THE INTRADAY VARIABLE QUASAR-0917- VLBI AND X-RAY OBSERVATIONS(624 )

We present the first VLBI images of the extremely rapidly variable rad io source 0917+624, at frequencies ranging from 2.3 to 22 GHz. They re veal a compact core containing similar to 75% of the total flux densit y, and a jet extending to the northwest at position angle -20 degrees. The jet is curved on the sub-milliarcsecond scale, and one of the jet components is elongated perpendicular to the jet direction. This comp onent displays apparent superluminal motion with a speed of beta(app)h = 7.8 +/- 0.8(1)). A first detection of X-rays from 0917+624 with the ROSAT satellite enables us to estimate the magnetic field and the Dop pler factor from synchrotron self-Compton theory. The observational re sults are compared with models for the rapid variability. The orientat ion of the jet on the sky is consistent with a prediction from two-com ponent models that were developed to explain the polarization variatio ns in 0917+624. The physical parameters derived from the new observati ons can be accomodated both by intrinsic (shock-in-jet or coherent emi ssion) and extrinsic (interstellar scattering) explanations of the var iability.