code: def shift(self, delta):
          
          self.x0 = self.x0 + Quantity(delta, self.xunit)
docs: Shift this `Series` forward on the X-axis by ``delta``
  
          This modifies the series in-place.
  
          Parameters
          ----------
          delta : `float`, `~astropy.units.Quantity`, `str`
              The amount by which to shift (in x-axis units if `float`), give
              a negative value to shift backwards in time
  
          Examples
          --------
          >>> from gwpy.types import Series
          >>> a = Series([1, 2, 3, 4, 5], x0=0, dx=1, xunit='m')
          >>> print(a.x0)
          0.0 m
          >>> a.shift(5)
          >>> print(a.x0)
          5.0 m
          >>> a.shift('-1 km')
          -995.0 m