Simultaneous radio/X-ray observations of Cir X-1

We present a partial analysis of a multi-wavelength study of the X-ray binary Cir X-1, a system harboring the most relativistic outflow in our galaxy so far. The data were taken (almost) simultaneously in radio and X ray during a survey carried out in October 2000 and December 2002. Cir X-1 was observed at the radio frequencies of 4.8 and 8.6 GHz with the Australia Telescope Compact Array (ATCA). In the X-ray spectral domain we used the Rossi X-Ray Timing Explorer (RXTE). We found strong evidence for flaring activity in radio not only at the periastron but also at the apoastron passages. A comparison of our data against different correlations between radio and X ray found in other neutron star systems shows that Cir X-1 does not seem to follow the general trend. However, the fact that Cir X-1 is an `exotic' X-ray binary makes any interpretation more complicated.