Abstract
Evidence for a low-frequency gravitational-wave background using pulsar
timing arrays has generated recent interest into its underlying contributing
sources. However, multiple investigations have seen that the significance of
the evidence does not change with choice of pulsar modeling techniques but the
resulting parameters from the gravitational wave searches do. PSR J1455-3330 is
one of the longest-observed pulsars in the array monitored by the North
American Nanohertz Observatory for Gravitational Waves (NANOGrav) but showed no
evidence for long-timescale red noise, either intrinsic or the common signal
found among many pulsars in the array. In this work, we argue that NANOGrav's
piecewise-constant function used to model variations in
radio-frequency-dependent dispersive delay should not be used for this pulsar,
and a much simpler physical model of a fixed solar wind density plus a linear
trend in dispersion measure is preferred. When the original model is replaced,
(i) the pulsar's timing parallax signal changes from an upper limit to a
significant detection, (ii) red noise becomes significant, and (iii) the red
noise is consistent with the common signal found for the other pulsars. Neither
of these signals are radio-frequency dependent. While the same physical
motivation will not apply to many of the pulsars currently used in pulsar
timing arrays, we argue for careful physically-motivated timing and noise
modeling of pulsars used in precision timing experiments.