  We obtained relatively high signal-to-noise X-ray spectral data of the early
massive star tau Sco (B0.2V) with the Suzaku XIS instrument. This source
displays several unusual features that motivated our study: (a) redshifted
absorption in UV P Cygni lines to approximately +250 km/s suggestive of
infalling gas, (b) unusually hard X-ray emission requiring hot plasma at
temperatures in excess of 10 MK whereas most massive stars show relatively soft
X-rays at a few MK, and (c) a complex photospheric magnetic field of open and
closed field lines. In an attempt to understand the hard component better,
X-ray data were obtained at six roughly equally spaced phases within the same
epoch of tau Sco's 41 day rotation period. The XIS instrument has three
operable detectors: XIS1 is back illuminated with sensitivity down to 0.2 keV;
XIS0 and XIS2 are front illuminated with sensivitity only down to 0.4 keV and
have overall less effective area than XIS1. The XIS0 and XIS3 detectors show
relatively little variability. In contrast, there is a 4sigma detection of a 4%
drop in the count rate of the XIS1 detector at one rotational phase. In
addition, all three detectors show a 3% increase in count rate at the same
phase. The most optimistic prediction of X-ray variability allows for a 40%
change in the count rate, particularly near phases where we have pointings.
Observed modulations in the X-ray light curve on the rotation cycle is an order
of magnitude smaller than this, which places new stringent constraints on
future modeling of this interesting magnetic massive star.
