The End! Berkhuijsen E., Haslam C., Salter C., 1971, A&A, 14, 252-262Egger R. J., Aschenbach B., 1995, A&A, 294, L25-L28Snowden S. L. et al., 1995, ApJ, 454, 643-653Snowden S. L. et al., 1997, ApJ, 485, 125-135Willingale R., XMM AO-2 ProposalWillingale R., Hands A. D. P., Warwick R. S., Snowden S. L., Burrows D. N., 2003, MNRAS, 343, 995-1001.
Three data sets, downloaded from the XMM archive 4.0 keV (background subtraction unreliable here)
Astrophysical Plasma Emission CodeThe power law is given two fixed photon indices (), 2.0 before the break at 0.7keV, and 1.4 thereafter. The higher value before the break represents the contribution of the background quasar population, which has now been partly resolved at very faint fluxes in observations by ROSAT and ChandraA model of the local ISM depicts a local bubble filled with a cool, tenuous gas (nH ~0.2) surrounded by an absorbing Wall lying at some distance dw from the Earth
The gas density within the Wall is assumed to be ~25 times greater than that within the bubble. This model, utilised by the wall_info.qin script, was used to calculate dw for each of the three fields. 9.2 Dimensions of the NPS SuperbubbleThe NPS is located on the edge of the Loop 1 Superbubble, an enormous feature within the central region of the Milky Way that encompasses the bright x-ray structures visible in figure 2. The Loop can be modelled by a circle of radius 42o, centred at lll=352o, bll=15o . The bubble.qin script constructs a spherical volume based on this circle. The sphere encloses the bulk of the x-ray emission in this area as required, but also contains some emission from the Galactic Bulge and absorbing regions of the Galactic Plane. However, since the observations are closely placed, it is assumed that the conditions along the lines of sight will be uniform, rendering negligible any variations due to the Bulge and Plane. A distance of 210 parsecs was set as the distance to the centre of the bubble, consistent with polarisation observations of the NPS. The radius of the bubble was set to 140 parsecs. The predicted entrance and exit distances, dlo and dhi, were then calculated for each field (table 5, figure 5).
The LHB emission measure is almost constant, and quite small, of the order 10-4 cm-6 pc over the three fields (table 6), as would be expected. Since the Solar System lies embedded within the LHB, it is unlikely that we would see significant variation when observing it over so small a region. The electron density is similarly consistent. The pressure within the LHB varies considerably, increasing abruptly in SXRB3. Both figure 4 and the calculated dw (28 parsecs) reveal that the Wall is significantly closer in SXRB3 than the other two fields. The increase in pressure may indicate an interaction between the LHB and the absorbing Wall at this location.The distance to the Wall decreases sharply as the observations move northwards, but the Wall density shows the opposite trend, being more than four times higher in the SXRB1 than in the other two fields. Since the distance (dlo) to the near side of the NPS is constant at ~73 parsecs, it appears that the increase in density is due to compression of the cold material lying between the two expanding shells of the LHB and the NPS. In the SXRB1 field, the LHB and NPS are much closer than in the other two fields, leading to higher compression of the intervening cold material, producing a higher density. The fourfold increase in density is consistent with a compression factor in the range of 5 11, suggested in .