Документ взят из кэша поисковой машины. Адрес оригинального документа : http://xmm.vilspa.esa.es/sas/8.0.0/doc/flspec.ps.gz Дата изменения: Wed Jul 2 08:54:22 2008 Дата индексирования: Tue Oct 2 08:46:44 2012 Кодировка: Поисковые слова: annular

XMM-Newton Science Analysis System Page: 1
spec
July 2, 2008
Abstract
Computes the spectrum of the background uctuations for a specied spatial pixel
size and dierent oaxis angles.
1 Instruments/Modes
Instrument Mode
EPIC-MOS Imaging
EPIC-pn Imaging
2 Use
pipeline processing yes
interactive analysis yes
3 Description
spec computes the spectrum of the background uctuations in EPIC Imaging data in dierent oaxis
annular regions.
The rst step of the process is the ' atelding' (division) of the input image with the corresponding
exposure map. Since the borders of the exposure map can be aected by counting statistics, it is previously
'cleaned' with the output of emask using a value of 0.1 as a threshold, i.e, only the area of the map
with exposure time greater than 100% of maximum value is retained. Then the regions aected by the
observed sources (listed in the input source list) are removed taking into account the sizes obtained with
the task region (radiusmode=enfrac with an enclosed energy fraction of 95%).
Once the ' atelded' image is free from detected sources, its pixels are binned according to the input
parameter binsize and classied as 'positive' (if they have more counts than the median in the image)
and 'negative' pixels (less counts than the median). Those binned pixels with positive(negative) label
will lead to pixels with \1" (\0") in the positive(negative) mask that spec creates with the pixel size
of the input image. Those pixels that have null value in the atelded image (0 secs. in exposure time
or pixel inside a region source) are kept as \0" in both masks.
xmmsas 20080701 1801-8.0.0

XMM-Newton Science Analysis System Page: 2
These masks are then used to lter the input event list and extract positive(negative) spectra from a
number of equal-area annuli around the image centre, to account for variations of the eective area as a
function of the oaxis angle. The positive and negative spectra are extracted with an spectral binning of
15 eV (MOS) and 5 eV (PN).
Once created, positive and negative spectra are subtracted to obtain the ' uctuations' spectrum in each
annular region (the number of oaxis regions is xed by the number of output spectral les in the list
spectrumsets).
The subtraction is performed normalising the solid angle in units of detector pixels (squared pixels of side
0.05 arcseconds) to that of the annular extraction region, i.e.,
difference= (TotSA/PosSA)*positive_spec - (TotSA/NegSA)*negative_spec.
where PosSA and NegSA are the 'positive' and 'negative' spectrum solid angles, and TotSA is the solid
angle in the annular extraction region.
The BACKSCAL attribute in this dierence spectrum will then keep the value of the solid angle for the full
annular region. Provided one of these positive/negative spectra has zero area, a warning is raised and
the dierence spectrum stores the non zero area spectrum:
difference= (TotSA/PosSA)*positive_spec - 0.0*negative_spec
or
difference= 0.0*positive_spec - (TotSA/NegSA)*negative_spec
BACKSCAL=0 if both spectra have null extraction area.
The OFFAXIS attribute in the 'SPECTRUM' extension of each output spectral le stores the central
oaxis of the annular extraction region in arcmin.
If the observation is confusion dominated (as will be the case in most of them), the uctuation spectrum
is related to the average spectrum of the sources that dominate the uctuations (below the detection
threshold). This is necessary to estimate the systematic errors in the spectra of the faint detected
sources.
Otherwise, if the observation is counting-noise limited, the spectrum of the uctuations gives the shapes
of the errors in the spectra of the faint detected sources.
4 Parameters
This section documents the parameters recognized by this task (if any).
Parameter Mand Type Default Constraints
sourcelistset yes string emllist.fits valid data set name
Name of the FITS le containing the list of observed sources
xmmsas 20080701 1801-8.0.0

XMM-Newton Science Analysis System Page: 3
set yes string evtlist.fits valid data set name
Event list lename of the EPIC imaging observation
imageset yes string image.fits valid data set name
Image of set in a reference energy band
exposureset yes string expmap.fits valid data set name
Exposure map corresponding to image
tmpsrclistset no string src list.ds valid le name
Name of the temporary le used by region during ltering of source list
tmpbkgregionset no string bkg.reg valid le name
Name of the temporary le containing the background regions for the sources.
tmp atset no string img flat.fits valid le name
Name of the le containing the temporary atelded image.
tmpposmaskset no string mask pos.fits valid le name
Name of the le containing the temporary positive image mask
tmpnegmaskset no string mask neg.fits valid le name
Name of the le containing the temporary negative image mask
tmpposspecset no string spec pos.pi valid le name
Name of the le containing a temporary positive spectrum
tmpnegspecset no string spec neg.pi valid le name
Name of the le containing a temporary negative spectrum
binsize yes real 0.016666666 > 0:0
Size of the rebinned pixels in degrees to dene positive and negative regions. It will be rounded to the
nearest integer multiple of the pixel size in the input image
spectrumsets yes list of
data-sets
specfl0.fits
specfl1.fits
specfl2.fits
specfl3.fits
specfl4.fits
list of valid data sets
List of output FITS les containing the spectrum of the background uctuations extracted in equal-area
annular regions at dierent oaxis values (between 0. and 12 arcmin).
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.
NotImg (fatal)
xmmsas 20080701 1801-8.0.0

XMM-Newton Science Analysis System Page: 4
The input image does not contain an EPIC image
NotExpMap (fatal)
The input exposure map does not contain an EPIC exposure map
NonStandardInput (fatal)
The WCS keyword CDELT1 is missing in the input image
InvalidData (fatal)
Input image does not have valid data
ErrStat (fatal)
It cannot calculate statistics for input Event List File using FTOOLS task fstatistic
ErrFarith (fatal)
The FTOOLS task farith cannot be run in the process explained by the associated message
ErrFcolpar (fatal)
The FTOOLS task fcolpar cannot be run in the process explained by the associated message
ErrFimgstat (fatal)
The FTOOLS task fimgstat cannot be run in the process explained by the associated
message
ErrFkeypar (fatal)
The FTOOLS task fkeypar cannot be run in the process explained by the associated message
ErrCphead (fatal)
The FTOOLS task cphead cannot be run in the process explained by the associated message
ErrFparkey (fatal)
The FTOOLS task fparkey cannot be run in the process explained by the associated message
ErrFpartab (fatal)
The FTOOLS task fpartab cannot be run in the process explained by the associated message
ErrFstruct (fatal)
The FTOOLS task fstruct cannot be run in the process explained by the associated message
ErrFappend (fatal)
The FTOOLS task fappend cannot be run in the process explained by the associated message
ErrMathpha (fatal)
Error raised while trying to run the FTOOLS task mathpha to subtract positive and negative
spectra
ErrRegion (fatal)
The task region cannot be run on the input source list
ErrFlmask (fatal)
Mask les cannot be created
ErrEvselect (fatal)
Problem raised while trying to run the task evselect in the process described by the asso-
ciated message
xmmsas 20080701 1801-8.0.0

XMM-Newton Science Analysis System Page: 5
ErrPseudo (fatal)
Cannot create Pseudo Event List
ErrEmask (fatal)
Error raised while trying to run the emask
BadParamValue (fatal)
The requested binsize in parameter binsize is smaller than the input image bin size, larger
than the input image size or it results in a meaningless binned image with only one pixel
NoPixLeft (fatal)
The binned image does not have any pixels left after source subtraction
NullSpecPos (warning)
Positive spectrum has null extraction area for oaxis value and uctuations spectrum number
given in the message
corrective action:
NullSpecNeg (warning)
Negative spectrum has null extraction area for oaxis value and uctuations spectrum num-
ber given in the message
corrective action:
NullSpec (warning)
Positive and Negative spectrum have null extraction area for oaxis value and uctuations
spectrum number given in the message
corrective action:
NullExpos1 (warning)
Exposure value for positive and negative spectra cannot be properly updated by evselect
in a given uctuations spectrum (number specied)
corrective action: EXPOSURE is updated to 1.000 s
NullExposDs (warning)
Exposure value for positive and negative spectra cannot be properly updated by evselect
in a given uctuations spectrum (number specied) but Dataset has an EXPOSURE keyword
corrective action: EXPOSURE is updated to value in Dataset
6 Input Files
1. sourcelistset: FITS le containing the list of observed sources. This is a PPS product
called \EPIC OBSERVATION SOURCE LIST".
2. set: Event list of the EPIC imaging observation. This is a PPS product called \EPIC
IMAGE MODE EVENT LIST".
3. imageset: Image of set in a reference energy band. This is a PPS product called \EPIC
IMAGE".
4. exposureset: Exposure map corresponding to imageset. This is a PPS product called
\EPIC EXPOSURE MAP".
xmmsas 20080701 1801-8.0.0

XMM-Newton Science Analysis System Page: 6
7 Output Files
1. spectrumsets: List of output FITS spectral les containing the spectrum of the background
uctuations at dierent oaxis angles. This is a PPS product called \EPIC FLUCTUA-
TIONS SPECTRUM".
8 Algorithm
spec is a perl task which does the following:
1. Read input parameters
2. Run region on the observation source list to obtain a FITS le with the source free region.
3. Run the F90 module createpseudoevt to create a pseudo event list with one event in all
the X/Y and THETA positions of the input image:
module createpseudoevt
read input image and source-free region file
create output pseudo event file with X,Y and THETA (offaxis angle) columns
fill in X(Y) column with X(Y) position of input image pixels
calculate RA,DEC for each pixel
calculate THETA for each pixel from RA,DEC values
fill in THETA column
end module createpseudoevt
4. Filter pseudo event list with output of region and create mask with sources position hidden.
5. Cut exposure map borders with the output mask of emask
6. Run the FTOOLS task farith to ateld the input image with the exposure map and mask
source positions.
7. Run the F90 module flmask to create masks selecting areas with intensity above and below
the median:
module flmask
Read input flatfielded (source masked) image and parameters
Rebin the image
Compute median intensity of rebinned image
Define positive and negative rebinned pixels above and below the median
Create and write out image mask for positive regions
xmmsas\_20080701\_1801-8.0.0

XMM-Newton Science Analysis System Page: 7
Create and write out image mask for negative regions
end module flmask
8. Filter pseudo event list with annular regions to create a mask
9. Combine positive/negative masks with the annular regions mask
10. Run evselect to lter input event list with the positive combined mask and extract the
spectra of positive uctuations in standard spectral ranges.
11. Calculate solid angle of extraction area.
12. Run evselect to lter input event list with the negative combined mask and extract the
spectra of negative uctuations in standard spectral ranges.
13. Calculate solid angle of extraction area.
14. Set EXPOSURE keyword (equal to 1.0) in positive and negative spectra in case evselect cannot
do it properly.
15. Run the FTOOLS task mathpha to subtract both sets of spectra (one for each annular
region). The resulting spectrum is the 'EPIC FLUCTUATIONS SPECTRUM' at given
oaxis value.
9 Comments
 Rounds up rebinned pixel size to the nearest integer multiple of the elementary size of the
input image
 Ignores pixels on the edges that do not t in an integer number of rebinned pixels
 The ancilliary response le for the output spectra should be created with SAS task arfgen.
When dealing with lter masks, arfgen works by averaging the ARF in a number of grid
elements on an internal map, thus, it is necessary to allow a large number of elements in the
internal arfgen map:
arfgen spectrumset=spec 0.ts arfset=spec 0.arf extendedsource=yes detxbins=100 dety-
bins=100
 Temporary les are created with the names specied in the parameters tmpsrclistset,
tmpbkgregionset, tmpflatset, tmpposmaskset, tmpnegmaskset, tmpposspecset, tmpnegspecset,
and are deleted when they are no longer needed, at the end of the task.
10 Future developments
References
xmmsas 20080701 1801-8.0.0