A Rare Millisecond Pulsar with Cross-Pole Emission: Single-Pulse Insights from PSR J1857+0943

TL;DR

This study uses FAST to reveal, for the first time in PSR J1857+0943, component-dependent single-pulse fluctuations in an MSP. Through LRFS, 2DFS, and LRCCF analyses, it finds that MP_C3 likely shares a pole with the interpulse, while MP_C2 shows weak drifting, indicating cross-pole emission and complex magnetospheric dynamics. The averaged polarization and single-pulse PPA features further support a cross-pole configuration, with a measured one-hour jitter of $\sigma_{J,1\rm h} = 78 \pm 3$ ns at 1.25 GHz, highlighting the importance of single-pulse diagnostics for MSP emission geometry. Collectively, the results advance our understanding of how multiple emission regions contribute to MSP profiles and how jitter affects timing precision at high sensitivity.

Abstract

Studies of subpulse variability in millisecond pulsars (MSPs) offer important constraints on their emission physics. Using the high sensitivity of FAST, we present the first identification of distinct single pulse fluctuation behaviour in PSR J1857+0943. We find that the third component(MP\_C3) of the main pulse may originate from a different region than the other two main-pulse components and may instead share a common origin with the interpulse. This conclusion is supported by four observational evidence as follows: First, the LRCCF shows a clear anticorrelation between MP\_C3 and the interpulse. Second, the single-pulse polarization at the main-pulse longitude reveals obvious component mixing. Third, the modulation period of the interpulse components is roughly twice that of MP\_C3. Fourth, the reduced modulation index in MP\_C3 suggests possible mixing of emission from different regions. The interpretation in this letter contrasts with the usual assumption that the main pulse and interpulse originate from opposite magnetic poles. Hence, PSR J1857+0943 provides a rare laboratory for probing component-dependent plasma behaviour in an MSP magnetosphere. Our results offer direct evidence that the main pulse can include emission associated with more than one magnetic pole and highlight the importance of single-pulse diagnostics for understanding the geometry and dynamics of pulsars with interpulse emission. In addition, we analyse the jitter properties of this pulsar and measure a one-hour jitter of $σ_{J,1\rm h} = 78 \pm 3~\mathrm{ns}$ at 1.25 GHz, consistent with previous studies.

Figures (8)

• Figure 1: Single-pulse sequence and integrated pulse profile for PSR J1857+0943. The upper panel shows the first 200 pulses in grayscale. The middle panel displays the integrated profile from all 322,046 pulses, with the main pulse (MP) and interpulse (IP) each resolved into three components. The lower panel shows the phase-resolved modulation index computed from the full set of 322,046 pulses. The cyan dashed lines mark the boundaries of the different profile components.
• Figure 2: Longitude-resolved fluctuation power spectra for the main pulse (left) and interpulse (right) of PSR J1857+0943. The main panel in each plot shows the LRFS, the left panel displays the integrated pulse profile, and the bottom panel shows the total power spectrum of $P/P_{3}$. The total power spectrum in the bottom panel is obtained by vertically integrating the LRFS within the region enclosed by the cyan dashed lines. The red, blue, and purple curves represent the total $P/P_3$ power for the components MP_C1, MP_C2, and MP_C3, respectively.
• Figure 3: Two-dimensional fluctuation power spectra (2DFS) for the six resolved profile components of PSR J1857+0943. Each main panel presents the full spectrum as a color-coded plot, with the vertical axis representing the subpulse repetition frequency ($P/P_3$, in cycles per period, cpp) and the horizontal axis representing the longitudinal spacing repetition rate ($P/P_2$, in cpp). The left-hand side sub-panel shows the vertically integrated total $P_3$ power, where the horizontal red dashed line indicates the Gaussian fit to the spectral feature, and the horizontal red band marks the corresponding $P_3$ 3$\sigma$ uncertainty range from the fit. Similarly, the bottom sub-panel displays the horizontally integrated total $P_2$ power, in which the vertical red dashed line represents the Gaussian fit to the $P_2$ feature, and the vertical red band denotes the $P_2$ 3$\sigma$ uncertainty range.
• Figure 4: Longitude-resolved cross-correlation map with itself at a delay of $1 P$ calculated over the entire 322,046 single-pulses. The main panel shows the correlation between different longitudes as marked by the profile in both the top and left panels. The cyan dashed lines mark the boundaries of the different profile components.
• Figure 5: Polarized pulse profile for PSR J1857+0943. The top panel shows the polarized profile, where the black solid line, the red dashed line, and the blue dashed line represent the total intensity (I), linear polarization (L), and circular polarization (V), respectively. The middle panel is an expanded plot showing low-level details of the polarization profiles, with the horizontal grey dashed line indicating the baseline (0). The bottom panel shows the PPA of the average profile(yellow) and the single-pulse PPA distribution (grey scale). The cyan dashed lines mark the boundaries of the different profile components.