Suzaku X-ray Spectra and Pulse Profile Variations During the Superorbital Cycle of LMC X-4
Abstract
We present results from spectral and temporal analyses of Suzaku and RXTE observations of the high-mass X-ray binary LMC X-4. Using the full 13 years of available RXTE/all-sky monitor data, we apply the ANOVA and Lomb Normalized Periodogram methods to obtain an improved superorbital period measurement of 30.32 ± 0.04 days. The phase-averaged X-ray spectra from Suzaku observations during the high state of the superorbital period can be modeled in the 0.6-50 keV band as the combination of a power law with Γ ~ 0.6 and a high-energy cutoff at ~25 keV, a blackbody with kT BB ~ 0.18 keV, and emission lines from Fe Kα, O VIII, and Ne IX (X Lyα). Assuming a distance of 50 kpc, the source has luminosity L X ~ 3 × 1038 erg s-1 in the 2-50 keV band, and the luminosity of the soft (blackbody) component is L BB ~ 1.5 × 1037 erg s-1. The energy-resolved pulse profiles show single-peaked soft (0.5-1 keV) and hard (6-10 keV) pulses but a more complex pattern of medium (2-10 keV) pulses; cross-correlation of the hard with the soft pulses shows a phase shift that varies between observations. We interpret these results in terms of a picture in which a precessing disk reprocesses the hard X-rays and produces the observed soft spectral component, as has been suggested for the similar sources Her X-1 and SMC X-1.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- September 2010
- DOI:
- 10.1088/0004-637X/720/2/1202
- arXiv:
- arXiv:1007.3280
- Bibcode:
- 2010ApJ...720.1202H
- Keywords:
-
- accretion;
- accretion disks;
- pulsars: individual: LMC X-4;
- stars: neutron;
- X-rays: binaries;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 13 emulateapj pages, 11 figures, 4 tables