Pulsar Observations
Pulsar observing is an expert mode of the VLBA, requiring additional understanding and effort on the part of the user. Those willing to learn to use them can take advantage of the following enhanced capabilities supporting pulsar observations, available in the DiFX correlator:
- Binary Gating: A simple pulse-phase driven on-off accumulation window can be specified, with "on" and "off" phases. Such gating increases the signal to noise ratio of pulsar observations by a factor of typically 3 to 6, and can also be used to search for off-pulse emission.
- Matched-filter Gating: If the pulse profile at the observation frequency is well understood and the pulse phase is very well predicted by the provided pulse ephemeris, additional signal to noise over binary gating can be attained by appropriately scaling the correlation coefficients as a function of pulse phase. Depending on the pulse shape, additional gains of up to 50% in sensitivity over binary gating can be realized.
- Pulsar Binning: This mode entails generating a separate visibility spectrum for each requested range of pulse phase. There are no explicit limits to the number of pulse phase bins that are supported, however, data rates can become increasingly large. Currently AIPS does not support databases with multiple phase bins. Until post-processing support is available, a separate FITS file will be produced for each pulsar phase bin.
In all cases, the user will be responsible for providing a pulsar spin ephemeris. Except for certain applications of mode 3, the ephemeris must be capable of predicting the absolute rotation phase of the pulsar. Pulsar modes incur a minimum correlation-time penalty of about 50%. High output data rates may require greater correlator resource allocations. Details of pulsar observing, including practical aspects of using the pulsar modes, and limitations imposed by operations, are documented by Brisken (2009).
