2001/02/05 by Tsunefumi Mizuno, T. Mizuno, Aya Kubota +3 · 5 citations
Physics and Astronomy · #Accretion (finance) #Accretion disc #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Cosmic Phenomena #Black hole (networking) #Flux (metallurgy) #Galaxy #Luminosity #Optics #Physics #RADIUS #Spiral galaxy #X-ray #astro-ph
paper · pdf · doi:10.1086/321418
13 pages, 11 figures, ApJ accepted
arxiv created 2001/02/05 · openalex publication_date 2001/06/20 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
Using the X-ray data taken with ASCA , a detailed analysis was made of intensity and spectral variations of three ultraluminous extragalactic compact X-ray sources (ULXs): IC 342 source 1, M81 X-6, and NGC 1313 source B, all exhibiting X-ray luminosity in the range from 2 × 10 39 to 1.5 × 10 40 ergs s -1 . As already reported, IC 342 source 1 showed short-term X-ray intensity variability by a factor of 2.0 on a typical timescale of 10 ks. M81 X-6 varied by a factor of 1.6 across seven observations spanning 3 yr, while NGC 1313 source B varied by a factor of 2.5 between two observations conducted in 1993 July and 1995 November. The ASCA spectra of these sources acquired on these occasions were all described successfully as optically thick emission from standard accretion disks around black holes. This confirms previous ASCA works that explained ULXs as mass-accreting massive black hole binaries. In all three sources, the disk color temperature was uncomfortably high at T in = 1.0-2.0 keV and was found to vary in proportion to the square root of the source flux. The apparent accretion disk radius is hence inferred to change as inversely proportional to T in . This suggests a significant effect of advection in the accretion disk. However, even taking this effect fully into account, the too high values of T in of ULXs cannot be explained. Further invoking the rapid black hole rotation may give a solution to this issue.