This page describes the configuration management scheme used within the fermiPy package and the documents the configuration parameters that can be set in the configuration file.

Class Configuration

Classes in the fermiPy package follow a common convention for configuring the runtime behavior of a class instance. Internally every class instance has a dictionary that defines its configuration state. Elements of the configuration dictionary can be scalars (str, int ,float) or dictionaries defining nested blocks of the configuration.

The class configuration dictionary is initialized at the time of object creation by passing a dictionary or a path to YAML configuration file to the class constructor. Keyword arguments can be optionally passed to the constructor to override configuration parameters in the input dictionary. For instance in the following example the config dictionary defines values for the parameters emin and emax. By passing a dictionary for the selection keyword argument, the value of emax in the keyword argument (10000) overrides the value of this parameter in the input dictionary.

config = {
'selection' : { 'emin' : 100,
                'emax' : 1000 }

gta = GTAnalysis(config,selection={'emax' : 10000})

The first argument can also be the path to a YAML configuration file rather than a dictionary:

gta = GTAnalysis('config.yaml',selection={'emax' : 10000})

Configuration File

fermiPy uses YAML files to read and write its configuration in a persistent format. The configuration file has a hierarchical structure that organizes parameters into groups that are keyed to a section name (data, binnig, etc.).

Sample Configuration
   evfile : ft1.fits
   scfile : ft2.fits

  roiwidth   : 10.0
  binsz      : 0.1
  binsperdec : 8

The configuration file mirrors the layout of the configuration dictionary. The parameters that can be set in each section are described below.


Options in the binning section control the spatial and spectral binning of the data.

Sample binning Configuration

  # Binning
  roiwidth   : 10.0
  npix       : null
  binsz      : 0.1 # spatial bin size in deg
  binsperdec : 8   # nb energy bins per decade
  projtype   : WCS
binning Options
Option Default Description
binsperdec 8 Number of energy bins per decade.
binsz 0.1 Spatial bin size in degrees.
coordsys CEL Coordinate system of the spatial projection (CEL or GAL).
enumbins None Number of energy bins. If none this will be inferred from energy range and binsperdec parameter.
hpx_ebin True Include energy binning
hpx_order 10 Order of the map (int between 0 and 12, included)
hpx_ordering_scheme RING HEALPix Ordering Scheme
npix None Number of pixels. If none then this will be set from roiwidth and binsz.
proj AIT Spatial projection for WCS mode.
projtype WCS Projection mode (WCS or HPX).
roiwidth 10.0 Width of the ROI in degrees. The number of pixels in each spatial dimension will be set from roiwidth / binsz (rounded up).


The components section can be used to define analysis configurations for a sequence of independent subselections of the data. Each subselection will have its own binned likelihood instance that will be combined in a global likelihood likelihood function for the whole ROI (implemented with the SummedLikelihood class in pyLikelihood). This section is optional and when this section is empty (the default) fermiPy will construct a single likelihood with the parameters of the root analysis configuration.

The component section can be defined as either a list or dictionary of dictionary elements where each element sets analysis parameters for a different subcomponent of the analysis. Dictionary elements have the same hierarchy of parameters as the root analysis configuration. Parameters not defined in a given element will default to the values set in the root analysis configuration.

The following example illustrates how to define a Front/Back analysis with the a list of dictionaries. In this case files associated to each component will be named according to their order in the list (e.g. file_00.fits, file_01.fits, etc.).

# Component section for Front/Back analysis with list style
  - { selection : { evtype : 1 } } # Front
  - { selection : { evtype : 2 } } # Back

This example illustrates how to define the components as a dictionary of dictionaries. In this case the files of a component will be appended with its corresponding key (e.g. file_front.fits, file_back.fits).

# Component section for Front/Back analysis with dictionary style
  front : { selection : { evtype : 1 } } # Front
  back  : { selection : { evtype : 2 } } # Back


The data section defines the input data files for the analysis (FT1, FT2, and livetime cube). evfile and scfile can either be individual files or group of files. The optional ltcube option can be used to choose a pre-generated livetime cube. If ltcube is null a livetime cube will be generated at runtime with gtltcube.

Sample data Configuration
data :
  evfile : ft1.lst
  scfile : ft2.fits
  ltcube : null
data Options
Option Default Description
evfile None Path to FT1 file or list of FT1 files.
ltcube None Path to livetime cube. If none a livetime cube will be generated with gtmktime.
scfile None Path to FT2 (spacecraft) file.


The options in extension control the default behavior of the extension method. For more information about running this method see the Extension Fitting page.

extension Options
Option Default Description
fix_background False Fix any background parameters that are currently free in the model when performing the likelihood scan over extension.
save_model_map False  
save_templates False  
spatial_model GaussianSource Spatial model use for extension test.
update False Update the source model with the best-fit spatial extension.
width None Parameter vector for scan over spatial extent. If none then the parameter vector will be set from width_min, width_max, and width_nstep.
width_max 1.0 Maximum value in degrees for the likelihood scan over spatial extent.
width_min 0.01 Minimum value in degrees for the likelihood scan over spatial extent.
width_nstep 21 Number of steps for the spatial likelihood scan.


The fileio section collects options related to file bookkeeping. The outdir option sets the root directory of the analysis instance where all output files will be written. If outdir is null then the output directory will be automatically set to the directory in which the configuration file is located. Enabling the usescratch option will stage all output data files to a temporary scratch directory created under scratchdir.

Sample fileio Configuration
   outdir : null
   logfile : null
   usescratch : False
   scratchdir  : '/scratch'
fileio Options
Option Default Description
logfile None Path to log file. If None then log will be written to fermipy.log.
outdir None Path of the output directory. If none this will default to the directory containing the configuration file.
savefits True Save intermediate FITS files.
scratchdir /scratch Path to the scratch directory.
usescratch False Run analysis in a temporary directory under scratchdir.
workdir None Override the working directory.


Options in the gtlike section control the setup of the likelihood analysis include the IRF name (irfs).

gtlike Options
Option Default Description
bexpmap None  
convolve True  
edisp True Enable the correction for energy dispersion.
edisp_disable None Provide a list of sources for which the edisp correction should be disabled.
irfs None Set the IRF string.
minbinsz 0.05 Set the minimum bin size used for resampling diffuse maps.
resample True  
rfactor 2  
srcmap None  


The model section collects options that control the inclusion of point-source and diffuse components in the model. galdiff and isodiff set the templates for the Galactic IEM and isotropic diffuse respectively. catalogs defines a list of catalogs that will be merged to form a master analysis catalog from which sources will be drawn. Valid entries in this list can be FITS files or XML model files. sources can be used to insert additional point-source or extended components beyond those defined in the master catalog. src_radius and src_roiwidth set the maximum distance from the ROI center at which sources in the master catalog will be included in the ROI model.

Sample model Configuration
model :

  # Diffuse components
  galdiff  : '$FERMI_DIR/refdata/fermi/galdiffuse/gll_iem_v06.fits'
  isodiff  : '$FERMI_DIR/refdata/fermi/galdiffuse/iso_P8R2_SOURCE_V6_v06.txt'

  # List of catalogs to be used in the model.
  catalogs :
    - '3FGL'
    - 'extra_sources.xml'

  sources :
    - { 'name' : 'SourceA', 'ra' : 60.0, 'dec' : 30.0, 'SpectrumType' : PowerLaw }
    - { 'name' : 'SourceB', 'ra' : 58.0, 'dec' : 35.0, 'SpectrumType' : PowerLaw }

  # Include catalog sources within this distance from the ROI center
  src_radius  : null

  # Include catalog sources within a box of width roisrc.
  src_roiwidth : 15.0
model Options
Option Default Description
assoc_xmatch_columns [‘3FGL_Name’] Choose a set of association columns on which to cross-match catalogs.
catalogs None  
diffuse None  
extdir Extended_archive_v15  
extract_diffuse False Extract a copy of all mapcube components centered on the ROI.
galdiff None Set the galactic IEM mapcube.
isodiff None Set the isotropic template.
limbdiff None  
merge_sources True Merge properties of sources that appear in multiple source catalogs. If merge_sources=false then subsequent sources with the same name will be ignored.
sources None  
src_radius None Set the maximum distance for inclusion of sources in the ROI model. Selects all sources within a circle of this radius centered on the ROI. If none then no selection is applied. This selection will be ORed with sources passing the cut on src_roiwidth.
src_radius_roi None Half-width of the ROI selection. This parameter can be used in lieu of src_roiwidth.
src_roiwidth None Select sources within a box of RxR centered on the ROI. If none then no cut is applied.


optimizer Options
Option Default Description
min_fit_quality 3 Set the minimum fit quality.
optimizer MINUIT Set the optimization algorithm to use when maximizing the likelihood function.
retries 3 Set the number of times to retry the fit when the fit quality is less than min_fit_quality.
tol 0.0001 Set the optimizer tolerance.
verbosity 0  


plotting Options
Option Default Description
catalogs None  
cmap ds9_b Set the colormap for 2D plots.
erange None  
format png  
graticule_radii None Define a list of radii at which circular graticules will be drawn.
label_ts_threshold 0.0 TS threshold for labeling sources in sky maps. If None then no sources will be labeled.


The options in the sed section controls the default behavior of the sed method. For more information about running this method see the SED Analysis page.

sed Options
Option Default Description
bin_index 2.0 Spectral index that will be use when fitting the energy distribution within an energy bin.
cov_scale 3.0  
fix_background True Fix background parameters when fitting the source flux in each energy bin.
ul_confidence 0.95 Confidence level for upper limit calculation.
use_local_index False Use a power-law approximation to the shape of the global spectrum in each bin. If this is false then a constant index set to bin_index will be used.


The selection section collects parameters related to the data selection and target definition. The majority of the parameters in this section are arguments to gtselect and gtmktime. The ROI center can be set with the target parameter by providing the name of a source defined in one of the input catalogs (defined in the model section). Alternatively the ROI center can be defined by giving explicit sky coordinates with ra and dec or glon and glat.


  # gtselect parameters
  emin    : 100
  emax    : 100000
  zmax    : 90
  evclass : 128
  evtype  : 3
  tmin    : 239557414
  tmax    : 428903014

  # gtmktime parameters
  filter : 'DATA_QUAL>0 && LAT_CONFIG==1'
  roicut : 'no'

  # Set the ROI center to the coordinates of this source
  target : 'mkn421'
selection Options
Option Default Description
convtype None Conversion type selection.
dec None  
emax None Maximum Energy (MeV)
emin None Minimum Energy (MeV)
evclass None Event class selection.
evtype None Event type selection.
filter None Filter string for gtmktime selection.
glat None  
glon None  
logemax None Maximum Energy (log10(MeV))
logemin None Minimum Energy (log10(MeV))
ra None  
radius None Radius of data selection. If none this will be automatically set from the ROI size.
roicut no  
target None Choose an object on which to center the ROI. This option takes precendence over ra/dec or glon/glat.
tmax None Maximum time (MET).
tmin None Minimum time (MET).
zmax None Maximum zenith angle.


sourcefind Options
Option Default Description
max_iter 3 Set the number of search iterations.
min_separation 1.0 Set the minimum separation in deg for sources added in each iteration.
model None Set the source model dictionary. By default the test source will be a PointSource with an Index 2 power-law specturm.
sources_per_iter 3  
sqrt_ts_threshold 5.0 Set the threshold on sqrt(TS).
tsmap_fitter tsmap Set the method for generating the TS map.


tsmap Options
Option Default Description
erange None Lower and upper energy bounds in log10(E/MeV). By default the calculation will be performed over the full analysis energy range.
max_kernel_radius 3.0  
model None Dictionary defining the properties of the test source.
multithread False  


tscube Options
Option Default Description
cov_scale -1.0 Scale factor to apply to broadband fitting cov. matrix in bin-by-bin fits ( < 0 -> fixed )
cov_scale_bb -1.0 Scale factor to apply to global fitting cov. matrix in broadband fits. ( < 0 -> no prior )
do_sed True Compute the energy bin-by-bin fits
max_iter 30 Maximum number of iterations for the Newtons method fitter.
model None Dictionary defining the properties of the test source. By default the test source will be a PointSource with an Index 2 power-law specturm.
nnorm 10 Number of points in the likelihood v. normalization scan
norm_sigma 5.0 Number of sigma to use for the scan range
remake_test_source False If true, recomputes the test source image (otherwise just shifts it)
st_scan_level 0 Level to which to do ST-based fitting (for testing)
tol 0.001 Critetia for fit convergence (estimated vertical distance to min < tol )
tol_type 0 Absoulte (0) or relative (1) criteria for convergence.