Mode changing in J1909$-$3744: the most precisely timed pulsar

TL;DR

This paper reports on mode switching in the highly precisely timed millisecond pulsar J1909$-$3744, demonstrating that timing only the strong mode pulses can improve overall timing precision and discussing implications for gravitational wave detection.

Contribution

It is the first detailed study of pulse mode changing in J1909$-$3744 and shows how mode-specific timing can enhance pulsar timing accuracy.

Findings

Two pulse modes identified with a 9.26 μs arrival time difference.

Timing the strong mode alone improves precision by about 10%.

Jitter noise measured at 8.20 ns, consistent with some previous measurements.

Abstract

We present baseband radio observations of the millisecond pulsar J1909$-$3744, the most precisely timed pulsar, using the MeerKAT telescope as part of the MeerTime pulsar timing array campaign. During a particularly bright scintillation event the pulsar showed strong evidence of pulse mode changing, among the first millisecond pulsars and the shortest duty cycle millisecond pulsar to do so. Two modes appear to be present, with the weak (lower signal-to-noise ratio) mode arriving $9.26$ $\pm 3.94$ $\mu$s earlier than the strong counterpart. Further, we present a new value of the jitter noise for this pulsar of $8.20 \pm 0.14$ ns in one hour, finding it to be consistent with previous measurements taken with the MeerKAT ($9 \pm 3$ ns) and Parkes ($8.6 \pm 0.8$ ns) telescopes, but inconsistent with the previously most precise measurement taken with the Green Bank telescope ($14 \pm 0.5$ ns). Timing analysis on the individual modes is carried out for this pulsar, and we find an approximate $10\%$ improvement in the timing precision is achievable through timing the strong mode only as opposed to the full sample of pulses. By forming a model of the average pulse from templates of the two modes, we time them simultaneously and demonstrate that this timing improvement can also be achieved in regular timing observations. We discuss the impact an improvement of this degree on this pulsar would have on searches for the stochastic gravitational wave background, as well as the impact of a similar improvement on all MeerTime PTA pulsars.