| Abstract : | For pulsar observations the signals from the individual antennas in
an interferometric array are usually combined together to
synthesize a single dish. To maximize the sensitivity towards a
celestial source like pulsar, the antenna signals are added in
phase (phased array). For a phased array with N identical antennas,
the signal to noise ratio (SNR) improves by a factor of N with
respect to single antenna. In conventional phased array like the
one used in the GMRT, the antenna based phases (ionospheric and
instrumental) are derived from phase calibrator observations
interleaved with the target scans. This approach of using external
field at regular intervals for deriving antenna gains is not
optimal, specially for the longer baselines and introduces
significant reduction in SNR along with adding observing overheads.
In this talk we will present a new approach of using in-field
phasing with the upgraded GMRT (uGMRT), where the antenna phases
are determined in real-time using a model for the intensity
distribution in the target field.
The antennas are kept in phase throughout the observation by
applying antenna based phase corrections derived from visibilities
that are obtained in parallel with the phased array beam data, and
which are flagged and calibrated in real-time using a model for the
continuum emission in the target field. We are probing the scope
of in-field phasing such that it can give enhanced sensitivity for
full GMRT array.
We will highlight the methodology that has been demonstrated using
few pulsars and our findings from in-field phasing experiments
during active ionospheric conditions. The time-domain sensitivity
of the GMRT improves with the in-field phasing (compared to
conventional phasing) for any number of antennas added to form a
beam. The possible applications of in-field phasing in the study of
pulsars with the GMRT will also be discussed. |
