1996A&A...306...27S

We present the first VLBI images of the extremely rapidly variable radio source 0917+624, at frequencies ranging from 2.3 to 22GHz. They reveal a compact core containing ∼75% of the total flux density, and a jet extending to the northwest at position angle -20deg. The jet is curved on the sub-milliarcsecond scale, and one of the jet components is elongated perpendicular to the jet direction. This component displays apparent superluminal motion with a speed of β_apph=7.8±0.8 (H₀=100h.km/s/Mpc; q₀=0.5). A first detection of X-rays from 0917+624 with the ROSAT satellite enables us to estimate the magnetic field and the Doppler factor from synchrotron self-Compton theory. The observational results are compared with models for the rapid variability. The orientation of the jet on the sky is consistent with a prediction from two-component models that were developed to explain the polarization variations in 0917+624. The physical parameters derived from the new observations can be accomodated both by intrinsic (shock-in-jet or coherent emission) and extrinsic (interstellar scattering) explanations of the variability.