Correct the HEASARC link
@@ -148,7 +148,7 @@ def wstat(n_on, n_off, alpha, mu_sig, mu_bkg=None, extra_terms=True):
* `Habilitation M. de Naurois, p. 141
<http://inspirehep.net/record/1122589/files/these_short.pdf>`_
* `XSPEC page on Poisson data with Poisson background
- <https://heasarc.nasa.gov/xanadu/xspec/manual/XSappendixStatistics.html>`_
+ <https://heasarc.gsfc.nasa.gov/xanadu/xspec/manual/XSappendixStatistics.html>`_
"""
# Note: This is equivalent to what's defined on the XSPEC page under the
# following assumptions
