Suzaku Observations of Orbital Phase-Dependent Dipping and Obscuration in Cyg X-1
Abstract
The black hole candidate Cygnus X-1 is in orbit around O9.7Iab companion which has a significant wind component that intersects our line of sight to the X-ray source. At superior conjunction (orbital phase 0, i.e., the O-star companion in front of the black hole), strong absorption lines of hydrogen-like and helium-like ions are clearly detected, as we have shown with prior high-resolution X-ray spectroscopy observations utilizing Chandra-HETG and XMM-Newtown RGS. But along with a highly ionized component, the wind contains colder, denser clumps of material which lead to deep dipping periods at soft X-ray. Such dips have been seen and characterized with lower resolution X-ray instruments as well. These dense clumps appear over all orbital phases, although they are most prevalent near phase 0, and least prevalent near phase 0.5. In this poster, we show how the ionized wind and dense clumps manifest themselves in the CCD-quality spectra obtained with Suzaku. Suzaku has a combination of large effective area, moderate spectral resolution, and a spectral response extending to energies as low as 500 eV. The presence of the ionized wind is clearly required in the Suzaku spectra, even outside of dipping periods, and we describe how we model it in the CCD spectra. Additionally, we describe the dipping behavior as a function of orbital phase. Some of the Suzaku observations have one of the CCDs run in high time resolution mode, which allows us to characterize the temporal profile of the dips. Some of the dips can be extremely deep over remarkably short time scales, leading one to describe the average spectra with "partial covering models" wherein the partial covering may be better described as being temporal rather than spatial. This research is supported by NASA Grant ADP_2011_NNX12AE37G.
- Publication:
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AAS/High Energy Astrophysics Division #13
- Pub Date:
- April 2013
- Bibcode:
- 2013HEAD...1312619N