code: def merge_DA_ph_times(ph_times_d, ph_times_a):
      
      ph_times = np.hstack([ph_times_d, ph_times_a])
      a_em = np.hstack([np.zeros(ph_times_d.size, dtype=np.bool),
                        np.ones(ph_times_a.size, dtype=np.bool)])
      index_sort = ph_times.argsort()
      return ph_times[index_sort], a_em[index_sort]
docs: Returns a merged timestamp array for Donor+Accept. and bool mask for A.