A Details for Applying the Software ToolsSIXTEandSRCTOOL psfdesc erosita.psf.fits
xgrid 1.0 tstep 1.0
srcreg file defining the source region backreg file defining the background region badpix BADPIX.txt
A more detailed explanation of the different parameters is presented in theeROSITA-wiki18.
Following the set of the above stated steps, we finally generate one spectral file for each source region and one for each additional background-only region as they are observed for the total of seveneROSITA telescopes. To continue with the spectral analysis inxspec, the value of the exposure time and the name of the instrumental response file need to be added manually to the header of the spectral file. In our case, no tool was available yet to compute the exact exposure time of the simulated sky region, and we define the position of the region such, that it is observed with the effective exposure time oftexp =1.6 ks based on the exposure maps by J. Robrade (comp. Fig. 2.12). For the instrumental response, we apply the survey resolution, averaged over all seven telescopes, "erosita_iv_7telfov_ff.rsp". The final analysis steps to re-obtain the source characteristics are analogous to the approach described in Sects. 4.2.3 &
4.2.4.
18https://wiki.mpe.mpg.de/eRosita/TaskDescriptions?action=AttachFile&do=view&target=srctool_doc.html
APPENDIX B
Brief Manual for Running COSMOMC
The following sections briefly summarise, how theCOSMOMCsoftware package is structured in gen-eral as well as how additional likelihood modules and data are added. The described features are valid and have been tested for the software versions of 02/2015 and 06/2015, and applying theIntel Fortran Compiler, ifort15. We would like to note to the reader, that only those applications required for our simulations are discussed. More general information on the software and its installation are expressed in theCOSMOMCreadme19by A. Lewis.
B.1 General Outline of COSMOMC
COSMOMCcontains the likelihoods as well as the data samples for a variety of different cosmological probes, including e.g. supernovae type Ia, BAO, and also the CMB. These different information are organised in the folders “./source/” together with the modules, which perform theMCMC simulation, and “./data/”, respectively. Running theMCMCsimulations is managed by “.ini”-files, which contain all the required information on the characteristics of the simulations, such as e.g. the number of vari-able parameters, the convergence criterium, which sampling method to use and which likelihoods to compute. Per default, there exists one main, driver “.ini”-file, called “params.ini”, in theCOSMOMC home directory and many sub-files, which are launched by this driver and are located generally in the
“/batch1/”-directory. The main file e.g. includes the information on the names and the output directory of the created files and defines the action to be executed. For performing aMCMCsimulation based on the Metropolis-Hastings algorithm, one needs to set
root_dir=
file_root=
action=0
sampling_method=1
while the first two parameters define the output directory as well as the name of the resulting chains, respectively. This driver also calls additional “.ini”-files, such as e.g. “./batch1/likelihood_batch1.ini”, which defines the likelihoods to be applied during the simulation, or
“./batch1/params_CMB_defaults.ini”. The latter file describes which parameters to vary during the fit, their priors as well as the values of the frozen parameters. By default, the variables are defined e.g. as
19TheCOSMOMCreadme is available athttp://cosmologist.info/cosmomc/readme.html
B Brief Manual for RunningCOSMOMC
param[name]= centre, min, max, starting width, proposed width
with an applied flat prior between the minimum and maximum boundary of the parameter value and an estimate for the width of its proposal density. However, the option exists to update the latter property during the simulation based on the distribution of the chain steps.
In addition to these definitions, an additional parameter file “.paramnames” needs to be available for each simulation. It lists all parameters, which are stated in the “.ini”-file, with their names and their LATEX notations, as e.g.
omegabh2 \Omega_b h∧2 #physical baryon density.
These parameter files are stored in the “./paramnames/”-directory and are referenced by the likelihood codes (Sect. B.2). For those likelihoods already contained withinCOSMOMC, these files have been defined and do not need to be edited.
Having adapted the performance of the simulations to your requests, you can launch one single chain with the command
./cosmomc params.ini
To run several chains at the same time, an additional tool is required to manage the communication between the individual chains, for example to update the proposal width or to test for convergence. This parallelisation is commonly achieved by applying the software MPI (Message Passing Interface)20, where both this software andCOSMOMCneed to be built by the same compiler. After this set-up, the MCMCsimulations can be launched as
mpirun -np #chains ./cosmomc params.ini
with #chains representing the number of chains. Each chain is then run on a separate core.