SPECTROSCOPIC SIGNATURES OF THE SUPERORBITAL PERIOD IN THE NEUTRON STAR BINARY LMC X-4

Journal Article · Fri May 01 04:00:00 EDT 2009 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/696/1/182; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)· OSTI ID:21296211

Neilsen, Joseph; Lee, Julia C ^[1]; Nowak, Michael A ^[2]; Dennerl, Konrad ^[3]

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1. Astronomy Department, Harvard University, Cambridge, MA 02138 (United States)
2. MIT Kavli Institute for Astrophysics and Space Research, Cambridge, MA 02139 (United States)
3. Max-Planck-Institut fuer extraterrestrische Physik, Giessenbachstrasse, 85748 Garching (Germany)

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 He{alpha} 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 {approx}25,000 km s{sup -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.

• OSTI ID: 21296211
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 696; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

99 GENERAL AND MISCELLANEOUS
ACCRETION DISKS
FLUORESCENCE
HELIUM
HYDROGEN
IRON
NEUTRON STARS
NEUTRONS
PHOTOIONIZATION
RECOMBINATION
SPECTROMETERS
STELLAR WINDS
X RADIATION
X-RAY SPECTROSCOPY