Pulse stacks of PSR J2129+4119 observed on September 29, 2024, showing three distinct behaviors: steady drifting (left), intermittent drifting with breaks (middle), and beat-like modulation (right). Credit: arXiv (2025). DOI: 10.48550/arxiv.2510.26209
Using the Five-hundred-meter Aperture Spherical Radio Telescope (FAST), astronomers from the Chinese Academy of Sciences (CAS) and elsewhere have observed a nearby pulsar known as PSR J2129+4119. Results of the observational campaign, published October 30 on the arXiv pre-print server, deliver important insights into the behavior and properties of this pulsar.
Radio emission from pulsars exhibits a variety of phenomena, including subpulse drifting, nulling, or mode changing. In the case of subpulse drifting, radio emission from a pulsar appears to drift in spin phase within the main pulse profile. When it comes to nulling, the emission from a pulsar ceases abruptly from a few to hundreds of pulse periods before it is restored.
Discovered in 2017, PSR J2129+4119 is an old and nearby pulsar located some 7,500 light years away. It has a pulse period of 1.69 seconds, dispersion measure of 31 cm/pc3, and characteristic age of 342.8 million years. The pulsar lies below the so-called “death line”—a theoretical boundary in the period-period derivative diagram below which the coherent radio emission is sustained.
Now, a team of astronomers led by Habtamu Menberu Tedila of CAS has inspected PSR J2129+4119 with high-sensitivity FAST observations, which revealed a plethora of emission phenomena from this pulsar.
“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 researchers write in the paper.
In particular, the observations reveal that PSR J2129+4119 showcases sustained and multi-modal emission behavior, including three distinct modes: nulls, weak pulses, and regular pulses. It also occasionally emits bright pulses, quasi-periodic microstructure, and displays clear subpulse modulation features. The nulling fraction was measured to be approximately 8.13%.
Furthermore, the observations found that both regular and weak pulses of PSR J2129+4119 show high linear polarization. The collected data indicate a small impact angle of about -3 degrees, which is consistent with a near-tangential line of sight.
It appears that post-null regular pulses of the pulsar display enhanced trailing components relative to pre-null pulses. This, according to the authors of the paper, suggests gradual magnetospheric reactivation rather than a purely geometric origin.
The obtained data also show that microstructure is present in about 64% of the pulsar’s regular pulses, with mean periodicity of 4.57 milliseconds and mean width of 4.3 milliseconds.
Therefore, all the new findings indicate that PSR J2129+4119 remains magnetospherically active and coherently emitting despite its low energy loss rate.
“The pulsar’s diverse observational behavior, including beat-like modulation, emission asymmetries near nulls, and quasi-periodic microstructure, suggests that its magnetosphere operates near the threshold for coherent emission, providing valuable constraints on the physical conditions that enable or suppress pulsar radio emission,” the researchers conclude.
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More information:
Habtamu Menberu Tedila et al, Multi-Faceted Emission Properties of PSR J2129+4119 Observed with FAST, arXiv (2025). DOI: 10.48550/arxiv.2510.26209
Journal information:
arXiv
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Nearby pulsar offers insights into emission physics near the death line (2025, November 6)
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