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 observations of the high mass X-ray binary LMC X-4 at different phases in its superorbital cycle, which is due to the precession of a warped accretion disk. Using the full 13 years of available RXTE ASM data, we apply the ANOVA and Lomb Normalized Periodogram methods to obtain an improved superorbital period measurement of 30.32 ± 0.04 days, which accurately determines superorbital phases of Suzaku observations. The phase averaged X-ray spectra from Suzaku observations during the high state of the superorbital period can be modeled as the combination of emission lines, a power-law with Γ 0.67, and a blackbody with kTBB 0.17 keV, which most likely originates from reprocessing of the hard X-rays by the inner accretion disk. We calculate the source luminosity and the blackbody radius, assuming the distance to the source is 50 kpc. The energy resolved profiles show single--peaked soft pulses but a more complex pattern of hard pulses; cross--correlation of the hard with the soft pulses shows a phase shift between the two. As with the similar systems SMC X-1 and Her X-1, the variation of this phase shift throughout the superorbital period in LMC X-4 is broadly consistent with the picture in which a precessing disk reprocesses the hard X-rays and produces the observed soft spectral component at different orientations. This work is supported in part by the NSF REU and DOD ASSURE programs under NSF grant no. 0754568 and by the Smithsonian Institution.
- Publication:
-
American Astronomical Society Meeting Abstracts #215
- Pub Date:
- January 2010
- Bibcode:
- 2010AAS...21541909H