2006/06/05 by Roberto Soria, R. Soria, Z. Kuncic +3 · 1 citation
Physics and Astronomy · #Astrophysical Phenomena and Observations #Astrophysics and Cosmic Phenomena #Galaxies: Formation, Evolution, Phenomena #astro-ph
paper · pdf · doi:10.1111/j.1365-2966.2006.10629.x
published as Mon.Not.Roy.Astron.Soc.370:1666-1676,2006 · 12 pages, 11 figures. Accepted by MNRAS. High-resolution colour images of NGC 7424 from the Gemini observations are available at http://www.gemini.edu/2001igpr
arxiv created 2006/06/05 · openalex publication_date 2006/07/17 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
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 (∼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.