XMM-Newton Data Files Handbook

4.1.7.5 ``Priority files''

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

• Priority Field Acquisition Auxiliary (*OM*PAX.FIT) File (the so-called ``DP_FAQ'' data)

• Priority Window Data Auxiliary (*OM*WDX.FIT) File (the so-called ``DP_WDW'' data)

• Priority Fast Auxiliary (*OM*PFX.FIT) File (the so-called ``DP_BFAST'' data)

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.