# Relativistic spin precession in the binary PSR J1141$-$6545

## TL;DR

This study analyzes the relativistic spin precession of pulsar PSR J1141-6545 to understand its emission geometry and predicts its future observational visibility based on Bayesian modeling.

## Contribution

It provides the first polarization-independent estimate of the pulsar's beam scale factor and models its precessional evolution using multiple prior distributions.

## Key findings

- Line-of-sight crossed the magnetic pole around MJD 54000.
- Pulsar likely to precess out of line-of-sight in 3-5 years.
- Estimated beam scale factor > 6 deg s^{0.5} at 1.4 GHz.

## Abstract

PSR J1141$-$6545 is a precessing binary pulsar that has the rare potential to reveal the two-dimensional structure of a non-recycled pulsar emission cone. It has undergone $\sim 25 \deg$ of relativistic spin precession in the $\sim18$ years since its discovery. In this paper, we present a detailed Bayesian analysis of the precessional evolution of the width of the total intensity profile, to understand the changes to the line-of-sight impact angle ($\beta$) of the pulsar using four different physically motivated prior distribution models. Although we cannot statistically differentiate between the models with confidence, the temporal evolution of the linear and circular polarisations strongly argue that our line-of-sight crossed the magnetic pole around MJD 54000 and that only two models remain viable. For both these models, it appears likely that the pulsar will precess out of our line-of-sight in the next $3-5$ years, assuming a simple beam geometry. Marginalising over $\beta$ suggests that the pulsar is a near-orthogonal rotator and provides the first polarization-independent estimate of the scale factor ($\mathbb{A}$) that relates the pulsar beam opening angle ($\rho$) to its rotational period ($P$) as $\rho = \mathbb{A}P^{-0.5}$ : we find it to be $> 6 \rm~deg~s^{0.5}$ at 1.4 GHz with 99\% confidence. If all pulsars emit from opposite poles of a dipolar magnetic field with comparable brightness, we might expect to see evidence of an interpulse arising in PSR J1141$-$6545, unless the emission is patchy.