2008/04/23 by A. R. King, King, A. R.
Engineering · Physics and Astronomy · #Astronomical Observations and Instrumentation #Astrophysical Phenomena and Observations #Astrophysics (astro-ph) #Calibration and Measurement Techniques #FOS: Physical sciences
paper · pdf · doi:10.48550/arxiv.0804.3760
openalex publication_date 2008/04/23 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
A recent paper (arXiv:0804.3463) claims that the presence of a soft X-ray component in an X-ray source in NGC 6946 provides strong evidence that its black hole mass is definitely >100\msun, and more probably ∼ 400\msun, even if the source is beamed. I show that the data are instead very compatible with a black hole mass of only 5\msun, radiating isotropically (i.e. no beaming) and a mass transfer rate about 60 times the Eddington value, i.e. 1.25 × 10-5 \msun \rm yr-1. Such a system is very similar to the probable descendant of the Galactic X-ray binary Cygnus X--1 once the supergiant companion evolves to fill its Roche lobe.