ATCA observations probe peculiar pulsar wind nebula Vela X
by Tomasz NowakowskiTomasz Nowakowski
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Astronomers have employed the Australia Telescope Compact Array (ATCA) to investigate a peculiar pulsar wind nebula known as Vela X. Results of the new observations, published March 2 on the arXiv pre-print server, provide more hints about the properties and nature of this nebula.
Pulsar wind nebulae (PWNe) are nebulae powered by the wind of a pulsar. Pulsar wind is composed of charged particles; when it collides with the pulsar's surroundings, in particular with the slowly expanding supernova ejecta, it develops a PWN.
A PWN with a 'cocoon'
Vela X is a PWN located some 1,000 light years away, powered by the Vela pulsar (also known as PSR J0835–4510 or PSR B0833–45) and associated with a supernova remnant (SNR) designated G263.9−3.3. It has a collimated filament of high-energy particles, dubbed the "Cocoon," extending asymmetrically south-southwest from the pulsar.
Previous observations of the Vela X Cocoon have found that its significant synchrotron emissions are visible in many wavelengths, for example, radio and X-rays, but distinct from each other. It is still uncertain how the Cocoon was formed and some studies suggest that a reverse shock back from the north may have collided and disrupted the original PWN.
Therefore, in order to address the questions of why the Cocoon's radio and X-ray emissions are so separated and why there are only significant radio and X-ray features far away from the pulsar, a team of astronomers led by Yihan Liu of Sun Yat-Sen University in China decided to perform high-resolution ATCA observations of Vela X.
"We performed new radio observations of the Vela X PWN with ATCA on November 23, 24, and 25, 2024 as project C3579. All observations used 750 m array configurations of ATCA (750D), obtaining both good resolution and uv coverage," the researchers wrote in the paper.
What do the new images show?
The new high-resolution observations revealed a large-scale morphology of curved filaments in the Cocoon region. Moreover, the collected images show chaotic wisp-like features with much smaller scales within or out of these filaments.
It turned out that the identified large-scale filamentary features are highly polarized, with the magnetic tangential to the filaments. The rotation measure in the major filament shows a hump along it while remaining fluctuating in other regions. The current map of radio spectral indices suggests that radio features in the Cocoon region are related to the pulsar rather than purely generated by the supernova remnant.
Comparison with previous images and the need for further studies
The comparison of the new images to the previous ones confirmed that radio and X-ray filaments are distinctive, pointing to a highly dynamical environment in this PWN-SNR system.
The astronomers note that while the total intensity and rotation measure distributions across the Cocoon can be explained with a spiral filament with a Doppler-boosting effect in a chaotic circumstellar medium environment, the polarization distribution may require further studies.
The authors of the paper propose more observations of the Vela X Cocoon, which might provide an important estimate of local magnetic field strength. This could help astronomers build better magneto-hydrodynamical simulations for this system.
Written for you by our author Tomasz Nowakowski, edited by Sadie Harley, and fact-checked and reviewed by Robert Egan—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive. If this reporting matters to you, please consider a donation (especially monthly). You'll get an ad-free account as a thank-you.
Publication details
Yihan Liu et al, Radio Study of Vela X Cocoon, arXiv (2026). DOI: 10.48550/arxiv.2603.02046
Journal information: arXiv
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