GINGA X-ray observation of EX Hya : new constraints on the accretion model.

The results of a Ginga X-ray observation of the eclipsing intermediate polar system EX Hya are presented. These new data probe the characteristics of the 67-min modulation and the 98-min orbital eclipses at higher energies than was possible with Exosat. The average fractional depth of the X-ray eclipse goes up with increasing X-ray energy between 1.5 and 4 keV. Above 4 keV, the fractional eclipse depth is consistent with a constant level of 40-50 percent. Conversely, the pulse fraction of the rotational modulation decreases with increasing X-ray energy in the 1.5-6 keV range, but tends to a constant value of about 9-10 percent at energies above 6 keV; the modulation is significantly detected at energies up to at least 15 keV. There is a correlation between the depth of the individual eclipses and the local out-of-eclipse flux at energies below 4.5 keV. Current models for EX Hya are reviewed in the context of these new constraints.