Re: question about aglc

    juan> why the first row of the time column is
    >> different than 0.0?,
    juan> is it possible to have the number of seconds
    >> since
    juan> 2450814.5?

    juan> But in my case the 1st value in the time column is different
    juan> that 0 (something aroun 400 s, but depends on the
    juan> observation). It should be equal to 0 if you do
    juan> TSTART-TIMEZERO?. the fact that it is different than 0 means
    juan> that the first photon didn't arrive when the observation
    juan> started?

Sorry, I missed the "different than 0.0" detail - and responded to the
"is it possible" part.

It is possible that there are no photons for 400s.  But it's unusual
to have 400 seconds without some event, though using the evt2 file
does reject background rather severely. Is it a faint source?  You are
using a narrow band, so that reduces the rate, also.

I specifically use the stat1 file as the primary reference to get the
exposure time vs frame ("expno"), even if there are no photons detected.

The HETGS background is roughly something like 1 count/bin/Ms, so in
0.1A, you have about 20 bins (MEG), so in 400s would have ~0.01
counts, if just background.  So hopefully your source is a couple orders of
magnitude above background.


-- Dave

David Huenemoerder  617-253-4283 (o); -253-8084 (f); http://space.mit.edu/home/dph
MIT Kavli Institute for Astrophysics and Space Research
70 Vassar St., NE80-6065,
Cambridge, MA  02139
[Admin. Asst.: Elaine Tirrell, 617-253-7480, egt_at_email.domain.hidden
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