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XMM-Newton Science Analysis System Page: 1
omlcbuild
July 9, 2007
Abstract
Constructs an OM OSW FITS source timeseries from separate source and back-
ground rates les produced by evselect
1 Instruments/Modes
Instrument Mode
OM FAST
2 Use
pipeline processing yes
interactive analysis yes
3 Description
This task constructs the PPS product OM OSW FITS source timeseries from two rate les (source and
background) produced by separate runs of evselect on a tracking-shifted, QE-corrected OM fast-mode
event-list. The output timeseries has 4 columns (background subtracted source rate & error, background
rate & error). All rates are in counts/s.
In addition to the two rate les, the two region les (generated by omregion) are read to deduce the
extraction areas. The following procedure is performed for each time bin. The counts measured in
the source and `background` regions, together with the PSF function evaluated over the corresponding
regions, are used to set up equations which are then solved to yield source and background rates evaluated
for the nomimal coincidence-loss region (r=12 pixels). Note that allowance is made for proximity of the
source to the edge of the OSW - the fraction of PSF which falls out of the window is restored. These rates
are separately corrected for coincidence loss. Subsequent background subtraction, followed by corrections
for dead-time and any PSF beyond 12 pixels, leads to the nal source rate. The code allows for cases
where the time-binning of the source and `background` rate les dier a little - linear interpolation is
employed and the binning and timing alignment of the emerging source light curve matches that of the
input source rate le.
Errors are computed assuming Poisson statistics though a systematic error of 2% is later included as a
measure of non-Poissonian eects at high count rates.
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4 Parameters
This section documents the parameters recognized by this task (if any).
Parameter Mand Type Default Constraints
srcrateset yes string
Source rates le (output from evselect)
srcregionset yes string
Source region (output from omregion)
bkdrateset yes string
Background rates le (output from evselect)
bkgregionset yes string
Background region le (output from omregion)
sourcelistset yes string
Source list lename (output from omdetect)
wdxset yes string
OSW window data lename
outset yes string
Name of output rates le
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.
Block RATE does not exist in the background rates le (warning)
corrective action: Issue a warning. Background corrections are not applied
Input background rates table is empty (warning)
corrective action: Issue a warning. Background corrections are not applied
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Source and background rates les from dierent exposures (warning)
corrective action: Issue a warning. Check the ODF les
Background rates and region les have dierent EXP IDs (warning)
corrective action: Issue a warning. Check the ODF les
High value of the source rate (warning)
corrective action: Issue a warning; set the count rate to the maximal possible value corre-
sponding to the current frame time.
Background subtracted rate has negative values (warning)
corrective action: Issue a warning
Block RATE does not exist in the source rates le (warning)
corrective action: Issue a warning. Check the ODF les
6 Input Files
1. OM source rates le (output from evselect)
2. OM background rates le (output from evselect)
3. OM OSW window data le (ODF)
4. OM ASC compatible FITS detected source list le (output from omdetect)
5. OM ASC compatible FITS source region le (output from omregion)
6. OM ASC compatible FITS background region le (output from omregion)
7 Output Files
1. PPS product OM OSW FITS source timeseries
8 Algorithm
subroutine omlcbuild
read parameters
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loop i=0, nSources
get handle on source rates file
get handle on source region file
if (exposure IDs are different) issue warning
get handle on background rates file
get handle on background region file
if (exposure IDs are different) issue warning
if (exposure ID source != exposure ID background) call fatal
get source extraction radius = s_radius
get CAL coincidence loss correction radius = cal_radius
get photometry radius = ph_radius
calculate the instrumental limiting magnitude from the
detection limit count rate
compute area of source region = s_area
compute area of background region = b_area
tStart = max(tBack[0], tSource[0])
eEnd = min(tBack[nBack-1], tSource[nSource-1]
tDel = (tEnd - tStart)/(nSource-1)
determine the PSF fraction within the source extraction region
determine the PSF fraction within the `background` extraction region
% calculate the ratio between counts inside and outside OSW:
% PSF fraction = sum(PSF inside OSW)/ sum(complete PSF inside s_radius area)
loop i = 0, ntimebins
newTime = tStars + i * tDel
% linear interp to get source rate
linear interp to get background rate for each source bin
% compute background subtracted rate error
compute source rate error
compute background rate error
% scale background counts to the source area:
% backround count rate = background count rate * source area / b_area
% subtract background from the source:
% background subracted rate = source rate - background count rate
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% correct source counts for the PSF fraction inside extraction area
% (correction is to value expected within CAL (r=12 pixels) aperture):
% source = source / PSF_fraction
set up equations for counts recorded in each region. These allow
for (point) source contamination of the `background` region:
C(S+B) = PSF(S+B) *S + NPIX(S+B) * Bpix
C(B) = PSF(B) *S + NPIX(B) * Bpix
solve these for S, the source counts over the coincidence loss (CL)
region (ie the CAL aperture) and for Bpix, the background counts
per pixel.
scale background to the CAL aperture area:
bkgnd count rate = background count rate * cal_radius area / s_area
recombine these bkgnd and source rates (now determined for the
CAL aperture)
apply CL correction to the source+bkgnd rate
apply CL correction to the bkgnd rate
CL corrected source rate = source+bkgnd rate - bkgnd rate
correct result for dead time
correct for PSF beyond the 12 pixel Cal aperture (mainly for UV)
end loop
write time keywords to header
write output rates file
release handle
end loop
end subroutine omlcbuild
9 Comments
10 Future developments
 Eventually the areas of the extraction regions will be available from the input rates le in
the form of data subspace keywords.
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References
xmmsas 20070708 1801-7.1.0