XMM-newton spectroscopy of four bright ultraluminous X-ray sources in the Antennae galaxies (NGC 4038/4039).
MILLER J.M., ZEZAS A., FABBIANO G. and SCHWEIZER F.
Abstract (from CDS):
We report the results of spectral fits to four bright ultraluminous X-ray sources (ULXs) in the Antennae galaxies (NGC 4038/4039) observed for 41 ks with XMM-Newton. Although emission regions are not resolved as well as in prior Chandra observations, at least four ULXs (X-11, X-16, X-37, and X-44 in the Zezas and Fabbiano scheme) are sufficiently bright and well separated with XMM-Newton that reliable extractions and spectral analyses are possible. We find that the single-component multicolor disk blackbody models cannot describe any of the spectra. Sources X-11 and X-16 are acceptably fitted with simple power-law models. A thermal bremsstrahlung model provides a better fit to the spectrum of X-44. Including a disk blackbody component to the spectrum of X-37 improves the fit and reveals an apparently cool disk (kT=0.13±0.02 keV). This would suggest a parallel to cool disks recently found in other very luminous ULXs, which may contain intermediate-mass black holes; however, the complex diffuse emission of the Antennae demands that this finding be regarded cautiously.
Galaxies: Individual: NGC Number: NGC 4038/4039 - X-Rays: Galaxies