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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