XMM-Newton Data Files Handbook


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4.1.7.5 ``Priority files''

Three kinds of OM ``Priority'' data exist:

They are called ``priority'', because they are issued with a higher priority by the Digital Processing Unit (DPU: 1024sec) than the regular data. These files are created before the start of the actual science exposure.

DP_FAQ data contain information on the OM field acquisition made at the beginning of the observation. The purpose of the field acquisition exposure is to recenter the window for more accurate coordinates, which is fundamentally important for the fast mode. The coordinates of a set of uplinked Guide Star (GS) positions are compared to the actual measured positions in the field acquisition frame. From this comparison, the actual pointing direction of OM is derived as offset from the nominal position. Each instance of this file consists of a single binary table, whose columns are described in Table 20.

Table 20: OM Priority Field Acquisition Auxiliary file (*OM*PAX.FIT) binary table columns
Name Type$^a$ Units Description
ITERATN 1J COUNTER No. of iterations to solution
XCOMMAND 1J PIXEL Commanded X coordinate
YCOMMAND 1J PIXEL Commanded Y coordinate
DX 1J 1/1000th PIXEL Pointing error in x
DY 1J 1/1000th PIXEL Pointing error in y
SINTHETA 1J   Absolute roll error [1/1000th ${\rm\sin (\theta)}$]
NGSUP 1J COUNTER No. of uplinked guide stars
NGSFOUND 1J   No. of guide stars found
GSX 16J PIXEL X coordinates of the guide stars
GSY 16J PIXEL Y coordinates of the guide stars
RSX 16J PIXEL X coordinates of the reference stars
RSY 16J PIXEL X coordinates of the reference stars
$^a$See Sect. 9 for convention

The main purpose of the DP_WDW (*OM*WDX.FIT) files is to determine the effective exposure time by correcting for dead time (time intervals during which no photons are recorded because of read out). DP_WDW data contain the position of the science window (up to 5) during an exposure and the associated memory window and detector windows, together with the position of the autonomously selected guide star windows (up to 16). The dataset also lists the tracking window positions and the finally calculated memory and detector window configurations. Each instance of this file consists of a single binary table, whose columns are described in Table 21.

Table 21: OM Priority Field Window Data Auxiliary file (*OM*WDX.FIT) binary table columns
Name Type$^a$ Units Description
DETWINS 1J   No. of detector windows
SCIWIND 1J   No. of science windows
MEMWIND 1J   No. of memory windows
DWX0 16J PIXEL Bottom left X coordinate of detector window
DWY0 16J PIXEL Bottom left Y coordinate of detector window
DWXSIZE 16J PIXEL X dimension of detector window
DWYSIZE 16J PIXEL Y dimension of detector window
DWMMWID 16J   Identificator of corresponding memory window
DWKOMPX 16J   MIC data decoder parameter
DWBB 16J   MIC data decoder parameter
DWAA 16J   MIC data decoder parameter
DWKOMPY 16J   MIC data decoder parameter
SWX0 16J PIXEL Bottom left X coordinate of science window
SWY0 16J PIXEL Bottom left Y coordinate of science window
SWXSIZE 16J PIXEL X dimension of memory window
SWYSIZE 16J PIXEL Y dimension of memory window
SWMODE 16J   Science window operating mode (0=Imaging; 1=Fast)
      15: placeholder for non-science windows
SWP1 16J   Science window mode dependent parameter$^b$
SWP2 16J   Science window mode dependent parameter$^c$
SWP3 16J   Science window mode dependent parameter$^d$
SWP4 16J   Science window mode dependent parameter$^e$
SWBASE 16J   Science window data storage address
SWMMWID 16J   Science window identificator of the corresponding memory window
MWX0 16J PIXEL Bottom left X coordinate of memory window
MWY0 16J PIXEL Bottom left Y coordinate of memory window
MWXSIZE 16J PIXEL X dimension of memory window
MWYSIZE 16J PIXEL Y dimension of memory window
MWBASE 16J   Memory window retrieval address

$^a$See Sect. 9 for convention
$^b$If Imaging mode: Pixel binning factor in X ( ${\rm 2^{\hbox{\tt SWP1}}}$); If Fast mode: sampling time (in DPU units: 1024sec)

$^c$Only if imaging mode: Pixel binning factor in Y ( ${\rm 2^{\hbox{\tt SWP2}}}$)
$^d$Not used

$^e$Starting address in DPU global memory to which the accumulated image is written

The DP_BFAST data contain information on the fast mode data. A single file is produced for each exposure of the observation (excluding the Field Acquisition Exposure) if there are windows configured in fast mode. Conversely, this file is not present during exposures, where no fast windows are active. The file consists of a single binary table, whose columns are described in Table 22.

Table 22: OM Priority Fast Auxiliary file (*OM*PFX.FIT) binary table columns
Name Type$^a$ Units Description
BFASTID 1J   Blue DSP 1 or 2
SAMPTIME 1J   Sample time
NFASTPIX 1J   No. of pixels for fast time slice
FASTDEST 1J   Memory address of fast mode data stream
FASTEND 1J   Termination address of fast mode data
NFASTEVT 1J   Total no. of events in mode data
FASTADDR 503J   Fast addresses
$^a$See Sect. 9 for convention
There is one record per fast mode window.


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Next: 4.1.8 OM diagnostics files Up: 4.1.7 OM science files Previous: 4.1.7.4 OM Reference Frame Data Auxiliary File
European Space Agency - XMM-Newton Science Operations Centre