SIMBAD references

The total 0.45-1.0 keV luminosity of M101 is 3.2x10³⁹ ergs s^–1, of which 2.3x10³⁹ ergs s^–1 is due to diffuse emission. (Chandra observes only ∼60% of the diffuse emission observed by ROSAT because of its superior point-source detection.) Of the diffuse emission seen by Chandra, no more than 6% can be due to luminous unresolved point sources, such as X-ray binaries, and ∼10% is likely due to dwarf stars. The diffuse emission traces the spiral arms and is roughly correlated with the Hα and far-UV emission. The radial distribution closely follows the optical profile. The bulk of the diffuse emission is characterized by a two-thermal component spectrum with kT=0.20 and 0.75 keV, and the ratio of the emission measures of the two components is roughly constant as a function of both radius and surface brightness. The softer component has a sufficiently large covering factor that the bulk of the emission is likely extraplanar. We find no evidence of an extended axisymmetric X-ray halo, suggesting that any such halo has a strength much smaller than current predictions.