Pulsator-like spectra from Ultraluminous X-ray sources and the search for more ultraluminous pulsars

摘要: Ultraluminous X-ray sources (ULXs) are a population of extragalactic objects whose luminosity exceeds the Eddington limit for 10 Msun black hole (BH). Their properties have been widely interpreted in terms accreting stellar-mass or intermediate-mass BHs. However at least three neutron stars (NSs) recently identified ULXs through discovery periodic pulsations. Motivated by these findings we studied spectral sample bright using simple continuum model which was extensively used to fit spectra magnetic NSs Galaxy. We found that such model, consisting power-law with high-energy exponential cut-off, fits very well most ULX analyzed here, level comparable models involving an BH. On grounds alone suggest other non-pulsating may host NSs. also above 2 keV spectrum known pulsating is harder than majority sample, only IC 342 X-1 and Ho IX displaying hardness. thus two NS encourage searches pulsations flux.