Holographic Beam Mapping of the CHIME Pathfinder Array
  The Canadian Hydrogen Intensity Mapping Experiment (CHIME) Pathfinder radio
telescope is currently surveying the northern hemisphere between 400 and 800
MHz. By mapping the large scale structure of neutral hydrogen through its
redshifted 21 cm line emission between $z \sim 0.8-2.5$ CHIME will contribute
to our understanding of Dark Energy. Bright astrophysical foregrounds must be
separated from the neutral hydrogen signal, a task which requires precise
characterization of the polarized telescope beams. Using the DRAO John A. Galt
26 m telescope, we have developed a holography instrument and technique for
mapping the CHIME Pathfinder beams. We report the status of the instrument and
initial results of this effort.
