Display PHA background data set information
show_bkg([id=None, bkg_id=None, outfile=None, clobber=False] )
The show_bkg() function displays the details of the PHA background data sets which have been loaded into Sherpa, by data set ID. Numerous pieces of information are returned, including any filters which may have been applied to the data, the grouping settings, mission-specific header keywords, the details of any associated instrument responses files (ARF, RMF), to name a few. This information can be saved to a text file by specifying a filename in the 'outfile' argument.
- id - the id of the source data set to use; default is to show information for all available data sets.
- bkg_id - the id of the background data set to use (e.g., bkg_id=1 represents the first background data set loaded in association with the source data set specified in the 'id' argument); default is bkg_id=1 for id=1.
- outfile - name of the file to which to save the output of the function
- clobber - a Boolean switch which indicates whether or not the 'outfile' should be overwritten, if the file already exists; default=False
The command output looks like:
Background Data Set: 1:1 Filter: 0.1248-12.4100 Energy (keV) Noticed Channels: 1-1024 meta = object = 3C 273 obs_id = 459 mission = AXAF telescope = CHANDRA instrument = ACIS detector = ACIS-56789 grating = HETG name = 3c273_bg.pi channel = Float64 counts = Float64 staterror = None syserror = None bin_lo = None bin_hi = None grouping = Int16 quality = Int16 exposure = 38564.6089269 backscal = 1.87253514146e-05 areascal = 1.0 grouped = True subtracted = False units = energy rate = True plot_fac = 0 response_ids =  background_ids =  Background RMF Data Set: 1:1 meta = telescope = CHANDRA instrument = ACIS name = 3c273.rmf detchans = 1024 energ_lo = Float64 energ_hi = Float64 n_grp = Int16 f_chan = UInt32 n_chan = UInt32 matrix = Float64 offset = 1 e_min = Float64 e_max = Float64 Background ARF Data Set: 1:1 meta = telescope = CHANDRA instrument = ACIS grating = HETG detector = ACIS-7 name = 3c273.arf energ_lo = Float64 energ_hi = Float64 specresp = Float64 bin_lo = None bin_hi = None exposure = 38564.1414549
The behavior of the screen output is determined by the user's $PAGER environment variable setting, which is usually a variant of "more." If PAGER is not found, '/usr/bin/more' is attempted before error. To disable paging within show_bkg() - i.e. print the entire contents, even if it scrolls offscreen - change this setting to "cat" before starting Sherpa:
unix% setenv PAGER cat unix% sherpa
The function show_bkg() can be called with no arguments, in which case the details of all available background data sets will be displayed.
sherpa> show_bkg(3, 1)
The data set id arguments are used to specify that the first background data set loaded in association with source data set 3 should be displayed (id=3, bkg_id=1). If only the source data set id "3" had been entered, without specifying a background id, all background data sets associated with data set 3 would be returned.
sherpa> show_bkg(3, "sherpa.bkg", True)
Here, the outfile argument is used to store information pertaining to all background data sets loaded for source data set 3 in the file 'sherpa.bkg'. This file will be overwritten if it already exists in the current working directory, since 'clobber' is set to True.