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XMM-Newton Science Analysis System Page: 1
eregionanalyse
November 22, 2004
Abstract
A routine to analyse regions in an input image and return information about it in
a set of parameters
1 Instruments/Modes
Instrument Mode
EPIC IMAGING
2 Use
pipeline processing no
interactive analysis yes
3 Description
This task takes as input an image and a source and background region and calculates the source box
centroid, the optimum radius for extraction of a point source and the number of counts in the source
region.
The essential input parameters are the name of an input image and a spatial selection expression for the
source and background areas, e.g. srcexp="((DETX,DETY) IN circle(572,-635,1340))"
backexp="((DETX,DETY) IN circle(2572,-1635,1340))". The selection required in the source and back-
ground expressions is the spatial region, which may be specied in sky (X/Y) or detector coordinates.
The task eregionanalyse calculates the source centroid (returned in the parameters xcentroid and
ycentroid), the optimum radius for point source extraction (parameter optradius) and the number of
counts in the source box (parameter srccnts)
The optimum radius is calculated using the PSF (EXTENDED mode) for the particular Epic camera for
a photon energy of 1.5 keV.
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3.1 Examples
3.1.1 Analyse a central source
eregionanalyse imageset=emosimage.ds srcexp="(DETX,DETY) in CIRCLE(639,-769,1200)"
backexp="(DETX,DETY) in CIRCLE(11400,-700,1200)"
This will set the parameters, xcentroid and ycentroid, to be the centre of the counts distribution within
the source box; the optimum radius from the source and background count distribution and the number
of counts in the source box.
3.1.2 Use a xed background value
eregionanalyse imageset=emosimage.ds srcexp="(DETX,DETY) in CIRCLE(639,-769,1200)"
backval=0.1
Finds the source centroid and optimum extraction radius for a background value of 0.1 counts per
arcsecond squared.
4 Parameters
This section documents the parameters recognized by this task (if any).
Parameter Mand Type Default Constraints
imageset yes string image
The name of the input image.
srcexp yes string
Expression for extracting the source events.
backexp no string NotSet
Expression for extracting the background events. If not set the background value is taken from the pa-
rameter backval.
backval no double 0.0
The background value in cnts per square arcsecond. This value is used if a backexp expression has not
been set, otherwise the parameter is ignored.
xcentroid no double
Output parameter that contains the X coordinate centroid. This will be in the units of the input image,
e.g. sky pixels, detector pixels or degrees.
ycentroid no double
Output parameter that contains the Y coordinate centroid. In the units of the input image.
optradius no double
Output parameter that contains the optimum extraction radius in the units of the input image (sky
pixels, detector pixels or degrees).
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srccnts no double
Output parameter that contains the total src (+backgnd) counts within the source region.
status no boolean
Output parameter. This is set to false if the input image was from a Timing or Burst mode observation
which eregionanalyse can not yet handle. Otherwise it is set true.
5 Errors
This section documents warnings and errors generated by this task (if any). Note that warnings and
errors can also be generated in the SAS infrastructure libraries, in which case they would not be docu-
mented here. Refer to the index of all errors and warnings available in the HTML version of the SAS
documentation.
InvalidExpression (error)
The input expression for this spatial region was not valid.
invalidArraySize (error)
The image is not two dimensional.
InvalidWCSType (error)
The image axes epecied in the CTYPE1 and CTYPE2 keywords are not compatible.
UnknownModeString (warning)
If the spectrum contains an observing mode (in the keyword SUBMODE) which is not
recognised then the software assumes that that the common PrimeFullWindow mode was
in use. The mode is used to calculate certain calibration quantities.
corrective action:
NoInstrument (warning)
If the INSTRUME keyword is not set in the image header a warning is issued and the default
of MOS-1 is taken.
corrective action:
InvalidPosWCSInfo (warning)
The REFerence keywords in the image header, e.g. REFXCRPX, REFXCRVL, REFXCDLT
are incomplete. Defaults are chosen but there is likely to be a problem later.
corrective action:
6 Input Files
 an EPIC image produced by evselect or xmmselect.
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7 Output Files
8 Algorithm
8.1 Optimisation
SNRMAX=0
TOTAL_SRC_COUNTS = counts in the input image within the source region
corrected for the encircled energy fraction of the
source region
Loop TEST_RADIUS = 1 to 300 arcseconds
EEF = calculate encircled energy fraction for this TEST_RADIUS
using the PSF relevant for this Epic camera at the
position of the source box for a photon energy of 1.5 keV
SRC_COUNTS = TOTAL_SRC_COUNTS * EEF
BGD_COUNTS = background counts per arcsec^2 * PI * TEST_RADIUS**2
S/N ratio = SRC_COUNTS / sqrt(SRC_COUNTS + BGD_COUNTS)
if (S/N ratio > SNRMAX) {
SNRMAX = S/N ratio
}
EndLoop
9 Comments
This task could be expanded to cover many aspects of simple image analysis.
References
xmmsas 20041122 1834-6.1.0