SIMBAD references

We seek clarification of the nature of X-ray sources detected in M 31. Here we focus on CXOM31 J004253.1+411422, the brightness of which suggests that it belongs to the class of ultraluminous X-ray sources. We determine the X-ray properties of sources detected in the XMM-Newton/Chandra monitoring program. We investigate spectral properties and search for periodic or quasi-periodic oscillations. A multicomponent model was applied to the spectra obtained from XMM-Newton data to evaluate the relative contributions from thermal and nonthermal emission. The time dependence of this ratio was evaluated over a period of forty days. We simultaneously fit data from XMM-Newton EPIC-pn, MOS1, and MOS2 detectors with (nonthermal) powerlaw and (thermal) multicolored blackbody. The X-ray spectrum is best fit by the combination of a thermal component with kT∼1keV and a powerlaw component with a photon index of approximately 2.6. From combined analysis of Chandra, Swift, and XMM-Newton data, the unabsorbed total luminosity of this source decreases from ∼3.8x10³⁹erg/s in the first observation to ∼0.5x10³⁹erg/s over a period of three months. The decay closely follows an exponential decline with a time constant of 32 days. The source spectrum evolves significantly, exhibiting a faster decline of the thermal component. We do not find evidence of any significant temporal features in the power density spectrum. The presence of a thermal component at kT ∼1keV in conjunction with a nonthermal high-energy tail, is also consistent with spectral properties of other ULXs in the ``high state''. Our analysis indicates that the underlying source of this first ULX in M 31 is a black hole of mass, M≥13M_☉, accreting near the Eddington limit, that underwent a transient outburst followed by an exponential decay reminiscent of transients associated with galactic X-ray novae.