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Last modified: 17 Dec 2014


Single Chip ACIS Exposure Map and Exposure-corrected Image

CIAO 4.9 Science Threads



mkexpmap generates an exposure map which may be used to convert a counts image of a source to an image in flux units. The computed exposure map is essentially an image of the effective area at each sky position, accounting for the effects of dither motion which are especially important near the edges of the detector. The fluximage script automates the creation of an exposure-corrected image for a Chandra observation.


To build an exposure map for a single ACIS chip. create an exposure-corrected image, and find an approximation for the source flux.

If more than one chip is being used, follow the ACIS Exposure Map (Multiple Chips) and Exposure-corrected Image thread.

Related Links:

Last Update: 17 Dec 2014 - Reviewed for CIAO 4.7; minor edits only.


Get Started

Download the sample data: 11823 (ACIS-I, RCW 103)

unix% cd 11823
unix% punlearn chandra_repro
unix% chandra_repro mode=h

Using the fluximage Script

How fluximage works

When running fluximage, you are only required to provide an input event file. The script will read the related data product filenames - bad pixels, aspect solution, mask (ACIS), and dead time correction (HRC) - and look for them in the working directory. If the files are in a different location or you wish to be explicit in what files are used, all of the input filenames may be set in the parameter file.

The fluximage script runs the following tools:

  • dmcopy: to create an event image at with the specified binning factor
  • hrc_bkgrnd_lookup, reproject_events, and dmimgcalc: to subtract the particle background (HRC-I only)
  • asphist: to build the aspect histogram(s)
  • mkinstmap: to calculate the instrument map(s) for the center of each energy band
  • mkexpmap: to calculate the exposure map(s) in each energy band
  • dmimgcalc: to combine the exposure maps (multi-chip/plate case only)
  • dmimgthresh: to make a "threshold cut" before dividing the image by the exposure map, removing the hot pixels at the edges (optional)
  • dmimgcalc: to normalize the image by the exposure map

For the multi-chip ACIS or multi-plate HRC-S cases, the tools are run once per chip or plate and are then combined into an image of the full detector.

By default, the intermediate per-chip data products are removed after the script has completed running. To save these (potentially numerous) files, set the cleanup parameter to no.

Run the script

In this example, the script is run for a single ACIS chip. The input event file is provided, and the supporting data filenames are read from the header.

The energy range is restricted from 0.5 keV to 7 keV, and a center-band energy of 2.3 keV is used. This corresponds to the Chandra Source Catalog broad band, so we can set the bands parameter as bands=0.5:7.0:2.3 or bands=broad (which is the default value).

unix% punlearn fluximage
unix% fluximage "repro/acisf11823_repro_evt2.fits[ccd_id=1]" chip1 bin=2
Running fluximage
Version: 13 December 2013

Using CSC ACIS broad science energy band.
Aspect solution repro/pcadf391758163N002_asol1.fits found.
Bad pixel file repro/acisf11823_repro_bpix1.fits found.
Mask file repro/acisf11823_001N002_msk1.fits found.

The output images will have 596 by 597 pixels, pixel size of 0.984 arcsec,
    and cover x=4096.5:5288.5:2,y=2972.5:4166.5:2.

Running tasks in parallel with 4 processors.
Creating aspect histogram for obsid 11823
Creating instrument map for obsid 11823
Creating exposure map for obsid 11823
Thresholding data for obsid 11823
Exposure-correcting image for obsid 11823

The following files were created:

 The clipped counts image is:

 The clipped exposure map is:

 The exposure-corrected image is:

Since we added a DataModel filter, to restrict the analysis to just the ACIS-I1 chip, we had to explicitly list the event file, rather than just giving the directory name (e.g. setting infile=repro/). You can check the parameter file that was used with plist fluximage.

Now proceed to the Calculate the Source Flux section, using the exposure-corrected image (here, chip1_broad_flux.img).

Step-by-Step Guide

Please ensure that you have set up ardlib to use the bad pixel file for your observation before following this thread.

In this example, the energy range was restricted from 0.5 keV to 7 keV:

unix% dmcopy "acisf11823_repro_evt2.fits[energy=500:7000]" 11823.evt2

Note: do not use the energy-filtered file (11823.evt2 in this case) to extract spectra (e.g. as input to specextract); instead use the original file.

1. Create An Image

First, we need to create the image which will ultimately be normalized by the exposure map.

Check Which Chips Are On

The list of chips used in the observation is stored in the DETNAM keyword of the event file:

unix% dmkeypar 11823.evt2 detnam echo+

In this case, four chips were on for the observation. Using ds9 to display 11823.evt2, we know that the source we are interested in is at sky coordinates (called "physical coordinates" in ds9) close to x = 4181, y = 3942. We can use dmcoords to find out which chip the source is on.

In some cases there will be more than one aspect solution file (pcadXXX_asol1.fits) for an observation. All the files must be input, either as a list or as a stack. If you used chandra_repro to re-process the data then it has created a stack file for you, called acisf<obsid>_asol1.lis, which we use in this case (although as we only have a single aspect solution we could also have just used it directly):

unix% cat acisf11823_asol1.lis 

unix% dmcoords 11823.evt2 asolfile=@acisf11823_asol1.lis
dmcoords>: sky 4181 3942
(RA,Dec):     16:17:36.232    -51:02:24.46   
(RA,Dec):      244.40097      -51.04013 deg
THETA,PHI          1.444'        290.43 deg
(Logical):        4181.00       3942.00
SKY(X,Y):         4181.00       3942.00
DETX,DETY         4157.96       3931.47
CHIP ACIS-I1        69.59        967.34
TDET              4164.66       4176.59
dmcoords>: q

This tells us that the chip we want is ACIS-I1, i.e. ccd_id = 1. A description of the layout of the ACIS focal plane can be found in the caption of Figure 6.1 in the The Chandra Proposers' Observatory Guide.

We could have also used the non-interactive mode of dmcoords:

unix% punlearn dmcoords
unix% dmcoords 11823.evt2 asolfile=@acisf11823_asol1.lis x=4181 y=3942 option=sky
unix% pget dmcoords chip_id

Bin the Event File

For this example we decide to bin by 2, so that each pixel has a size of 0.984 arcseconds (2 * 0.492), and use the FOV file to spatially filter the file:

unix% dmcopy "11823.evt2[ccd_id=1,sky=region(acisf11823_001N002_fov1.fits[ccd_id=1])][bin sky=2]" 11823.i1.img
unix% dmstat 11823.i1.img centroid-
    min:	0 	      @:	( 4243.224052 2974.7345895 )
    max:	2981 	      @:	( 4181.224052 3942.7345895 )
   mean:	2.4351529464 
  sigma:	8.7556795397 
    sum:	684709 
   good:	281177 
   null:	73443 
unix% get_sky_limits 11823.i1.img 
Running: get_sky_limits
  version: 12 September 2012
Checking binning of image: 11823.i1.img
  Image has 595 x 596 pixels
  Pixel size is 2.0 by 2.0
  Lower left (0.5,0.5) corner is x,y= 4098.2, 2973.7
  Upper right (595.5,596.5) corner is x,y= 5288.2, 4165.7
  DM filter is:
  mkexpmap xygrid value is:

By spatially filtering the events we include knowledge of the edge of the CHIP in the data subsapce of the image; this can be seen in the output of the dmstat call, where those pixels that lie outside the chip are ignored (i.e. the null row is not zero). It also means that the "bin sky=2" directive applies only to the SKY range covered by the chip rather than the default 8192 by 8192 area (this is seen in the output of get_sky_limits above). See the chip region FAQ for more ways of finding the chip boundaries.

2. Compute Exposure Map

What is the spectrum of the source?

We selected a region around the central source, using ds9, and saved it as obj.reg:

unix% cat obj.reg
# Region file format: CIAO version 1.0

We can use this file to extract a spectrum of the object in energy space and find the peak energy.

First, we use the CIAO tool dmextract to create a histogram of count-rate as a function of energy. Since we are not binning on pi or pha, we set opt=generic, and we use a bin size of 50 eV to improve the signal to noise:

unix% punlearn dmextract
unix% pset dmextract opt=generic
unix% dmextract "11823.evt2[sky=region(obj.reg)][bin energy=500:7000:50]"

The dmstat tool is used to find the maximum count from the histogram, followed by dmlist to locate the corresponding energy:

unix% dmstat "[cols counts]" sigma-
    min:	1 	      @:	3
    max:	265 	      @:	25
   mean:	69.446153846
    sum:	9028
   good:	130
   null:	0

unix% dmlist "[counts>250][cols energy,counts]" data,clean
#  ENERGY               COUNTS
               1675.0        254
               1725.0        265
               1775.0        260

For this dataset, the peak of the measured spectrum is ~1.7 keV (which is expected since this is close to the peak of the ACIS effective area). Using the peak value would mean that we would be under-estimating the flux if the energy band is too broad; see the discussion of band selection in the Chandra Source Catalog for more information. So we will use the 2.3 keV used by the CSC, but note that this is something that depends on the spectrum of the source (or sources) being analysed.

[There is a strong peak aroung 1.7 keV, with few counts below 1 keV and a longer tail at higher energies.]

[Version: postscript, PDF]

[Print media version: There is a strong peak aroung 1.7 keV, with few counts below 1 keV and a longer tail at higher energies.]

Figure 1: Energy spectrum of the central source in RCW 103

The two vertical lines indicate the 1.7 keV peak and the 2.3 keV value defined by the Chandra Source Catalog for its "broad" band.

Compute the Aspect Histogram

With the aspect solution file we can create a binned histogram for the chip that was on, detailing the aspect history of the observation. We use the same aspect solution file (acisf11823_asol1.lis) as above:

unix% cat acisf11823_asol1.lis 

unix% punlearn asphist
unix% asphist @acisf11823_asol1.lis 1.asphist "11823.evt2[ccd_id=1]"

You can check the parameter file that was used with plist asphist.

Calculate the Instrument Map

Since the mirror effective area is used to create the instrument map, and that area is energy dependent, it is necessary to decide at what energy to perform the calculation (or whether to use a spectrum as weights). In this example we are going to assume a monoenergetic distribution of source photons of 2.3 keV (monoenergy parameter). The Calculating Spectral Weights for mkinstmap thread shows how to create a weighted instrument map using mkinstmap.

Note that it is not necessary for the instrument map to be congruent with the exposure map; the instrument map should describe the chip with full resolution.

At this point make sure that you have set up ardlib to use the bad pixel file for your observation. For this observation, since we are only interested in ACIS-I1:

unix% pget ardlib AXAF_ACIS1_BADPIX_FILE

where we are using the bad-pixel file created by chandra_repro for this observation.

unix% punlearn mkinstmap
unix% pset mkinstmap pixelgrid="1:1024:#1024,1:1024:#1024"
unix% pset mkinstmap obsfile=11823.evt2
unix% pset mkinstmap maskfile=acisf11823_001N002_msk1.fits
unix% pset mkinstmap detsubsys=ACIS-1
unix% mkinstmap 1.instmap NONE 2.3
Pixel grid specification x0:x1:#nx,y0:y1:#ny (1:1024:#1024,1:1024:#1024):
Name of fits file + extension with obs info (11823.evt2):
Detector Name (ACIS-1):
Grating for zeroth order ARF (NONE|LETG|HETG) (NONE):
NONE, or name of ACIS window mask file (acisf11823_001N002_msk1.fits):
NONE, or the name of the parameter block file ():

Including the maskfile parameter is particularly important if you are interested in having an accurate exposure map at the very edge of a CCD, subarray or window. The pixelgrid parameter should not be changed for the case of a subarray or window; the mask file will account for the detector range being different. For more information, see the dictionary entry on mask files.

You can check the parameter file that was used with plist mkinstmap.

The pbkfile parameter has been deprecated and should be left empty; more details can be found on the Watchout page. The obsfile parameter should use the event file rather than the aspect histogram, as used in previous versions of CIAO.

Calculate the Exposure Map

Now we use mkexpmap and the aspect information stored in the histogram to project the instrument map onto the sky. We need to set the xygrid parameter to produce an exposure map that is the same size as the image created from the event list. The get_sky_limits script can be used to easily calculate this information from the existing image:

unix% get_sky_limits 11823.i1.img 
Running: get_sky_limits
  version: 12 September 2012
Checking binning of image: 11823.i1.img
  Image has 595 x 596 pixels
  Pixel size is 2.0 by 2.0
  Lower left (0.5,0.5) corner is x,y= 4098.2, 2973.7
  Upper right (595.5,596.5) corner is x,y= 5288.2, 4165.7
  DM filter is:
  mkexpmap xygrid value is:

You can then set the xygrid parameter using the information provided by the script, either manually or via

unix% pset mkexpmap xygrid=")get_sky_limits.xygrid"

(if the latter, do not run get_sky_limits again until after running mkexmap).

Note: If you are computing a low-resolution exposure map and speed is more important than accuracy, set useavgaspect=yes. In doing so, only the average aspect pointing will be used to derive the exposure map; otherwise all points in the aspect histogram will be used. The time required to compute the exposure map is proportional to the number of bins in the aspect histogram; if the aspect histogram contains 100 bins, then the use of this option reduces the run time by a factor of 100, approximately (you may also want to set verbose to 2, since this causes mkexpmap to output percentage-completed information). Using the full aspect solution will help accurately account for chip edges, bad pixels, etc.

unix% set xygrid = `pget get_sky_limits xygrid`
unix% echo $xygrid
unix% punlearn mkexpmap
unix% pset mkexpmap xygrid=$xygrid normalize=no
unix% mkexpmap 1.asphist 1.expmap 1.instmap
grid specification syntax x0:x1:#nx,x0:x1:ny (4098.2:5288.2:#595,2973.7:4165.7:#596): 
Use Average Aspect Pointing (no): 

You can check the mkexpmap parameter file that was used with plist mkexpmap. The exposure map may be displayed in ds9 (Figure 2).

[Thumbnail image: The exposure map of the chip shows several bad columns.]

[Version: full-size]

[Print media version: The exposure map of the chip shows several bad columns.]

Figure 2: Exposure map for the ACIS-I1 chip

unix% ds9 1.expmap -cmap b -scale pow

The stripes are due to bad columns in the instrument map and the "power-law" scaling has been chosen to highlight the presence of bad pixels.

Since we set the normalize parameter = no, the exposure map has units of [cm2*s*counts/photon]. This allows us to simply divide the image by the exposure map to derive an image in units of flux [photons/cm2/s/pixel]. If the setting had been left as yes (the default), the units of the exposure map would be [cm2*counts/photon]. The units can be added to the exposure map using dmhedit

unix% dmhedit expmap.fits file= op=add key=BUNIT value="cm**2 sec"

Please see the help file for mkexpmap for more details on this.

3. Normalize the Image by the Exposure Map

The strongly variable exposure near the edge of a dithered field may produce "hot" pixels when divided into an image. While technically proper, these hot pixels can be an eyesore, drawing attention to a noisy, uninteresting portion of the image. The dmimgthresh tool is used to make a "threshold cut" before dividing the image by the exposure map, thus removing the hot pixels:

unix% punlearn dmimgthresh
unix% dmimgthresh 11823.i1.img 11823.i1.thresh.img expfile=1.expmap cut=1.5%
unix% dmimgthresh 1.expmap 1.thresh.expmap cut=1.5%

We also threshold the exposure map so that we can use the exposure map to determine whether a pixel is 0 because there were no counts or because it was removed by the threshold process.

Here we set our threshold at 1.5% of the maximum value of the exposure map. All image pixels with values of exposure less than this value will be set to 0.0 in the output file. You may want to adjust these values for your own observation.

You can check the parameter file that was used with plist dmimgthresh.

The exposure map is in units of [cm2*s*counts/photon] since it was created by projecting the instrument map (in [cm2*counts/photon]) onto the tangent plane of the observation. To create an image in units of [photon/cm2/s/pixel], we simply need to divide by the exposure map. This is done by the tool dmimgcalc.

unix% punlearn dmimgcalc
unix% dmimgcalc 11823.i1.thresh.img 1.thresh.expmap 11823.i1.norm div
warning: CONTENT has 1 different values.
warning: DETNAM has different value...Merged...

The messages are related to how the tool merges the header information in the input files. The merging_rules ahelp file explains the rules and how they affect the output file header.

The units of 11823.i1.norm (Figure 3) are [photon/cm2/s/pixel].

You can check the parameter file that was used with plist dmimgcalc.

It is also possible to use dmimgcalc to create an exposure-corrected image where those pixels with no exposure are set to NaN (see Figure 4):

unix% dmimgcalc infile=11823.i1.thresh.img,1.thresh.expmap \
          infile2= outfile=11823.i1.norm2 \
warning: CONTENT has 1 different values.
warning: DETNAM has different value...Merged...
[Thumbnail image: The areas of the image where no data is collected are colored in red.]

[Version: full-size]

[Print media version: The areas of the image where no data is collected are colored in red.]

Figure 4: Exposure-corrected image containing NaN values

unix% ds9 11823.i1.norm2 -scale log -cmap hsv -prefs nancolor red

The red pixels indicate the NaN values, where the exposure map is 0.

Many CIAO tools will exclude NaN values, as shown in the dmstat output:

unix% dmstat 11823.i1.norm\* centroid-
    min:	0 	      @:	( 4099.224052 2974.7345895 )
    max:	0.00022522023937 	      @:	( 4181.224052 3942.7345895 )
   mean:	1.3903681672e-07
  sigma:	5.7686120868e-07
    sum:	0.049305235944
   good:	354620
   null:	0
    min:	0 	      @:	( 4253.224052 2974.7345895 )
    max:	0.00022522023937 	      @:	( 4181.224052 3942.7345895 )
   mean:	1.7630358164e-07
  sigma:	6.4450939927e-07
    sum:	0.049305235944
   good:	279661
   null:	74959

Calculate the Source Flux

Since the units of the exposure-corrected image are [photon/cm2/s/pixel], adding up the pixel values around a source results in the source flux in [photon/cm2/s]. Note that this flux is an approximation - as discussed in An Introduction to Exposure Maps (PS, 12pp) - since a spectral shape was assumed when using mkinstmap (in this example, a monochromatic source).

Using the source region "obj.reg":

unix% cat obj.reg
# Region file format: CIAO version 1.0

The flux can be calculated in several ways (note that for this example we are ignoring the contribution from the background):

  1. From the CIAO analysis menu in ds9. Load the data and region file, then run "Analysis → CIAO → Statistics → All (no centroid)".

  2. with dmstat:

    unix% punlearn dmstat
    unix% dmstat "11823.i1.norm[sky=region(obj.reg)]" centroid-
        min:	9.0578458867e-07 	      @:	( 4181.224052 3948.7345895 )
        max:	0.00022522023937 	      @:	( 4181.224052 3942.7345895 )
       mean:	1.3121088069e-05
      sigma:	3.9140987982e-05
        sum:	0.00065605440346
       good:	50
       null:	31
  3. with dmextract:

    unix% punlearn dmextract
    unix% dmextract "11823.i1.norm[bin sky=@obj.reg]" sources.flux opt=generic
    unix% dmlist "sources.flux[cols counts]" data,clean
    #  COUNTS

    Since the input to dmextract was an image, not an event list, the COUNTS column actually reports the total flux (in [photon/cm2/s]) for the source region. While slightly more involved, the dmextract method can be used on multiple sources in a single command, and the results are conveniently stored in a table.

To compute robust source intensity quantities (net counts, source rate, photon flux, energy flux) and the related confidence intervals, use the aprates tool. The Compute Net Counts, Rate, or Flux for Point Sources thread shows how to run aprates.

If you are working with event lists, the eff2evt tool can be used to compute the approximate flux, and calculate the QE and Effective Area for sources. The Calculate the Flux for a Position thread describes how to use this tool.

The srcflux script can be used to compute net counts rates, photon, and energy fluxes automatically.

Analysis Caveats

Users should be cautious about analyzing the data for sources near the edges of the ACIS CCDs.

  1. For X-rays passing through the mirrors, the very bottom of each CCD is obscured by the frame store. As a result, some of the events in rows with CHIPY <= 8 are not detected. (The set of rows affected varies from CCD to CCD.) Since the CIAO tools do not compensate for this effect, the ARFs and exposure maps for sources in these regions may be inaccurate.

  2. For sources within about thirty-two pixels of any edge of a CCD, the source may be dithered off the CCD during part of an observation. The aspect histogram, which is used to create ARFs and exposure maps, is designed to compensate for this effect.

  3. An ARF calculated at the edge of a chip will not be accurate since the response tools for spectral extraction (specifically the ARF) assume that 100% of the PSF is enclosed - i.e. on the chip - all the time, which may not be the case. The amount of error introduced depends on how close the source is to the edge, the morphology of the source, and the characteristics of the PSF, which depends on the source spectrum.

  4. A contaminant has accumulated on the optical-blocking filters of the ACIS detectors, as described in the ACIS QE Contamination why topic. Since there is a gradient in the temperature across the filters (the edges are colder), there is a gradient in the amount of material on the filters. (The contaminant is thicker at the edges.) Within about 100 pixels of the outer edges of the ACIS-I and ACIS-S arrays, the gradient is relatively steep. Therefore, the effective low-energy (' 1 keV) detection efficiency may vary within the dither pattern in this region. The ARF and instrument map tools are designed to read a calibration file which describes this spatial dependence.

Parameters for /home/username/cxcds_param/fluximage.par

        infile = repro/acisf11823_repro_evt2.fits[ccd_id=1] Input events file
       outroot = chip1            Root of output files
        (bands = default)         Energy bands, comma-separated list, min:max:center in keV or ultrasoft, soft, medium, hard, broad, wide, CSC
       (xygrid = )                xygrid for output or filename
      (binsize = INDEF)           Image binning factor
     (asolfile = )                Input aspect solutions
   (badpixfile = )                Input bad pixel file
     (maskfile = )                Input mask file
      (dtffile = )                Input dtf file for HRC observations
        (units = default)         Units for the exposure map
 (expmapthresh = 1.5%)            Remove low-exposure regions? '2%' excludes pixels where exposure is < 2% of the maximum
   (background = default)         Method for background removal (HRC-I)
     (parallel = yes)             Run processes in parallel?
        (nproc = INDEF)           Number of processors to use
       (tmpdir = ${ASCDS_WORK_PATH} -> /tmp) Directory for temporary files
      (cleanup = yes)             Delete intermediary files?
      (clobber = no)              OK to overwrite existing output file?
      (verbose = 1)               Verbosity level
         (mode = ql)              

Parameters for /home/username/cxcds_param/asphist.par

#       Parameter file for the ASPECT HISTOGRAM Tool
        infile = @acisf11823_asol1.lis Aspect Solution List Files
       outfile = 1.asphist        Aspect Histogram Output File
       evtfile = 11823.evt2[ccd_id=1] Event List Files
       dtffile =                  Live Time Correction List Files for HRC
      (geompar = geom)            Parameter file for Pixlib Geometry files
       (res_xy = 0.5)             Aspect Resolution x and y in arcsec
     (res_roll = 600.)            Aspect Resolution roll in arcsec
      (max_bin = 10000.)          Maximal number of bins
      (clobber = no)              Clobber output
      (verbose = 0)               Verbose
         (mode = ql)              

Parameters for /home/username/cxcds_param/mkinstmap.par

       outfile = 1.instmap        Output File Name
# Energy Band Info
# Currently, this file is a simple ascii file with two columns
  spectrumfile = NONE             Energy Spectrum File (see docs)
    monoenergy = 2.3              Energy for mono-chromatic map [keV]
     pixelgrid = 1:1024:#1024,1:1024:#1024 Pixel grid specification x0:x1:#nx,y0:y1:#ny
       obsfile = 11823.evt2       Name of fits file + extension with obs info
     detsubsys = ACIS-1           Detector Name
       grating = NONE             Grating for zeroth order ARF
      maskfile = acisf11823_001N002_msk1.fits NONE, or name of ACIS window mask file
       pbkfile =                  NONE, or the name of the parameter block file
       (mirror = HRMA)            Mirror Name
       (dafile = CALDB)           NONE, CALDB, or name of ACIS dead-area calibration file
(ardlibparfile = ardlib.par)      name of ardlib parameter file
      (geompar = geom)            Parameter file for Pixlib Geometry files
      (verbose = 0)               Verbosity
      (clobber = no)              Overwrite existing files?
         (mode = ql)              Enter mode for parameter file.

Parameters for /home/username/cxcds_param/mkexpmap.par

   asphistfile = 1.asphist        Aspect Histogram File
       outfile = 1.expmap         Output File Name
   instmapfile = 1.instmap        Name of Instrument Map
        xygrid = 4098.2:5288.2:#595,2973.7:4165.7:#596 grid specification syntax x0:x1:#nx,x0:x1:ny
  useavgaspect = no               Use Average Aspect Pointing
#  Aspect Histogram Parameters
#  If UseAvgAspect is set to yes, then only the average pointing derived from
#  the many pointings in the aspect histogram will be used.
#asphistfile,f,a,"../data/aciss_asphist.fits",,,"Aspect Histogram File"
    (normalize = no)              Normalize exposure map by exposure time
      (geompar = geom)            Parameter file for Pixlib Geometry files
      (verbose = 0)               Verbosity
      (clobber = no)              Overwrite existing files?
         (mode = ql)              Enter mode for parameter file.

Parameters for /home/username/cxcds_param/dmimgthresh.par

        infile = 11823.i1.img     Input dataset/block specification
       outfile = 11823.i1.thresh.img Output dataset/block specification
      (expfile = )                Exposure map file
          (cut = )                Threshold value
        (value = 0.0)             Replacement value
      (verbose = 0)               Debug Level(0-5)
      (clobber = no)              Clobber existing file
         (mode = ql)              

Parameters for /home/username/cxcds_param/dmimgcalc.par

# parameter file for dmimgcalc
        infile = 11823.i1.thresh.img Input file #1
       infile2 = 1.expmap         Input file #2
       outfile = 11823.i1.norm    output file 
     operation = div              arithmetic operation
       (weight = 1)               weight for first image
      (weight2 = 1)               weight for second image
    (lookupTab = ${ASCDS_CALIB}/dmmerge_header_lookup.txt -> /export/local/ciao-4.4/data/dmmerge_header_lookup.txt) lookup table
      (clobber = no)              delete old output
      (verbose = 0)               output verbosity
         (mode = ql)              


09 Jan 2012 reviewed for CIAO 4.4: added the option of using the CIAO analysis menu in ds9 to calculate the source flux
06 Feb 2012 fluximage updates were released in the 06 Feb 2012 scripts package: setting badpixfile=CALDB uses the bad pixel file from the CALDB rather than the per-observation version.
16 Feb 2012 fluximage updates were released in the 16 Feb 2012 scripts package: setting badpixfile=NONE uses no bad pixel file when creating the instrument, and hence exposure, maps.
15 Oct 2012 The fluximage script has been updated in the 15 Oct 2012 scripts package: changes include an updated parameter file; output file names are different; and support for spectrally-weighted exposure maps. The observation used as an example has been changed to ObsId 11823, an observation of the supernova remnant RCW 103. The step-by-step guide has been updated to better match the fluximage script: e.g. use of a FOV file for filtering the observation; using the same energy value for the exposure map rather than taking the peak of the spectrum; the exposure map is now also thresholded; and the exposure-corrected image is created with pixels containing 0 (Figure 3) or NaN (Figure 4) where there is no data.
03 Dec 2012 Review for CIAO 4.5; removed mkexpmap chatter
04 Dec 2013 Review for CIAO 4.6; the pbkfile parameter for fluximage has been removed and is deprecated for mkinstmap; an event file, rather than aspect histogram, should be used for the obsfile parameter of mkinstmap.
17 Dec 2014 Reviewed for CIAO 4.7; minor edits only.

Last modified: 17 Dec 2014
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