Last modified: December 2023

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AHELP for CIAO 4.16 Sherpa


Context: data


Load an ARF from a file and add it to a PHA data set.


load_arf(id, arg=None, resp_id=None, bkg_id=None)

id - int or str, optional
resp_id - int or str, optional
bkg_id - int or str, optional


Load in the effective area curve for a PHA data set, or its background. The `load_bkg_arf` function can be used for setting most background ARFs.


Example 1

Use the contents of the file 'src.arf' as the ARF for the default data set.

>>> load_arf('src.arf')

Example 2

Read in an ARF from the file 'bkg.arf' and set it as the ARF for the background model of data set "core":

>>> load_arf('core', 'bkg.arf', bkg_id=1)


The parameters for this function are:

Parameter Definition
id The data set to use. If not given then the default identifier is used, as returned by `get_default_id` .
arg Identify the ARF: a file name, or a data structure representing the data to use, as used by the I/O backend in use by Sherpa: a tablecrate for crates, as used by CIAO, or a list of AstroPy HDU objects.
resp_id The identifier for the ARF within this data set, if there are multiple responses.
bkg_id Set this to identify the ARF as being for use with the background.


The function does not follow the normal Python standards for parameter use, since it is designed for easy interactive use. When called with a single un-named argument, it is taken to be the `arg` parameter. If given two un-named arguments, then they are interpreted as the `id` and `arg` parameters, respectively. The remaining parameters are expected to be given as named arguments.

If a PHA data set has an associated ARF - either from when the data was loaded or explicitly with the `set_arf` function - then the model fit to the data will include the effect of the ARF when the model is created with `set_model` or `set_source` . In this case the `get_source` function returns the user model, and `get_model` the model that is fit to the data (i.e. it includes any response information; that is the ARF and RMF, if set). To include the ARF explicitly, use `set_full_model` .

The `minimum_energy` setting of the `ogip` section of the Sherpa configuration file determines the behavior when an ARF with a minimum energy of 0 is read in. The default is to replace the 0 by the value 1e-10, which will also cause a warning message to be displayed.


See the bugs pages on the Sherpa website for an up-to-date listing of known bugs.

See Also

dataspace1d, dataspace2d, datastack, fake, get_arf, get_bkg, get_bkg_arf, get_bkg_model, get_bkg_rmf, get_bkg_source, load_arrays, load_ascii, load_bkg, load_bkg_arf, load_bkg_rmf, load_data, load_grouping, load_image, load_multi_arfs, load_multi_rmfs, load_pha, load_quality, load_rmf, load_staterror, load_syserror, load_table, pack_image, pack_pha, pack_table, set_arf, unpack_arf, unpack_arrays, unpack_ascii, unpack_bkg, unpack_data, unpack_image, unpack_pha, unpack_rmf, unpack_table
get_default_id, list_bkg_ids, list_data_ids, list_response_ids
add_model, add_user_pars, get_response, load_table_model, load_template_interpolator, load_template_model, load_user_model, save_model, save_source
save_arrays, save_data, save_delchi, save_error, save_filter, save_grouping, save_image, save_pha, save_quality, save_resid, save_staterror, save_syserror, save_table