I have a discussion concerning doing this in the appendix of 1997 AJ 113,
1286. In that case we raytraced asca arfs for moderately-extended
On Tue, 31 Oct 2000, Keith A. Arnaud wrote:
> It is worth noting that averaging ARFs is only valid if the vignetting does
> not vary significantly over the region from which the spectrum was extracted.
> For large regions the correct procedure is to raytrace a spatial model of
> your source. I'm curious to know whether anyone is actually doing this.
> Keith Arnaud
> (Admittedly it took about 5 years for us to add this ability to the ASCA s/w
> so I don't expect this to be a priority, especially since Chandra's strength
> is small sources. I expect this to be more of an issue with XMM-Newton).
> On Tue, Oct 31, 2000 at 08:35:53AM -0500, Pat Broos wrote:
> > I intend to stick to the well-behaved FTOOL addarf for the time being. Addarf
> > is also more flexible, allowing you to average ARFs instead of adding them --
> > something very useful if you care to worry about the fact that real sources
> > are extracted over a finite region of the detector (which might include a chip
> > gap where the effective area is changing on scales of 10's of pixels), whereas
> > mkarf computes an ARF for a single point on the sky.
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