Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998apj...503l.143a&link_type=abstract
Astrophysical Journal Letters v.503, p.L143
Astronomy and Astrophysics
Astronomy
11
Stars: Binaries: Close, Stars: Binaries: Eclipsing, Stars: Individual Alphanumeric: Cal 87, Stars: White Dwarfs, X-Rays: Stars
Scientific paper
We have investigated the energy spectrum and the orbital modulation of the supersoft X-ray source CAL 87 using the ASCA satellite. We have detected a deep absorption edge at 0.85^{+0.02}_{-0.01} keV superposed on a continuum that can be approximated with an absorbed blackbody ( kT=0.05^{+0.06}_{-0.01} keV). The edge structure may be produced by the highly ionized species of O VIII and O VII. Such deep edge structures from highly ionized heavy elements are expected for X-ray emission from a white dwarf with an envelope of stable hydrogen burning and strongly supports the model that a white dwarf with a large mass accretion rate is involved in the supersoft X-ray sources. Epoch-folding analysis reveals the presence of a partial X-ray eclipse with broad wings at orbital phase 0; the eclipse covers a quarter of the orbital phase and the X-ray flux decreases down to ~40% of the out-of-eclipse level. We discuss the possible cause of the partial eclipse, including the extended emission region due to the accretion disk corona, and the X-ray scattering site formed by the gas escaping from the binary system, where the gas is highly ionized by the large X-ray luminosity from the white dwarf.
Asai Kikuo
Dotani Tadayasu
Ebisawa Ken
Kotani Takao
Mukai Kazuhiko
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