Hi again,
I downloaded the new xspec version, and have been trying
the pileup model. I'm wondering if a fixed frame time of 3.2sec is
correct, given that the spacecraft is dithering. Wouldn't the effective
frame time be less (although probably somewhat complicated)? If so,
any guesses as to what it might be?
Thanks again,
Mallory
On Sat, 11 Aug 2001, Keith A. Arnaud wrote:
> Hi Mallory,
>
> You are quite right and I think this point is under-appreciated. Even a very
> modest amount of pile-up can skew a fit and you can forget any attempt to
> learn about the high-energy behaviour of the spectrum.
>
> The method that Pat alluded to in his message was developed by John Davis at
> MIT and is released in their ISIS package. I have included an implementation
> of John's algorithm in the new version of XSPEC (11.1) which was made public
> this week. I would be interested in having people test this. This algorithm
> does not provide a complete solution in that a simple parametrization is
> adopted to handle grade migration (ie when two or more photons pile-up they
> may be assigned a worse grade than the individual events would have been).
>
> The only person I know who has done a complete solution to pile-up is George
> Chartas at PSU who analyzed the Chandra focus data using XSPEC, MARX, and
> their ACIS simulator, all running in a big loop.
>
> Keith
>
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