LETG/ACIS-S Grating ARFs

About the Chandra Grating Data Archive and Catalog

The Chandra Grating Data Archive and Catalog (TGCat) is a browsable interface to analysis-quality spectral products (binned spectra and corresponding response files). TGCat makes it easy to find observations of a particular object, type of object, or type of observation, to quickly assess the quality and potential usefulness of the spectra with pre-computed graphics or custom-generated plots of binned and combined counts or fluxe spectra. Spectra, responses, event files, and summary products may be downloaded as a package.

TGCat runs standard CIAO tools, but also includes customized extractions for non-standard cases to refine the zeroth order position or to use regions appropriate for extended sources. Non-standard extractions details are provided in "verification and validation" comments for users.

Most public grating observations are available and new ones are added soon after they are released. See the list of of observations not included for exceptions. Many of the observations currently in this list will be included when we add enhanced processing for more difficult cases (multiple sources, very extended sources).

Please consider using the spectrum and responses (PHA, ARF, and RMF files) from TGCat in your analysis.

Repro V (5) data

Script It

The creation of the grating ARF and RMF is now automated.

chandra_repro will now automatically create the RMF and ARF for grating spectra. The results are stored in a tg/ subdirectory of the output directory.

Also, the mktgresp tool will create all the ARFs and RMFs for the grating spectra in a type II PHA file using the default grids and standard calibrations files. Just simply run

unix% mktgresp pha2 evt2 root_filename

where pha2 and evt2 are the filenames of your spectra output from tgextract or tgextract2 and the corresponding event file.

Thread Complete

If you have run chandra_repro or mktgresp then you are done with this thread and may move onto fitting and modeling your spectra. If you need to customize your responses or want to learn more details of the step by step processing steps you can continue with this thread.

Get Started

Download the sample data: 1198 (LETG/ACIS-S, 3C 273)

unix% download_chandra_obsid 1198 

It is assumed that you have created a gRMF for your observation by running the Create Grating RMFs for ACIS-S Observations thread, which is called rmf.fits.

Determine the Orders of the Observation

An ARF needs to be calculated for each order in the observation. We can use dmlist to examine the pha2 file and determine how many orders there are:

unix% dmlist acisf01198_repro_pha2.fits"[cols tg_m,tg_part]" data,clean
#  TG_M TG_PART
   -3    3
   -2    3
   -1    3
    1    3
    2    3
    3    3

The tg_m column indicates the order of the observation (+/- 1, +/- 2, +/- 3) and the tg_part column indicates the grating (1 = HEG, 2 = MEG, 3 = LEG). The six rows (all +/- orders for LEG) for the LETG observation are shown in .

Run fullgarf

It is necessary to run fullgarf for each order that will be modeled, up to six times (once for each row in the PHA file).

For row 2, LEG, order = -2:

unix% punlearn fullgarf
unix% pset fullgarf phafile=acisf01198_repro_pha2.fits
unix% pset fullgarf pharow=2
unix% pset fullgarf evtfile=acisf01198_repro_evt2.fits
unix% pset fullgarf asol=@pcad_asol1.lis
unix% pset fullgarf engrid="grid(rmf.fits[cols ENERG_LO,ENERG_HI])"
unix% pset fullgarf badpix=acisf01198_repro_bpix1.fits
unix% pset fullgarf maskfile=acisf01198_000N004_msk1.fits
unix% pset fullgarf dafile=CALDB
unix% pset fullgarf rootname=acisf01198

In some rare cases, there will be more than one aspect solution file (pcad_asol1.fits) for an observation. All the files must be input to the asol parameter, either as a list or a stack. Here we use:

unix% cat pcad_asol1.lis
pcadf01198_000N001_asol1.fits

Now run the tool:

unix% fullgarf
Will use /home/username/cxcds_param4/fullgarf.par for the parameter file.
   
/home/username/cxcds_param4/fullgarf.par contains 15 parameters . . . 
   
Input PHA file (Type I or II) (acisf01198_repro_pha2.fits): 
Row in Type II PHA file (ignored if Type I) (0:99) (2): 
Event file  (acisf01198_repro_evt2.fits): 
Aspect offsets file (@pcad_asol1.lis): 
Energy grid spec (grid(rmf.fits[cols ENERG_LO,ENERG_HI])): 
Dead time correction factor; ACIS->evt file; HRC -> dtf file (): 
Bad pixel file; (filename|NONE|CALDB) (acisf01198_repro_bpix1.fits): 
Output rootname (acisf01198): 
NONE, or name of ACIS window mask file (acisf01198_000N004_msk1.fits):    
Getting the pha file type . . .

Grating arm is LEG, order=-2  
Source location is X=4162.240234375, Y=4084.679931640625
  
Detector is ACIS 
Will run asphist for ccd_id= 4 5 6 7 
  
   
asphist infile=@pcad_asol1.lis outfile=acisf01198_ah4.fits 
evtfile=acisf01198_repro_evt2.fits[ccd_id=4] dtffile=
   
asphist infile=@pcad_asol1.lis outfile=acisf01198_ah5.fits 
evtfile=acisf01198_repro_evt2.fits[ccd_id=5] dtffile=
   
asphist infile=@pcad_asol1.lis outfile=acisf01198_ah6.fits 
evtfile=acisf01198_repro_evt2.fits[ccd_id=6] dtffile=
   
asphist infile=@pcad_asol1.lis outfile=acisf01198_ah7.fits 
evtfile=acisf01198_repro_evt2.fits[ccd_id=7] dtffile=
   
Finished creating aspect histograms for ccd_id= 4 5 6 7 
Will run mkgarf for the same ccd_id list 
   
mkgarf detsubsys=ACIS-S0 order=-2 grating_arm=LEG outfile=acisf01198_S0_LEG_-2.fits 
asphistfile=acisf01198_ah4.fits[ASPHIST] engrid=grid(rmf.fits[cols ENERG_LO,ENERG_HI]) osipfile=CALDB dafile=CALDB
pbkfile= maskfile=acisf01198_000N004_msk1.fits mode=hl verb=0
  
mkgarf detsubsys=ACIS-S1 order=-2 grating_arm=LEG outfile=acisf01198_S1_LEG_-2.fits 
asphistfile=acisf01198_ah5.fits[ASPHIST] engrid=grid(rmf.fits[cols ENERG_LO,ENERG_HI]) osipfile=CALDB dafile=CALDB
pbkfile= maskfile=acisf01198_000N004_msk1.fits mode=hl verb=0
   
mkgarf detsubsys=ACIS-S2 order=-2 grating_arm=LEG outfile=acisf01198_S2_LEG_-2.fits 
asphistfile=acisf01198_ah6.fits[ASPHIST] engrid=grid(rmf.fits[cols ENERG_LO,ENERG_HI]) osipfile=CALDB dafile=CALDB
pbkfile= maskfile=acisf01198_000N004_msk1.fits mode=hl verb=0 
   
mkgarf detsubsys=ACIS-S3 order=-2 grating_arm=LEG outfile=acisf01198_S3_LEG_-2.fits 
asphistfile=acisf01198_ah7.fits[ASPHIST] engrid=grid(rmf.fits[cols ENERG_LO,ENERG_HI]) osipfile=CALDB dafile=CALDB
pbkfile= maskfile=acisf01198_000N004_msk1.fits mode=hl verb=0 
   
Finished creating grating arfs for ccd_id= 4 5 6 7 
   
dmarfadd @thisfile.istemporary acisf01198LEG_-2_garf.fits
  
fullgarf finished. 

You may also see an aspect-related error from mkgarf; it is explained in the fullgarf bug page. The content of the parameter file may be checked using plist fullgarf.

The script is run in a similar way for the remaining rows.

Fitting

At this point, you should have the spectra, gARFs, and gRMFs necessary for fitting the data. The Fitting Grating Data thread shows how to load the data and responses, define a model, and fit the spectra.

In order to use Gaussian statistics to fit a model to a dataset, it is often necessary to "group" the data - i.e. combine channels until you have enough counts. Before fitting the data in Sherpa, read the Grouping a Grating Spectrum thread for more information.