Data Analysis #1


Note that problems on home work #2 include printing out a ds9 image including your source and background regions, a plot of your fitted spectrum, and the results of your fitting.

Each group has an account (xrayn n=1, 2, ...) on alcina.physics.uiowa.edu which is set up to use the tsch shell.

Log into alcina using X-windows
From a linux machine do: ssh -Y xrayn@alcina.physics.uiowa.edu
From a Windows machine, start X-Win32, then configure alcina as an ssh connection, finally connect

Setup to run ciao, the Chandra data analysis package
- add the following line to your .cshrc file (nedit .cshrc &)
alias ciao "source /soft/ciao/ciao-4.2/bin/ciao.csh"
- then either "source .csrhc" or logout and log back in
- type "ciao" and you should get a message that CAIO 4.2 is configured

FYI: ciao resides in /soft/ciao.  Your data analysis will also use the calibration data base, CALDB, which resides in  /soft/caldb.

Get the data set
- make a directory under your home directory called 3c273 (cd ~; mkdir 3c273)
- open a web browser on alcina (firefox &)
- set up firefox so that it asks where to download files: Edit/Preferences then select "Always ask me where to save files" under the "Downloads" section on the "Main" tab.
- go to http://asc.harvard.edu/
- you may want to make this your home page
- click on "Archive and Data Processing" and then on "Web ChaSeR"
- type "3c273" as the target name and search for observations
- put a check mark by ObsID 459 and make sure both primary and secondary products are checked, then click "Add to Retrieval List"
- click "Retrieve Products"
- wait a bit
- click on the ftp link where your data will be available
- save the data file "package..." to the directory you just made for 3c273 data: xrayn/3c273
- once the data is downloaded, on the command line, move to xrayn/3c273 (cd ~/3c273)
- untar the data using "tar xvf package..."
- this makes a subdirectory 459 with files and directories below that
- unzip the data (gunzip */*/*.gz; gunzip */*/*/*.gz)

Extract ACIS Spectra and create Response Files
- Follow the thread "Using psextract to Extract ACIS Spectra and Response Files for Pointlike Sources" which can be found at
http://asc.harvard.edu/ciao/threads/psextract/
- Start by setting the observation-specific bad pixel files:
  - move to ~/3c273/459/primary and then do the following commands:
punlearn ardlib
acis_set_ardlib acisf00459_000N003_bpix1.fits absolutepath=yes

- For now, don't worry about reprocessing your data.
- Note that psextract is a script which runs several different ciao tools. Read over the documentation on each tool (click on the tool name under the "Run psextract" entry) so that you understand its function.  Also, run psextract with verbose=2 in order to see the steps as they are executed.
- For now, don't worry about creating an RMF with mkacisrmf, just use the one made by the script using mkrmf
- Be sure to print out your ds9 image showing your source and region files.

Fit the spectrum
- Fit the spectrum, following the "Introduction to Fitting PHA Spectra" thread at http://asc.harvard.edu/sherpa/threads/pha_intro/
- Do the Python version of the tread, since S-lang support will be removed from ciao in future versions.
- Using the absorbed power-law model is fine.
- Be sure to print out a plot of your spectrum along with your best fit.  Also, record the best fit parameters and the quality of the fit.