Date Name Description
2009-10-28 C. Schmid 1st version
2009-11-17 H. Brunner reordered section headings
filled in change log
2009-11-17 all format approved
The PSFs for the 7 telescopes of eROSITA are stored in individual files with the filename format TBD. For each telescope the 2-dimensional PSF is given by a set of FITS images for different configurations in parameter space (specific energy, off-axis angle THETA and azimuthal angle PHI). The naming convention for the individual image extensions is "???eV_???arcmin" as for XMM-Newton, where the question marks have to be replaced by the corresponding parameter values for the photon energy, the off-axis angle, and the azimuthal angle (considering different azimuthal angles it might be necessary to switch to "???eV_???arcmin_???deg" in order to conserve uniqueness). The different configurations are located on a cubic grid in the 3-dimensional parameter space. The images should be normalized to unity (i.e., the sum of all pixel values should be 1) as indicated by the SUMRCTS keyword.
In the following a description of one individual 2-dimensional PSF FITS image extension is given.
The FITS file consists of several image extensions, each having the following format:
Name Value Description
EXTNAME '???eV_???arcmin' photon energy and off-axis angle the PSF was generated for
HCUCLASS 'OGIP' the name of the organization that defined this file format
HDUDOC 'CAL/GEN/92-027'
HDUCLAS1 'IMAGE'
HDUCLAS2 'PSF'
HDUCLAS3 'PREDICTED' origin of dataset, either PREDICTED or OBSERVED
HDUCLAS4 'NET' TOTAL: PSF includes background, NET: background subtracted
HDUVERS '1.0.0'
TELESCOP 'FM4'
INSTRUME 'eROSITA'
CTYPE1 'DETX' the names of the coordinates respresented by the first and
CTYPE2 'DETY' second axes
CRPIX1 & CRPIX2 the locations of a reference point along the first and second axes
in units of the axis index. This value is based upon counters which
run from 1 to NAXIS1/NAXIS2 with an increment of 1 per pixel. The
reference point vlaues need not be that for the center of a pixel nor
lie within the actual data array.
CRVAL1 & CRVAL2 the values of the coordinate system specified by the corresponding
CTYPE keyword at the reference point given by the CRPIX keywords
in units specified by the CUNIT keywords.
CDELT1 & CDELT2 the length of one side of the pixel at the reference point given
by the CRPIX keywords in units specified by the CUNIT keywords.
CUNIT1 'mm' the units of the physical quantities specified by the CTYPE keywords.
CUNIT2 'mm' Allowed values are given in CAL/GEN/93-001.
BACKGRND the background count rate in units of counts per pixel (where the
pixel size is defined by PIXSIZ). If no underlying instrument or
cosmic background is expected, the a value of zero should be entered.
ENERG_LO the minimum energy (in keV) for which the PSF dataset was constructed
or is valid. The value -99.0 indicates that the value is unknown.
ENERG_HI the maximum energy (in keV) for which the PSF dataset was constructed
or is valid. The value -99.0 indicates that the value is unknown.
The order of the energy bins should be sequential, starting
from the lowest value (>=0). In no case should there be any
overlap between consecutive energy bins, i.e., ENERG_LO(i) >=
ENERG_HI(i-1) (actually this should be an equality).
CHANMIN the minimum detector channel number for which the PSF dataset was
constructed or is valid. The value -99.0 indicates that the value
is unknown.
CHANMAX the maximum detector channel number for which the PSF dataset was
constructed or is valid. The value -99.0 indicates that the value
is unknown.
CHANTYPE 'PHA' type of detector channels in CHANMIN & CHANMAX, either 'PHA' or 'PI'
SUMRCTS 1.0 the sum of the raw counts under the PSF dataset (normalization);
recommended to be 1.0
CCLS0001 'BCF' the OGIP class of this calibration file
CDTP0001 'DATA' the OGIP class of the data type
CCNM0001 '2D_PSF' the OGIP codename for the contents
CBDn0001 the parameter-space limitations of the dataset (see CAL/GEN/92-003);
examples: CBD10001 = 'ENERG( 1- 2)keV'
CBD20001 = 'THETA( 6.0)arcmin'
CBD30001 = 'PHI( 9.0)deg'
CVSD0001 calibration validity start date
CVST0001 calibration validity start time
CDES0001 a descriptive string of the calibration dataset
ENERGY photon energy the PSF was generated for [eV]
THETA off-axis angle [arcmin]
PHI azimuthal angle [deg]
Y_PIXSZ & Z_PIXSZ XMM: pixel size in [mm] (should be the same as CDELT1 and CDELT2)
Y_EXTENT & Z_EXTENT XMM: number of pixels along Y and Z respectively (should be the same
as NAXIS1 and NAXIS2)
Type: image (floating point pixel values)