Pulsar J1059-5742 Caught in a Rare Non-Drifting Emission State

Deep in the southern sky, a rotating neutron star has been caught doing something it almost never does. PSR J1059-5742, a radio pulsar whose emission normally marches steadily across its pulse window, was observed by astronomers using the 64-m Parkes radio telescope in Australia to briefly abandon its signature behavior. In a single-pulse study published in Astrophysics and Space Science, researchers L. H. Shang and H. X. Ma of Guizhou Normal University report that the vast majority of the pulsar’s radio emission comes in a subpulse-drifting state, but that two rare events revealed a brighter, non-drifting mode that persisted for just over a hundred rotation periods each. The discovery offers a fresh window into the physics of pulsar magnetospheres, the twisted plasma-filled environments where some of the universe’s most extreme physics plays out on timescales of milliseconds.

Subpulse drifting is one of the most striking phenomena in radio pulsar astronomy. Rather than emitting a perfectly repeating pulse, many pulsars produce subpulses, discrete blobs of radio emission within the broader pulse profile, that shift systematically in spin longitude from one rotation to the next. When these subpulses are tracked across successive pulses, they appear to march, or drift, through the pulse window in a quasi-regular pattern. The prevailing interpretation, rooted in the polar-cap spark model developed by Michael Ruderman and Peter Sutherland in 1975 and refined by Jaroslaw Gil and colleagues, is that the drifting reflects a carousel of spark-associated plasma columns rotating around the star’s magnetic pole. As these sparks circulate, the radio beams they generate sweep across our line of sight at slightly different longitudes each rotation, producing the characteristic drifting pattern. The rate at which subpulses drift, and the spacing between drift bands, encode information about the geometry of the emission region and the conditions in the pulsar’s inner acceleration region.

For PSR J1059-5742, the new analysis shows that this carousel behavior dominates the star’s output to a remarkable degree. The team found that 96.2 percent of the pulsar’s radio radiation occurs in the drifting state, with subpulses drifting toward earlier longitudes across successive rotations. Quantitatively, the drift pattern is characterized by a vertical drift period of P3 equal to 5.7 plus or minus 0.5 times the pulsar’s spin period, meaning a full drift cycle repeats roughly every six rotations, and a horizontal spacing of P2 equal to 5.6 plus or minus 0.7 degrees of spin longitude. These parameters place J1059-5742 among the growing catalog of pulsars whose drifting behavior can be precisely characterized, joining objects studied in surveys such as the Meterwavelength Single-pulse Polarimetric Emission Survey and the Thousand-Pulsar-Array programme on MeerKAT, which have catalogued subpulse modulation across more than a thousand pulsars.

But the real surprise came from the small fraction of time when the drifting stopped. The Parkes single-pulse observation revealed two distinct non-drifting state events, each lasting 107 and 108 consecutive rotation periods respectively. Together these two episodes accounted for just 3.8 percent of the total observing time, making them genuinely rare interruptions to an otherwise relentlessly periodic pattern. During these events, the subpulses did not march across the pulse window at all; instead, the emission remained anchored at fixed longitudes, rotation after rotation, for stretches lasting on the order of a hundred spins. Given that pulsars rotate with clockwork regularity, often hundreds of times per second or, in slower cases, roughly once per second, a hundred-rotation interval represents a brief but unmistakable episode of magnetospheric reorganization.

What makes these events even more intriguing is that the emission did not merely stop drifting; it changed character. Single pulses recorded during the non-drifting state were brighter than those in the drifting state, and the peak of the average pulse profile for the non-drifting state led that of the drifting state by about 2 degrees in spin longitude. That longitudinal shift is small in absolute terms, a tiny sliver of the pulse phase, but it is systematic and measurable, and it signals that something physical changed in the emission geometry. The authors interpret this as evidence that changes may have occurred in the polar-cap discharge process or in the magnetospheric configuration itself. In other words, the carousel of sparks that normally produces the drifting pattern may have temporarily halted its rotation, or the entire discharge mechanism underpinning the radio emission may have switched to a different operating mode.

This interpretation connects J1059-5742 to a broader family of pulsar state-switching phenomena. Pulsars are known to alternate between emission modes, a behavior called mode changing, in which the average pulse profile abruptly switches between two or more stable shapes. Some pulsars also exhibit nulling, in which the radio emission ceases entirely for stretches of time, a phenomenon first reported by Donald Backer in 1970. More dramatically, the landmark 2010 study by Andrew Lyne and colleagues published in Science showed that switched magnetospheric states in several pulsars correlate with changes in the rate at which the stars spin down, implying that the magnetosphere and the star’s rotational evolution are intimately linked. The occasional cessation of drifting in J1059-5742 may represent a milder cousin of these phenomena, a mode change confined to the polar-cap discharge rather than a global magnetospheric reconfiguration.

The energy analysis of individual pulses added another layer to the picture. By examining the energies of all detected single pulses, the team found that the pulsar may have a nulling fraction of 13 plus or minus 1 percent, meaning that roughly one pulse in eight simply fails to appear. Notably, the study found that pulse nulling occurs only within the drifting state. The non-drifting state, despite its rarity, never nulls; when the pulsar enters this mode, it shines steadily and brightly. This asymmetry suggests that the two states represent genuinely different plasma conditions above the magnetic pole. In the drifting state, the spark discharge is active but intermittent, occasionally failing to produce detectable emission. In the non-drifting state, the discharge appears to operate in a more stable, luminous configuration, one in which the emission is both stronger and more reliable.

The theoretical stakes here are considerable. In the Ruderman-Sutherland framework, the inner acceleration region above the pulsar’s polar cap sustains a large electric field that tears charges from the stellar surface in discrete spark discharges. The pattern of these sparks, their number, their spacing, and their circulation speed around the magnetic axis, determines the observed drifting parameters. A halt in the carousel motion implies that the conditions governing the spark plasma’s E-cross-B drift, the electric and magnetic field interplay that carries the plasma around the pole, changed abruptly and then reverted. Alternatively, the magnetospheric configuration, the large-scale geometry of field lines and currents threading the light cylinder, may have shifted into a different stable state. Distinguishing between these possibilities requires comparing J1059-5742 with other pulsars that show similar behavior, such as PSR B1918+19, which displays drifting, moding, and nulling in combination, or PSR J1326-6700, a well-studied mode switcher.

For now, J1059-5742 joins a short list of pulsars in which drifting has been observed to stop entirely while emission continues. Each such object constrains the models in a different way, and the fact that the non-drifting state here is brighter and longitudinally offset rather than dimmer makes it a particularly clean diagnostic. The authors suggest that the occasional cessation of drifting in PSR J1059-5742 may thus reveal a mode change of the polar-cap discharge, a conclusion that, if confirmed by longer observations and multi-frequency follow-up, would add an important piece to the puzzle of how pulsars generate their beams. As single-pulse studies with instruments like Parkes, FAST, and MeerKAT accumulate ever larger samples, rare events like these two hundred-rotation episodes are shifting from curiosities into quantitative tests of the physics of neutron-star magnetospheres, reminding astronomers that even the most regular clocks in the universe occasionally change their tune.

Subject of Research: A single-pulse radio study of the subpulse-drifting pulsar PSR J1059-5742 revealing a rare brighter non-drifting emission state and pulse nulling.

Article Title: A rare non-drifting state in the subpulse drifting pulsar J1059-5742

Article References: Shang, L. H., & Ma, H. X. (2026). A rare non-drifting state in the subpulse drifting pulsar J1059-5742. Astrophysics and Space Science, 371(9), Article 108. https://doi.org/10.1007/s10509-026-04640-x

Image Credits: AI Generated

DOI: 10.1007/s10509-026-04640-x

Keywords: pulsar, PSR J1059-5742, subpulse drifting, nulling, Parkes telescope, magnetosphere, polar cap, mode changing, neutron star, radio emission, spark model, drift period