Dave,
On Mon, 19 Nov 2001, David P. Huenemoerder wrote:
>
> Eric> That's one possibility. But I have both a 0.4s frame-time
> Eric> dataset and a 3.2s frame-time dataset, with the former
> Eric> nearly unaffected by pile-up but only 1/4 the length. So I
> Eric> have another possibility: to just ratio the two datasets and
> Eric> then correct the longer, 3.2s frame-time dataset by the
> Eric> fraction of photons lost to pile-up. Of course this won't
> Eric> do anything spectrally, but it will be a try at getting the
> Eric> deep data to have a PSF which agrees with what mkpsf gives
> Eric> me.
>
> Eric> Any thoughts on doing this?
>
> The ratio may be too noisy to get an empirical PSF correction term.
> But the 0.4s should be good at constraining the spectral model and
> thus better determining the pileup fraction and modeling the piled
> psf. (depending on the counts). Or, instead of ratioing the data
> directly, you could ratio a models, where you fit 2D gaussian to
> the sources. (or some 2D profile, lacking an empirical
> parameterization of the psf).
>
> Are all sources near the optical axis, or near the same off-axis
> poisition? Off-axis psf nowhere near gaussian, so parametric fitting
> might be out of the question.
All the sources are within 30" of the optical axis, so psf-wise the situation
is near optimal (except for pile-up).
You (and everyone else) have given me a lot to think about here, that's for
sure. A lot to try out. Thanks!
Eric
-- Eric S. Perlman E-mail: perlman@jca.umbc.edu Joint Ctr. for Astrophysics, Physics Dept. Phone: +1 410 455 1982 University of Maryland, Baltimore County Fax: +1 410 455 1072 1000 Hilltop Circle WWW: www.jca.umbc.edu/~perlman Baltimore, MD 21250
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