Mysterious Pulsar J2144-5237 Reveals Polarization Shifts Over Time

A team of astronomers has conducted the first detailed study of millisecond pulsar J2144-5237, uncovering striking variations in its polarisation over time. Led by Rahul Sharan, Bhaswati Bhattacharyya, Simon Johnston, and colleagues, the research sheds new light on how the pulsar's magnetic field and surrounding environment interact with its white dwarf companion.

Observations were carried out using the Parkes UWL receiver, with data collected on 29 May 2023, 22 June 2023, 26 August 2023, and 28 May 2025. The team processed this information using PSRPYPE and CLFD3 software, while also developing a new tool to track time-varying spectral changes across all Stokes parameters.

The study revealed systematic shifts in the pulsar's polarisation, linked to its rotational phase. Unlike some other pulsars, J2144-5237 did not show sign-changing Stokes parameters. Instead, its rotation measure (RM) fluctuated between 22 and 31 rad/m² over its roughly 10-day orbital cycle.

These variations were primarily driven by the white dwarf companion's magnetosphere. Density changes in the intrabinary medium and a bow shock during superior conjunction played key roles, as earlier noted by Johnston et al. in MeerKAT observations. The team also calibrated their data carefully, accounting for ionospheric effects with Spinifex software.

A Poincaré sphere representation illustrated how the pulsar's polarisation properties shifted over time. The findings highlight the complex interplay between the pulsar's emission, its magnetic field, and the interstellar environment.

The research marks a significant step in exploring the spectro-polarimetric behaviour of pulsars, an area that remains largely unexplored. By demonstrating correlated changes in Stokes I, Q, and V—alongside intricate patterns in Stokes U—the study provides a clearer picture of J2144-5237's physics. These results could help refine models of pulsar magnetospheres and their interactions with companion stars.