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

TL;DR

This study presents simultaneous X-ray and radio observations of Cir X-1, revealing radio flares near specific orbital phases and associating them with X-ray spectral changes, contributing to understanding neutron star binary behaviors.

Contribution

First simultaneous X-ray/radio observations of Cir X-1 that clearly associate radio flares with specific orbital phases and X-ray spectral changes.

Findings

Radio flares occur near orbital phases 0.0 and 0.5.

Radio flare and X-ray spectral changes are associated at phase 0.0.

Radio flares near phase 0.5 are confirmed with clearer evidence.

Abstract

We analysed simultaneous X-ray/radio observations of Circinus X-1 collected respectively with RXTE and ATCA in 2000 October and 2002 December and identified radio flares close to phase 0.0 and 0.5 of the orbital period. To date, there is only circumstantial evidence for radio flares near phase 0.5. Moreover, in our data set, we clearly associated both a radio flare and X-ray spectral timing changes with phase 0.0. While for black hole X-ray binaries the picture of the association between the X-ray and the radio bands is quite well understood, for neutron star X-ray binaries a clear and complete picture is still missing.