Simulate and Analyze SciSim MOS data

This thread contains a step-by-step recipe to simulate MOS SciSim data and how to procede to analyze this data using SAS.

In this example we will simulate a Raymond-Smith model with a temperature of 0.86 kT(keV), and an abundance of 0.27 in solar units. The column density and the redshift were set to 0. With these values an XSPEC spectrum can be created (following the steps that can be read in Cosmic Simulator guide, chapter 7) and afterwards will be imported into SciSim.

• Set up Scisim:

  Set SCISIM_DIR varaible to the path where SciSim is located:

  For bash shell execute:

  
  export SCISIM_DIR=/path/to/SciSim 
  
  

  For tcsh shell execute:

  
  setenv SCISIM_DIR /path/to/SciSim
  
  

  Run the set up script.

  For bash shell execute:

  
  . $SCISIM_DIR/setup.sh 
  
  

  For tcsh shell execute:

  
  source $SCISIM_DIR/setup
  
  

• Load the default configuration for the telescope you are going to use.

  SciSim has three different telescopes configurations:

  • Telescope 1 loads the default configuration for MOS1, RGS1 and OM.
  • Telescope 2 loads the default configuration for MOS2, RGS2 and OM.
  • Telescope 3 loads the default configuration for PN and OM.

    In this example, we are explaining how to proceed in order to run a MOS simulation, so we have to load the Telescope-1 default configuration, if we want to simulate MOS1 and RGS1. Or, we have to load the Telescope-2 configuration, if we want to simulate MOS2 and RGS2. We want a MOS1 simulation, so we will load the Telescope-1 default configuration.

    File -> Load Telecope 1

    

  • Introduce the Attitude coordinates:
    • RA=70.453
    • Dec=46.038

      Note that these are J2000 coordinates

      The astronomical position angle (pos) can be left to zero.

• Create a source

  Select the Source menu and the Edit... option. A blank dialogue should appear:

  To create a source, hit the New button at the bottom dialogue. The display now shows default information about the newly created source, positioned at RA,Dec=(0,0).

  The window consists of a General pane, and a pane that contains the tabs denoting the properties of the current source: Optical,Spectrum,Brightness and Shape:

  The Incident Angle and Azimuthal angle in the pane called General are with respect to the pointing of the Spacecraft. As we want the source to be in the Center of View of the Spacecraft, we have to introduce the same coordinates that in the Attitude GUI.

  We now need to address the X-ray properties for our example.

  Select the Brightness tab and enter the following values:

  • Flux=1.7935e-2
  • Energy band=250 12000

  Now select the Spectrum tab. Currently a monochrome source is selected. However, we want to specify (as we said before) an XSPEC spectrum that we have created previously, so we pull down the pop-up menu, and select xspec.

  Now enter the followiong values:

  • FileFile=raymondSmith.qdp
  • Column=0.0

  Your Source Editor window should look like:

  

  Now that we have specified a source, we just simply click on Close button in the Source Editor window.

• Select the background radiation.

  Select the Source menu and the Background... option. A blank dialogue should appear. Introduce the following background value.

  • Background=0.04

    Notice that the background simulation will increase the time needed to perform the simulation.

  • Select the simulator.

    As we said above, in this example our goal is to simulate 1000 seconds exposure of the MOS1 instrument. The first step in this thread was to load the default configuration for MOS1. Nevertheless, we will check that all the parameters are properly defined.

    Select the Configure menu and the Configure... option. Another dialogue appears, showing icons for each simulator sub-system.

    By default, the simulators are connected to eachother. This means the (from left to right) the output of one simulator is redirected to another. The end of the so-called pipe-lines show a file icon. Such a file icon denotes the name of the file, in which the results will be stored.

    

    In this dialogue, clicking on the left button while pointing the cursor at an icon will select the instrument simulator in question; clicking using the right mouse button will cause a new dialogue to appear which allows the user to configure the specific simulator.

    In this thread we are only interested in a MOS1 simulation, so we can remove the connections to the OM and RFC simulators. We can do that simply using the left-clicking the mouse button, while hitting the icons labelled OM and RFC.

    Using the right mouse button, while pointing at one of the icons, will show the next window:

    

    This dialog is specific to the icon selected, and allows us to modify the simulator or the file, whichever is pointed at. We could change the parameters to meet our needs.

    Hit OK to close the dialogue.

    Now we can change the exposure duration. Click on the S/C icon with the right button and change the value in the Duration window:

    • Duration=1000
    

    Hit OK to close the dialogue.

    Finally, hit the Close button to close the Simulator configuration dialogue.

• Run the simulation

  Press the Start button, which is situated near the bottom and should now be highlighted. The Start button should now be greyed-out and the Stop button highlighted.

• Post-Analysis

  When the simulation has finished, we are left with a file called epic.out. This binary file has a SciSim specifc format and contains the results of the exposure as seen by the MOS1 camera.

  The file can be converted to an Observation Data File, wiht the following command:

  
  modf < epic.out
  
  

  This command creates a number of FITS files, that can be viewed by the FTOOLS package. Analysis of these files are intended to be done with the XMM-Newton Science Analysis Subsystem package SAS.

• Analysing SciSim data with SAS
  • Set up SAS environment following the steps that you can read in the Start up thread
  • Set up the SAS_ODF environmental variable to you SciSim FITS directory.
  • Set up the SAS_CCF environmental variable. In the ccf directory under SCISIM directory you can find a CCF_scisim.cif file that has been produced with the CCF files needed by SciSim. You can use it to analyze SciSim data with SAS. Also, you can run cifbuild task with the option category=SCISIM in order to create the ccf.cif file used by SAS.
  • Set up the SAS_CCFPATH environmental variable to your directory where the SCISIM CCF files are located.
  • Finally, and before the execution of any SAS task, you have to run odffix task. This task creates a set of files needed by SAS, such as: housekeeping and summary file. To run this application you have to set the following option parameters: ra, dec, posangle and findnominalpointing.

    
    odffix ra=70.354 dec=46.038 posangle=0.0 findnominalpointing=no
    
    

  • Run emproc with the parameter analyzingSciSimdata set to yes.
  • Run xmmselect. Display the image and select a Source region and a background region. Then click on OGIP products and wait until the process finishes.

    At this stage you will have the spectral products ready to be analyze with XSPEC

• Analysing the spectrum wiht XSPEC

  Now that we have the spectrum, background, rmf and arf files, we can run xspec and load the files.

  
  xspec
  data stem_src.ds
  
  

  We did the SciSim Simulation using a Raymod-Smith model with the following parameters:

  • nH=0
  • kT=0.86
  • Abundace=0.27
  • redshift=0

  Then, now we can try to fit our data with an absorbed Raymod-Smith model. After introducing the values and fit the spectrum, you should have to obtain the following plot.

  

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  [Last update: 29-Dec-2004 Aitor Ibarra Ibaibarriaga]