Radio detection of LAT PSRs J1741-2054 and J2032+4127: no longer just gamma-ray pulsars

Sixteen pulsars have been discovered so far in blind searches of photons collected with the Large Area Telescope on the Fermi Gamma-ray Space Telescope. We here report the discovery of radio pulsations from two of them. PSR J1741-2054, with period P=413ms, was detected in archival Parkes telescope data and subsequently has been detected at the Green Bank Telescope (GBT). Its received flux varies greatly due to interstellar scintillation and it has a very small dispersion measure of DM=4.7pc/cc, implying a distance of ~0.4kpc and possibly the smallest luminosity of any known radio pulsar. At this distance, for isotropic emission, its gamma-ray luminosity above 0.1GeV corresponds to 25% of the spin-down luminosity of dE/dt=9.4e33erg/s. The gamma-ray profile occupies 1/3 of pulse phase and has three closely-spaced peaks with the first peak lagging the radio pulse by delta=0.29P. We have also identified a soft Swift source that is the likely X-ray counterpart. In many respects PSR J1741-2054 resembles the Geminga pulsar. The second source, PSR J2032+4127, was detected at the GBT. It has P=143ms, and its DM=115pc/cc suggests a distance of ~3.6kpc, but we consider it likely that it is located within the Cyg OB2 stellar association at half that distance. The radio emission is nearly 100% linearly polarized, and the main radio peak precedes by delta=0.15P the first of two narrow gamma-ray peaks that are separated by Delta=0.50P. Faint, diffuse X-ray emission in a Chandra image is possibly its pulsar wind nebula. PSR J2032+4127 likely accounts for the EGRET source 3EG J2033+4118, while its pulsar wind is responsible for the formerly unidentified HEGRA source TeV J2032+4130.

💡 Research Summary

This paper reports the first radio detections of two pulsars that were originally discovered as γ‑ray sources in blind searches of Fermi LAT data. The two objects, PSR J1741‑2054 and PSR J2032+4127, were identified as radio pulsars through re‑analysis of archival Parkes data and new observations with the Green Bank Telescope (GBT), respectively.

PSR J1741‑2054 has a spin period of 413 ms. Its dispersion measure (DM) of only 4.7 pc cm⁻³ places it at a very small distance of roughly 0.4 kpc, making it one of the nearest γ‑ray pulsars known. The radio flux is highly variable because of interstellar scintillation, ranging from a few tens of µJy up to a few hundred µJy. Its inferred 1.4 GHz luminosity (≈ 0.025 mJy kpc²) is possibly the lowest ever measured for a radio pulsar. The γ‑ray light curve occupies about one‑third of the rotation phase and shows three closely spaced peaks; the first γ‑ray peak lags the radio pulse by Δ ≈ 0.29 P (≈ 120 ms). A soft X‑ray source detected by Swift is likely the X‑ray counterpart, and faint diffuse X‑ray emission around the pulsar hints at a pulsar‑wind nebula (PWN). The overall phenomenology—low radio luminosity, modest spin‑down power (Ė ≈ 9.4 × 10³³ erg s⁻¹), and a γ‑ray efficiency of ~25%—makes PSR J1741‑2054 reminiscent of the classic Geminga pulsar, which is bright in γ‑rays but radio‑quiet.

PSR J2032+4127 spins faster, with P = 143 ms, and has a DM of 115 pc cm⁻³. The NE2001 electron‑density model yields a distance of about 3.6 kpc, but the authors argue that the pulsar is probably associated with the massive Cyg OB2 stellar association, which would place it at roughly half that distance (~1.8 kpc). The radio emission is almost 100 % linearly polarized, indicating a highly ordered magnetic field geometry aligned with the line of sight. The radio pulse precedes the first of two narrow γ‑ray peaks by Δ ≈ 0.15 P, and the two γ‑ray peaks are separated by Δ ≈ 0.50 P, a pattern that fits well with outer‑gap or slot‑gap models where high‑altitude emission produces widely spaced γ‑ray components. Chandra imaging reveals faint, diffuse X‑ray emission that may be a PWN powered by the pulsar’s spin‑down energy (Ė ≈ 2.7 × 10³⁵ erg s⁻¹). The source likely accounts for the previously unidentified EGRET source 3EG J2033+4118, and its energetic wind provides a natural explanation for the TeV emitter TeV J2032+4130 discovered by HEGRA.

The paper’s broader significance lies in demonstrating that many LAT‑discovered γ‑ray pulsars are not truly radio silent; rather, their radio beams may be weak, highly variable, or narrowly directed, requiring deep, targeted searches. By combining radio timing, dispersion‑measure based distance estimates, polarization measurements, and multi‑wavelength (X‑ray and TeV) imaging, the authors build a coherent picture of each pulsar’s geometry, emission zones, and surrounding environment. PSR J1741‑2054 adds a new member to the “Geminga‑like” class of nearby, low‑luminosity radio pulsars, while PSR J2032+4127 links a young, energetic pulsar to both a massive OB association and a high‑energy TeV source, illustrating how pulsar winds can power extended nebular emission. The work underscores the importance of coordinated radio and high‑energy observations for fully characterizing the Galactic pulsar population and for interpreting unidentified γ‑ray and TeV sources.