Giant H II Regions in M101. I. X-ray Analysis of Hot Gas
  We performed a Chandra X-ray study of three giant H II regions (GHRs), NGC
5461, NGC 5462, and NGC 5471, in the spiral galaxy M101. The X-ray spectra of
the three GHRs all contain a prominent thermal component with a temperature of
~0.2 keV. In NGC 5461, the spatial distribution of the soft (< 1.5 keV) X-ray
emission is generally in agreement with the extent of H1105, the most luminous
H II region therein, but extends beyond its southern boundary, which could be
attributed to outflows from the star cloud between H1105 and H1098. In NGC
5462, the X-ray emission is displaced from the H II regions and a ridge of blue
stars; the H-alpha filaments extending from the ridge of star cloud to the
diffuse X-rays suggest that hot gas outflows have occurred. The X-rays from NGC
5471 are concentrated at the B-knot, a "hypernova remnant" candidate. Assuming
a Sedov-Taylor evolution, the derived explosion energy, on the order of 10^52
ergs, is consistent with a hypernova origin. In addition, a bright source in
the field of NGC 5462 has been identified as a background AGN, instead of a
black hole X-ray binary in M101.
