Remove ACIS Pixel Randomization

Overview

Last Update: 1 Dec 2006 - updated for CIAO 3.4: removed use of "rand_pha=no" in acis_process_events, as most users should keep the PHA randomization (see the Apply/Remove PHA Randomization thread); CIAO version in warnings

Synopsis:

The CXC standard data processing (SDP) randomizes the positions of events detected within a given pixel. This randomization is done to remove the instrumental "gridded" appearance of the data and to avoid any possible aliasing affects associated with this spatial grid. The default randomization is adequate for most users.

Purpose:

To generate a new level=2 event file with the pixel randomization removed. Disabling pixel randomization can somewhat improve the resolution of on-axis Chandra sources. This procedure may be useful for users interested in closely-spaced point sources in a crowded field or closely-spaced features in an extended source.

Read this thread if:

you are working with an ACIS observation and would like to remove the randomization. Be aware that there are no calibration products appropriate for data processed with the randomization disabled.

Related Links:

• Analysis Guide: ACIS Data Preparation

• Apply the ACIS CTI Correction thread: it is strongly recommended that you reprocess imaging data with this new calibration which became part of standard data processing in DS 6.11. Note that the CTI correction is on by default (apply_cti=yes) in the acis_process_events.

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


#--------------------------------------------------------------------------
#
#  acis_process_events.par- Parameter file for acis_process_events program
#
#--------------------------------------------------------------------------
        infile = acisf01838_000N001_evt1.fits   Input event file or stack
       outfile = acis_1838_new_evt1.fits Output event file name
    acaofffile = pcadf084244404N001_asol1.fits aspect offset file ( NONE | none | <filename>)
    (apply_cti = yes)             Apply CTI adjustment?
  (apply_tgain = yes)             Apply time-dependent gain adjustment?
(alignmentfile = )acaofffile -> pcadf084244404N001_asol1.fits) sim/fam alignment file ( NONE | none | <filename>)
      (obsfile = NONE)            obs.par file for output file keywords ( NONE | none | <filename>)
      (geompar = geom)            Parameter file for Pixlib Geometry files
      (logfile = stdout)          debug log file ( STDOUT | stdout | <filename>)
    (gradefile = CALDB)           grade mapping file ( NONE | none | CALDB | <filename>)
     (gainfile = CALDB)           acis gain file ( NONE | none | CALDB | <filename>)
   (badpixfile = acis_1838_new_bpix1.fits) acis bad pixel file ( NONE | none | <filename>)
   (threshfile = CALDB)           split threshold file ( NONE | none | CALDB | <filename>)
      (ctifile = CALDB)           acis CTI file ( NONE | none | CALDB | <filename>)
    (tgainfile = CALDB)           gain adjustment file ( NONE | none | CALDB | <filename>)
     (eventdef = )stdlev1 -> {d:time,s:ccd_id,s:node_id,i:expno,s:chip,s:tdet,f:det,f:sky,s:phas,l:pha,l:pha_ro,
f:energy,l:pi,s:fltgrade,s:grade,x:status}) output format definition
   (doevtgrade = yes)             Determine event flight grade?
 (check_vf_pha = no)              Check very faint pixels?
(calc_cc_times = no)              Estimate the times of arrival for CC-mode observation?
        (trail = 0.027)           Trail fraction
     (spthresh = 13)              Default split threshold level (overridden by values in threshfile)
  (time_offset = 0)               Offset to add to event time field to synch w/ fam data
   (docentroid = no)              Determine pixel centroid for coord. conversion?
 (calculate_pi = no)              perform pha->pi conversion? (requires gain file)
 (pi_bin_width = 14.6)            Width of Pi bin in eV
  (pi_num_bins = 1024)            Number of values to bin energy into
 (max_cti_iter = 15)              Maximum iterations for the CTI adjustment of each event
 (cti_converge = 0.1)             The convergence criterion for each CTI-adjusted pixel in adu
       (tstart = TSTART)          header key containing start/default time value
        (tstop = TSTOP)           header key containing time of last event
      (clobber = no)              Overwrite output event file if it already exists?
      (verbose = 0)               level of debug detail (0=none, 5=most)
         (stop = sky)             end transformations at [chip,tdet,det,tan,sky,none]
     (instrume = acis)            axaf instrument- used for instrument parameter file
    (rand_seed = 1)               random seed (for pixlib), 0 = use time dependent seed
     (rand_pha = yes)             Randomize the pha value used in gain calculations
(rand_pix_size = 0)               pixel randomization width (-size..+size) 0=no randomization
      (stdlev1 = {d:time,s:ccd_id,s:node_id,i:expno,s:chip,s:tdet,f:det,f:sky,s:phas,l:pha,l:pha_ro,f:energy,
l:pi,s:fltgrade,s:grade,x:status}) TE faint modes event definition string
      (grdlev1 = {d:time,s:ccd_id,s:node_id,i:expno,s:chip,s:tdet,f:det,f:sky,l:pha,l:pha_ro,s:corn_pha,f:energy,
l:pi,s:fltgrade,s:grade,x:status}) TE graded event format definition string
       (cclev1 = {d:time,s:ccd_id,s:node_id,i:expno,s:chip,s:tdet,f:det,f:sky,f:sky_1d,s:phas,l:pha,l:pha_ro,
f:energy,l:pi,s:fltgrade,s:grade,x:status}) CC faint event format definition string
    (ccgrdlev1 = {d:time,s:ccd_id,s:node_id,i:expno,s:chip,s:tdet,f:det,f:sky,f:sky_1d,l:pha,l:pha_ro,s:corn_pha,
f:energy,l:pi,s:fltgrade,s:grade,x:status}) cc graded event format definition string
         (mode = ql)