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15 PULSAR OBSERVATIONS
Pulsar observing remains 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 software correlator
(Section 7):
- 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
(Section 20.1) 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 (Section 7.4) 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).
Next: 16 SPECTRAL LINE OBSERVATIONS
Up: VERY LONG BASELINE ARRAY
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Jon Romney
2012-01-05