Shadowing of the 0.25-keV extragalactic X-ray background by the disc of NGC 55
Open Access
- 1 September 1996
- journal article
- Published by Oxford University Press (OUP) in Monthly Notices of the Royal Astronomical Society
- Vol. 282 (1) , 157-166
- https://doi.org/10.1093/mnras/282.1.157
Abstract
ROSAT observations are used to search for a shadow in the 0.25-keV X-ray background cast by the disc of the nearby spiral galaxy NGC 55. Several factors, including the close to edge-on aspect of this galaxy, its extensive H i disc and its location in a direction of relatively low Galactic foreground column density, make NGC 55 an excellent target in which to search for such effects. The ROSAT PSPC image shows a clear deficit of 0.25-keV counts coincident with the outer disc of NGC 55. From the depth of the shadow we obtain an estimate of the total extragalactic background signal at 0.25 keV of 29.4 ± 7.2 keV cm−2s−1 sr−1 keV−1. We compare this measurement with other recent estimates of the 0.25-keV background intensity, and briefly discuss the implications of the result in the context of the source populations which may produce the X-ray background radiation.Keywords
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