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24th of July 2017
Farnes et al.
The radio source W50 is believed to be a shell-like supernova remnant which is being re-energized by the jets from the micro-quasar SS433. Farnes et al. used the Australia Telescope Compact Array to make a new wide-field image of the source. In order to cover the whole 2-degree by 3-degree extent of the supernova remnant, a 198 pointing mosaic was observed, in each of the three most compact array configurarions (H75, H168 and H214). Using information from the polarisation of the radio emission, an Rotation Measure gradient is detected across the central region of W50, which is interpreted as a loop magnetic field with a symmetry axis offset by about 90 degrees to the east–west jet-alignment axis, and implying that the evolutionary processes of both the jets and the supernova remnant must be coupled.

The image above combines data over the frequency range from 1.4 to 3.1 GHz, with an effective bandwidth of 1.7 GHz. There are artefacts around bright point sources due to the assumption of zero spectral index during simultaneous imaging. A negative bowl is visible surrounding the W50/SS433 system due to the gap in the shortest (u,v)-spacings. The surrounding field-of-view contains several bright extragalactic radio sources, and additionally the nearby HII region S74 to the north-west, and one half of the shell of the Galactic SNR candidate G38.7-1.4 to the south-west. The microquasar SS433 is clearly visible as the bright compact source at the approximate geometric centre of the nebula. The pseudo-colour scale is in units of jansky per beam. The synthesized beam is shown in green to the lower left-hand panel.

The paper describing these results has been published in Monthly Notices of the Royal Astronomical Society, vol. 467, p. 4777.

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