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Observations of a nearby pulsar wind nebula reveal a radio jet feature with a helical magnetic field inside

Using the Australia Telescope Compact Array (ATCA), astronomers have performed high-resolution observations of a nearby pulsar wind nebula in the supernova remnant G11.2−0.3. Results of the observational campaign, March 3 on the arXiv preprint server, deliver important insights into the structure and properties of this nebula.

Pulsar wind nebulae (PWNe) are nebulae powered by the wind of a pulsar. Pulsar wind is composed of charged particles and when it collides with the pulsar's surroundings, in particular with the slowly expanding supernova ejecta, it develops a PWN. Observations of PWNe have shown that the particles in these objects lose their energy to radiation and become less energetic with distance from the central pulsar. Some PWNe may produce extended X-ray structures in the form of tails and prominent jets.

G 11.2–0.3 is a young core-collapse supernova remnant (SNR) at a distance of some 16,000 light years. It contains a pulsar, designated PSR J1811−1925, and a pulsar wind nebula. The PWN in G11.2−0.3 is powered by PSR J1811−1925, which is located near the SNR's shell.

Previous observations of G 11.2–0.3 have found that its PWN hosts a possible jet feature close to the X-ray pulsar region, and complex filaments. Recently, a team of astronomers led by Yu Zhang of the Sun Yat-Sen University in Zhuhai, China, decided to employ ATCA in order to take a closer look at these features and the overall structure of the nebula.

"We present a study of G 11.2–0.3 PWN using new ATCA observations at 3 and 6 cm in 2022, as well as at 16 cm in 2024," the researchers wrote in the paper.

High-resolution ATCA observations allowed the Sun Yat-Sen team to resolve detailed structures inside the SNR and PWN regions. They found a radio jet feature in the PWN with a helical magnetic field inside. The astronomers noted that no such feature has yet been observed in similar sources.

The astronomers noted that the multi-band spectrum of the jet is less likely to be a simple power-law. This possibly indicates complex particle acceleration mechanisms such as magnetic reconnection.

Moreover, the images show complicated structures farther away from the pulsar. For instance, the observations identified a filamentary structure with a thickness of approximately 20 arcseconds in the southeastern part of the SNR.

The collected data also allowed the researchers to calculate the magnetic field strength close to the jet region. The strength of this magnetic field was estimated to be around 85 µG.

Summing up the results, the authors of the paper concluded that follow-up observations at higher frequencies are required in order to better understand the spectral properties of the PWN in G 11.2–0.3.