The X‐Ray‐Emitting Components toward ℓ = 111o: The Local Hot Bubble and Beyond

Abstract

We have obtained an XMM-Newton spectrum of the diffuse X-ray emission toward (l,b)=(111.14deg,1.11deg), a line of sight with a relatively simple distribution of absorbing clouds: >9×1019 cm-2 at R>170 pc, a 6×1021 cm-2 molecular cloud at 2.5-3.3 kpc, and a total column of 1.2×1022 cm-2. We find that the analysis of the XMM-Newton spectrum in conjunction with the ROSAT All-Sky Survey (RASS) spectral energy distribution for the same direction requires three thermal components to be well fit: a ``standard'' Local Hot Bubble component with kT=0.095, a component beyond the molecular cloud with kT=0.57, and a component before the molecular cloud with kT=0.24. The strength of the O VII 0.56 keV line from the Local Hot Bubble, 1.75+/-0.7 photons cm-2 s-1 sr-1, is consistent with other recent measures. The 0.24 keV component has an emission measure of 0.0021+/-0.0006 cm-6 pc and is not localized save as diffuse emission within the Galactic plane. Rough calculations show that only about a quarter of this component is due to unresolved stellar emission; it is the best candidate for a pervasive hot medium. The spatial separation of the ~0.2 keV component from the ~0.6 keV component suggests that the spectral decompositions of the emission from late-type spiral disks found in the literature do represent real temperature components rather than reflecting more complex temperature distributions.