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The nature of ultraluminous X-ray sources in nearby galaxies

T. P. Roberts·M. R. Goad·M. J. Ward·R. S. Warwick·P. Lira
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Abstract

The advanced capabilities of the Chandra and XMM-Newton observatories mean that, for the first time, the detailed study of the brightest point-like X-ray sources in nearby galaxies outside of the local group is a realistic aim. Here, we present the results of a Chandra ACIS-S study of two of the nearest and brightest sources in the rare ultraluminous (L(X) > 10^39 erg s^-1) X-ray source (ULX) class, NGC 5204 X-1 and NGC 4559 X-1. When considered with new optical integral field spectroscopy data this provides powerful diagnostics as to the nature of these sources, in particular suggesting that NGC 5204 X-1 is a high-mass X-ray binary, and showing new evidence linking it to the Galactic microquasar phenomenon. We also find that both ULX appear to be located in cavities in emission-line gas nebulae that surround the sources. In addition, we present the results of a Chandra observation of the interacting galaxies NGC 4485/NGC 4490, a pair of late-type spiral galaxies that, remarkably, contain a total of six ULX. We identify one as a supernovae, and the remainder as probable black hole X-ray binaries. All six are located in star formation regions, underlining the emerging link between ULX and active star formation activity.

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T. P. Roberts, M. R. Goad, M. J. Ward, R. S. Warwick, P. Lira. 2002-02-01. The nature of ultraluminous X-ray sources in nearby galaxies. https://arxiv.org/abs/astro-ph/0202017

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