Configuration

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

Class Configuration

Classes in the Fermipy package own a configuration state dictionary that is initialized when the class instance is created. Elements of the configuration dictionary can be scalars (str, int, float) or dictionaries containing groups of parameters. The settings in this dictionary are used to control the runtime behavior of the class.

When creating a class instance, the configuration is initialized by passing either a configuration dictionary or configuration file path to the class constructor. Keyword arguments can be passed to the constructor to override configuration parameters in the input dictionary. 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 emax 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 groups parameters into dictionaries that are keyed to a section name (data, binning, etc.).

Sample Configuration

data:
  evfile : ft1.lst
  scfile : ft2.fits
  ltcube : ltcube.fits

binning:
  roiwidth   : 10.0
  binsz      : 0.1
  binsperdec : 8

selection :
  emin : 100
  emax : 316227.76
  zmax    : 90
  evclass : 128
  evtype  : 3
  tmin    : 239557414
  tmax    : 428903014
  filter  : null
  target : 'mkn421'

gtlike:
  edisp : True
  edisp_bins : -1
  irfs : 'P8R3_SOURCE_V2'
  edisp_disable : ['isodiff']
  # For analysis using older diffuse models (gll_iem_v06.fits or older) the energy dispersion should also be turned off for the diffuse model

model:
  src_roiwidth : 15.0
  galdiff  : '$FERMI_DIFFUSE_DIR/gll_iem_v07.fits'
  isodiff  : 'iso_P8R3_SOURCE_V2_v1.txt'
  catalogs : ['4FGL']

The configuration file has the same structure as the configuration dictionary such that one can read/write configurations using the load/dump methods of the yaml module :

import yaml
# Load a configuration
config = yaml.load(open('config.yaml'))
# Update a parameter and write a new configuration
config['selection']['emin'] = 1000.
yaml.dump(config, open('new_config.yaml','w'))

Most of the configuration parameters are optional and if not set explicitly in the configuration file will be set to a default value. The parameters that can be set in each section are described below.

binning

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

Sample binning Configuration

binning:

  # 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 in the x and y direction. 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).

components

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

The component section is defined as a list of dictionaries where each element sets analysis parameters for a different subcomponent of the analysis. The component configurations follow the same structure and accept the same 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 two components. Files associated to each component will be given a suffix according to their order in the list (e.g. file_00.fits, file_01.fits, etc.).

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

data

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
cacheft1	True	Cache FT1 files when performing binned analysis. If false then only the counts cube is retained.
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.

extension

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

extension Options

Option, Default, Description
fit_ebin	False	Perform a fit for the angular extension in each analysis energy bin.
fit_position	False	Perform a simultaneous fit to the source position and extension.
fix_shape	False	Fix spectral shape parameters of the source of interest. If True then only the normalization parameter will be fit.
free_background	False	Leave background parameters free when performing the fit. If True then any parameters that are currently free in the model will be fit simultaneously with the source of interest.
free_radius	None	Free normalizations of background sources within this angular distance in degrees from the source of interest. If None then no sources will be freed.
make_plots	False	Generate diagnostic plots.
make_tsmap	True	Make a TS map for the source of interest.
psf_scale_fn	None	Tuple of two vectors (logE,f) defining an energy-dependent PSF scaling function that will be applied when building spatial models for the source of interest. The tuple (logE,f) defines the fractional corrections f at the sequence of energies logE = log10(E/MeV) where f=0 corresponds to no correction. The correction function f(E) is evaluated by linearly interpolating the fractional correction factors f in log(E). The corrected PSF is given by P’(x;E) = P(x/(1+f(E));E) where x is the angular separation.
reoptimize	False	Re-fit ROI in each energy bin. No effect if fit_ebin=False or there are no free parameters
save_model_map	False	Save model counts cubes for the best-fit model of extension.
spatial_model	RadialGaussian	Spatial model that will be used to test the sourceextension. The spatial scale parameter of the model will be set such that the 68% containment radius of the model is equal to the width parameter.
sqrt_ts_threshold	None	Threshold on sqrt(TS_ext) that will be applied when update is True. If None then nothreshold is applied.
tsmap_fitter	tsmap	Set the method for generating the TS map. Valid options are tsmap or tscube.
update	False	Update this source with the best-fit model for spatial extension if TS_ext > tsext_threshold.
width	None	Sequence of values in degrees for the likelihood scan over spatial extension (68% containment radius). If this argument is None then the scan points will be determined from width_min/width_max/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 scan points between width_min and width_max. Scan points will be spaced evenly on a logarithmic scale between width_min and width_max.
write_fits	True	Write the output to a FITS file.
write_npy	True	Write the output dictionary to a numpy file.

fileio

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

fileio:
   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.
outdir_regex	[’\.fits$|\.fit$|\.xml$|\.npy$|\.png$|\.pdf$|\.yaml$’]	Stage files to the output directory that match at least one of the regular expressions in this list. This option only takes effect when usescratch is True.
savefits	True	Save intermediate FITS files.
scratchdir	/scratch	Path to the scratch directory. If usescratch is True then a temporary working directory will be created under this directory.
usescratch	False	Run analysis in a temporary working directory under scratchdir.
workdir	None	Path to the working directory.
workdir_regex	[’\.fits$|\.fit$|\.xml$|\.npy$’]	Stage files to the working directory that match at least one of the regular expressions in this list. This option only takes effect when usescratch is True.

gtlike

Options in the gtlike section control the setup of the likelihood analysis include the IRF name (irfs). The edisp_bin option has been recently added to implement the latest handling of the energy dispersion (see FSSC for further details).

gtlike Options

Option, Default, Description
bexpmap	None
bexpmap_base	None	Set the basline all-sky expoure map file. This will be used to generate a scaled source map.
bexpmap_roi	None
bexpmap_roi_base	None	Set the basline ROI expoure map file. This will be used to generate a scaled source map.
convolve	True
edisp	True	Enable the correction for energy dispersion.
edisp_bins	-1	Number of bins to use for energy correction.
edisp_disable	None	Provide a list of sources for which the edisp correction should be disabled.
expscale	None	Exposure correction that is applied to all sources in the analysis component. This correction is superseded by src_expscale if it is defined for a source.
irfs	None	Set the IRF string.
llscan_npts	20	Number of evaluation points to use when performing a likelihood scan.
minbinsz	0.05	Set the minimum bin size used for resampling diffuse maps.
resample	True
rfactor	2
src_expscale	None	Dictionary of exposure corrections for individual sources keyed to source name. The exposure for a given source will be scaled by this value. A value of 1.0 corresponds to the nominal exposure.
srcmap	None	Set the source maps file. When defined this file will be used instead of the local source maps file.
srcmap_base	None	Set the baseline source maps file. This will be used to generate a scaled source map.
use_external_srcmap	False	Use an external precomputed source map file.
use_scaled_srcmap	False	Generate source map by scaling an external srcmap file.
wmap	None	Likelihood weights map.

lightcurve

The options in lightcurve control the default behavior of the lightcurve method. For more information about using this method see the Light Curves page.

lightcurve Options

Option, Default, Description
binsz	86400.0	Set the lightcurve bin size in seconds.
free_background	False	Leave background parameters free when performing the fit. If True then any parameters that are currently free in the model will be fit simultaneously with the source of interest.
free_params	None	Set the parameters of the source of interest that will be re-fit in each time bin. If this list is empty then all parameters will be freed.
free_radius	None	Free normalizations of background sources within this angular distance in degrees from the source of interest. If None then no sources will be freed.
free_sources	None	List of sources to be freed. These sources will be added to the list of sources satisfying the free_radius selection.
make_plots	False	Generate diagnostic plots.
max_free_sources	5	Maximum number of sources that will be fit simultaneously with the source of interest.
multithread	False	Split the calculation across number of processes set by nthread option.
nbins	None	Set the number of lightcurve bins. The total time range will be evenly split into this number of time bins.
nthread	None	Number of processes to create when multithread is True. If None then one process will be created for each available core.
outdir	None	Store all data in this directory (e.g. “30days”). If None then use current directory.
save_bin_data	True	Save analysis directories for individual time bins. If False then only the analysis results table will be saved.
shape_ts_threshold	16.0	Set the TS threshold at which shape parameters of sources will be freed. If a source is detected with TS less than this value then its shape parameters will be fixed to values derived from the analysis of the full time range.
systematic	0.02	Systematic correction factor for TS:subscript:var. See Sect. 3.6 in 2FGL for details.
time_bins	None	Set the lightcurve bin edge sequence in MET. This option takes precedence over binsz and nbins.
use_local_ltcube	True	Generate a fast LT cube.
use_scaled_srcmap	False	Generate approximate source maps for each time bin by scaling the current source maps by the exposure ratio with respect to that time bin.
write_fits	True	Write the output to a FITS file.
write_npy	True	Write the output dictionary to a numpy file.

model

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
diffuse_dir	None
diffuse_xml	None
extdir	None	Set a directory that will be searched for extended source FITS templates. Template files in this directory will take precendence over catalog source templates with the same name.
extract_diffuse	False	Extract a copy of all mapcube components centered on the ROI.
galdiff	None	Set the path to one or more galactic IEM mapcubes. A separate component will be generated for each item in this list.
isodiff	None	Set the path to one or more isotropic templates. A separate component will be generated for each item in this list.
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	Radius of circular region in degrees centered on the ROI that selects sources for inclusion in the model. If this parameter is none then no selection is applied. This selection is ORed with the src_roiwidth selection.
src_radius_roi	None	Half-width of src_roiwidth selection. This parameter can be used in lieu of src_roiwidth.
src_roiwidth	None	Width of square region in degrees centered on the ROI that selects sources for inclusion in the model. If this parameter is none then no selection is applied. This selection will be ORed with the src_radius selection.

optimizer

optimizer Options

Option, Default, Description
init_lambda	0.0001	Initial value of damping parameter for step size calculation when using the NEWTON fitter. A value of zero disables damping.
max_iter	100	Maximum number of iterations for the Newtons method fitter.
min_fit_quality	2	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	0.001	Set the optimizer tolerance.
verbosity	0

plotting

plotting Options

Option, Default, Description
catalogs	None
cmap	magma	Set the colormap for 2D plots.
cmap_resid	RdBu_r	Set the colormap for 2D residual plots.
figsize	[8.0, 6.0]	Set the default figure size.
format	png
graticule_radii	None	Define a list of radii at which circular graticules will be drawn.
interactive	False	Enable interactive mode. If True then plots will be drawn after each plotting command.
label_ts_threshold	0.0	TS threshold for labeling sources in sky maps. If None then no sources will be labeled.
loge_bounds	None

residmap

The options in residmap control the default behavior of the residmap method. For more information about using this method see the Residual Map page.

residmap Options

Option, Default, Description
exclude	None	List of sources that will be removed from the model when computing the residual map.
loge_bounds	None	Restrict the analysis to an energy range (emin,emax) in log10(E/MeV) that is a subset of the analysis energy range. By default the full analysis energy range will be used. If either emin/emax are None then only an upper/lower bound on the energy range wil be applied.
make_plots	False	Generate diagnostic plots.
model	None	Dictionary defining the spatial/spectral properties of the test source. If model is None the test source will be a PointSource with an Index 2 power-law spectrum.
use_weights	False	Used weighted version of maps in making plots.
write_fits	True	Write the output to a FITS file.
write_npy	True	Write the output dictionary to a numpy file.

roiopt

The options in roiopt control the default behavior of the optimize method. For more information about using this method see the ROI Optimization and Fitting page.

roiopt Options

Option, Default, Description
max_free_sources	5	Maximum number of sources that will be fit simultaneously in the first optimization step.
npred_frac	0.95
npred_threshold	1.0
shape_ts_threshold	25.0	Threshold on source TS used for determining the sources that will be fit in the third optimization step.
skip	None	List of str source names to skip while optimizing.

sed

The options in sed control the default behavior of the sed method. For more information about using 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	Scale factor that sets the strength of the prior on nuisance parameters that are free. Setting this to None disables the prior.
free_background	False	Leave background parameters free when performing the fit. If True then any parameters that are currently free in the model will be fit simultaneously with the source of interest.
free_pars	None	Set the parameters of the source of interest that will be freed when performing the global fit. By default all parameters will be freed.
free_radius	None	Free normalizations of background sources within this angular distance in degrees from the source of interest. If None then no sources will be freed.
make_plots	False	Generate diagnostic plots.
ul_confidence	0.95	Confidence level for flux upper limit.
ul_ts_threshold	4	Minimum threshold of TS for displaying flux point below this vlaue an Upper Limit is calculated.
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.
write_fits	True	Write the output to a FITS file.
write_npy	True	Write the output dictionary to a numpy file.

selection

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.

selection:

  # 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))
phasemax	None	Maximum pulsar phase
phasemin	None	Minimum pulsar phase
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

The options in sourcefind control the default behavior of the find_sources method. For more information about using this method see the Source Finding page.

sourcefind Options

Option, Default, Description
free_params	None
max_iter	5	Maximum number of source finding iterations. The source finder will continue adding sources until no additional peaks are found or the number of iterations exceeds this number.
min_separation	1.0	Minimum separation in degrees between sources detected in each iteration. The source finder will look for the maximum peak in the TS map within a circular region of this radius.
model	None	Dictionary defining the spatial/spectral properties of the test source. If model is None the test source will be a PointSource with an Index 2 power-law spectrum.
multithread	False	Split the calculation across number of processes set by nthread option.
nthread	None	Number of processes to create when multithread is True. If None then one process will be created for each available core.
sources_per_iter	4	Maximum number of sources that will be added in each iteration. If the number of detected peaks in a given iteration is larger than this number, only the N peaks with the largest TS will be used as seeds for the current iteration.
sqrt_ts_threshold	5.0	Source threshold in sqrt(TS). Only peaks with sqrt(TS) exceeding this threshold will be used as seeds for new sources.
tsmap_fitter	tsmap	Set the method for generating the TS map. Valid options are tsmap or tscube.

psmap

The options in psmap control the default behavior of the psmap method. For more information about using this method see the PS Map page.

psmap Options

Option, Default, Description
chatter	1	Output verbosity.
cmap		Data 3d map file or list of files (separated by colons).
dpix	-1	PS computation: sub-ROI half-width in pixel (ignoring central pixel; dpix=0 corresponds to the central pixel only).
emax	1000000.0	PS computation: maximum energy/MeV.
emin	100	PS computation: minimum energy/MeV.
fixedradius	-1.0	Spatial integration: fixed radius (deg). If negative (default), the PSF-like parameters are used.
ipix	-1	PS computation: sub-ROI central pixel i-axis position.
jpix	-1	PS computation: sub-ROI central pixel j-axis position.
make_plots	False	Generate diagnostic plots.
maxpoissoncount	100	LL computation: number of counts up to which Poisson statistics is considered.
mmap		Model 3d map file or list of files (separated by colons).
nbinloge	20	PS computation: number of log10 energy bins. It is recommended to set nbinloge so that the log10(E) bin width is between 0.2 and 0.3.
nbinpdf	50	LL computation: number of bins.
outfile		Output fits file, which contains the PS map (hdu0: -log10(deviation probability), hdu1: in sigma units).
prob_epsilon	1e-07	LL computation: precision parameter.
psfpar0	4.0	Spatial integration: PSF-like parameter 0 (deg) of the parameterization sqrt(p0^2*pow(E/p1,-2*p2) + p3^2).
psfpar0lst		Spatial integration: list of the PSF-like parameters 0 of all components (separated by colons). By default, psfpar0 is used for all components.
psfpar1	100	Spatial integration: PSF-like parameter 1 (MeV) of the parameterization sqrt(p0^2*pow(E/p1,-2*p2) + p3^2).
psfpar2	0.9	Spatial integration: PSF-like parameter 2 of the parameterization sqrt(p0^2*pow(E/p1,-2*p2) + p3^2).
psfpar3	0.1	Spatial integration: PSF-like parameter 3 (deg) of the parameterization sqrt(p0^2*pow(E/p1,-2*p2) + p3^2).
scaleaxis	20	LL computation: scale axis.
wmap		Weight 3d map file or list of files (separated by colons).
write_fits	True	Write the output to a FITS file.

tsmap

The options in tsmap control the default behavior of the tsmap method. For more information about using this method see the TS Map page.

tsmap Options

Option, Default, Description
exclude	None	List of sources that will be removed from the model when computing the TS map.
loge_bounds	None	Restrict the analysis to an energy range (emin,emax) in log10(E/MeV) that is a subset of the analysis energy range. By default the full analysis energy range will be used. If either emin/emax are None then only an upper/lower bound on the energy range wil be applied.
make_plots	False	Generate diagnostic plots.
max_kernel_radius	3.0	Set the maximum radius of the test source kernel. Using a smaller value will speed up the TS calculation at the loss of accuracy.
model	None	Dictionary defining the spatial/spectral properties of the test source. If model is None the test source will be a PointSource with an Index 2 power-law spectrum.
multithread	False	Split the calculation across number of processes set by nthread option.
nthread	None	Number of processes to create when multithread is True. If None then one process will be created for each available core.
write_fits	True	Write the output to a FITS file.
write_npy	True	Write the output dictionary to a numpy file.

tscube

The options in tscube control the default behavior of the tscube method. For more information about using this method see the TS Cube page.

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
exclude	None	List of sources that will be removed from the model when computing the TS map.
init_lambda	0	Initial value of damping parameter for newton step size calculation. A value of zero disables damping.
max_iter	30	Maximum number of iterations for the Newtons method fitter.
model	None	Dictionary defining the spatial/spectral properties of the test source. If model is None the test source will be a PointSource with an Index 2 power-law spectrum.
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.