AnXMM‐NewtonObservation of the Local Bubble Using a Shadowing Filament in the Southern Galactic Hemisphere

We present an analysis of the X-ray spectrum of the Local Bubble, obtained bysimultaneously analyzing spectra from two XMM-Newton pointings on and off anabsorbing filament in the Southern galactic hemisphere (b ~ -45 deg). We usethe difference in the Galactic column density in these two directions to deducethe contributions of the unabsorbed foreground emission due to the LocalBubble, and the absorbed emission from the Galactic halo and the extragalacticbackground. We find the Local Bubble emission is consistent with emission froma plasma in collisional ionization equilibrium with a temperature $\log T_{LB}= 6.06^{+0.02}_{-0.04}$ and an emission measure of 0.018 cm^{-6} pc. Ourmeasured temperature is in good agreement with values obtained from ROSATAll-Sky Survey data, but is lower than that measured by other recent XMM-Newtonobservations of the Local Bubble, which find $\log T_{LB} \approx 6.2$(although for some of these observations it is possible that the foregroundemission is contaminated by non-Local Bubble emission from Loop I). The highertemperature observed towards other directions is inconsistent with our data,when combined with a FUSE measurement of the Galactic halo O VI intensity. Thistherefore suggests that the Local Bubble is thermally anisotropic. Our data are unable to rule out a non-equilibrium model in which the plasmais underionized. However, an overionized recombining plasma model, whileobservationally acceptable for certain densities and temperatures, generallygives an implausibly young age for the Local Bubble ($\la 6 \times 10^5$ yr).Comment: Accepted for publication in the Astrophysical Journal. 16 pages, 9 figure