The XMM-Newton long look of NGC 1365: lack of a high-soft state in its ultraluminous X-ray sources - Astrophysics > High Energy Astrophysical PhenomenaReportar como inadecuado




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Abstract: Based on our long ~ 300 ks 2007 XMM-Newton observation of the Seyfertgalaxy NGC 1365, we report here on the spectral and timing behaviour of twoultraluminous X-ray sources, which had previously reached isotropic X-rayluminosities L X ~ 4 x 10^{40} erg-s 0.3-10 keV band. In 2007, they were in alower state L X ~ 5 x 10^{39} erg-s, and L X ~ 1.5 x 10^{39} erg-s for X1 andX2, respectively. Their X-ray spectra were dominated by power-laws with photonindices Gamma ~ 1.8 and Gamma ~ 1.2, respectively. Thus, their spectra weresimilar to those at their outburst peaks. Both sources have been seen to varyby a factor of 20 in luminosity over the years, but their spectra are alwaysdominated by a hard power-law; unlike most stellar-mass BHs, they have neverbeen found in a canonical high-soft state dominated by a standard disk. Thelack of a canonical high-soft state seems to be a common feature of ULXs. Wespeculate that the different kind of donor star and-or a persistentlysuper-Eddington accretion rate during their outbursts may prevent accretionflows in ULXs from settling into steady standard disks.



Autor: Roberto Soria MSSL-UCL, Guido Risaliti Harvard CfA and INAF Arcetri, Martin Elvis Harvard CfA, Giuseppina Fabbiano Harvard CfA, S

Fuente: https://arxiv.org/



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