Hi Jifeng and Chandra Users,
I'd like to point out that PIMMS is a proposal tool and should not be
used for detailed analysis. The Cycle 5 effective area curves are
actually projections of what we expect the EA to be in the middle of
Cycle 5, taking into account the slow degradation in the efficiency of
ACIS due to molecular contamination on the filter/CCD chips. Comparing
results from Cycle 5 PIMMS and actual data is invalid. This may (or may
not!) account for Jifeng's discrepancy. Jifeng's question has been
entered into helpdesk. We're working on understanding the discrepancy
and will circulate the answer when we have one.
Happy New Year everyone!
-- Andrea Prestwich
Jifeng Liu wrote:
>
> hello,
> i tried to obtain fluxes for sources detected by wavdetect, by two ways.
>
> the first, i use the net counts and the exptime (in unit of
> cm^2 sec count/photon), netcounts/exptime gives photon/cm^2/sec, and then i
> assume the incident photons have a power-law spectral shape with photonindex
> of 1.7, elow 0.3Kev, ehigh 8.0 Kev, and nH 1.57e20 cm^-2. such a spectrum gives
> 1 photon = 2.25e-09 erg. with this conversion factor, photon fluxes can be
> converted to fluxes with unit of erg/cm^2/sec.
>
> the second way, I don't use the exposure map, but just the exposure time as in
> the header. i use webpimms to convert ROSAT ACIS-S netcounts/exposure to fluxes.
> assuming the same spectrum and absorption, 1count/sec = 8.06e-12 erg/cm^2/sec.
>
> the fluxes obtained from the above two methods are different, the flux from the
> first method is usually 60% of the flux from the second method, regardless of
> their different off-axis angles.
>
> so what is the problem here? is pimms using old effective area data?
>
> I'll appreciate your remarks on this problem,
>
> happy holidays, still
>
> jifeng,
>
> --
> jifeng
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