Face-on SS433 stars as a possible new type of extragalactic X-ray sources

Abstract

The SS433 objects is a well-known source of relativistic jets, which are formed in supercritical accretion disk. It is very probable that the disk has polar channels and their radiation is collimated (the photocones). The face-on SS433 object can appear as beamed ultra-bright (and highly variable) X-ray source, L_x = 10^39 - 10^42 erg/s. We discuss properties of these hypothetical objects and their frequency expected in galaxies. We describe a search for such objects using the ROSAT ASS Bright Source Catalog and Faint Source Catalog (99528 point-like sources) and the RC3 catalog (16741 spiral and irregular galaxies). Among in total 418 positive correlations in all types of galaxies we find that in S and Irr galaxies 142 sources are unknown as AGNs. We isolated by visual inspection 37 clear non-nuclear, 43 probably non-nuclear and 35 probably nuclear sources. The last two classes certainly contain many unknown AGNs. The sources of the 1-st class have X-ray luminosities mainly 10^39 - 3 10^41 erg/s. Their observed frequency is about 4% - 5% per S/Irr galaxy, what is in agreement with expected frequency of face-on SS433 stars. The only way to recognize such stars is their expected violent variability in X-rays.