Subpixel Event Repositioning (SER) Algorithms
for Chandra/ACIS Imaging (V2)
Subpixel Event Repositioning (SER) techniques have been demonstrated to
significantly improve the already unprecedented spatial resolution of Chandra
X-ray imaging with the Advanced CCD Imaging Spectrometer (ACIS). Chandra
CCD SER techniques are based on the premise that the impact position of events
can be refined, based on the distribution of charge among affected CCD pixels.
ACIS SER models proposed thus far are restricted to corner split (3- and
4-pixel) events, and assume that such events take place at the split pixel
corners. The modified SER techniques available below use two-pixel splits
as well, and incorporate more realistic estimates of photon impact positions,
according to results described in Li et al ( 2003, ApJ) and Li et al. ( 2004, ApJ, in press). These modifications were
developed in Chester F. Carlson Center
for Imaging Science at RIT, under the
guidance of prof.
Joel H. Kastner, with the helps from PSU and MIT faculty members. Current
SER version is v2. Compare to v1 version, the new
parts include FI energy-dependent SER and charge-split dependent SER for
both BI and FI CCDs.
poster2 (pdf file (8.7MB), PS file (13 MB)) -- Static SER method and its
2. Tsunemi et al. 2001 ApJ,
554, 496 -- Tsunemi
et al. (2001) SER method, i.e., static method restricted to corner split events
Li et al 2003, ApJ, 590, 586 -- Energy dependent SER
method for BI CCDs.
4. Li et
al. 2004, ApJ, 610, 1204 (astro-ph/0401592)
-- Charge Split dependent SER, and comparison of various
SER methods for both BI and FI CCDs
2. Implementation Steps
3. IDL code you will need
-- For level 1 event list, following the CIAO steps and remove
randomization applied by standard ACIS processes.
- Event Relocation -- Apply IDL program SER_V2.PRO,
following the usage specification. NOTE: The code hasn't been completely
tested. Please let me know if you have any error messages.
- (Note that some peers have encountered a problem with 'findpro.pro'
routine to locate tables. If you meet same trouble, please try 'findfile.pro',
like ' PL = findfile("BIshifts.fits"). Thanks to Duncan Galloway.)
- Result Comparison -- The spatial resolution improvement is strongly
dependent on your source spectra, employed CCD type (FI or BI), and source
4. What do you need to do
- SER_V2.PRO with other external functions and data
(included in the SER tar file)
- the IDL programs in ASTROLIB
5. Download SER package
- Install CIAO
in your system (for unrandomization).
- Some IDL programs in ASTROLIB were impicitly
used. Download and make them available under your IDL path.
- Download SER_V2.PRO and other external functions, as
well as the necessary
data set (they are within a tar file). Unpack
the tar file and keep all the files in same directory.
6. An example
- Click here for the SER
package, including the IDL codes
and shift tables
- Unpack the tar file, by typing [tar -xvf ser_v2.tar]
- Refer to the comments, especially the keyword usages, in SER.PRO
for further information
7. SER on HETG data (preliminary results, furnished upon
- Assume that you have an event file named "acissf00630_000N002_evt1.fits",
and you want to apply Energy and Charge-split dependent SER on it.
- The first step is to remove the randomization. Assume the new file
name is "acissf00630_000_unran_evt1.fits"
- Apply the SER method, and you want to write the new file as "acissf00630_000_csdser_evt1.fits"
- evt = mrdfits("acissf00630_000_unran_evt1.fits",
- ser_v2, evt, header, /energyAndCharge,
/writetofile, infile="acissf00630_000_unran_evt1.fits", outfile="acissf00630_000_csdser_evt1.fits"
Problems? Comments? Please contact Dylan Li.
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