Resolving the Effects of Resonant X-ray Line Scattering in Cen X-3
Abstract
The massive X-ray binary Cen X-3 was observed over approximately one quarter of the system's 2.08 day orbit, beginning before eclipse and ending slightly after eclipse center with the Chandra X-ray Observatory using its High-Energy Transmission Grating Spectometer. The n=2→1 emission triplet of helium-like silicon is resolved. Outside of eclipse, the component fluxes are consistent with emission from recombination and subsequent cascades in a photoionized plasma with temperature ~100 eV. In eclipse, the component flux ratios are consistent with emission from a collisionally ionized plasma with temperature ~1 keV. However, the triplet component flux ratios at both phases can be explained as arising from a photoionezed plasmas if the effects of resonant line scattering, a process which has generally been neglected in X-ray spectroscopy are included in addition to recombination radiation. We show that resonant line scattering in photoionized plasmas may increase the emissivity of n=2→1 line emission in hydrogen and helium-like ions by a factor as large as four relative to that of pure recombination and so previous studies, in which resonant scattering has been neglected, may contain significant errors in the derived plasma parameters. The emissivity due to resonance scattering depends sensitively on the line optical depth and, in the case of winds in X-ray binaries, this allows lower limits on the wind velocity even when Dopper shifts cannot be resolved.
- Publication:
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APS April Meeting Abstracts
- Pub Date:
- April 2002
- Bibcode:
- 2002APS..APRN17069W