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J.S. Kaastra, N. Roos, R. Mewe
EUVE observations of the Seyfert 1 galaxy NGC 5548 show the presence of line emission features identified as a Ne VII/Ne VIII blend at 88A and Si VII emission at 70A. The lines show significant broadening (FWHM 3800km/s) placing the emitting region at the same distance as the inner broad-line region. A fit to a thermal plasma yields a temperature of 6x10^5^K. The lines are possibly variable on a time scale of weeks. The line emission can be attributed to the warm absorbing material discovered before from oxygen and Fe absorption features, which then at a distance of ~3x10^14^m is near pressure equilibrium with the hot medium confining also the broad-line clouds. The material should have a low spatial filling factor. The plasma is probably closer to collisional ionisation equilibrium than to photo-ionisation equilibrium. Extra heat supply of the order of 10 % of the total AGN luminosity is required to sustain the high temperature.
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