Generating a residual spectrum

In the previous tutorial you have used the :ref:`csresmap` script to inspect the spatial residuals. You can also inspect the spectral residuals using the :ref:`csresspec` script.

The :ref:`csresspec` script can deal with any observation type (unbinned, binned, stacked, On/Off). For the example case with unbinned observations the script is then used as follows:

$ csresspec components=yes
Input event list, counts cube, or observation definition XML file [obs.xml]
Calibration database [prod2]
Instrument response function [South_0.5h]
Lower energy limit (TeV) [0.1]
Upper energy limit (TeV) [100.0]
Number of model cube energy bins [30]
Stack observations [yes]
Coordinate System (CEL|GAL) [CEL]
Projection method (AIT|AZP|CAR|GLS|MER|MOL|SFL|SIN|STG|TAN) [CAR]
First coordinate of image/source region center in degrees (RA or galactic l) (0-360) [83.63]
Second coordinate of image/source region center in degrees (DEC or galactic b) (-90-90) [22.01]
Size of the X axis in pixels [200] 51
Size of the Y axis in pixels [200] 51
Pixel size (deg/pixel) [0.02]
Input model definition XML file [crab_results.xml]
Mask data to calculate residuals in ROI [yes] no
Residuals computation algorithm (SUB|SUBDIV|SUBDIVSQRT|SIGNIFICANCE) [SIGNIFICANCE]
Output residual spectrum file [residual_spectrum.fits]

In our example, the residuals will cover energies from 100 GeV to 100 TeV, in 30 energy bins. Since we have decided to stack multiple unbinned observations we have also entered parameters to perform a spatial binning. Note that we have defined the spatial grid such that we will obtain the residuals in a 1 degree square region around the Crab. Optionally, a mask can be applied to either unbinned or binned 3D observations. We have used the hidden components parameter to include the individual model components in the results file.

The :ref:`csresspec` script created the FITS file residual_spectrum.fits that contains the results of the residual computation. A graphical display of the fit results is shown below.

Data, model, and residuals from the spectral fit of the Crab nebula

$ $CTOOLS/share/examples/python/show_spectrum.py residual_spectrum.fits