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A Rare Non-drifting State in the Subpulse Drifting Pulsar PSR J1059-5742

Using Parkes radio telescope observations, this study identifies a rare, brighter non-drifting emission state in pulsar PSR J1059-5742 that accounts for 3.8% of the observing time and suggests a mode change in the polar-cap discharge process, distinct from the dominant drifting state and nulling behavior.

Original authors: Lunhua Shang, Huixin Ma

Published 2026-09-01

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CC BY 4.0

Original authors: Lunhua Shang, Huixin Ma

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Deep in the cosmos, spinning like lighthouses, are neutron stars known as pulsars. These are the dense, collapsed cores of massive stars that have exploded, now rotating so fast that they sweep beams of radio waves across the universe with clockwork precision. To the radio telescopes listening from Earth, these beams arrive as regular pulses, a heartbeat that never seems to skip a beat. However, for astronomers, the story is rarely that simple. Sometimes, the rhythm changes. The pulses might flicker out entirely for a moment, or the bright spots within the pulse might shift their position, sliding backward or forward with every rotation. This shifting, known as subpulse drifting, is a clue to the invisible machinery inside the star. Scientists believe these shifts are caused by a carousel of electrical discharges spinning near the star's magnetic pole, but the rules governing how this carousel moves, or why it sometimes stops, remain one of the great puzzles of stellar physics.

A team of researchers recently turned their attention to a specific pulsar, PSR J1059−5742, located about 1,600 light-years away. Using the massive 64-meter Parkes radio telescope in Australia, they listened to this star for two hours, capturing thousands of individual pulses to see exactly how it behaved. What they found was a star that mostly played by the rules but occasionally broke them in a surprising way. For the vast majority of the time, the pulsar behaved exactly as expected: the bright spots within its radio pulse drifted steadily backward, like a pattern moving across a spinning wheel. This drifting state accounted for more than 96 percent of the star's activity. The researchers measured this drift carefully, noting that the pattern took about 5.7 rotations to complete a full cycle and that the bright spots were spaced roughly 5.6 degrees apart.

But then, the star did something rare. Twice during the observation, the drifting pattern simply stopped. Instead of the bright spots sliding backward, they froze in place, holding a steady position while the star continued to spin. During these moments, the radio signal became noticeably brighter and the shape of the pulse changed slightly, becoming more symmetrical and narrower than usual. These "non-drifting" episodes were short-lived, lasting for about 107 and 108 rotations respectively, and together they made up less than 4 percent of the total time. The researchers also noticed that the pulsar occasionally went completely silent for just one or two beats, a phenomenon called nulling, but only when it was in the drifting state. When the star switched to the rare, frozen state, the silence never happened.

The discovery suggests that the engine driving the pulsar's radio beams is more complex than a single, steady machine. The drifting state fits a model where a ring of electrical sparks spins around the star's magnetic pole, creating the sliding pattern. However, the sudden switch to a brighter, stationary state implies that the entire configuration of these sparks can change abruptly. It is as if the carousel of sparks suddenly locks into a different gear or rearranges itself entirely, altering how the radio beam is fired. The fact that the silence only occurs when the sparks are moving, and not when they are frozen, hints that the mechanism causing the star to go quiet is tied specifically to the movement of these sparks. While the researchers cannot yet say exactly what causes the star to switch modes, their work provides a clear, real-world example of a pulsar changing its behavior, offering a new window into the turbulent physics of the star's magnetic pole.

Technical Summary: A Rare Non-drifting State in the Subpulse Drifting Pulsar PSR J1059−5742

Problem and Context
Rotation-powered pulsars are believed to generate coherent radio emission via spark discharges in the polar-cap regions of their magnetospheres. The classic inner-gap model (Ruderman & Sutherland, 1975) and the subsequent carousel model describe how these sparks circulate, producing characteristic subpulse drifting. While phenomena such as nulling (temporary cessation of emission) and mode changing (abrupt switching between quasi-stable states) are known, the specific interplay between subpulse drifting, nulling, and rare non-drifting states in individual pulsars requires further investigation. PSR J1059−5742, a pulsar with a rotation period of 1.185 s and a characteristic age of 4.36 Myr, was identified as a candidate for such study due to its known drifting behavior.

Methodology
The authors conducted single-pulse observations of PSR J1059−5742 using the 64-m Parkes radio telescope equipped with the Ultra-Wideband Low-Noise (UWL) receiver. The observation, conducted on December 27, 2018, utilized a center frequency of 1369 MHz with a 256 MHz bandwidth, recording 5,681 single pulses over approximately two hours.

The data processing pipeline involved:

De-dispersion and Folding: Single pulses were de-dispersed and folded into 512 phase bins using DSPSR, based on ephemeris from the ATNF catalogue.
RFI Mitigation: Narrow-band radio-frequency interference was removed using PSRCHIVE.
Nulling Analysis: Pulse energies were calculated by summing intensities within the emission window (defined as the range where the mean profile exceeds 10% of its peak). A $3\sigma$ threshold (where $\sigma$ is derived from off-pulse noise) was used to classify pulses as "null" or "burst."
Drifting Analysis: Fluctuation-spectral analysis was performed using PSRSALSA to compute the Longitude-Resolved Fluctuation Spectrum (LRFS) and the Two-Dimensional Fluctuation Spectrum (2DFS). This allowed for the measurement of the drift period ( $P_3$ ) and subpulse phase spacing ( $P_2$ ).
State Classification: To identify non-drifting states, the single pulses were grouped into sub-integrations of five consecutive pulses. A mode metric ( $\Delta\chi^2$ ) was calculated by comparing each sub-integration against templates of the drifting and non-drifting states. A bimodal distribution of this metric was used to separate the two states, with a requirement of at least three consecutive sub-integrations to confirm a state change.

Key Results
The analysis revealed three distinct emission states for PSR J1059−5742:

Dominant Drifting State: The pulsar spends 96.2% of the observation time in a subpulse-drifting state.
- Parameters: The drift period is $P_3 = 5.7 \pm 0.5 P$ (where $P$ is the spin period), and the subpulse phase spacing is $P_2 = 5.6 \pm 0.7^\circ$ .
- Drift Direction: Subpulses drift toward earlier longitudes (negative drifting) at a rate of $D = 0.98 \pm 0.15^\circ$ per pulse period.
- Model Consistency: The parameters suggest an aliased drift. Using a carousel model with $n \approx 66$ sparks, the intrinsic drift period is estimated at $P'_3 \approx 1.2 P$ , and the carousel circulation period is $P_4 \approx 80 P$ . This is consistent with the partially screened gap (PSG) model, as the pulsar lies within the population showing an anti-correlation between $P_3$ and spin-down energy loss ( $\dot{E}$ ).
Rare Non-Drifting State: Two distinct non-drifting episodes were detected, lasting approximately 108 and 107 rotation periods, respectively. These events account for 3.8% of the total observing time.
- Characteristics: In this state, the pulsar is brighter, and the subpulse structure disappears, resulting in a phase-stationary profile.
- Profile Differences: The average profile in the non-drifting state peaks at a phase of $\sim 47.3^\circ$ , leading the drifting state peak ( $\sim 49.4^\circ$ ) by about $2^\circ$ . The non-drifting profile is also slightly narrower and more symmetric than the drifting profile.
Nulling: The pulsar exhibits a nulling fraction (NF) of $13 \pm 1\%$ .
- Duration and Location: Nulls are short, typically lasting one to two pulse periods (rarely up to six). Crucially, nulls occur exclusively within the drifting state; no nulls were identified during the non-drifting episodes.

Significance and Conclusions
The paper establishes PSR J1059−5742 as a clean example of a carousel-driven drifting pulsar where the occasional cessation of drifting reveals a mode change in the polar-cap discharge.

Physical Interpretation of Nulls: The short, isolated nulls occurring only in the drifting state are interpreted within the rotating-carousel picture. They likely correspond to the line of sight passing through gaps between adjacent sparks (pseudo-nulls) or the temporary extinction of a sampled spark, rather than a global magnetospheric reconfiguration.
Physical Interpretation of the Non-Drifting State: The abrupt transition to a brighter, phase-stationary, non-drifting state suggests a fundamental change in the polar-cap discharge structure or magnetospheric configuration, rather than a simple geometric effect. The phase shift of the profile peak implies a potential change in emission altitude or the magnetic azimuth sampled by the line of sight.
Limitations: The authors note that these conclusions are based on a single epoch. While the drift parameters appear stable compared to previous independent observations, multi-epoch observations with polarimetry are required to verify the stability of the drift parameters and to constrain the emission height and physical origin of the mode change.

The study underscores that changes in the polar-cap discharge process can manifest as distinct, rare non-drifting states, offering a window into the complex dynamics of pulsar magnetospheres.

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