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XMM-Newton Science Analysis System Page: 1
Data conventions
July 1, 2008
Abstract
Several conventions are described for passing around data in the SAS, such as
parameter names, le structure, attribute names, column names etc.
1 Introduction
With this note we would like to set the wheels turning on the denition of a number of conventions to
be used across the XMM SAS. Eventually this document would be part of the SAS user documentation.
We are aware that the SSC have started some work in this area, and we would like to reach a common
view of the matter.
2 Dataset structure
Input and output data is processed in the form of data sets, usually saved on disk as a FITS le. A data
set can contain several blocks, such as tables and arrays (FITS's HDU).
Traditionally blocks in a data set have been addressed by number (their position in the data set). However
the DAL allows the task programmer to address blocks by name, so that it would seem appropriate to
ask that all blocks (extensions) have a name (that means the EXTNAME FITS key word is set), and that
in a data set block names should be unique.
The OGIP conventions for data products all have the block name set, so it is a matter of extending this
concept also to utility tasks that normally wouldn't bother with the extension name.
The OGIP HDUCLASS set of key words will be used. Possibly it will be necessary to extend the OGIP
conventions to describe some other intermediate data set that may be produced during the interactive
analysis (TBD).
2.1 Event lists
Events are stored in a table in a data set. There is only one event list in a data set. The name of the
table is 'events'.
Each row in a column can contain associated information. This has the form of a column in the table.
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Work on the XMM event list denition is done by the SSC. The various columns in the event list would
be described here, or a suitable reference given.
2.1.1 Event status
Data type integer (16 bits?)
Values 0 means the event is good, > 0 the event is agged as being bad 1
Location an extra column in the events table
Naming column name: STATUS
2.1.2 Errors
Data type real
Units same as column it refers to
Location a column in the same table as the column it refers to
Naming column name: name of the column plus 'Error'
2.1.2.1 Note The error column could also contain the fractional error ('fError'?). Also, should there
be a ag indicating what type os statistics applies to the error?
2.2 Images
Images are stored in an array ( 2 dimensions) in a data set. There can be multiple images in a data
set. The name of the image should indicate its contents.
An image can have several associated arrays. The size of these arrays has to be identical to the image it
refers to. The name of the associated array is the name of the image followed by a label indicating the
contents of the arrays.
2.2.0.1 Note Should the associated arrays immediately follow the data array they refer to?
2.2.1 ExposureMap
Data type real
Units seconds
Location a block in the same le as the image
Naming array name: name of the image plus 'Exposure'
2.2.1.1 Note Exposure maps are also products [2].
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2.2.2 BadPixelMap
Data type boolean
Values true: good pixel, false: bad pixel
Location a block in the same le as the image
Naming array name: name of the image plus 'BadPixel'
2.2.2.1 Note Note that the task BADPIX is writing a bad pixel extension into the event list.
2.2.3 Errors
Data type real
Units same as image
Location a block in the same le as the image
Naming array name: name of the image plus 'Error'
3 Parameter names
Parameters are used to congure the behaviour of a task. Several parameters are shared amongst dierent
tasks. The following list contains parameter names and what they are used for.
Name Data type Value/units Description
inle string Input data set in case there is only one input
inleN string Input data set in case there are multiple inputs
outle string Output data set in case there is only one output
outleN string Output data set in case there are multiple outputs
As a general note: no underscores, parameter names are only lower case, names are as long as necessary
to be understabdable.
3.0.0.1 Note Has Dean Hinshaw circulated a note on this?
4 Attributes
Attributes are keyword-value pairs that are used to describe component of a data le. For the FITS input
les and FITS output les there are several standards that are obeyed by the SAS:
 OGIP (ref?)
 ODF ICD [1]
 SAS products ICD [2]
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4.1 OGIP compliance
4.1.1 Relevant OGIP standards
To be written.
4.1.2 XMM-specic extensions of the OGIP standard
To be written.
4.2 Automatically generated attributes
4.2.1 CREATOR
The attribute CREATOR is automatically added to each data set created by a SAS task (via the DAL).
The value is the name and version of the task that created the data set.
4.2.2 DATE
The date of creation is automatically added to the data set as the attribute DATE (via the DAL).
4.2.3 HISTORY
The SAS (via the DAL) will automatically log the command line format of the task, containing the values
of all arguments, to the history attribute of a data set.
5 Column names
Column names are upper case.
5.1 Events lists
Name Values/Units Description
6 Units
IN general the OGIP convention will be used.
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Quantity Units Comments
time s in UTC TBC
spacecraft position km
position in spacecraft reference frame mm
energy eV
7 Coordinate systems
TBD
7.0.0.1 Note Here we should list column names versus reference frame. For instance, RAWX and RAWY
are CCD node-oriented pixel coordinates etc.
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.
[2] SSC. XMM Survey Science Centre to Science Operations ICD for SSC Products. Technical Report
XMM-SOC-ICD-0006-SSC Issue 2.1, SSC, Mar 2000.
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