code: def fwhm(self, **kwargs):
          
          return np.sqrt(8 * np.log(2)) * self.photbw(**kwargs)
docs: Calculate :ref:`synphot-formula-fwhm` of equivalent gaussian.
  
          Parameters
          ----------
          kwargs : dict
              See :func:`photbw`.
  
          Returns
          -------
          fwhm_val : `~astropy.units.quantity.Quantity`
              FWHM of equivalent gaussian.