SPECTROSCOPIC SIGNATURES OF THE SUPERORBITAL PERIOD IN THE NEUTRON STAR BINARY LMC X-4
Author(s)Neilsen, Joseph M. G.; Lee, Julia C.; Nowak, Michael A.; Dennerl, Konrad; Vrtilek, Saeqa Dil
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We present the first high-resolution X-ray study of emission line variability with superorbital phase in the neutron star binary LMC X-4. Our analysis provides new evidence from X-ray spectroscopy confirming accretion disk precession as the origin of the superorbital period. The spectra, obtained with the Chandra High-Energy Transmission Grating Spectrometer and the XMM-Newton Reflection Grating Spectrometer, contain a number of emission features, including lines from hydrogen-like and helium-like species of N, O, Ne, and Fe, a narrow O VII radiative recombination continua (RRCs), and fluorescent emission from cold Fe. We use the narrow RRC and the Heα triplets to constrain the temperature and density of the (photoionized) gas. By comparing spectra from different superorbital phases, we attempt to isolate the contributions to line emission from the accretion disk and the stellar wind. There is also evidence for highly ionized iron redshifted and blueshifted by ~25,000 km s[superscript –1]. We argue that this emission originates in the inner accretion disk and show that the emission line properties in LMC X-4 are natural consequences of accretion disk precession.
DepartmentMIT Kavli Institute for Astrophysics and Space Research
Institute of Physics/American Astronomical Society
Neilsen, Joseph, Julia C. Lee, Michael A. Nowak, Konrad Dennerl, and Saeqa Dil Vrtilek. “SPECTROSCOPIC SIGNATURES OF THE SUPERORBITAL PERIOD IN THE NEUTRON STAR BINARY LMC X-4.” The Astrophysical Journal 696, no. 1 (April 15, 2009): 182–191. © 2009 American Astronomical Society.
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