LETG/HRC-I Grating ARFs
CIAO 4.13 Science Threads
Using HRC-I with the transmission grattings is a non-standard configuration typically used for calibration observations. The standard mktgresp and fullgarf do not work in this mode. Users need to create the ARFs manually as shown in this thread.
To create grating ARFs for an LETG/HRC-I observation.
- About the Instrument: HRC & LETG
- Analysis Guide for Chandra High Resolution Spectroscopy: an in-depth discussion of grating analysis.
Last Update: 2 Apr 2019 - Updated to use matplotlib for plotting.
- About the Chandra Grating Data Archive and Catalog
- Get Started
- Determine Orders
- Compute the Aspect Histogram (asphist)
- Get Source Position (dmlist)
- Run mkgarf
- Parameter files:
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.
Download the sample data: 1801 (LETG/HRC-I, PKS2155-304)
unix% download_chandra_obsid 1801 evt2,pha2,asol,bpix,dtf
If you created a new bad pixel file by running the New Observation-Specific HRC Bad Pixel File thread, make sure that you have set up ardlib to use the same bad pixel file.
An ARF needs to be calculated for each order in the observation. We can use Prism to examine the pha2 file and determine how many orders there are:
unix% prism hrcf01801N006_pha2.fits &
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). Figure 1 shows the two rows for the LETG observation. HRC-I cannot resolve orders; +/- 1 refer to the total positive- and negative-side counts respectively.
Figure 1: HRC-I/LETG dataset in prism
Compute the Aspect Histogram (asphist)
The aspect solution files are used to create a binned histogram detailing the aspect history of the observation:
unix% punlearn asphist unix% pset asphist infile=@pcad_asol1.lis unix% pset asphist outfile=asphist.fits unix% pset asphist evtfile=hrcf01801N006_evt2.fits unix% pset asphist dtffile=hrcf01801_000N006_dtf1.fits unix% asphist Aspect Solution List Files (@pcad_asol1.lis): Aspect Histogram Output File (asphist.fits): Event List Files (hrcf01801N006_evt2.fits[chip_id=0]): Live Time Correction List Files for HRC (hrcf01801_000N006_dtf1.fits): # asphist (CIAO): WARNING: skipping 8 livetime correction records (from time: 82336842.920992 to time: 82337011.020998)
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 infile parameter, either as a list or a stack. Here we use:
unix% cat pcad_asol1.lis pcadf082337011N004_asol1.fits
The content of the parameter file may be checked using plist asphist.
Get Source Position (dmlist)
The source position is required as one of the inputs to mkgarf. This information can be easily obtained from the PHA2 file with dmlist:
unix% dmlist "hrcf01801N006_pha2.fits[SPECTRUM][cols x,y]" opt=data rows=1 -------------------------------------------------------------------------------- Data for Table Block SPECTRUM -------------------------------------------------------------------------------- ROW X Y 1 1 16500.097656250 16367.0107421875
The source in this example is located at (16500.17968750, 16366.7568359375).
Now we have all the information needed to run mkgarf. We will have to run the tool twice, once for each row in the PHA file:
A. For row 1, LEG, order = -1
unix% punlearn mkgarf unix% pset mkgarf outfile=1801_-1_LEG_garf.fits unix% pset mkgarf order=-1 unix% pset mkgarf asphistfile="asphist.fits[ASPHIST]" unix% pset mkgarf obsfile="hrcf01801N006_evt2.fits[EVENTS]" unix% pset mkgarf engrid="grid(rmf.fits[cols ENERG_LO,ENERG_HI])" unix% pset mkgarf detsubsys=HRC-I grating_arm=LEG unix% pset mkgarf sourcepixelx=16500.17968750 sourcepixely=16366.7568359375 unix% mkgarf Aspect Histogram File (include extension) (asphist.fits[ASPHIST]): Output File Name (1801_-1_LEG_garf.fits): Enter Grating order (-1): Source X Pixel (16500.17968750): Source Y Pixel (16366.7568359375): Energy grid spec (grid(rmf.fits[cols ENERG_LO,ENERG_HI])): Name of fits file with obs info (include extension) (hrcf01801N006_evt2.fits[EVENTS]): NONE or Name of fits file with order sorting info (NONE): Detector Name (HRC-I): Enter Grating Arm (HEG|MEG|LEG) (LEG): NONE, or name of ACIS window mask file (NONE):
B. For row 2, LEG, order = 1
unix% pset mkgarf order=1 unix% pset mkgarf outfile=1801_1_LEG_garf.fits unix% mkgarf Aspect Histogram File (include extension) (asphist.fits[ASPHIST]): Output File Name (1801_1_LEG_garf.fits): Enter Grating order (1): Source X Pixel (16500.17968750): Source Y Pixel (16366.7568359375): Energy grid spec (grid(rmf.fits[cols ENERG_LO,ENERG_HI])): Name of fits file with obs info (include extension) (hrcf01801N006_evt2.fits[EVENTS]): NONE or Name of fits file with order sorting info (NONE): Detector Name (HRC-I): Enter Grating Arm (HEG|MEG|LEG) (LEG): NONE, or name of ACIS window mask file (NONE):
The content of the parameter file may be checked using plist mkgarf.
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.
The grating ARFs for this dataset are 1801_-1_LEG_garf.fits and 1801_1_LEG_garf.fits. Since this source is at the aimpoint/on-axis, the two garfs are nearly identical; Figure 2 shows the +1 order plotted on top of the -1 order. This is normal and is due to the fact that the detector is symmetric, flat, and has no holes or filter boundaries. Also, the HRC-I QEU file is fairly uniform. Off-axis observations will not have such a high degree of similarity between the -1 and +1 orders.
Figure 2: +1 order plotted over the -1 order
Parameters for /home/username/cxcds_param/asphist.par #-------------------------------------------------------------------------- # # Parameter file for the ASPECT HISTOGRAM Tool # #-------------------------------------------------------------------------- infile = @pcad_asol1.lis Aspect Solution List Files outfile = asphist.fits Aspect Histogram Output File evtfile = hrcf01801N006_evt2.fits Event List Files dtffile = hrcf01801_000N006_dtf1.fits Live Time Correction List Files for HRC (geompar = geom) Parameter file for Pixlib Geometry files (res_xy = 0.5) Aspect Resolution x and y in arcsec (res_roll = 600.) Aspect Resolution roll in arcsec (max_bin = 10000.) Maximal number of bins (clobber = no) Clobber output (verbose = 0) Verbose (mode = ql)
Parameters for /home/username/cxcds_param/mkgarf.par asphistfile = asphist.fits[ASPHIST] Aspect Histogram File (include extension) outfile = 1801_1_LEG_garf.fits Output File Name order = 1 Enter Grating order sourcepixelx = 16511.48046875 Source X Pixel sourcepixely = 16367.2802734375 Source Y Pixel engrid = grid(rmf.fits[cols ENERG_LO,ENERG_HI]) Energy grid spec obsfile = hrcf01801N006_evt2.fits[EVENTS] Name of fits file with obs info (include extension) #engrid,f,a,"0.3:10:0.1",,,"Energy grid spec" #engrid,f,a,"grid(rmf.fits[cols ENERG_LO,ENERG_HI])",,,"Energy grid spec" osipfile = NONE NONE or Name of fits file with order sorting info maskfile = NONE NONE, or name of ACIS window mask file detsubsys = HRC-I Detector Name grating_arm = LEG Enter Grating Arm pbkfile = NONE, or the name of the parameter block file (mirror = hrma) Mirror Name (dafile = CALDB) NONE, CALDB, or name of ACIS dead-area calibration file (geompar = geom) Parameter file for Pixlib Geometry files (verbose = 0) Verbosity (clobber = no) Overwrite existing files? (mode = ql) Enter mode for parameter file.
|22 Dec 2004||updated for CIAO 3.2: minor changes to parameter files; canned gARFs are no longer available in the CALDB, removed "Choosing an RMF" section|
|20 Jun 2005||CIAO 3.2.2 patch: change to asphist parameter file|
|06 Dec 2005||updated for CIAO 3.3: new asphist tool syntax (the GTI filter is associated with the event file instead of the aspect solution file)|
|01 Dec 2006||updated for CIAO 3.4: CIAO version in warning; ChIPS version; parameter file updates for mkgarf|
|23 Jan 2008||updated for CIAO 4.0: parameter file update for mkgarf (obsfile parameter is set to event file instead of aspect histogram file); updated ChIPS syntax; removed outdated calibration updates; filenames and screen output updated for reprocessed data (version N006 files)|
|12 Feb 2009||updated for CIAO 4.1: images are inline|
|19 Feb 2009||added Fitting section|
|16 Jun 2009||added About the Chandra Grating Data Archive and Catalog section|
|14 Jan 2009||reviewed for CIAO 4.2: no changes|
|12 Jan 2011||reviewed for CIAO 4.3: no changes|
|10 Jan 2012||reviewed for CIAO 4.4: no changes|
|03 Dec 2012||Review for CIAO 4.5; file version name updates|
|24 Apr 2013||Add pointer to new mktgresp tool.|
|10 Dec 2013||Review for CIAO 4.6. No changes.|
|22 Dec 2014||Review for CIAO 4.7; clarified that HRC-I/LETG is an unusual configuration.|
|02 Apr 2019||Updated to use matplotlib for plotting.|