arXiv subjects
Publications and source records attributed to D. C. Hannikainen.
In the hard X-ray spectra of some X-ray binaries line features around 500 keV are detected. We interpret these as arising from pair annihilation in relativistic outflows leading to a significant Doppler shift of the frequencies of the lines. We show that a small fraction of pairs escaping the annihilation region may give rise to the radio synchrotron emission observed in Nova Muscae 1991.
We report multifrequency radio observations of GRO J1655-40 obtained with the Australia Telescope Compact Array, the Molonglo Observatory Synthesis Telescope and the Hartebeesthoek Radio Astronomy Observatory at the time of the major hard X-ray and radio outbursts in 1994 August-September. The radio emission reached levels of the order of a few Jy and was found to be linearly polarized by up to 10%, indicating a synchrotron origin. The light curves are in good agreement with those measured with the VLA, but our closer time sampling has revealed two new short-lived events and significant deviations from a simple exponential decay. The polarization data show that the magnetic field is well ordered and aligned at right angles to the radio jets for most of the monitoring period. The time evolution of the polarization cannot be explained solely in terms of a simple synchrotron bubble model, and we invoke a hybrid `core-lobe' model with a core which contributes both synchrotron and free-free emission and `lobes' which are classical synchrotron emitters.
The Molonglo Observatory Synthesis Telescope (MOST) has been monitoring the candidate Galactic black hole binary system GX 339-4 at 843 MHz since 1994 April. We present the results of this program up to 1997 February and show a possible correlation between radio and X-ray light curves.