MPIfR: Eduardo Ros

The intraday variable quasar 0917+624: VLBI and X-ray observations,
K. J. Standke, A. Quirrenbach, T. P. Krichbaum, A. Witzel, K. Otterbein, W. Alef, A. Eckart, A. Alberdi, J. M. Marcaide, E. Ros, H. Lesch, W. Steffen, A. Kraus, & J. A. Zensus,
Astronomy & Astrophysics, 306:27-36 (1996)
- Abstract We present the first VLBI images of the extremely rapidly variable radio source 0917+624, at frequencies ranging from 2.3 to 22 GHz. They reveal a compact core containing similar to 75% of the total flux density, 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 component 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 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.