Last modified: December 2022

AHELP for CIAO 4.15


Context: Tools::Gratings


Adjust the tg_d values of LETG/HRC-S evt2 data to make cross-dispersion profiles more symmetric


symmetrize infile outfile


symmetrize reads in an LETG/HRC-S evt2 file (usually this will be the output of the detilt command) and adjusts the TG_D values of all events. This makes the cross-dispersion profiles more symmetric about TG_D=0 so that EEFRAC values (used in the gRMF) will be accurate even when using narrower-than-standard spectral extraction regions. See Corrections to TG_D for Wiggles, Tilt, and Asymmetry for details. Only TG_D values are affected; the output file will not exhibit any changes if displayed in sky or detector coordinates.

symmetrize is generally used in combination with the dewiggle and detilt commands--also contributed software tools--to prepare LETG/HRC-S spectra so that narrower spectral extraction regions can be used to improve the S/N of low-S/N data.


symmetrize input_evt2.fits output_evt2.fits clobber+

Run the program with the clobber parameter enabled.


name type ftype def min max reqd stacks
infile file         yes no
outfile file output       yes no
sfile file   ${ASCDS_CONTRIB}/data/eefracIDEAL09.symm78corr       no
verbose integer   0 0 5    
clobber boolean   no        

Detailed Parameter Descriptions

Parameter=infile (file required stacks=no)

Input FITS file event list with columns TG_D and TG_MLAM.

Parameter=outfile (file required filetype=output default= stacks=no)

Output FITS file event list with modified TG_D column.

Parameter=sfile (file default=${ASCDS_CONTRIB}/data/eefracIDEAL09.symm78corr stacks=no)

File containing the TG_D correction as a function of wavelength.

Parameter=verbose (integer default=0 min=0 max=5)

Tool chatter level

Controls the amount of information tool prints to the screen.

Parameter=clobber (boolean default=no)

Remove outfile if it already exists?

About Contributed Software

This tool is not an official part of the CIAO release but is made available as "contributed" software via the CIAO scripts page. Please see this page for installation instructions.


See the bugs page on the CIAO website for an up-to-date listing of known bugs.

Refer to the CIAO bug pages for an up-to-date listing of known issues.

See Also

simple_hist, simple_stats
combine_grating_spectra, detilt, dewiggle, dmtype2split, mktgresp, symmetrize, tg_bkg, tg_choose_method, tg_create_mask, tg_findzo, tg_resolve_events, tgdetect, tgdetect2, tgextract, tgextract2, tgidselectsrc, tgmask2reg, tgmatchsrc, tgsplit