AI Insight
Astronomers using the FAST radio telescope have detected for the first time radio pulsations from PSR J2238+5903, an extremely faint pulsar with a flux density of approximately 3 microjanskys. The pulsar has a spin period of 162.8 milliseconds and a dispersion measure of 247.5 pc/cm³, which places it at an estimated distance of 7.4 kiloparsecs. This distance measurement suggests that the pulsar may power the extended TeV gamma-ray source 1LHAASO J2238+5900, which spans approximately 132 parsecs and emits about 8% of the pulsar's spin-down energy as TeV radiation.
Why it matters
This discovery provides the first direct distance measurement for evaluating whether 1LHAASO J2238+5900 represents a transitional system between a pulsar wind nebula and a TeV halo, helping astronomers understand how pulsars inject high-energy particles into the surrounding interstellar medium and contribute to cosmic ray populations in our galaxy.
Understand the Science
arXiv:2607.08596v2 Announce Type: replace
Abstract: We report the first detection of radio pulsations from PSR J2238+5903, a gamma-ray pulsar spatially coincident with the extended TeV source 1LHAASO J2238+5900. Our 3000 s FAST L-band observation reveals a weak periodic signal at the known Fermi-LAT spin period, with $P=162.76568$ ms and $mathrm{DM}=247.5pm3.0~mathrm{pc~cm^{-3}}$. The signal is independently confirmed by both FFT-based and Fast Folding Algorithm searches. The radiometer equation gives a flux density of $S_{1250}simeq3,mu$Jy, placing PSR J2238+5903 among the faintest radio-detected Fermi pulsars. Interpreting the DM with Galactic electron-density models gives $d_{rm DM}=7.4pm3.9$ kpc. At this distance, the LHAASO WCDA 39% containment radius corresponds to a characteristic diameter of $sim132$ pc, and the $>1$ TeV luminosity is $L_{rm TeV}simeq7.1times10^{34}$ erg s$^{-1}$, about 8% of the pulsar’s spin-down power. The radio DM thus provides the first pulsar-specific distance constraint for assessing whether 1LHAASO J2238+5900 is a young relic-PWN / TeV-halo transition system.