Phase-dependent X-ray observations of the beta Lyrae system: No eclipse in the soft band

R Ignace$^1$, L M Oskinova$^2$, W L Waldron$^3$, J L Hoffman$^4$, W-R Hamann$^5$

$^1$ East Tennessee State University, $^2$ Universitat Potsdam, $^3$ Eureka Scientific Inc, $^4$ University of Denver

We report on observations of the eclipsing and interacting binary beta
Lyrae from the Suzaku X-ray telescope. This system involves an early
B star embedded in an optically and geometrically thick disk that is
siphoning atmospheric gases from a less massive late B II companion.
Motivated by an unpublished X-ray spectrum from the Einstein X-ray
telescope suggesting unusually hard emission, we obtained time with
Suzaku for pointings at three different phases within a single orbit.
From the XIS detectors, the softer X-ray emission appears typical of
an early-type star. What is surprising is the remarkably unchanging
character of this emission, both in luminosity and in spectral shape,
despite the highly asymmetric geometry of the system. We see no eclipse
effect below 10 keV. The constancy of the soft emission is plausibly
related to the wind of the embedded B star and Thomson scattering
of X-rays in the system, although it might be due to extended shock
structures arising near the accretion disk as a result of the unusually
high mass-transfer rate. There is some evidence from the PIN instrument
for hard emission in the 10-60 keV range. Follow-up observations with
the RXTE satellite will confirm this preliminary detection.

Reference: to appear as a Letter in A&A
Status: Manuscript has been accepted

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