Low-frequency radio observations of persistent X-ray binary systems

Anna D. Kapinska

Research supervisors:

Dr. J.C.A. Miller-Jones & Prof. R.A.M.J. Wijers

Sterrenkunding Instituut 'Anton Pannekoek'

Universiteit van Amsterdam

M.Sc. Thesis accepted by the Universitet van Amsterdam

August 2007


Low-frequency radio observations (< 1 GHz) have been neglected for a long time in astronomical research. However, due to upcoming new radio facilities, interest in low radio frequencies has started to undergo rebirth. Here, we present a detailed examination of three well known Galactic X-ray binaries, i.e. SS 433, GRS 1915+105 and Cygnus X-3, observed with the Westerbork Synthesis Radio Telescope at radio frequencies of 117 - 175 and 310 - 380 MHz.

Before we present our results, we give a short introduction to X-ray binary systems; both basic accretion physics and properties of the high-mass and low-mass binary systems are outlined. Further, synchrotron radiation physics is introduced and dis- cussed. Finally, we discuss the radio interferometry theory in detail and present extensively used methodology.

We report on the detection of two out of the three sources we have chosen. SS 433 and GRS 1915+105 are detected in the 346 MHz maps. Only SS 433 is detected in the 160 MHz map. The spectral behaviour of the sources shows different stages of their activity at the time of the observations. Particularly, in the case of SS 433 we report on the detection of newly ejected jet material at 346 MHz, which is superimposed on the underlying steep spectrum. GRS 1915+105 is relatively radio weak and shows a steep radio spectrum. Only Cygnus X-3 was not detected, which suggests that this source is self-absorbed at these low radio frequencies.

We report on the attempts to detect extended radio emission that could be associated with outflows of GRS 1915+105 and Cygnus X-3. None of shock features associated with jets are detected in the surroundings of Cygnus X-3. Only two symmetric IRAS sources on the either side of GRS 1915+105 have been detected. The sources have been suggested previously as possible hot spots of GRS 1915+105. However, the link between the sources and the binary remain still unclear.

Additionally, we have performed examinations of background sources detected in the analysed fields. Most detected sources are expected to be steep spectrum extragalac- tic sources, and only a small fraction of the sources, which show flat spectra, seem to come from the Galactic Plane. This is consistent with predictions. We find that only approximately half of the sources detected at 346 MHz have their counterparts at 160 MHz.

Finally, based on our results, we discuss the possibilities and difficulties appearing at low radio frequencies and try to help with investigating good observing strategies for future LOFAR observations.