A High Resolution X–ray Spectrum of the Liner Galaxy M81

We present the soft X–ray spectrum of the LINER galaxy M81 from a long observation with the XMM-Newton RGS. As well as continuum emission from the active nucleus , the spectrum shows emission lines from multi temperature collisionally ionized gas. The emission lines are significantly broader than the RGS point-source spectral resolution, and in the cross dispersion direction the emission lines are detected adjacent to, as well as coincident with, the active nucleus. This implies that they originate in a region of more than an arcminute (∼ 1 kpc) spatial extent. A good fit to the whole RGS spectrum can be found using a model consisting of an absorbed power law from the active nucleus and a 3 temperature thermal plasma. Two of the thermal plasma components have temperatures of 0.18±0.04 keV and 0.64±0.04 keV, characteristic of the hot interstellar medium produced by supernovae; the combined luminosity of these two plasma components accounts for all the unresolved bulge X–ray emission seen in the Chandra observation by Tennant et al. (2001). The third component has a higher temperature (1.7 +2.1 −0.5 keV) and we propose X–ray binaries in the bulge of M81 as the most likely source of this emission.