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Register a new userThe optical counterpart of the ultra-luminous x-ray source NGC 5204 X-1
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M.R. Goad
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We use archival HST/WFPC2 V and I band images to show that the optical counterpart to the ultra-luminous x-ray source NGC 5204 X-1, reported by Roberts et al., is composed of two sources separated by 0.5. We have also identified a third source as a possible counterpart, which lies 0.8 from the nominal x-ray position. PSF fitting photometry yields V-band magnitudes of 20.3, 22.0 and 22.4 for the three sources. The V-I band colours are 0.6, 0.1, and -0.2, respectively (i.e. the fainter sources are bluer). We find that all V-I colours and luminosities are consistent with those expected for young stellar clusters (age <10 Myr).
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We present the results of two XMM-Newton observations of the ultraluminous X-ray source (ULX) NGC 5204 X-1. The EPIC spectra are well-fit by the standard spectral model of a black-hole X-ray binary, comprising a soft multi-colour disc blackbody component plus a harder power-law continuum. The cool (kT_in ~ 0.2 keV) inner-disc temperature required by this model favours the presence of an intermediate-mass black hole (IMBH) in this system, though we highlight a possible anomaly in the slope of the power-law continuum in such fits. We discuss the interpretation of this and other, non-standard spectral modelling of the data.
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