text: import os
  
  PYBURST_PATH = os.environ['PYBURST']
  OBS_DATA_PATH = os.path.join(PYBURST_PATH, 'files', 'obs_data')
  
  full_source_labels = {'gs1826': 'gs1826-24',
                        '4u1820': '4u1820-303'}
  
  def summary_filepath(source):
      """Returns filepath to source summary table file
  
      parameters
      ----------
      source : str
      """
      filename = f'{source}.dat'
      return os.path.join(OBS_DATA_PATH, source, filename)
  
  
  def epoch_filepath(epoch, source):
      """Returns filepath to epoch file
  
      parameters
      ----------
      epoch : int
      source : str
      """
      full_source = full_source_labels[source]
      filename = f'{full_source}_{epoch}.dat'
      return os.path.join(OBS_DATA_PATH, source, filename)
  