The two Ultraluminous X-ray sources in the galaxy NGC 925
Abstract
NGC 925 ULX-1 and ULX-2 are two ultraluminous X-ray sources in the galaxy NGC 925, at a distance of 8.5 Mpc. For the first time, we analyzed high quality, simultaneous XMM-Newton and NuSTAR data of both sources. Although at a first glance ULX-1 resembles an intermediate mass black hole candidate (IMBH) because of its high X-ray luminosity ( erg s) and its spectral/temporal features, a closer inspection shows that its properties are more similar to those of a typical super-Eddington accreting stellar black hole and we classify it as a `broadened disc' ultraluminous X-ray source. Based on the physical interpretation of this spectral state, we suggest that ULX-1 is seen at small inclination angles, possibly through the evacuated cone of a powerful wind originating in the accretion disc. The spectral classification of ULX-2 is less certain, but we disfavour an IMBH accreting at sub-Eddington rates as none of its spectral/temporal properties can be associated to either the soft or hard state of Galactic accreting black hole binaries.
Keywords
Cite
@article{arxiv.1806.11444,
title = {The two Ultraluminous X-ray sources in the galaxy NGC 925},
author = {F. Pintore and L. Zampieri and S. Mereghetti and A. Wolter and G. Rodríguez and G. L. Israel and P. Esposito and S. Paiano and G. Trinchieri and P. Ochner},
journal= {arXiv preprint arXiv:1806.11444},
year = {2018}
}
Comments
Accepted on MNRAS with very minor comments, 7 pages, 5 figures, 1 table