ROSAT PSPC OBSERVATIONS OF THE EXTRAGALACTIC H-II REGION NGC-5408

We report the first ROSAT PSPC observations of the extragalactic H II region NGC 5408. The source is spatially unresolved and its spectrum is soft. Optically thin plasma models for the spectrum require a low metal abundance and a mean temperature of about 0.52 keV. The 0.2-2 keV luminosity of the source is 2 x 10(40) erg s-1. angstrom localized, violent starburst, in which 1000 supernovae occur within 100 000 yr, can account for the observed X-ray properties of NGC 5408. The low metallicity means that the expanding bubble produced by the supernovae becomes radiative much later than under Galactic conditions, so radiating much more of its energy as soft X-rays.