Add Grating Spectra and Average ARFs

[CIAO 3.4 Science Threads]

Overview

Last Update: 4 Feb 2008 - add_grating_orders updated to v3.4 (several broken Unix "tail" commands were replaced with the tool dmkeypar)

Synopsis:

add_grating_spectra is a script which lets the user add two grating spectra and average their associated ARFs. The output spectrum can be grouped if desired. It can be used, for example, to add up spectra of sources from different observations.

Purpose:

To generate and group two coadded grating spectra and ARFs.

Read this thread if:

you are working with ACIS/HETG, ACIS/LETG, or HRC/LETG observational data and would like to add the grating orders.

Related Links:

Analysis Guide for Chandra High Resolution Spectroscopy: an in-depth discussion of grating analysis.

Proceed to the HTML or hardcopy (PDF: A4 | letter) version of the thread.

Get Started
Downloading add_grating_spectra
Run add_grating_spectra
Summary
Parameter files:
- add_grating_spectra
History

Get Started

Sample ObsIDs used: 459 (HETG/ACIS-S, 3C 273); 2463 (HETG/ACIS-S, 3C 273)

File types needed: evt1; flt1; asol1

To run this thread, you need two PHA grating spectra and the corresponding ARFs:

unix% ls
2463_MEG_1.arf          459_MEG_1.arf
2463_MEG_1_NONE.pha     459_MEG_1_NONE.pha

Both observations must have been taken with the same instrumental configuration:

ACIS-HETG-HEG
ACIS-HETG-MEG
ACIS-LETG-LEG
HRC-LETG-LEG

The files used here were created with the Extract Coadded and Grouped Nth-Order Source & Background Spectra and ARFs thread.

Downloading add_grating_spectra

The most recent version of add_grating_spectra is 3.2.0 (09 December 2004):

unix% grep version_ `which add_grating_spectra`
version_str="3.4"
version_date="04 February 2008"

Please check that you are using the most recent version before continuing. If you do not have the script installed or need to update to a newer version, please refer to the Scripts page.

Run add_grating_spectra

The script executes the following tools in order:

dmtcalc: to rename columns and perform math on them in temporary PHA and ARF files.
dmpaste: to merge the final columns into the output PHA and ARF files.
dmgroup: to group the final PHA file.
dmhedit: to update header keywords of the output files.

In this example, we are summing together the first-order MEG arms of HETG spectra and the corresponding gARFs:

unix% punlearn add_grating_spectra
unix% pset add_grating_spectra pha1=2463_MEG_1_NONE.pha
unix% pset add_grating_spectra pha2=459_MEG_1_NONE.pha
unix% pset add_grating_spectra garf1=2463_MEG_1.arf
unix% pset add_grating_spectra garf2=459_MEG_1.arf
unix% pset add_grating_spectra gtype=BIN
unix% pset add_grating_spectra gspec=10
unix% pset add_grating_spectra root=3C273_summed
unix% add_grating_spectra
First input PHA spectrum (2463_MEG_1_NONE.pha): 
Second input PHA spectrum (459_MEG_1_NONE.pha): 
First input ARF (2463_MEG_1.arf): 
Second input ARF (459_MEG_1.arf): 
Root name for output files (3C273_summed): 

Input pha1 file is: 2463_MEG_1_NONE.pha (INSTRUMENT=ACIS-MEG, ORDER=1)
Input pha2 file is: 459_MEG_1_NONE.pha (INSTRUMENT=ACIS-MEG, ORDER=1)
Using ACIS-MEG grating ARF order 1: 2463_MEG_1.arf
Using ACIS-MEG grating ARF order 1: 459_MEG_1.arf
The root filename for the output files is: 3C273_summed


Exposure(2463_MEG_1_NONE.pha) = 26686.9077228220
Exposure(459_MEG_1_NONE.pha) = 38564.6089268890
New Exposure = 65251.5166497110


BACKSCUP(2463_MEG_1_NONE.pha) = 4.50
BACKSCDN(2463_MEG_1_NONE.pha) = 4.50
BACKSCUP(459_MEG_1_NONE.pha) = 4.50
BACKSCDN(459_MEG_1_NONE.pha) = 4.50
New BACKSCUP = 4.50
New BACKSCDN = 4.50


ACIS-MEG 3C273_summed_ACIS-MEG_1.pha will be grouped by 10 = .0500000000 Angstrom

The output spectrum is named     3C273_summed_ACIS-MEG_1_BIN10.pha
The Averaged Effective Area is named 3C273_summed_ACIS-MEG_1.arf

The content of the parameter file may be checked using plist add_grating_spectra.

Summary

The thread is now complete. The output containing the summed counts from both input PHA files is 3C273_summed_ACIS-MEG_1_BIN10.pha; the averaged effective area is named 3C273_summed_ACIS-MEG_1.arf.

To fit this data in Sherpa:

sherpa> data 3C273_summed_ACIS-MEG_1_BIN10.pha
sherpa> rsp[arfname](,3C273_summed_ACIS-MEG_1.arf,)
sherpa> instrument = arfname

See the Fitting PHA Data with Multi-Component Source Models thread for more information.


Parameters for /home/username/cxcds_param/add_grating_spectra.par


          pha1 = 2463_MEG_1_NONE.pha First input PHA spectrum
          pha2 = 459_MEG_1_NONE.pha Second input PHA spectrum
         garf1 = 2463_MEG_1.arf   First input ARF
         garf2 = 459_MEG_1.arf    Second input ARF
          root = 3C273_summed     Root name for output files
        (gtype = BIN)             Spectrum grouping type
        (gspec = 10)              Spectrum grouping specs (NONE,10,etc)
      (clobber = no)              Clobber existing output files?
      (verbose = 0)               Debug Level(0-5)
         (mode = ql)

History

14 Dec 2004	updated for CIAO 3.2: created Downloading add_grating_spectra section
06 Dec 2005	reviewed for CIAO 3.3: no changes
01 Dec 2006	reviewed for CIAO 3.4: no changes
04 Feb 2008	add_grating_orders updated to v3.4 (several broken Unix "tail" commands were replaced with the tool `dmkeypar`)