CLOUDS, WINDS, AND JETS IN THE LUMINOUS X-RAY SOURCE CIRCINUS X-1

摘要

One of the early highlights of high resolution X-ray spectroscopy was the discovery of P Cygni lines in the highly variable and luminous X-ray source Circinus X-1 during the early days of the Chandra mission. By adapting the preceding paradigm established from ASCA observations that the accretion disk around the neutron star is viewed edge-on, the complex line structure was interpreted as a combination of accretion disk coronal line emission and absorption from a radiatively driven equatorial disk wind. The detection of ultra-relativistic radio jets at about the same time seemed to support the image of Circinus X-1 as a powerful microquasar, but also casted some doubt on the assumption that the source is viewed edge-on, but instead featured a face-on view. This not only challenges the current model for the observed X-ray emission, it could also force a complex scenario involving jets, winds, and clouds that seems quite unique among accreting compact sources. Furthermore the X-ray emission of Circinus X-1 has undergone radical changes since then as it gradually slipped into a low intensity state which is even at times devoid of the typical outburst pattern with its binary orbit. We observed Circinus X-1 several times with the Chandra HETG spectrometer during this transition. We show some preliminary results from the first of these observations, which provided the unobstructed high resolution X-ray image of this source as well as an X-ray spectrum that is devoid of P Cygni lines but shows line emission as expected from ADC sources. We discuss the results in conjunction with its long-term light-curve and investigate possible scenarios with respect to its line of sight.