Apply the Time-Dependent ACIS Gain Correction

Overview

Last Update: 8 Feb 2008 - added deprecated thread message to Synopsis

Synopsis:

This thread has been deprecated and will be removed in the next CIAO release. Instead of running this thread, follow the Reprocessing Data to Create a New Level=2 Event File thread.

The tool acis_process_events includes a time-dependent gain adjustment. This adjustment is necessary because the "effective gains" of the detectors are drifting with time as the result of an increasing CTI.

There is CTI calibration data and time-dependent gain calibration data for the entire ACIS detector (chips I0-3 and S0-5).

The correction for this problem became part of standard data processing (SDP) in DS 7.3.1.

Purpose:

To generate a new level=1 event file with the time-dependent gain adjustment applied.

Read this thread if:

you are working with a -120 C ACIS observation (imaging or grating) that took place after February 2000. Get Started shows how to check the temperature of your observation.

Data taken since February 2000 may need to be reprocessed to apply newer TGAIN calibration. Read the Calibration Updates for a history of TGAIN calibration changes.

Users interested in CCD spectroscopy should apply the T_GAIN adjustment. Grating spectroscopy may benefit marginally, in the form of improved order sorting. It is not necessary to apply this adjustment if you are only doing timing or imaging analysis, but it will not have a negative effect, either.

Calibration Updates:

• CALDB v3.4.2 (14 Dec 2007): New time-dependent gain calibration files for 01 August 2007 - 31 December 2007 (Epoch 31) were added to the CALDB. The CALDB 3.4.2 section of the CIAO release notes explains how the files will affect your analysis.

Related Links:

• Analysis Guide: ACIS Data Preparation

• Why topic: ACIS Time-dependent Gain

• Corrections for Time-dependence of ACIS Gain: a calibration page that explains technical details of the gain adjustment.

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


#--------------------------------------------------------------------------
#
#  acis_process_events.par- Parameter file for acis_process_events program
#
#--------------------------------------------------------------------------
        infile = acisf01838_000N002_evt1.fits   Input event file or stack
       outfile = acis_1838_new_evt1.fits Output event file name
    acaofffile = NONE             aspect offset file ( NONE | none | <filename>)
    (apply_cti = yes)             Apply CTI adjustment?
  (apply_tgain = yes)             Apply time-dependent gain adjustment?
(alignmentfile = )acaofffile -> NONE) 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 = yes)             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 = none)            where to end transformations
     (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 = 0.5)             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,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,f:energy,l:pi,
s:fltgrade,s:grade,x:status}) cc graded event format definition string
         (mode = ql)