Re: puzzlin Chandra proposal thread

Just a brief followup to be on the isis-users record ---

Adrienne didn't write the thread; it was a thread based on some of her
data.  It looks like the thread is interpreting the significance
incorrectly --- the conf() is done at 90%, and a 2.6e-5 (the upper
confidence level) flux would be detected at 90% (1.6 sigma)
confidence.  I'm consulting w/ the thread's actual author on the
5-sigma detection statement.

--Dave



    David> I reviewed this thread (from Adrienne Juett), but missed
    David> that subtle detail.  I think the thread is conveniently
    David> circular, having been written with the desired answer
    David> known.  If it didn't come out the way you wanted it, you
    David> would either have to adjust the exposure time, or flux and
    David> significance.  Does this make sense, or am I missing
    David> something more critical?

    David> --Dave


    Saku> Looking at the Chandra proposal thread:

    Saku> Calculate Exposure Time for a Single Line Detection using ACIS-S/HETG

    Saku> which is at 

    Saku> http://cxc.harvard.edu/proposer/threads/ldet_hetg/index.html


    Saku> At the start of the page it says:

    Saku> ``We would like to determine the exposure time needed to make a 5 sigma 
    Saku> detection of hydrogen-like Ne at 0.9-1.3 keV with a flux of 2.0e-5 photons 
    Saku> cm^-2 s^-1.''

    Saku> They start with a guess of 35ks.  After going through several steps 
    Saku> (a bit more than half way down the page) they say:

    Saku> ``The lowest flux that could be detected is therefore 2.6584e-05 photons cm^-2 
    Saku> s^-1. The chosen 35ks exposure time is adequate to detect the line of 
    Saku> interest.''

    Saku> Is this a misprint?

    Saku> Thanks,
    Saku> Saku 
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-- 
Dave
David Huenemoerder (617-253-4283; fax: 253-8084)
MIT Center for Space Research/Chandra X-ray Center
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