Документ взят из кэша поисковой машины. Адрес оригинального документа : http://xmm.vilspa.esa.es/sas/6.0.0/doc/rgsoffsetcalc.ps.gz Дата изменения: Thu Mar 18 23:12:34 2004 Дата индексирования: Tue Oct 2 11:58:27 2012 Кодировка: Поисковые слова: optical telescope

XMM-Newton Science Analysis System Page: 1
rgsosetcalc
March 18, 2004
Abstract
Calculate the mean and the standard deviation of the pulse height distribution of
RGS diagnostic images.
1 Instruments/Modes
Instrument Mode
RGS DIAGNOSTIC
2 Use
pipeline processing yes
interactive analysis yes
3 Description
Visible stray light and bright stars in the RGS avoidance elds can alter the zero energy level (CCD
electronics oset or pedestal) measure by the RGS CCDs. This eect, if not properly taken into account,
can aect the energy calibration of X-ray events. 1
It is ensured procedurally during the operations of the instrument that DIAGNOSTIC mode data of all
CCD's are available at the start and at the end of each observation. Furthermore, if enough telemetry
bandwidth is available, DIAGNOSTIC mode data are also transmitted interleaved with science data (this
type of DIAGNOSTIC data is called Q-memory). Q-memory data are not guaranteed to be present for
all CCDs in all observations, due to the uncertainties in the predicted event rates (hence in the telemetry
requirements).
DIAGNOSTIC and Q-memory data can be used to determine the oset and noise levels of the CCD elec-
tronic chains at the actual telescope pointing. Q-memory data could be used to devise a time dependent
1 Light of stars outside the telescope eld of view may reach the RGS focal plane after re ections on the front side of the
gratings. Optical light may also be re ected on the back surface of the gratings; before launch the exact magnitude of this
eect is not known. Regions around the pointing direction from which light could be re ected on the RGS focal plane are
called avoidance elds.
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correction of the oset levels by interpolation. This will only be implemented at a later time, if in-orbit
experience warrants it.
rgsosetcalc accepts a list of DIAGNOSTIC datasets (refer to the ODF ICD [1]. For each DIAGNOSTIC
dataset rgsosetcalc calculates the mean and standard deviation of the pulse height distribution. This
calculation is performed by CCD node. The mean and standard deviation are calculated by tting a
Gaussian to the pulse height distribution.
Before being processed each diagnostic dataset is examined to determine if it is likely to yield a good t.
The dataset is ignored if any of the following conditions is false:
 less than 10% of the pixels are empty. A pixel is considered to be empty if the pulse height
amplitude it measures is equal to the value indicated by the attribute BLANK ([1]).
rgsosetcalc stores the results of the computation in the dataset specied by outset. The output
dataset can be used as a CCF constituent, and this is usually how rgsevents will use it. Because the
output dataset is a valid CCF constituent, it can only contain data relative to one CCF scope [2]. If
the list of input datasets contains more that one CCF scope (this is identied through the attribute
INSTRUME), rgsosetcalc will process only the datasets belonging to the rst CCF scope identied (this
is the scope of the rst dataset in the input list). A warning is issued.
rgsosetcalc can also operate on a list of datasets that do not conform to the ODF ICD. The only
requirement is that the arrays be of type integer16. In this case the output dataset is not formatted as a
valid CCF constituent. In the output table, null values are used to indicate information that could not
be obtabined from the input datasets.
Optionally, rgsosetcalc can store the pulse height distributions for each input dataset and node in a
dataset (see the description of withhistogramset and histogramset).
4 Parameters
This section documents the parameters recognized by this task (if any).
Parameter Mand Type Default Constraints
sets yes set " none
The list of DIAGNOSTIC mode datasets
outset no set 'rgsosetcalc.ds' none
The output dataset
withhistogramset no boolean no none
This controls whether the pulse height distributions shold be saved to a dataset
histogramset no set histo.ds none
The dataset where to store the pulse height distributions
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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.
CalibrationScopeIgnored (warning)
rgsosetcalc cannot identify a CCF scope (attribute INSTRUME) in the input datasets.
corrective action: The output dataset (parameter outset) is not a valid CCF constituent.
DatasetIgnored (warning)
rgsosetcalc identied a second CCF scope.
corrective action: The dataset is ignored.
DatasetRejected (warning)
The dataset failed at least one of the tests described in Section 3.
corrective action: The dataset is ignored.
NoOdfArrayName (warning)
The task could not nd an array named R1DII1 or R2DII1.
corrective action: If possible, try to get the rst available array.
nothingToFit (error)
Ignore the dataset.The pulse height distribution contains less than 3 bins.
6 Input Files
1. list of RGS diagnostic mode image les [1]
7 Output Files
1. The output dataset (outset) consists of a binary table (RGSOFFSETS) with the following
columns:
 TIME, double: number of seconds since the XMM Mission Reference Time.
 CCD ID, integer: the CCD identier
 NODE ID, integer: the node identier
 CCD OCB, integer: the CCD on-chip binning factor
 MEAN, real: the mean of the tted Gaussian
 STD DEV, real: the standard deviation of the tted Gaussian
 NORMALIZATION, real: the normalization of the tted gaussian
 EUCLIDEAN NORM, real: the sum of the squares of the residuals
2. The histogram dataset (histogramset) consists of a binary table (pulse height spectra)
with the following columns:
 pha, real: the pulse height axis
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 a number of real columns, each containing a pulse height spectrum. Columns have
names like phs 0000. The rst column corresponds to the rst input dataset (rst
node), the second column correspond to the second node (if applicable), and so on.
The mapping of column names to input datasets is recorded in the table comments.
8 Algorithm
begin loop sets
next if isNotValid(set)
begin loop nodes
create_pha_histogram(all CCD pixels)
fit_peak_with_Gaussian(return: mean, sigma, normalization)
write (outset) time_of_diag_image, ccdid, node, &
mean, sigma, &
refined_rejection_thresholds(per node), &
refined_acceptance_thresholds(per node)
end loop nodes
end loop sets
9 Comments
 RGS diagnostic datasets taken with on-chip binning factor of one require six les per CCD.
This task does not try to piece them together, as this functionality belongs to a separate
piece of software.
10 Future developments
These are possible future improvements:
 add facilities to debug the tting engine
 make the bin size of pulse height distributions a parameter
 allow for more t functions
 use the OAL to determine which datasets should be processed
References
[1] ESA. XMM Interface Control Document: Observation and Slew Data Files (XSCS to SSC) (SciSIM
to SOCSIM). Technical Report XMM-SOC-ICD-0004-SSD Issue 2.5, ESA/SSD, June 2000. Found
at the URL: ftp://astro.estec.esa.nl/pub/XMM/documents/odf icd.ps.gz.
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[2] ESA. Interface control document for the XMM current calibration le. Technical Report XMM-GEN-
ICD-0005, ESA/SSD, Dec 2001.
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