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A.P. Marscher, S.G. Jorstad (Boston U.), M.F. Aller (U. Michigan), I.M. McHardy (U. Southampton)
We have compiled over the past decade well-sampled light curves of several blazars with RXTE, the University of Michigan Radio Astronomy Observatory, Lowell Observatory, and the Liverpool Telescope, supplemented by data from many other telescopes supplied by collaborators. Over the same time span, we have followed changes in the parsec-scale jets through monthly or bimonthly imaging in both total and polarized intensity at 43 GHz (7 mm) with the VLBA. The X-ray flux varies on all sampled time scales, with power spectral densities corresponding to red noise. It is clear that the X-ray variations are correlated with those at lower frequencies. The correlations are complex, owing to gradients and inhomogeneities in the physical conditions of the emission regions, as well as to changes in the Doppler beaming factor caused by swings in the direction of the compact jet and possibly fluctuations in the bulk Lorentz factor of the jet flow. An unanticipated result is the existence of a time delay between changes in the synchrotron flux at lower frequencies and the X-ray variations. The X-rays therefore mostly come from regions in the jet that also produce optical and, at least in one quasar (PKS 1510-089), radio emission.
The correlations of the multiwaveband light curves, along with separately discovered correlations in mm-wave to optical polarization direction, provide a new method for mapping the multiwaveband emission in blazars. Through simultaneous monitoring of polarization at mm, near-IR, and optical wavelengths as well as polarization imaging with the VLBA at 7 mm, we can establish which feature in the mm-wave jet is responsible for the higher frequency emission and can determine the timing between events in the same feature at different wavelengths. We can use the correlations of variations in total flux to relate flares at these higher synchrotron frequencies to X-ray flares, thereby pinpointing the locations of the emission from radio to X-ray frequencies. We will show preliminary results from our program that apply this technique.
This work is based on research supported by NASA through the RXTE Guest Investigator Program and by NSF through grants to Boston U. and U. Michigan.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.