'nuexpomap' first generates a set of instrument maps in Focal Plane Bench DET1 coordinates where bad/hot pixels and detector gaps are marked using information from the 'BADPIX' extension of the input event file (parameter 'infile') and from the CALDB Instrument Probability Map File (parameter 'instrprobmapfile'), respectively.
The set of DET1 instrument maps is constructed as follows. First, the task reads the input file 'det1reffile' which stores the X/Y SKY position as a function of time of a reference pixel in the DET1 coordinate system (see help file of 'nuskypos' for further details). Second, the X/Y offsets relative to their minimum value in the 'det1reffile' are calculated. Third, the X/Y offsets are binned with a bin size in pixels specified by the input parameter 'pixbin'. Each bin defines a time interval during which the spatial fluctuations due to attitude variations and mast movements are below the 'pixbin' value and are considered constant. This information is then used by 'nuexpomap' to build the aspect histogram which defines, for each spatial offset bin, the time interval and duration of each single DET1 instrument map. By setting the parameters 'offsetfile' and 'aspecthistofile' not to 'NONE' the task saves in the current directory the spatial offset and aspect histogram files, respectively.
Each DET1 instrument map is then transformed in the Optics Bench DET2 frame using the mast aspect solution (parameter 'mastaspectfile') and the CALDB align file (parameter 'alignfile'). In this step, 'nuexpomap' makes use of the multi-mission FTOOLs 'combinexform' and 'imagetrans'. Optionally, if the parameter 'vignflag' is set to 'yes', the task applies the vignetting correction to the DET2 instrument maps using the vignetting CALDB file (parameter 'vignfile'). The vignetting correction is applied at the energy value specified by the parameter 'energy'.
Next, the DET2 instrument maps are transformed in the SKY frame using the attitude information provided in input through the parameter 'attfile'. To this end, the multi-mission FTOOLs 'getxform', 'imagetrans' and 'getwcs' are used by 'nuexpomap'. The total exposure map, storing in each pixel the net exposure time of the observation, is then calculated by summing the single exposure maps in sky coordinates. Dead time corrections are included in the total exposure map.
By setting the parameters 'det1instrfile','det2instrfile' and 'skyinstrfile' not to 'NONE' the task saves in the current directory the single DET1, DET2 and SKY instrument maps as FITS IMAGE extensions in the corresponding output files.
Optionally, the task allows to generate reduced exposure maps covering a user region of the SKY grid defined by the input parameters 'skyx', 'skyy' and 'skysize'.
The 'nuexpomap' task can also generate an ouput exposure map using as input a DET2 instrument map not corrected for vignetting produced in a previous run. This can be achieved by setting the input parameter 'indet2instrfile'. Note that in this case maps with reduced size cannot be generated.
> nuexpomap infile=nu40060001001A01_cl.evt attfile=nu40060001001_att.fits mastaspectfile=nu40060001001_mast.fits det1reffile=nu40060001001A_det1.fits energy=25 expomapfile=nu40060001001A01_ex.img
> nuexpomap infile=nu40060001001A01_cl.evt attfile=nu40060001001_att.fits energy=25 expomapfile=nu40060001001A01_ex.img indet2instrfile=nu40060001001A01_det2.fits