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Consider the example of an ASCA SIS spectrum extracted from a circular region of radius 80 detector pixels centered on the detector coordinate position (430.32,410.60). The rebinning factor used to make the WMAP is 8 (ie WMREBIN is set to 8). The event file specifies the ASCA SIS detector pixel has a size of 0.027 mm so the CDELT1 and CDELT2 are set to $0.027 * 8 = 0.216$. The original detector coordinates have a reference pixel of the center of the array (640.5, 640.5) and assign this a physical position of (0mm, 0mm). The CRPIX1/2 keywords give the WMAP pixel positions of the physical position (0mm, 0mm).

The keywords ending in P document the relation between the original detector pixels and the WMAP pixels. Thus CDELT1/2P is 8 for the rebinning factor while CRVAL1/2P give the original detector coordinate position of the WMAP pixel (1,1) (as specified by CRPIX1/2P).

WMREBIN =                           8 / Weighted Map rebinning
CRPIX1  = 3.687500000000000E+01 / X axis reference pixel
DRPIX1  = 6.405000000000000E+02 / original X axis reference pixel
CRVAL1  = 0.000000000000000E+00 / coord of X ref pixel
CDELT1  = 2.160000000000000E-01 / X axis increment
DDELT1  = 2.700000000000000E-02 / original X axis increment
CRPIX2  = 3.937500000000000E+01 / Y axis reference pixel
DRPIX2  = 6.405000000000000E+02 / original Y axis reference pixel
CRVAL2  = 0.000000000000000E+00 / coord of Y ref pixel
CDELT2  = 2.160000000000000E-01 / Y axis increment
DDELT2  = 2.700000000000000E-02 / original Y axis increment
CTYPE1P = 'DETX    '           / Source of X-axis
CRPIX1P = 1.000000000000000E+00 / X axis reference pixel
CRVAL1P = 3.535000000000000E+02 / coord of X ref pixel in original image
CDELT1P = 8.000000000000000E+00 / X axis increment
CTYPE2P = 'DETY    '           / Source of Y-axis
CRPIX2P = 1.000000000000000E+00 / Y axis reference pixel
CRVAL2P = 3.335000000000000E+02 / coord of Y ref pixel in original image
CDELT2P = 8.000000000000000E+00 / Y axis increment
OPTIC1  = 6.627222290000000E+02 / X Optical axis in detector pixels
OPTIC2  = 5.590184936500000E+02 / Y Optical axis in detector pixels
HDUVERS = '2.0.0   '           / Version of format (OGIP memo OGIP-96-001)
HDUCLASS= 'ogip    '           / Format conforms to OGIP/GSFC conventions
HDUCLAS1= 'IMAGE   '           / Extension contains an image
HDUCLAS2= 'WMAP    '           / Extension contains a weighted map
HDUDOC  = 'OGIP/96-001'        / OGIP memo describing format
BLANK   =                          -1 / Null value

next up previous
Up: ogip_96_001 Previous: Upgrading software from HDUVERS=1
Keith Arnaud