A 34 Yr Timing Solution of the Redback Millisecond Pulsar Terzan 5A

TL;DR

This paper presents a comprehensive 34-year timing solution for the redback millisecond pulsar Terzan 5A, revealing its high variability, orbital decay, and implications for pulsar timing techniques.

Contribution

It provides the longest timing solution for a redback pulsar, demonstrating the pulsar's high variability and the need for careful short-term timing for accurate measurements.

Findings

Ter5A exhibits the noisiest timing behavior among known redbacks.

No strong correlation between orbital and spin variability was observed.

Orbital period contraction is consistent with general relativistic decay.

Abstract

We present a 34-year timing solution of the redback pulsar system Terzan 5A (Ter5A). Ter5A, also known as B1744$-$24A or J1748$-$2446A, has a 11.56 ms pulse period, a $\sim$0.1 solar mass dwarf companion star, and an orbital period of 1.82 hours. Ter5A displays highly variable eclipses and orbital perturbations. Using new timing techniques, we have determined a phase-connected timing solution for this system over 34 years. This is the longest ever published for a redback pulsar. We find that the pulsar's spin variability is much larger than most globular cluster pulsars. In fact, of the nine redback pulsars with published or in preparation long-term timing solutions, Ter5A is by far the noisiest. We see no evidence of strong correlations between orbital and spin variability of the pulsar. We also find that long-term astrometric timing measurements are likely too contaminated by this variability to be usable, and therefore require careful short-term timing to determine reasonable positions. Finally, we measure an orbital period contraction of $-2.5(3) \times 10^{-13}$, which is likely dominated by the general relativistic orbital decay of the system. The effects of the orbital variability due to the redback nature of the pulsar are not needed to explain the observed orbital period derivative, but they are constrained to less than $\sim$30% of the observed value.