A Low-State Eclipse Spectrum of Hercules X-1 Observed with ASCA

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©1997. The American Astronomical Society. All rights reserved. Printed in U.S.A.
, , Citation C. S. Choi et al 1997 ApJ 476 L81 DOI 10.1086/310499

1538-4357/476/2/L81

Abstract

We analyzed the ASCA data of Her X-1 obtained during the "extended low" intensity state on 1993 August 13 and August 28. Both observations cover orbital phases ranging from 0.7 to 1.25 including an X-ray eclipse. We find that the eclipse spectrum is modeled by a single power law with a photon index of 0.8 plus a soft blackbody of kT ~ 0.1 keV in the energy range of 0.5-10 keV. The estimated eclipse flux is (8.1 ± 0.6) × 10-12 ergs cm-2 s-1 (2-10 keV). The spectral shape is consistent with that obtained from the eclipse data of the "main high" with Ginga, although the flux is reduced by a factor of 3. Similarity of the eclipse spectra between the "low" and "high" state suggests the presence of a steady circumstellar matter surrounding the Her X-1 system. We interpret the flux reduction in the "low" state because of time variations of the X-ray scattering site.

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10.1086/310499