sherpa.astro.ui.unpack_bkg(arg, use_errors=False)

Create a PHA data structure for a background data set.

Any instrument information referenced in the header of the PHA file - e.g. with the ANCRFILE and RESPFILE, keywords - will also be loaded. Unlike unpack_pha, background files will not be loaded.

  • arg – Identify the PHA file: 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.

  • use_errors (bool, optional) – If True then the statistical errors are taken from the input data, rather than calculated by Sherpa from the count values. The default is False.



Return type

a sherpa.astro.data.DataPHA instance

See also


Load the background from a file and add it to a PHA data set.


Set the background for a data set.


>>> pha1 = unpack_arf("src1.pi")
>>> pha2 = unpack_bkg("field.pi")
>>> set_data(1, pha1)
>>> set_bkg(1, pha2)

Read in a PHA file using Crates:

>>> cr = pycrates.read_file("bg.fits")
>>> pha = unpack_pha(cr)

Read in a PHA file using AstroPy:

>>> hdus = astropy.io.fits.open("bg.fits")
>>> pha = unpack_pha(hdus)