Pulse-phase Spectroscopy of Her X-1

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Session 10 -- Variable Stars
Display presentation, Monday, June 12, 1995, 9:20am - 6:30pm

[10.04] Pulse-phase Spectroscopy of Her X-1

Chun Xu (UMd), S.D. Vrtilek (UMd and CfA), B. Boroson, \& R. McCray (University of Colorado)

ASCA observations of Hercules X-1 obtained in August 1994 during the ``main-on'' state of the 35-day cycle show the system back in its ``normal'' state following the anomalous low state (X-ray flux down by a factor of 50 from expected) seen by ASCA a year earlier (Vrtilek \etal~1994). The continuum emission is well fit by a power-law with photon index $\alpha$ = 0.98 $\pm$0.01 and a blackbody at 0.11 $\pm$ .01 keV consistent with previous ``normal'' state observations. Strong spectral features are observed at 6.43 $\pm$0.03 and 0.91 $\pm$0.04 keV that can be attributed to Fe K-shell and L-shell emission. The strength of the Fe K shell emission and the black-body component change dramatically as a function of pulse phase. The X-ray pulse profile shows double-peak structure in both the main pulse and the interpulse; the latter has been seen previously only during the ``short-on'' state. This profile can be explained in terms of a thick funnel-shaped X-ray emission beam that sweeps past the observer.

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