Temporal Variations in Pulsar Spectro-Polarimetry: Findings from millisecond pulsar J2144-5237 using Parkes UWL receiver

TL;DR

The paper addresses how pulsar spectro-polarimetric properties evolve in time, particularly for the MSP J2144−5237 in a binary, using the Parkes UWL to obtain full-Stokes spectra across approximately 0.7–4 GHz. It introduces a processing workflow to track time-resolved Stokes spectra, apply ionospheric RM corrections, estimate $RM$ in ~20-minute chunks, and visualize polarization via the Poincaré sphere. Key findings include $RM$ variation in the range $22$–$31 \,rad\,m^{-2}$ with no clear orbital-phase dependence, correlated evolution of Stokes $I$, $Q$, and $L$, phase-dependent $U$ behavior, and the first reported GPS-like polarization turnover in an MSP, with Poincaré-sphere trajectories revealing component- and phase-dependent polarization changes. These results highlight the potential of time-varying spectro-polarimetry to probe emission mechanisms, magnetospheric propagation, and binary interactions, motivating broader, higher-cadence, multi-frequency studies across MSPs.

Abstract

While the temporal variations of the spectro-polarimetric nature of pulsars remains unexplored, this investigation offers significant potential for uncovering key insights into pulsar emission mechanisms, magnetic field geometry, and propagation effects within the magnetosphere. We developed a package for investigating time-varying spectral behavior for full Stokes parameters and demonstrate it on a millisecond pulsar (MSP) J2144-5237 in a binary system (orbital period ~10 days) using the Parkes UWL receiver. In this study we report rotation measure (RM) variation with orbital phase. We find that the temporal variations in the spectra of Stokes I, Q, and V are generally correlated throughout the orbit, while Stokes U exhibits intervals of both correlation and anticorrelation with Stokes I, depending on the orbital phase. We also provide a Poincare sphere representation of the polarization properties of J2144-5237, demonstrating a systematic temporal change of Poincare sphere location for the main component with orbital phase. To our knowledge, this is the first investigation of time-varying properties of the spectro-polarimetric nature of any pulsars or MSPs. Extending this study to probe the spectro-temporal nature of full Stokes data on a larger sample of MSPs or pulsars has the potential to provide vital information on emission mechanisms inside the magnetosphere, interstellar propagation effects, and binary interactions.

Figures (7)

• Figure 1: Temporal evolution of RM (in $rad \: m^{-2}$) across the orbital phase for all observing epochs.
• Figure 2: Results from Spectro-polarimetric analysis of Parkes UWL data for PSR J2144$-$5237 considering all the components (marked in coloured dots in the $2^{nd}$ row of the Figure). The columns display Stokes parameters ($I$, $Q$, $U$, $V$), linear polarization ($L$), and a Poincaré representation of Stokes $Q$, $U$, and $V$. The $1^{st}$ row shows spectral-temporal variations for start, middle, and end time chunks denoted as $TC_S$, $TC_M$ and $TC_E$, while the $2^{nd}$ row provides time-frequency averaged Stokes profiles and the corresponding Poincaré sphere representation. The coloured dots, in the $2^{nd}$ row, in the Stokes $I$ and $L$ profiles (columns 1 and 5, respectively) serve as a visual aid for mapping the phase bin points onto the Poincaré sphere. The last three rows display time-averaged spectra for three different time chunks ($F(\nu)_S$, $F(\nu)_M$,$F(\nu)_E$ corresponds to the flux density at the start, middle and end time chunks of the observing epoch) and the corresponding Poincaré sphere representations.
• Figure 3: The Figure presents the Spectro-polarimetric results obtained from analysis of Parkes UWL data for PSR J2144$-$5237 observed on 22 June 2023, only for the main component. The Figure description is same as Figure \ref{['All_comp_spectra_fig']}.
• Figure 4: The Figure presents the Spectro-polarimetric results obtained from analysis of Parkes UWL data for PSR J2144$-$5237 observed on 29 May 2023, only for the main component. The Figure description is same as Figure \ref{['All_comp_spectra_fig']}. Since this epoch has low SNR for polarized signal, an average along phase bin axis by a factor of 8 was taken which results into 128 phase bins.
• Figure 5: The figure illustrates the Pearson correlation coefficient along with corresponding $p$ values. We plot the correlation for which the $p$ values are less than 0.05