We have studied the face-on , barred spiral NGC 7424 ( site of the rare Type IIb SN 2001ig ) with Chandra , Gemini and the Australia Telescope Compact Array .
After giving revised X-ray colours and luminosity of the supernova , here we focus on some other interesting sources in the galaxy : in particular , our serendipitous discovery of two ultraluminous X-ray sources ( ULXs ) .
The brighter one ( \sim 10 ^ { 40 } erg s ^ { -1 } ) has a power-law-like spectrum with photon index \Gamma \approx 1.8 .
The other ULX shows a spectral state transition or outburst between the two Chandra observations , 20 days apart .
Optical data show that this ULX is located in a young ( age \approx 7 – 10 Myr ) , bright complex rich with OB stars and clusters .
An exceptionally bright , unresolved radio source ( 0.14 mJy at 4.79 GHz , implying a radio luminosity twice as high as Cas A ) is found slightly offset from the ULX ( \approx 80 pc ) .
Its radio spectral index \alpha \approx - 0.7 suggests optically-thin synchrotron emission , either from a young supernova remnant or from a radio lobe powered by a ULX jet .
An even brighter , unresolved radio source ( 0.22 mJy at 4.79 GHz ) is found in another young , massive stellar complex , not associated with any X-ray sources : based on its flatter radio spectral index ( \alpha \approx - 0.3 ) , we suggest that it is a young pulsar wind nebula , a factor of 10 more radio luminous than the Crab .