ROSAT OBSERVATIONS OF THE ERIDANUS SOFT-X-RAY ENHANCEMENT

We present maps of the Eridanus soft X-ray enhancement made from the R OSAT all-sky survey data. The maps are in two energy bands: 1/4 keV (0 .12-0.284 keV at 10% response, the ROSAT R1 and R2 bands), and 3/4 keV (0.47-1.20 keV at 10% response, the ROSAT R4 and R5 bands). The entir e enhancement spans a total of similar to 35 degrees in Galactic latit ude and similar to 20 degrees in Galactic longitude, centered at l sim ilar to 200 degrees, b similar to -32 degrees. While the higher spatia l resolution of the ROSAT data reveals a pattern of detailed anticorre lations with 100 mu m intensity that was not evident in the HEAO 1 or earlier data, the basic morphology found in previous maps of this enha ncement is confirmed. The ROSAT data also clearly show that the X-ray enhancement continues up to the Orion region in the 3/4 keV band, conf irming the structure suggested by the Wisconsin sky survey maps. The R OSAT data are consistent with the interpretation of Reynolds and Ogden and Burrows et al, that this enhancement, the higher temperature-comp onent of Burrows et al., is generated for the most part by several-mil lion-degree gas filling a huge interstellar cavity. However, we interp ret the low-temperature component discussed by Burrows et al. as part of a more distant large scale (greater than or similar to 30 degrees) diffuse background enhancement. The part of this softer X-ray enhancem ent examined here appears to be produced by million degree gas in the galactic halo, and is therefore unlikely to be an isolated bubble as s uggested by Burrows et al, on the basis of lower resolution HEAO 1 dat a.