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N.S. Schulz (MIT), W.N. Brandt (PSU), D.K. Galloway, D. Chakrabarty, S. Heinz (MIT)
Observations of Circinus X-1 date back to the early days of X-ray astronomy. Still, its X-ray emission is poorly understood despite significant advances in recent years. The source has always appeared bright and is known to exhibit a remarkable variability pattern with its orbital period. To date, the compact object in the Cir X-1 system is thought to be a neutron star that can radiate at super-Eddington luminosities. Circinus X-1 shows various types of jets and outflows. Besides the existence of two arcminute-scale radio jets the presence of a highly relativistic outflow has recently been established in the radio band as well. P Cygni lines in X-ray spectra also revealed outflow activity, likely a disk wind with velocities of up to several thousand km/s. How these features are related is the subject of current studies, specifically in light of the currently derived limits from radio data of the jet's axis towards the line of sight. Circinus X-1 has now slipped into its lowest X-ray state in over 30 yrs. We will show results of new HETGS X-ray observations in this low state. Together with the previous HETGS observations we discuss the results in conjunction with its long-term X-ray lightcurve and investigate possible connections with the radio jets.
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Bulletin of the American Astronomical Society, 37 #2
© 2005. The American Astronomical Soceity.