The X-Ray-Emitting Components toward l = 111°: The Local Hot Bubble and Beyond

Abstract

We have obtained an XMM-Newton spectrum of the diffuse X-ray emission toward (l ,b) = (111.14°,1.11°) , 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.