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Variability of ultraluminous X-ray sources in the Cartwheel Ring

Published online by Cambridge University Press:  01 August 2006

Anna Wolter
Affiliation:
INAF, Osservatorio Astronomico di Brera, via Brera 28, 20121 Milano, Italy email: anna.wolter@brera.inaf.it, ginevra.trinchieri@brera.inaf.it
Ginevra Trinchieri
Affiliation:
INAF, Osservatorio Astronomico di Brera, via Brera 28, 20121 Milano, Italy email: anna.wolter@brera.inaf.it, ginevra.trinchieri@brera.inaf.it
Monica Colpi
Affiliation:
Dipartimento di Fisica G. Occhialini, Università degli Studi di Milano Bicocca, Piazza della Scienza 3, 20126 Milano, Italy email: Monica.Colpi@mib.infn.it
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Abstract

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The Cartwheel is one of the most outstanding examples of a dynamically perturbed galaxy where star formation is occurring inside the ring–like structure. In previous studies with Chandra, we detected 16 Ultra Luminous X-ray sources lying along the southern portion of the ring. Their Luminosity Function is consistent with them being in the high luminosity tail of the High Mass X-ray Binaries distribution, but with one exception: source N.10. This source, detected with Chandra at LX = 1 × 1041 erg s−1, is among the brightest non–nuclear sources ever seen in external galaxies. Recently, we have observed the Cartwheel with XMM-Newton in two epochs, six months apart. After having been at its brightest for at least 4 years, the source has dimmed by at least a factor of two between the two observations. This fact implies that the source is compact in nature. Given its extreme isotropic luminosity, there is the possibility that the source hosts an accreting intermediate–mass black hole. Other sources in the ring vary in flux between the different datasets. We discuss our findings in the context of ULX models.

Type
Contributed Papers
Copyright
Copyright © International Astronomical Union 2007

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