Multiband study of NGC 7424 and its two newly discovered ultraluminous X-ray sources

R. Soria*, Z. Kuncic, J. W. Broderick, S. D. Ryder

*Corresponding author for this work

Research output: Contribution to journalReview articlepeer-review

17 Citations (Scopus)


We have studied the face-on, barred spiral NGC7424 (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 (∼1040 erg s-1) has a power-law-like spectrum with photon index Γ ≈ 1.8. The other ULX shows a spectral state transition or outburst between the two Chandra observations, 20-d apart. Optical data show that this ULX is located in a young (age ≈ 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 (≈80 pc). Its radio spectral index α ≈ -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 (α ≈ -0.3), we suggest that it is a young pulsar wind nebula, a factor of 10 more radio luminous than the Crab.

Original languageEnglish
Pages (from-to)1666-1676
Number of pages11
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Publication statusPublished - 1 Aug 2006
Externally publishedYes


  • Black hole physics
  • Galaxies: individual: NGC 7424
  • Radio continuum: ISM
  • Supernova remnants
  • X-rays: binaries


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