On/Off analysis now supports any kind of background model (#2710)

Jürgen Knödlseder
1 parent c1981f9a
Showing 11 changed files with 187 additions and 165 deletions
ChangeLog
NEWS
cscripts/cslightcrv.par
cscripts/csphagen.par
cscripts/csphagen.py
cscripts/obsutils.py
doc/source/admin/release_history/1.6.rst
doc/source/users/reference_manual/cslightcrv.rst
doc/source/users/reference_manual/csphagen.rst
doc/source/users/tutorials/hess_dr1/classical.ipynb
test/test_cslightcrv.py
@@ -7,6 +7,7 @@
         Apply event bin weighting in ctmodel for stacked computation (#2721)
         Enable ctbin to produce counts cubes for a joint binned analysis (#2714)
         Add Jupyter notebooks for H.E.S.S. DR1 (#2712)
+        csphagen now supports any kind of background model (#2710)
         Add code generator (#2709)
         Add csbkgmodel script (#2694)
         Compute DETX and DETY in ctmodel if they are not available (#2694)
@@ -16,11 +17,11 @@
         Account for varying energy thresholds in ctbin weight computation (#2685)
         Add ctbkgcube::cntcube() method (#2685)
         Avoid ctselect error in case that RoI radius is unchanged (#2682)
-        Add "use_irf_bkg" parameter to cslightcrv
+        Add "use_model_bkg" parameter to cslightcrv
         Add "like_accuracy" parameter to likelihood tools and scripts (#2662)
         Do not skip bins with zero counts in csspec (#2671)
         Use "ENERG" instead of "ETRUE" in energy dispersion axis names in csroot2caldb (#2670)
-        Add hidden "use_irf_bkg" parameter to csphagen (#2659)
+        Add hidden "use_model_bkg" parameter to csphagen (#2659)
         Use full RMF true energy range for On/Off analysis in csspec (#2656)
         Defer import of ROOT module in csroot2caldb to run method (#2652)
         Transparently update parameter files (#2513)
@@ -270,7 +270,7 @@ None
 cslightcrv - Generate light curve
 ---------------------------------
-Add hidden "use_irf_bkg" parameter for forwarding to csphagen.
+Add hidden "use_model_bkg" parameter for forwarding to csphagen.
 Add hidden "nthreads" parameter and implement parallelisation of light
 curve computation (#2421).
@@ -323,16 +323,19 @@ Use time reference of input observations if time selection is given in MET
 csphagen - Generate On/Off observations
 ---------------------------------------
-Add hidden "use_irf_bkg" parameter. By default the parameter is set to "yes",
-which means that the background acceptance provided in the IRF is used for
-the computation of the alpha parameter and the background rate, stored in the
-"BACKSCAL" column of the On spectrum and the "BACKRESP" column of the Off
+The script now supports any kind of background model, not only IRF background
+models (#2710).
+
+Add hidden "use_model_bkg" parameter. By default the parameter is set to "yes",
+which means that the background model provided in the model container is used
+for the computation of the alpha parameter and the background rate, stored in
+the "BACKSCAL" column of the On spectrum and the "BACKRESP" column of the Off
 spectrum, respectively. If the parameter is set to "no" it is assumed that the
-background rate in the On and Off regions are the same, and the IRF background
-template is not used. In that case, the "BACKSCAL" column gives the ratio of
-the solid angles between On and Off regions, and the "BACKRESP" column is set
-to zero. The resulting data can only be fitted using the "wstat" statistic
-(#2659).
+background rate in the On and Off regions are the same, and the model background
+is not used. In that case, the "BACKSCAL" column gives the ratio of the solid
+angles between On and Off regions, and the "BACKRESP" column is set to the
+solid angle of the On region. The resulting data can only be fitted using the
+"WSTAT" statistic (#2659).
 Add hidden "nthreads" parameter and implement parallelisation of computations
 (#2421).
@@ -28,37 +28,37 @@ outfile,     f, a, lightcurve.fits,,, &quot;Output light curve file&quot;
 #
 # Script parameters
 #==================
-tbinalg,     s, a, GTI,FILE|LIN|GTI,, "Algorithm for defining time bins"
-tmin,        t, a, MJD 51544.5,,,"Lightcurve start time (UTC string, JD, MJD or MET in seconds)"
-tmax,        t, a, MJD 51544.6,,,"Lightcurve stop time (UTC string, JD, MJD or MET in seconds)"
-mjdref,      r, h, 51544.5,,, "Reference MJD for MET"
-tbins,       i, a, 5,1,10000, "Number of time bins"
-tbinfile,    f, a, NONE,,, "File defining the time binning"
-method,      s, a, 3D, 3D|ONOFF,, "Analysis method"
-emin,        r, a, 0.1,,, "Lower energy limit of events (TeV)"
-emax,        r, a, 100.0,,, "Upper energy limit of events (TeV)"
-enumbins,    i, a, 0,0,100, "Number of energy bins for binned (0=unbinned for 3D analysis only)"
-coordsys,    s, a, CEL,CEL|GAL,, "Coordinate System"
-proj,        s, a, CAR,AIT|AZP|CAR|GLS|MER|MOL|SFL|SIN|STG|TAN,, "Projection method"
-xref,        r, a, 83.63,0,360, "First coordinate of image/source region center in degrees (RA or galactic l)"
-yref,        r, a, 22.51,-90,90, "Second coordinate of image/source region center in degrees (DEC or galactic b)"
-nxpix,       i, a, 200,,, "Size of the X axis in pixels"
-nypix,       i, a, 200,,, "Size of the Y axis in pixels"
-binsz,       r, a, 0.02,,, "Pixel size (deg/pixel)"
-srcshape,    s, h, CIRCLE,CIRCLE,, "Shape of the source region"
-rad,         r, a, 0.2,0,180, "Radius of source region circle (deg)"
-bkgmethod,   s, h, REFLECTED,REFLECTED,, "Method for background estimation"
-bkgregmin,   i, h, 2,1,1000, "Minimum number of background regions"
-use_irf_bkg, b, h, yes,,, "Use IRF background template?"
-maxoffset,   r, h, 4.0,,, "Maximum offset of source from camera center to accept observation"
-etruemin,    r, h, 0.01,,, "Minimum true energy (TeV)"
-etruemax,    r, h, 300.0,,, "Maximum true energy (TeV)"
-etruebins,   i, h, 30,,, "Number of bins per decade for true energy bins"
-statistic,   s, h, DEFAULT,DEFAULT|CSTAT|WSTAT|CHI2,, "Optimization statistic"
-calc_ts,     b, h, yes,,, "Compute TS value for each bin?"
-calc_ulim,   b, h, yes,,, "Compute upper limit for each bin?"
-fix_srcs,    b, h, yes,,, "Fix other sky model parameters?"
-fix_bkg,     b, h, no,,, "Fix background model parameters?"
+tbinalg,       s, a, GTI,FILE|LIN|GTI,, "Algorithm for defining time bins"
+tmin,          t, a, MJD 51544.5,,,"Lightcurve start time (UTC string, JD, MJD or MET in seconds)"
+tmax,          t, a, MJD 51544.6,,,"Lightcurve stop time (UTC string, JD, MJD or MET in seconds)"
+mjdref,        r, h, 51544.5,,, "Reference MJD for MET"
+tbins,         i, a, 5,1,10000, "Number of time bins"
+tbinfile,      f, a, NONE,,, "File defining the time binning"
+method,        s, a, 3D, 3D|ONOFF,, "Analysis method"
+emin,          r, a, 0.1,,, "Lower energy limit of events (TeV)"
+emax,          r, a, 100.0,,, "Upper energy limit of events (TeV)"
+enumbins,      i, a, 0,0,100, "Number of energy bins for binned (0=unbinned for 3D analysis only)"
+coordsys,      s, a, CEL,CEL|GAL,, "Coordinate System"
+proj,          s, a, CAR,AIT|AZP|CAR|GLS|MER|MOL|SFL|SIN|STG|TAN,, "Projection method"
+xref,          r, a, 83.63,0,360, "First coordinate of image/source region center in degrees (RA or galactic l)"
+yref,          r, a, 22.51,-90,90, "Second coordinate of image/source region center in degrees (DEC or galactic b)"
+nxpix,         i, a, 200,,, "Size of the X axis in pixels"
+nypix,         i, a, 200,,, "Size of the Y axis in pixels"
+binsz,         r, a, 0.02,,, "Pixel size (deg/pixel)"
+srcshape,      s, h, CIRCLE,CIRCLE,, "Shape of the source region"
+rad,           r, a, 0.2,0,180, "Radius of source region circle (deg)"
+bkgmethod,     s, h, REFLECTED,REFLECTED,, "Method for background estimation"
+bkgregmin,     i, h, 2,1,1000, "Minimum number of background regions"
+use_model_bkg, b, h, yes,,, "Use background model?"
+maxoffset,     r, h, 4.0,,, "Maximum offset of source from camera center to accept observation"
+etruemin,      r, h, 0.01,,, "Minimum true energy (TeV)"
+etruemax,      r, h, 300.0,,, "Maximum true energy (TeV)"
+etruebins,     i, h, 30,,, "Number of bins per decade for true energy bins"
+statistic,     s, h, DEFAULT,DEFAULT|CSTAT|WSTAT|CHI2,, "Optimization statistic"
+calc_ts,       b, h, yes,,, "Compute TS value for each bin?"
+calc_ulim,     b, h, yes,,, "Compute upper limit for each bin?"
+fix_srcs,      b, h, yes,,, "Fix other sky model parameters?"
+fix_bkg,       b, h, no,,, "Fix background model parameters?"
 #
 # Standard parameters
@@ -28,28 +28,28 @@ prefix,      s, h, onoff,,, &quot;Prefix for output files&quot;
 #
 # Script parameters
 #==================
-ebinalg,     s, a, LOG,FILE|LIN|LOG,, "Algorithm for defining energy bins"
-emin,        r, a, 0.1,,, "Start value for first energy bin in TeV"
-emax,        r, a, 100.0,,, "Stop value for last energy bin in TeV"
-enumbins,    i, a, 120,,, "Number of energy bins"
-ebinfile,    f, a, NONE,,, "Name of the file containing the energy bin definition"
-srcshape,    s, h, CIRCLE,CIRCLE,, "Shape of the source region"
-coordsys,    s, a, CEL,CEL|GAL,, "Coordinate system (CEL - celestial, GAL - galactic)"
-ra,          r, a, 83.63,0,360, "Right Ascension of source region centre (deg)"
-dec,         r, a, 22.01,-90,90, "Declination of source region centre (deg)"
-glon,        r, a, 184.56,0,360, "Galactic longitude of source region centre (deg)"
-glat,        r, a, -5.79,-90,90, "Galactic latitude of source region centre (deg)"
-rad,         r, a, 0.2,0,180, "Radius of source region circle (deg)"
-srcregfile,  f, a, on.reg,,, "Source region file (ds9 or FITS WCS)"
-bkgmethod,   s, a, REFLECTED,REFLECTED|CUSTOM,, "Method for background estimation"
-bkgregfile,  f, a, bkg.reg,,, "Background regions file (ds9 or FITS WCS)"
-bkgregmin,   i, h, 2,1,1000, "Minimum number of background regions"
-use_irf_bkg, b, h, yes,,, "Use IRF background template?"
-maxoffset,   r, h, 4.0,,, "Maximum offset of source from camera center to accept observation"
-stack,       b, a, no,,, "Stack multiple observations into single PHA, ARF and RMF files?"
-etruemin,    r, h, 0.01,,, "Minimum true energy (TeV)"
-etruemax,    r, h, 300.0,,, "Maximum true energy (TeV)"
-etruebins,   i, h, 30,,, "Number of bins per decade for true energy bins"
+ebinalg,       s, a, LOG,FILE|LIN|LOG,, "Algorithm for defining energy bins"
+emin,          r, a, 0.1,,, "Start value for first energy bin in TeV"
+emax,          r, a, 100.0,,, "Stop value for last energy bin in TeV"
+enumbins,      i, a, 120,,, "Number of energy bins"
+ebinfile,      f, a, NONE,,, "Name of the file containing the energy bin definition"
+srcshape,      s, h, CIRCLE,CIRCLE,, "Shape of the source region"
+coordsys,      s, a, CEL,CEL|GAL,, "Coordinate system (CEL - celestial, GAL - galactic)"
+ra,            r, a, 83.63,0,360, "Right Ascension of source region centre (deg)"
+dec,           r, a, 22.01,-90,90, "Declination of source region centre (deg)"
+glon,          r, a, 184.56,0,360, "Galactic longitude of source region centre (deg)"
+glat,          r, a, -5.79,-90,90, "Galactic latitude of source region centre (deg)"
+rad,           r, a, 0.2,0,180, "Radius of source region circle (deg)"
+srcregfile,    f, a, on.reg,,, "Source region file (ds9 or FITS WCS)"
+bkgmethod,     s, a, REFLECTED,REFLECTED|CUSTOM,, "Method for background estimation"
+bkgregfile,    f, a, bkg.reg,,, "Background regions file (ds9 or FITS WCS)"
+bkgregmin,     i, h, 2,1,1000, "Minimum number of background regions"
+use_model_bkg, b, h, yes,,, "Use background model?"
+maxoffset,     r, h, 4.0,,, "Maximum offset of source from camera center to accept observation"
+stack,         b, a, no,,, "Stack multiple observations into single PHA, ARF and RMF files?"
+etruemin,      r, h, 0.01,,, "Minimum true energy (TeV)"
+etruemax,      r, h, 300.0,,, "Maximum true energy (TeV)"
+etruebins,     i, h, 30,,, "Number of bins per decade for true energy bins"
 #
 # Standard parameters
@@ -47,7 +47,9 @@ class csphagen(ctools.csobservation):
         self._etruebounds   = gammalib.GEbounds()
         self._src_dir       = gammalib.GSkyDir()
         self._src_reg       = gammalib.GSkyRegions()
-        self._src_model     = None
+        self._models        = gammalib.GModels()
+        self._srcname       = ''
+        self._use_model_bkg = True
         self._bkg_regs      = []
         self._excl_reg      = None
         self._has_exclusion = False
@@ -69,18 +71,20 @@ class csphagen(ctools.csobservation):
             Pickled instance
         """
         # Set pickled dictionary
-        state = {'base'         : ctools.csobservation.__getstate__(self),
-                 'ebounds'      : self._ebounds,
-                 'etruebounds'  : self._etruebounds,
-                 'src_dir'      : self._src_dir,
-                 'src_reg'      : self._src_reg,
-                 'src_model'    : self._src_model,
-                 'bkg_regs'     : self._bkg_regs,
-                 'excl_reg'     : self._excl_reg,
-                 'has_exclusion': self._has_exclusion,
-                 'srcshape'     : self._srcshape,
-                 'rad'          : self._rad,
-                 'nthreads'     : self._nthreads}
+        state = {'base'          : ctools.csobservation.__getstate__(self),
+                 'ebounds'       : self._ebounds,
+                 'etruebounds'   : self._etruebounds,
+                 'src_dir'       : self._src_dir,
+                 'src_reg'       : self._src_reg,
+                 'models'        : self._models,
+                 'srcname'       : self._srcname,
+                 'use_model_bkg' : self._use_model_bkg,
+                 'bkg_regs'      : self._bkg_regs,
+                 'excl_reg'      : self._excl_reg,
+                 'has_exclusion' : self._has_exclusion,
+                 'srcshape'      : self._srcshape,
+                 'rad'           : self._rad,
+                 'nthreads'      : self._nthreads}
         # Return pickled dictionary
         return state
@@ -99,7 +103,9 @@ class csphagen(ctools.csobservation):
         self._etruebounds   = state['etruebounds']
         self._src_dir       = state['src_dir']
         self._src_reg       = state['src_reg']
-        self._src_model     = state['src_model']
+        self._models        = state['models']
+        self._srcname       = state['srcname']
+        self._use_model_bkg = state['use_model_bkg']
         self._bkg_regs      = state['bkg_regs']
         self._excl_reg      = state['excl_reg']
         self._has_exclusion = state['has_exclusion']
@@ -157,8 +163,8 @@ class csphagen(ctools.csobservation):
             self._rad = self['rad'].real()
             self._src_reg.append(gammalib.GSkyRegionCircle(self._src_dir, self._rad))
-        # Query usage of IRF background template
-        self['use_irf_bkg'].boolean()
+        # Query usage of background model
+        self['use_model_bkg'].boolean()
         # Return
         return
@@ -223,19 +229,23 @@ class csphagen(ctools.csobservation):
         """
         Get parameters from parfile and setup observations
         """
+        # Clear source models
+        self._models.clear()
+
         # Setup observations (require response and allow event list, don't
         # allow counts cube)
         self._setup_observations(self.obs(), True, True, False)
-        # Get spatial component of source model if an input model is defined
+        # Get source model and source name. First try to extract models from
+        # observation container. If this does not work then try creating
+        # model from the inmodel parameter
         if self.obs().models().size() > 0:
-            name            = self['srcname'].string()
-            self._src_model = self.obs().models()[name].spatial().clone()
+            self._models  = self.obs().models().clone()
+            self._srcname = self['srcname'].string()
         elif self['inmodel'].is_valid():
             inmodel         = self['inmodel'].filename()
-            models          = gammalib.GModels(inmodel)
-            name            = self['srcname'].string()
-            self._src_model = models[name].spatial().clone()
+            self._models    = gammalib.GModels(inmodel)
+            self._srcname   = self['srcname'].string()
         # Set energy bounds
         self._ebounds = self._create_ebounds()
@@ -274,6 +284,16 @@ class csphagen(ctools.csobservation):
         # Set number of processes for multiprocessing
         self._nthreads = mputils.nthreads(self)
+        # If we have no model then create now a dummy model
+        if self._models.is_empty():
+            spatial  = gammalib.GModelSpatialPointSource(self._src_dir)
+            spectral = gammalib.GModelSpectralPlaw()
+            model    = gammalib.GModelSky(spatial, spectral)
+            model.name('Dummy')
+            self._models.append(model)
+            self._srcname       = 'Dummy'
+            self._use_model_bkg = False
+
         # Return
         return
@@ -481,21 +501,22 @@ class csphagen(ctools.csobservation):
             bkg_reg = self._set_background_regions(obs)
             # Get IRF background template usage flag
-            use_irf_bkg = self['use_irf_bkg'].boolean()
-            if not use_irf_bkg:
-                self._log_string(gammalib.NORMAL, 'IRF background template '
-                                 'not used, assume constant backround rate.')
+            use_model_bkg = self['use_model_bkg'].boolean()
+            if not use_model_bkg:
+                self._log_string(gammalib.NORMAL, 'Background model not used, '
+                                 'assume constant backround rate.')
             # If there are background regions then create On/Off observation
             # and append it to the output container
             if bkg_reg.size() >= self['bkgregmin'].integer():
                 onoff = gammalib.GCTAOnOffObservation(obs,
-                                                      self._src_model,
+                                                      self._models,
+                                                      self._srcname,
                                                       self._etruebounds,
                                                       self._ebounds,
                                                       self._src_reg,
                                                       bkg_reg,
-                                                      use_irf_bkg)
+                                                      use_model_bkg)
                 onoff.id(obs.id())
             else:
@@ -578,10 +599,6 @@ class csphagen(ctools.csobservation):
         outobs         = gammalib.GObservations()
         self._bkg_regs = []
-        # Set spatial model
-        if self._src_model == None:
-            self._src_model = gammalib.GModelSpatialPointSource(self._src_dir)
-
         # If there is more than one observation and we use multiprocessing
         if self._nthreads > 1 and self.obs().size() > 1:
@@ -809,13 +809,13 @@ def get_onoff_obs(cls, obs, nthreads=0):
     if cls._logExplicit():
         cls._log.header3('Creating On/Off observations')
-    # Initialise inmodel, srcname, inexclusion and use_irf_bkg
-    inmodel     = 'NONE'
-    srcname     = ''
-    inexclusion = 'NONE'
-    use_irf_bkg = True
+    # Initialise inmodel, srcname, inexclusion and use_model_bkg
+    inmodel       = 'NONE'
+    srcname       = ''
+    inexclusion   = 'NONE'
+    use_model_bkg = True
-    # Set inmodel, srcname, inexclusion and use_irf_bkg if they are available
+    # Set inmodel, srcname, inexclusion and use_model_bkg if they are available
     if cls.has_par('inmodel'):
         if cls['inmodel'].is_valid():
             inmodel = cls['inmodel'].value()
@@ -824,8 +824,8 @@ def get_onoff_obs(cls, obs, nthreads=0):
     if cls.has_par('inexclusion'):
         if cls['inexclusion'].is_valid():
             inexclusion = cls['inexclusion'].value()
-    if cls.has_par('use_irf_bkg'):
-        use_irf_bkg = cls['use_irf_bkg'].boolean()
+    if cls.has_par('use_model_bkg'):
+        use_model_bkg = cls['use_model_bkg'].boolean()
     # Create On/Off observations
     phagen = cscripts.csphagen(obs)
@@ -849,16 +849,16 @@ def get_onoff_obs(cls, obs, nthreads=0):
     phagen['bkgmethod'] = cls['bkgmethod'].string()
     if cls['bkgmethod'].string() == 'REFLECTED':
         phagen['bkgregmin'] = cls['bkgregmin'].integer()
-    phagen['use_irf_bkg'] = use_irf_bkg
-    phagen['maxoffset']   = cls['maxoffset'].real()
-    phagen['stack']       = True
-    phagen['etruemin']    = cls['etruemin'].real()
-    phagen['etruemax']    = cls['etruemax'].real()
-    phagen['etruebins']   = cls['etruebins'].integer()
-    phagen['chatter']     = cls['chatter'].integer()
-    phagen['clobber']     = cls['clobber'].boolean()
-    phagen['debug']       = cls['debug'].boolean()
-    phagen['nthreads']    = nthreads
+    phagen['use_model_bkg'] = use_model_bkg
+    phagen['maxoffset']     = cls['maxoffset'].real()
+    phagen['stack']         = True
+    phagen['etruemin']      = cls['etruemin'].real()
+    phagen['etruemax']      = cls['etruemax'].real()
+    phagen['etruebins']     = cls['etruebins'].integer()
+    phagen['chatter']       = cls['chatter'].integer()
+    phagen['clobber']       = cls['clobber'].boolean()
+    phagen['debug']         = cls['debug'].boolean()
+    phagen['nthreads']      = nthreads
     phagen.run()
     # Clone resulting observation container
@@ -52,7 +52,7 @@ Improvements
   Add ``ctbkgcube::cntcube()`` method
   Account for varying energy thresholds in :ref:`ctbin` weight computation
   Unnormalize background cube values in :ref:`ctbkgcube`
-* Add ``use_irf_bkg`` parameter to :ref:`cslightcrv`
+* Add ``use_model_bkg`` parameter to :ref:`cslightcrv`
 * [`2671 <https://cta-redmine.irap.omp.eu/issues/2671>`_] -
   Do not skip bins with zero counts in :ref:`csspec`
 * [`2670 <https://cta-redmine.irap.omp.eu/issues/2670>`_] -
@@ -63,7 +63,7 @@ Improvements
   :ref:`ctlike`, :ref:`cttsmap`, :ref:`ctulimit`, and :ref:`cstsmapsplit`
   to allow controlling the accuracy of the maximum likelihood computation
 * [`2659 <https://cta-redmine.irap.omp.eu/issues/2659>`_] -
-  Add hidden ``use_irf_bkg`` parameter to :ref:`csphagen`
+  Add hidden ``use_model_bkg`` parameter to :ref:`csphagen`
 * [`2656 <https://cta-redmine.irap.omp.eu/issues/2656>`_] -
   Use full ``RMF`` true energy range for On/Off analysis in :ref:`csspec`
 * [`2513 <https://cta-redmine.irap.omp.eu/issues/2513>`_] -
@@ -144,20 +144,20 @@ General parameters
     ``ONOFF`` analysis. If this number of background regions is not available the
     observation is skipped.
-``(use_irf_bkg = yes) [boolean]``
-    Specifies whether the IRF background template should be used for the
-    computation of the ``alpha`` parameter and the predicted background rate in
-    the Off region that is stored in the ``BACKRESP`` column of the Off spectrum
-    when using the ``ONOFF`` method.
-
-    If the parameter is set to ``no`` the IRF background template is not used and
-    the background rate is assumed identical within the On and Off regions. This
+``(use_model_bkg = yes) [boolean]``
+    Specifies whether the background model should be used for the computation
+    of the ``alpha`` parameter and the predicted background rate in the Off
+    region that is stored in the ``BACKRESP`` column of the Off spectrum when
+    using the ``ONOFF`` method.
+
+    If the parameter is set to ``no`` the background model is not used and the
+    background rate is assumed identical within the On and Off regions. This
     is the classical IACT analysis method that is used when using reflected Off
     regions. In that case the ``alpha`` parameter becomes independent of energy
     and only reflects the ratio between the solid angles of the On and Off
-    regions. The ``BACKRESP`` column in the Off spectrum will be filled with zeros.
-    The data need to be fitted with the ``wstat`` statistic, fitting with ``cstat``
-    will not work.
+    regions. The ``BACKRESP`` column in the Off spectrum will be filled with
+    the solid angle of the On region. The data need to be fitted with the ``wstat``
+    statistic, fitting with ``cstat`` will not work.
 ``(maxoffset = 4.0) [real]``
     Maximum offset in degrees of source from camera center to accept the
@@ -167,19 +167,20 @@ General parameters
     If this number of background regions is not available the observation is
     skipped.
-``(use_irf_bkg = yes) [boolean]``
-    Specifies whether the IRF background template should be used for the
-    computation of the ``alpha`` parameter and the predicted background rate in
-    the Off region that is stored in the ``BACKRESP`` column of the Off spectrum.
-
-    If the parameter is set to ``no`` the IRF background template is not used and
-    the background rate is assumed identical within the On and Off regions. This
+``(use_model_bkg = yes) [boolean]``
+    Specifies whether the background model should be used for the computation
+    of the ``alpha`` parameter and the predicted background rate in the Off
+    region that is stored in the ``BACKRESP`` column of the Off spectrum when
+    using the ``ONOFF`` method.
+
+    If the parameter is set to ``no`` the background model is not used and the
+    background rate is assumed identical within the On and Off regions. This
     is the classical IACT analysis method that is used when using reflected Off
     regions. In that case the ``alpha`` parameter becomes independent of energy
     and only reflects the ratio between the solid angles of the On and Off
-    regions. The ``BACKRESP`` column in the Off spectrum will be filled with zeros.
-    The data need to be fitted with the ``wstat`` statistic, fitting with ``cstat``
-    will not work.
+    regions. The ``BACKRESP`` column in the Off spectrum will be filled with
+    the solid angle of the On region. The data need to be fitted with the ``wstat``
+    statistic, fitting with ``cstat`` will not work.
 ``(maxoffset = 4.0) [real]``
     Maximum offset in degrees of source from camera center to accept the
@@ -100,7 +100,7 @@
     "phagen['dec'] = 22.01\n",
     "phagen['rad'] = 0.2\n",
     "phagen['bkgmethod'] = 'REFLECTED'\n",
-    "phagen['use_irf_bkg'] = False\n",
+    "phagen['use_model_bkg'] = False\n",
     "phagen['maxoffset'] = 2.0\n",
     "phagen['stack'] = True # treat observations separately in joint likelihood fit\n",
     "\n",
@@ -111,7 +111,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "Note that we have used the hidden parameter *use_irf_bkg* to specify that no background model should be used in the computation of the background normalisation factor, which is simply assumed to be the ratio of the solid angles of On/Off regions.\n",
+    "Note that we have used the hidden parameter *use_model_bkg* to specify that no background model should be used in the computation of the background normalisation factor, which is simply assumed to be the ratio of the solid angles of On/Off regions.\n",
     "\n",
     "## Likelihood fit\n",
     "\n",
@@ -241,31 +241,31 @@ class Test(test):
         # cslightcrv with classical analysis
         lcrv = cscripts.cslightcrv()
-        lcrv['inobs']       = self._offaxis_events
-        lcrv['inmodel']     = self._model_onoff
-        lcrv['srcname']     = 'Crab'
-        lcrv['caldb']       = self._caldb
-        lcrv['irf']         = self._irf
-        lcrv['tbinalg']     = 'LIN'
-        lcrv['tmin']        = '2020-01-01T00:00:00'
-        lcrv['tmax']        = '2020-01-01T00:05:00'
-        lcrv['tbins']       = 2
-        lcrv['method']      = 'ONOFF'
-        lcrv['use_irf_bkg'] = False  # Needed even if WSTAT
-        lcrv['emin']        = 1.0
-        lcrv['emax']        = 100.0
-        lcrv['enumbins']    = 2
-        lcrv['coordsys']    = 'CEL'
-        lcrv['xref']        = 83.63
-        lcrv['yref']        = 22.01
-        lcrv['rad']         = 0.2
-        lcrv['etruemin']    = 1.0
-        lcrv['etruemax']    = 100.0
-        lcrv['etruebins']   = 5
-        lcrv['statistic']   = 'WSTAT'
-        lcrv['outfile']     = 'cslightcrv_py5.fits'
-        lcrv['logfile']     = 'cslightcrv_py5.log'
-        lcrv['chatter']     = 4
+        lcrv['inobs']         = self._offaxis_events
+        lcrv['inmodel']       = self._model_onoff
+        lcrv['srcname']       = 'Crab'
+        lcrv['caldb']         = self._caldb
+        lcrv['irf']           = self._irf
+        lcrv['tbinalg']       = 'LIN'
+        lcrv['tmin']          = '2020-01-01T00:00:00'
+        lcrv['tmax']          = '2020-01-01T00:05:00'
+        lcrv['tbins']         = 2
+        lcrv['method']        = 'ONOFF'
+        lcrv['use_model_bkg'] = False  # Needed even if WSTAT
+        lcrv['emin']          = 1.0
+        lcrv['emax']          = 100.0
+        lcrv['enumbins']      = 2
+        lcrv['coordsys']      = 'CEL'
+        lcrv['xref']          = 83.63
+        lcrv['yref']          = 22.01
+        lcrv['rad']           = 0.2
+        lcrv['etruemin']      = 1.0
+        lcrv['etruemax']      = 100.0
+        lcrv['etruebins']     = 5
+        lcrv['statistic']     = 'WSTAT'
+        lcrv['outfile']       = 'cslightcrv_py5.fits'
+        lcrv['logfile']       = 'cslightcrv_py5.log'
+        lcrv['chatter']       = 4
         # Execute cslightcrv script
         lcrv.execute()