X-ray Spectroscopy of the Super Soft Source RXJ0925.7--475

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Session 48 -- Degenerate Stars and Pulsars
Display presentation, Thursday, June 15, 1995, 9:20am - 4:00pm

[48.01] X-ray Spectroscopy of the Super Soft Source RXJ0925.7--475

Ken Ebisawa,Koji Mukai (NASA/GSFC, USRA), Kazumi Asai, Tadayasu Dotani (ISAS, Japan)

Dozens of Super Soft Sources (SSS) have been discovered wtih Einsten and Rosat. Most SSS have X-ray emission in the narrow energy range between 0.1 and 0.5 keV. RXJ0925.7--475 is an unusual, the ``hardest'' SSS having the most X-ray emission above 0.5 keV. ASCA observed RXJ0925.7--475 with the energy resolution $\sim$ 10 \%; this is practically the first X-ray spectroscopy of SSS.

A blackbody model, which could fit ROSAT spectra, does not fit the data, and we clearly found several absorption edge structures. The edges are considered K or L-edges of ionized C, O, Ne and Fe, and optical depths are 0.6 -- 1.3. Steady nuclear burning on the surface of accreting white dwarves is a likely origin of SSS, and the hot white-dwarf atmosphere may yield such ionized heavy elements, However, the emission region size obtained from the current data is $R \sim$ 400 km ($d$/1kpc), much smaller than the white-dwarf surface area. This may suggest only a part of the white-dwarf surface is emitting X-rays.

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