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XMM-Newton Science Analysis System Page: 1
omfastshift
July 9, 2007
Abstract
Corrects FAST mode event list coordinates for spacecraft drift.
1 Instruments/Modes
Instrument Mode
OM FAST
2 Use
pipeline processing yes
interactive analysis yes
3 Description
In Fast mode, because of telemetry constraints, the shift-and-add performed on the spacecraft in IMAGE
mode is applied to FAST mode data on the ground. This is achieved using two SAS tasks. This task
applies the `shift' and evselect applies the `add'.
In IMAGE mode the DPU shift-and-add procedure is applied after every tracking frame integration,
t track  10-20 seconds. In FAST mode, a FAST mode time slice (FMTS) is dened with duration
t FMTS < t track . Each event is tagged with a frame number corresponding to the FMTS in which the
event was detected. It is therefore possible to correct each event with a ne shift calculated from a linear
interpolation of the tracking frame shifts
omfastshift calculates drift-corrected event positions based on a linear interpolation over a tracking
frame integration, of drifts stored in the ODF OM tracking history auxiliary data le. These are then
written as additional columns to the input ODF OM fast mode event list le.
The drift-corrected OM Fast mode event list le is passed to omfastflat which uses the OM in-orbit
ateld and the RAWX/RAWY values of the event list to ateld the event list on an event by event
basis. The output atelded event list is then passed to evselect to produce a Fast Mode atelded
image which can be treated by subsequent SAS tasks in the same way as an Image Mode atelded
image.
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4 Parameters
This section documents the parameters recognized by this task (if any).
Parameter Mand Type Default Constraints
set yes string none
OM Fast Mode Event List Intermediate File (output of OMPREP)
thxset yes string none
OM Tracking History Data Auxiliary Intermediate File (output of OMPREP)
nphset yes string none
OM ODF Non-Periodic Housekeeping le
interpolate no boolean T
Linearly interpolate s/c drift over FAST mode time slices?
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.
Wrong datamodes for input les (fatal)
6 Input Files
1. OM Fast Mode Event List Intermediate File (output of OMPREP)
2. OM Tracking History Data Auxiliary Intermediate File (output of OMPREP)
3. OM ODF Non-Periodic Housekeeping File
7 Output Files
1. Drift-corrected OM Fast Mode Event list le (input to omfastflat)
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8 Algorithm
subroutine omfastshift
Read parameters
Get a handle on the ODF OM Tracking History Data Auxiliary File.
Confirm datamode from DATAMODE keyword in primary header.
Get a handle on the tracking history data binary table extension.
Calculate drifts.
If BPE binning implemented divide drifts by two
Release handles on column and table.
Read in Intermediate Event List file.
Confirm datamode from DATAMODE keyword in primary header.
Get a handle on the event list binary table extension.
Get the number of rows in the event list binary table extension.
Read modes extension.
Get start and end time of exposure from the non-periodic housekeeping file.
Calculate tracking frame time stamps in OBT for middle of tracking frame.
Do 'shift and add' process.
Calculate On board Time for each event taking into acount wrap around for int16 values.
if (ibits(ftFineP(i-1), 15, 1) == 1) then
obtEvent(i) = REAL(ftCoarseP(i-1)) + REAL( ibits(ftFineP(i-1), 0, 15) + 2**15 ) / 65536.0
else
obtEvent(i) = REAL(ftCoarseP(i-1)) + REAL(ftFineP(i-1)) / 65536.0
end if
Locate tracking frame in which event occured.
If linear interpolation of drifts is required ...
Find time of event since previous tracking frame.
Interpolate drift to this time
If not use tracking frame drift
end do
Flag events outside Science window
Convert Onboard Timestamps (OBT) to event time tags (elapsed seconds since mission
reference time 1998-01-01T00:00:00).
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Write time attributes to input file.
Add new columns.
Write data to columns.
Release data.
end subroutine omfastshift
9 Comments
 FAST mode data is not binned by the DPU. The drifts from the ODF OM Tracking History
Auxiliary File need to be corrected for BPE only.
 All events are assumed to occur in the centre of their pixel. The output integer pixel
coordinate value is the integer truncation of the real coordinate value.
 For FAST mode, in addition to a tracking frame time, a FAST mode time slice (FMTS)
is dened with duration  SAMPTIME*10ms, where SAMPTIME is integer (i.e. integer
multiples of a CCD frame)
 Each event is tagged with a time stamp (FTCOARSE+FTFINE) corresponding to the spe-
cic FMTS integration within each tracking frame integration, in which each event occurred.
This allows the possibility to apply a `ne shift' to each event corresponding to the spacecraft
drift, after each FMTS integration.
 omfastshift produces by default a corrected event list in which all events within a FMTS are
shifted back to the reference frame using drifts calculated from a linear interpolation of the
tracking frame drifts in the OM Tracking History auxiliary data le.
 A corrected event list in which all events within a tracking frame are shifted back to the
reference frame using the tracking frame drifts can be called for by the setting ag interp ag
= F on the command line
 It is worth noting that there exists cases in which a FMTS crosses a tracking frame boundary.
Although events may belong to two tracking frames, all events within the FMTS are given
the same event timestamp and are treated equivalently.
 The drift-corrected OM FAST mode event list contains 4 additional columns: the corrected
X and Y pixel coordinates and OBT time for each event and a ag denoting whether the
shift-corrected event falls within the dened science window. This ag is necessary since
the s/c drift causes the science window to sample a region of the sky larger than the science
window. When these events are drift-corrected they may fall outside the GO dened science
window area. A value of WIN FLAG=0 is given for all events outside the science window,
and WIN FLAG=1 for all events in the science window.
 TLMIN and TLMAX are required by evselect.
10 Future developments
 It might be possible to improve on the linear interpolation scheme when the spacecraft drift
is better understood.
 Appropriate keywords associated with timing information will be written when XMM data
conventions on this issue have been nalised.
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References
xmmsas 20070708 1801-7.1.0