Composite image of the Galactic Plane and Potoroo region, with the red layer showing the ASKAP total intensity image at 1368 MHz, and the green and blue layers representing the WISE infrared images at 12 µm and 22 µm respectively. Known galactic SNRs are indicated by red circles (Green, 2019, 2022), while known galactic HII regions are marked by green circles (Anderson et al., 2014). The box highlights the section that is of great interest. The inset is the enlarged ASKAP image showing Potoroo where a red cross marks the position of the X-ray source, while a red dotted line is Potoroo’s axis of symmetry, which corresponds to the length of the tail studied in this article. Credit: arXiv (2023). DOI: 10.48550/arxiv.2312.06961
Astronomers from Western Sydney University in Australia and elsewhere report the detection of a new pulsar wind nebula and a pulsar that powers it. The discovery, presented in an article published December 12 on the preprint server arXivwas carried out using the Australian Square Kilometer Array Pathfinder (ASKAP), as well as the MeerKAT and Parkes radio telescopes.
Pulsar wind nebulae (PWNe) are nebulae powered by the wind of a pulsar. The pulsar wind is composed of charged particles; when it collides with the pulsar environment, particularly with slowly expanding supernova ejecta, it develops a PWN.
PWNe particles lose energy due to radiation and become less energetic with distance from the central pulsar. Multi-wavelength studies of these objects, including X-ray observations, particularly using spatially integrated spectra in the X-ray band, have the potential to uncover important information about particle flux in these nebulae. This could reveal important information about the nature of PWNe in general.
Now a team of astronomers led by Sanja Lazarević from Western Sydney University has discovered a new pulsar wind nebula in radio continuum studies obtained by ASKAP and MeerKAT. They nicknamed the new PWN “Potoroo,” after a small marsupial native to Australia.
Then, using the Parkes Ultra-Wideband Low (UWL) frequency receiving system, they detected the pulsar candidate, which received the designation PSR J1638-4713. Further observations of PSR J1638-4713 confirmed that it feeds the Potoroo.
Observations show that Potoroo exhibits a distinctive cometary morphology in the radio band and in the X-ray band. This suggests that the pulsar drives the PWN and moves supersonically through the ambient medium.
“For pulsars that are propelled through the ambient medium at supersonic speeds, the resulting dynamic pressure transforms the PWN into an arc shock. This process confines the pulsar wind in the direction opposite to that of the pulsar’s motion , forming a cometary-like tail-shaped wind,” the authors of the paper explained.
According to the study, Potoroo is located at a distance of at least 32,500 light years, has a radio size of about 68.5 light years, while its X-ray size appears to be 10 times smaller. Therefore, Potoroo has the longest PWN radio tracks known to date.
The results indicate that Potoroo has an unusually steep overall radio spectrum, at a level of -1.27. This is lower than typical values of known PWNe. Astronomers speculate that such a high overall spectral index could be due to the interaction of the reverse shock of the parent supernova with the PWN.
As for the PSR J1638-4713, it has a rotation period of 65.74 milliseconds and a dispersion measurement of 1,553 pc/cm.3—the second highest of all known radio pulsars. Observations revealed that PSR J1638-4713 is a young pulsar (with a characteristic age of 24,000 years), has a high rotational luminosity and a high projected velocity, exceeding 1,000 km/s.
More information:
Sanja Lazarević et al, Fast as Potoroo: Detection of the radio continuum of a Pulsar arc-shock aeolian nebula powered by Pulsar J1638-4713, arXiv (2023). DOI: 10.48550/arxiv.2312.06961
Journal information:
arXiv
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