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On the compact nature of the most luminous ULX in the Cartwheel ring

A. Wolter·G. Trinchieri·M. Colpi
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Abstract

We report the first detection of flux variability in the most luminous X-ray source in the southern ring of the Cartwheel galaxy. XMM--Newton data show that the luminosity has varied over a timescale of six months from L[0.5-10] keV \~1.3 10^{41} erg/s, consistent with the previous Chandra observation, to L[0.5-10] keV < 6.4 x10^{40} erg/s. This fact provides the first evidence that the source is compact in nature and is not a collection of individual fainter sources, such as supernova remnants. The source has been repeatedly observed at the very high luminosity level of L[0.5-10] keV ~1.3 x 10^{41} erg/s, for a period of at least 4 years before dimming at the current level. It represents then the first example of an accreting object revealed in a long lived state of extremely high luminosity.

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A. Wolter, G. Trinchieri, M. Colpi. 2006-10-19. On the compact nature of the most luminous ULX in the Cartwheel ring. https://doi.org/10.1111/j.1365-2966.2006.11116.x

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