Ultraluminous X-ray source (ULXs) are exciting objects basically observed only by X-ray satellites. Question whether they contain intermediate mass black hole with a mass of ~104 solar masses (IMBH) with sub-Eddington accretion disk or stellar mass black hole with a mass of ~10 solar masses and with super-Eddington accretion disk, is still unsolved.
In a recent paper in A&A, researchers from CAMK PAN reveal that the extreme ULX source NGC 5055 X-1 is accreting at super-Eddington rate. Due to the high accretion rate the outward radiation pressure pushes the boundary layer of the accretion disk and the disk becomes geometrically thick. The radiation pressure also throws away the excess surplus matter, leaving only the Eddington amount, and this results in optically thick wind from the accretion disk.
The authors: Samaresh Mondal, Agata Różańska, Eleonora V. Lai and Barbara De Marco, from spectral analysis of Chandra and XMM-Newton data, reported the extreme luminosity 2.3x1040 erg/s of the source X-1 located in the outskirt of the spiral galaxy NGC 5055 (the source indicated by arrow in the image). They found that the source exhibits negative correlation between flux and the inner disk temperature which is at odds with the observations of Galactic X-ray binaries. The negative correlation is a signature that the source emission is anisotropic. The authors concluded that the compact object in NGC 5055 X-1 is a stellar mass black hole and the high luminosity appears due to the geometrical beaming of the disk emission by optically thick wind.
The research has been accepted for publication in A&A.
Picture: Spiral galaxy NGC 5055 in optical light and X-ray image of X-1 source made by XMM-Newton satellite and marked by arrow.
Image credit: SIMBAD webpage, SDSS and XMM-Newton
