SIMBAD references

2009ApJ...704.1628L - Astrophys. J., 704, 1628-1639 (2009/October-3)

Multi-epoch multi-wavelength study of an ultraluminous X-ray source in M101: the nature of the secondary.


Abstract (from CDS):

Ultraluminous X-ray sources are non-nuclear point sources in external galaxies with LX= 2x1039-1041 erg/s, and thus are possibly stellar black holes with special radiation mechanisms or intermediate mass black holes of 100-105 M. To measure their dynamical mass, one needs to identify the secondary in the optical followed by photometric and spectroscopic monitoring. The counterpart light is usually contaminated, sometimes even dominated, by the X-ray irradiated accretion disk, which complicates the derivation of the properties of the secondary itself. Here, we report a study on M101-ULX1 with 26 Hubble Space Telescope (HST) observations and 33 X-ray observations over 16 years. There were three multi-band HST observations at different optical states over eight years, the spectral energy distributions (SEDs) of which cannot be fitted by the previously claimed secondary of a B supergiant or any other single star. All SEDs can be decomposed into the same stellar component plus a second component due to X-ray irradiation with different contributions at different optical states. The secondary in ULX1 is most likely a WR star as revealed by the SED decompositions and confirmed by the presence of He II λ4686 emission in the counterpart spectrum. Five X-ray outbursts and two optical peaks are revealed from X-ray and optical light curves, and optical peaks are identified as the optical response to X-ray outbursts. The correlated optical and X-ray variability analysis is suggestive of ellipsoidal modulation with a half-amplitude of 0.05 mag and a period in the range of 1.5-4.5 days. Future photometric and spectroscopic observations are required to confirm the orbital period and measure the dynamical mass for ULX1.

Abstract Copyright:

Journal keyword(s): galaxies: individual: M101 - X-rays: binaries

Simbad objects: 8

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