Source Finding¶

find_sources() is an iterative source-finding algorithm that uses peak detection on a TS map to find new source candidates. The procedure for adding new sources at each iteration is as follows:

• Generate a TS map for the test source model defined with the model argument.
• Identify peaks with sqrt(TS) > sqrt_ts_threshold and an angular distance of at least min_separation from a higher amplitude peak in the map.
• Order the peaks by TS and add a source at each peak starting from the highest TS peak. Set the source position by fitting a 2D parabola to the log-likelihood surface around the peak maximum. After adding each source, re-fit its spectral parameters.
• Add sources at the N highest peaks up to N = sources_per_iter.

Source finding is repeated up to max_iter iterations or until no peaks are found in a given iteration. Sources found by the method are added to the model and given designations PS JXXXX.X+XXXX according to their position in celestial coordinates.

Examples¶

model = {'Index' : 2.0, 'SpatialModel' : 'PointSource'}
srcs = gta.find_sources(model=model, sqrt_ts_threshold=5.0,
min_separation=0.5)


The method for generating the TS maps can be controlled with the tsmap_fitter option. TS maps can be generated with either tsmap() or tscube().

Reference/API¶

GTAnalysis.find_sources(prefix='', **kwargs)

An iterative source-finding algorithm that uses likelihood ratio (TS) maps of the region of interest to find new sources. After each iteration a new TS map is generated incorporating sources found in the previous iteration. The method stops when the number of iterations exceeds max_iter or no sources exceeding sqrt_ts_threshold are found.

Parameters: free_params (list) – (default : None) max_iter (int) – 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. (default : 5) min_separation (float) – 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. (default : 1.0) model (dict) – 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. (default : None) multithread (bool) – Split the calculation across all available cores. (default : False) sources_per_iter (int) – 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. (default : 4) sqrt_ts_threshold (float) – Source threshold in sqrt(TS). Only peaks with sqrt(TS) exceeding this threshold will be used as seeds for new sources. (default : 5.0) tsmap_fitter (str) – Set the method for generating the TS map. Valid options are tsmap or tscube. (default : tsmap) tsmap (dict) – Keyword arguments dictionary for tsmap method. tscube (dict) – Keyword arguments dictionary for tscube method. peaks (list) – List of peak objects. sources (list) – List of source objects.