The x-ray eclipse of the dwarf nova HT Cassiopeiae: Results from ASCA and ROSAT HRI observations

We report on a 1 day ASCA observation and ROSAT HRI observations of the eclipsing dwarf nova HT Gas. The presence of the X-ray eclipse, originally detected in a ROSAT PSPC observation, is confirmed at a much higher significance level. The quality of the ASCA light curve is high enough to allow detailed investigation of the eclipse depth, width, and shape. The eclipse is found to be deep, compatible with being total The eclipse width is comparable to that of the white dwarf, as derived from optical light curves, and in fact may be narrower. The eclipse transition is also found to be short, which puts a limit of 1.15 times the white dwarf radius as the total size of the X-ray emission region. The out-of-eclipse spectrum of HT Cas is found to be consistent with a single temperature (kT similar to 10 keV), absorbed (N-H similar to 3.3 x 10(21) cm(-2)), thermal model.