond an upper limit of ≲1 day. These lags and limits of the order of hours are much shorter than the most rapid observed single-band variations. Because of the very sparse radio sampling, it was not possible to measure quantitatively the correlation and lag with shorter wavelengths, but the data do suggest that the radio may lag the optical/ultraviolet by ~1 week, with longer delays and weaker variations to longer radio wavelengths. The epoch-folding Q2 statistic was used to test for periodicity, but no evidence for strict or quasi-periodicity was found in any of the light curves The implications of these results for the various models of continuum generation in BL Lac objects are presented

Duke Scholars

Author Jeffrey L. Krolik Electrical and Computer Engineering