Bolstering the IMBH hypothesis: Evidence for "Low" and "High" State ULX Sources from XMM-Newton

Details Bolstering the IMBH hypothesis: Evidence for "Low" and "High" State ULX Sources from XMM-Newton Bolstering the IMBH hypothesis: Evidence for "Low" and "High" State ULX Sources from XMM-Newton

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005aas...207.9005w&link_type=abstract

American Astronomical Society Meeting 207, #90.05; Bulletin of the American Astronomical Society, Vol. 37, p.1318

Astronomy and Astrophysics

Astronomy

1

Scientific paper

We have conducted an archival XMM-Newton study of the bright X-ray point sources in 32 nearby galaxies. From our list of approximately 100 point sources, we attempt to determine if there is a low-state counterpart to the Ultraluminous X-ray (ULX) population, testing the specific predictions of the IMBH hypothesis. Indeed, 16 sources in our sample match the criteria we set for a low-state ULX, namely, LX > 1038 erg s-1 and a spectrum well fit with an absorbed power law. Further, we find evidence for 26 high-state ULXs which are well fit by a combined blackbody and a power law. As in Galactic black hole systems, the spectral indices, Γ , of the low-state objects, as well as the luminosities, tend to be lower than those of the high-state objects. The observed range of blackbody temperatures is 0.1-1 keV with the most luminous systems tending toward the lowest temperatures. We also find a class of object whose properties (luminosity, blackbody temperature, and power law slopes) are very similar to those of galactic stellar mass black holes. In addition, we find a subset of these objects that can be best fit by a Comptonized spectrum similar to that used for Galactic black holes in the ``very high'' state, when they are radiating near the Eddington limit.

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