High‐Resolution Observations of the Elliptical Galaxy NGC 4636 with the Reflection Grating Spectrometer on BoardXMM‐Newton

We present the first high spectral resolution X-ray observation of the giantelliptical galaxy NGC 4636, obtained with the Reflection Grating Spectrometeron-board the XMM-Newton Observatory. The resulting spectrum contains a wealthof emission lines from various charge states of oxygen, neon, magnesium, andiron. Examination of the cross-dispersion profiles of several of these linesprovides clear, unambiguous evidence of resonance scattering by the highestoscillator strength lines, as well as a weak temperature gradient in the innerregions of the interstellar medium. We invoke a sophisticated new Monte Carlotechnique which allows us to properly account for these effects in performingquantitative fits to the spectrum. Our spectral fits are not subject to many ofthe systematics that have plagued earlier investigations. The derived metalabundances are higher than have been inferred from prior, lower spectralresolution observations of this source (Awaki et al. 1994), but are stillincompatible with conventional chemical enrichment models of ellipticalgalaxies. In addition, our data are incompatible with standard cooling flowmodels for this system - our derived upper limit to the mass deposition rate isbelow the predicted value by a factor of 3--5.Comment: 8 pages, 2 figures; submitted to Ap