Determine whether a suspicious pixel is hot or affected by an afterglow.
acis_classify_hotpix infile outfile badpixfile hotpixfile [expnothresh]
[clobber] [verbose]
acis_classify_hotpix is one of the tools used to find hot pixels and
cosmic-ray afterglows (see acis_run_hotpix). This tool is used to read the
output from acis_find_hotpix and determine whether the events on suspicious
pixels are associated with cosmic-ray afterglows or hot pixels. For pixels
affected by afterglows, acis_classify_hotpix determines the start and stop
times of the afterglow.
An "afterglow" is produced when a large amount of charge is deposited on a
CCD by a cosmic ray. Most of the charge is clocked off of the CCD
immediately. However, a small amount can be captured in charge traps, which
release the charge relatively slowly. As a result, a sequence of events can
appear in a single pixel over a few to a few dozen frames as the trapped
charge is released. The events need not occur in consecutive frames. There
can be gaps of a few frames with no events for the pixel. The amount of
charge released per frame appears to decay exponentially with time. If the
median number of frames between consecutive events on a suspicious pixel is
less than expnothresh, then the pixel is most likely associated with an
afterglow. The start and stop times are determined as described below (see
expnothresh). Legitimate X-ray events may be identified as afterglow events
if the X-ray source is relatively faint except during some time interval
which is short compared to the period of the dither.
A suspicious pixel is defined to be "hot" if the median number of frames
between consecutive events on the pixel is greater than or equal to
expnothresh.
The pixels that are identified as hot or affected by an afterglow are
written to the output file in addition to the bad pixels and columns in the
input bad-pixel file. The values of STATUS (see acis_build_badpix) and the
start and stop times of afterglows are set appropriately. The tool
acis_build_badpix should be rerun on the output of acis_classify_hotpix to
make sure that pixels adjacent to the newly-identified pixels are handled
properly.
acis_classify_hotpix acisf00732_000N002_evt1.fits tmp2_bpix1.fits
badpixfile="tmp1_bpix1.fits" hotpixfile="suspicious_pixels.fits"
This example shows the default use of the tool acis_classify_hotpix. The
input files acisf00732_000N002_evt1.fits and suspicious_pixels.fits are read
and used to determine whether a pixel is hot or affected by a cosmic-ray
afterglow. These pixels are added to the list of known bad pixels
(tmp1_bpix1.fits, which was produced by acis_build_badpix) and written
to the output file tmp2_bpix1.fits. The output file should be used as
input to the tool acis_build_badpix.
Parameter=infile (file required filetype=input stacks=yes)
The name(s) of the input event data file(s). acis_classify_hotpix can read
Level 0, Level 1 and Level 2 files, but users are urged to use Level 1 files
because these files contain all of the events. Some of the events are
excluded from Level 2 files.
The event data is used to determine when an afterglow begins and ends.
The name of the output bad-pixel file that contains information about each
bad pixel, including the values of SHAPE ("point" or "rectangle"), COMPONENT
(a sequential ID number), CHIPX, CHIPY, TIME (the beginning of the
observation or afterglow), TIME_STOP (the end of the observation or
afterglow), STATUS (a bit-encoded description of the reason the pixel is
identified as bad, see acis_build_badpix). This output file contains a list
of the newly-identified bad pixels as well as the bad pixels and columns in
the input bad-pixel file. The tool acis_build_badpix should be rerun on the
output file to make sure that pixels adjacent to the newly-identified pixels
are handled properly.
The name of the input bad-pixel file, which contains a list of pixels known
to be bad. Pixels that are hot or affected by afterglows are added to the
list and written to the output file.
The name of the input file that contains information about each suspicious
pixel, including the values of CCD_ID, CHIPX, CHIPY, the number of events on
the pixel (S), the expected number of events on the pixel (R), the number of
pixels used to compute R (N), the probability of obtaining S events for an
expected number R (P), the mean number of events per pixel on the node (M)
and the probability of obtaining R events for an expected number M (P_EXP).
This file, which is produced by the tool acis_find_hotpix, must be sorted in
ascending order by CHIPX (first) and CHIPY (second). Although the input
does not need to be sorted by CCD_ID, all of the suspicious pixels for a
CCD, must be grouped together in the file.
Parameter=expnothresh (integer not required default=10 min=2 max=10000)
This parameter is used to distinguish between pixels associated with
cosmic-ray afterglows and hot pixels. If the median number of frames between
consecutive events is less than expnothresh, then a suspicious pixel is most
likely affected by an afterglow. Otherwise, the suspicious pixel is
identified as a hot pixel. The default value of this parameter should be
adequate in most cases. Be cautious about using some other value.
The start and stop times of an afterglow are defined as follows. If the
events on a suspicious pixel have frame numbers EXPNO_1, EXPNO_2, ...,
EXPNO_n, then the start of an afterglow is the beginning of the first frame
i that satisfies the relation EXPNO_i+1 - EXPNO_i < expnothresh. The end
of the afterglow is the end of the first frame i (after the start time) that
satisfies the relation EXPNO_i+1 - EXPNO_i >= expnothresh. Events on the
pixel that do not occur during afterglow are considered valid X-ray events.
If clobber=yes and a file exists that has the same name as the name of the
output file, then the existing file is overwritten. If clobber=no and a file
exists that has the same name as the name of the output file, then an output
file is not created.
Parameter=verbose (integer not required default=0 min=0 max=5)
This parameter determines the amount of messages that is generated by
acis_classify_hotpix. If verbose=0, very few messages are reported. If
verbose=5, the largest amount of messages is produced.
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