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Quick Start

In the following, a quick tutorial for SIXTE is displayed to get you started. We still recommend to take a look into the tutorial section in the SIXTE manual (link to the most recent version at the bottom of this page) for a way more detailed tutorial with a lot of explanations.

Environment Variable and testing

To be able to use the tools, you have to set the environment variables $SIMPUT and $SIXTE to the respective installation directories and source the sixte-install.csh/sh script, like shown in the installation tab.

To follow along with this tutorial, you will need to have XSPEC installed.

Next, we are going to test if SIMPUT and SIXTE are running in general. Please enter to your terminal the following commands:

plist simputfile
plist sixte

Both give you a list with possible parameters to set for simputfile and sixte respectively.

For simputfile this should look like the following:

Parameters for /Your/directory/pfiles/simputfile.par
       Simput = some_fits_file.fits output SIMPUT catalog file
      (Src_ID = 1)               source ID
    (Src_Name = none)            source name
          (RA = 0.0)             right ascension (deg)
         (Dec = 0.0)             declination (deg)
     (srcFlux = 0.0)             source flux (erg/s/cm^2)
        (Elow = 0.1)             lower bound of the generated spectrum (keV)
         (Eup = 100.0)           upper bound of the generated spectrum (keV)
       (Estep = 0.0)             deprecated (resolution of the spectrum (keV) )
       (Nbins = 1000)            number of energy bins created from Elow to Eup
    (logEgrid = no)              use a logarithmic energy grid (from Elow to Eup with Nbins)
  (plPhoIndex = 2.0)             power law index
      (plFlux = 0.0)             power law flux (erg/s/cm^2)
        (bbkT = 1.0)             black body temperature (keV)
      (bbFlux = 0.0)             black body flux (erg/s/cm^2)
     (flSigma = 1.0e-3)          Fe line sigma (keV)
              .                            .
              .                            .
              .                            .

SIMPUT Source creation

Before starting an observation simulation, the sources need to be described in the SIMPUT format. The SIXTE software package contains tools to obtain such a file from several input files such as an XSPEC- or ISIS-parameter file for a spectrum, as well as for example an ASCII description of a lightcurve.

For a simple non-variable source with an absorbed power law spectrum, we are going to create a simple .xcm file with XSPEC:

computer:~/> xspec

		XSPEC version: 12.12.0
	Build Date/Time: Mon Dec 20 11:07:27 2021

XSPEC12>model phabs*pegpwrlw

Input parameter value, delta, min, bot, top, and max values for ...
              1      0.001(      0.01)          0          0     100000      1e+06
              1       0.01(      0.01)         -3         -2          9         10
              2      -0.01(      0.02)       -100       -100      1e+10      1e+10
             10      -0.01(       0.1)       -100       -100      1e+10      1e+10
              1       0.01(      0.01)          0          0      1e+20      1e+24

Model phabs<1>*pegpwrlw<2> Source No.: 1   Active/Off
Model Model Component  Parameter  Unit     Value
 par  comp
   1    1   phabs      nH         10^22    0.200000     +/-  0.0          
   2    2   pegpwrlw   PhoIndex            2.05000      +/-  0.0          
   3    2   pegpwrlw   eMin       keV      2.00000      frozen
   4    2   pegpwrlw   eMax       keV      10.0000      frozen
   5    2   pegpwrlw   norm                21.6000      +/-  0.0          

XSPEC12>flux 2 10
 Model Flux 0.0032845 photons (2.1157e-11 ergs/cm^2/s) range (2.0000 - 10.000 keV)
XSPEC12>save model mcrab.xcm

With this, we can now build our SIMPUT file, by writing a short shell script:


$SIXTE/bin/simputfile Simput=${base}.fits \
     Src_Name=first \
     RA=0.0 \
     Dec=0.0 \
     srcFlux=2.137e-11 \
     Elow=0.1 \
     Eup=15 \
     NBins=1000 \
     logEgrid=yes \
     Emin=2 \
     Emax=10 \

Make this shell script executable (run: chmod a+x ./mcrab.bash) and execute it.

Running the simulation

We are using the tool runsixt to run our sample simulation. Therefore, we write another shell script:




$SIXTE/bin/runsixt \
     XMLFile=${xml} \
     RA=0.000 Dec=0.000 \
     Prefix=sim_ \
     Simput=${base}.fits \
     EvtFile=evt_${base}.fits \

Again, make this shell script executable and execute it.

Analysing the simulation

Create an image

To take a look at our source, we can use the tool imgev:

$SIXTE/bin/imgev \
     EvtFile=sim_evt_mcrab.fits \
     Image=img_mcrab.fits \
     CoordinateSystem=0 Projection=TAN \
     NAXIS1=512 NAXIS2=512 CUNIT1=deg CUNIT2=deg \
     CRVAL1=0.0 CRVAL2=0.0 CRPIX1=256.5 CRPIX2=256.5 \
     CDELT1=-6.207043e-04 CDELT2=6.207043e-04 \
     history=true clobber=yes

Even if a point source is not that interesting to look at, this can be used in the same way for much more complex sources.

Spectral shape

More interesting for a single point source is the spectral shape, so using the tool makespec we can produce an X-ray spectrum:

$SIXTE/bin/makespec \
     EvtFile=sim_evt_mcrab.fits \
     Spectrum=spec_mcrab.pha \
     EventFilter="(RA>359.95 || RA<0.05) && Dec>-0.05 && Dec<+0.05" \
     RSPPath=${xmldir} clobber=yes

SIXTE Simulator Manual

The current version of the SIXTE simulator manual is available for download below. It includes a general description of SIXTE and the implementation of various X-Ray detectors such as the WFI, X-IFU, eROSITA and more. In addition, tutorials for Athena WFI and X-IFU simulations are included.

download: simulator_manual.pdf (v1.3.17, 2023-02-16)

supplementary files for the X-IFU tutorial (30MB!): X-IFU_clusters_tutorial.tgz

4 year eROSITA Attitude file for a launch in April 2019 (200MB!): eRASS_4yr_epc85_att.fits.bz2