Multi-Faceted Emission Properties of PSR J2129+4119 Observed with FAST

TL;DR

This study provides the first high-sensitivity single-pulse analysis of PSR J2129+4119 using FAST, revealing rich magnetospheric activity despite its low energy loss rate ($P=1.69\ \mathrm{s}$, $\dot{E}\approx0.65\times10^{30}\ \mathrm{erg\ s^{-1}}$) well below the death line. The authors identify three emission states (null, weak, regular) via a multimodal pulse-energy distribution, quantify nulling with $\mathrm{NF}=8.13\%\pm0.51\%$, and document long-term drift and beat-like subpulse modulations with well-defined $P_3$ and $P_2$ values, as well as quasi-periodic microstructure in a substantial fraction of regular pulses. Polarization analyses and RVM fitting show near-tangential geometry with $\beta\approx-3^{\circ}$ and an emission height around $h_{\mathrm{em}}\approx178\ \mathrm{km}$, consistent with aberration/retardation effects. The observation of a scintillation arc with curvature $\eta=0.342\pm0.072\ \mu\mathrm{s}/\mathrm{MHz^2}$ implies a localized scattering screen, highlighting propagation effects as a contributor to the observed variability. Collectively, these results demonstrate that coherent radio emission can persist in low-$\dot{E}$ pulsars and provide constraints on emission physics near the death line, including magnetospheric reactivation processes and the role of propagation effects.

Abstract

We present a detailed single-pulse study of the long-period pulsar PSR J2129+4119 using high-sensitivity FAST observations. Despite locating well below the traditional death line, the pulsar exhibits sustained and multi-modal emission behavior, including nulls, weak pulses, regular emission, and occasional bright pulses. The nulling fraction is measured to be $8.13\% \pm 0.51\%$, with null durations typically under four pulse periods. Fluctuation spectral analysis reveals both phase-modulated subpulse drifting and intermittent beat-like modulation. At the same time, polarization profiles show high linear polarization and stable polarization position angle (PPA) swings consistent with a near-tangential sightline geometry. Quasi-periodic microstructures are detected in 11.54\% of regular pulses, with a mean periodicity and width of 4.57 ms and 4.30 ms, respectively. A well-defined scintillation arc in the secondary spectrum confirms the presence of a localized scattering screen. These results indicate that PSR J2129+4119 remains magnetospherically active and coherently emitting despite its low energy loss rate, offering key insights into pulsar emission physics near the death line.

Figures (18)

• Figure 1: Pulse stacks of PSR J2129+4119 observed on 2024 September 29, showing three distinct behaviors: steady drifting (left), intermittent drifting with breaks (middle), and beat-like modulation (right).
• Figure 2: Pulse energy distributions for PSR J2129+4119. The magenta curve represents the Gaussian fit to the off-pulse distribution, while the yellow curve shows the composite fit to the on-pulse distribution using three Gaussian components. The blue, green, and red Gaussian components correspond to the null, weak, and regular emission states, respectively. The $x$-axis represents pulse energy normalized by the mean on-pulse energy.
• Figure 3: Integrated pulse profiles of PSR J2129+4119 for regular (red), weak (green), and null (blue) pulses. The regular and weak profiles are normalized to the integrated profile of the entire observation (black).
• Figure 4: Bright pulse profile at pulse numbers 686 (green) and 1143 (blue) compared with the integrated profile from the entire observation (black). The red line represents the integrated profile of all bright pulses detected.
• Figure 5: Polarization properties of PSR J2129+4119 for three cases: regular (red), weak (green), and the entire observation (black). Top panel: Position angle (PPA) as a function of pulse phase, with best-fit RVM curves for the full observation (magenta) and regular mode (cyan). The intersection of the vertical and horizontal dashed lines marks the point of steepest PPA gradient. Bottom panel: Normalized Stokes parameters of the total intensity ($I$), linear polarization ($L$), and circular polarization ($V$) are plotted across pulse phase for all three datasets. All values are normalized to the peak intensity of the entire observation profile.