Lecture 20. A couple of quick additions to past topics: WCS keywords of FITS files Common AIPS tasks Back to XMM calibration hardness ratios photon index vs energy index. WCS keywords of FITS files. WCS stands for W orld C oordinate S ystem. http://fits.gsfc.nasa.gov/fits_wcs.html
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WCS must encode the
relation between θ and the
Pixel grid on tangent plane
The general formula in this case is
(p - pref) * scale = tan(w – wref).
p is the pixel coordinate and w the
world coordinate. w might eg be
right ascension or declination.
(1) pref can be real-valued;
(2) By convention, p at the centre
of the 1st pixel = 1.0.
Silicon K edge
Oxygen K edge
Gold M edge
This is for pn – MOS is very similar.
where A is an effective area and the fractional exposure kernel X contains all the information about how the photon properties are attenuated and distributed.
erg s-1 eV-1 cm-2
photons s-1 eV-1
E of course is the photon energy.
All dimensionless except A.
This gets rid of the integral over r, and the r‘ in V and ρ become r0.
where the exposure mapε is
and the energy conversion factor (ECF) ψ is calculated by integrating over a model spectrum times R times A.
eV s-1 erg-1
erg s-1 eV-1 cm-2
where the ancillary response function (ARF) α is
This is a bit more rigorous because the resulting spectrum q is explicitly acknowledged to be pre-RM.
where the fractional exposuref is
This is probably the least rigorous of the three product-specific distillations of X.
Total energy S of all the N photons in a bin
of centre energy E is (about) N times E.
Matters aren’t helped by
the habit to use eV for the
photon energy but ergs
for the total energy!