Pat,
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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