Abstract
Pulsar timing array experiments have recently uncovered evidence for a
nanohertz gravitational wave background by precisely timing an ensemble of
millisecond pulsars. The next significant milestones for these experiments
include characterizing the detected background with greater precision,
identifying its source(s), and detecting continuous gravitational waves from
individual supermassive black hole binaries. To achieve these objectives,
generating accurate and precise times of arrival of pulses from pulsar
observations is crucial. Incorrect polarization calibration of the observed
pulsar profiles may introduce errors in the measured times of arrival. Further,
previous studies (e.g., van Straten 2013; Manchester et al. 2013) have
demonstrated that robust polarization calibration of pulsar profiles can reduce
noise in the pulsar timing data and improve timing solutions. In this paper, we
investigate and compare the impact of different polarization calibration
methods on pulsar timing precision using three distinct calibration techniques:
the Ideal Feed Assumption (IFA), Measurement Equation Modeling (MEM), and
Measurement Equation Template Matching (METM). Three NANOGrav pulsars-PSRs
J1643$-$1224, J1744$-$1134, and J1909$-$3744-observed with the 800 MHz and 1.5
GHz receivers at the Green Bank Telescope (GBT) are utilized for our analysis.
Our findings reveal that all three calibration methods enhance timing precision
compared to scenarios where no polarization calibration is performed.
Additionally, among the three calibration methods, the IFA approach generally
provides the best results for timing analysis of pulsars observed with the GBT
receiver system. We attribute the comparatively poorer performance of the MEM
and METM methods to potential instabilities in the reference noise diode
coupled to the receiver and temporal variations in the profile of the reference
pulsar, respectively.