2006/08/01 by Hua Feng, Philip Kaaret · 1 citation
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Black hole (networking) #Elliptical galaxy #Galaxies: Formation, Evolution, Phenomena #Galaxy #Globular cluster #Hubble sequence #Intermediate-mass black hole #Luminosity #astro-ph
paper · pdf · doi:10.1086/508141
published as Astrophys.J.653:536-544,2006 · 10 pages, 9 figures, accepted for publication in ApJ
arxiv created 2006/08/01 · openalex publication_date 2006/12/05 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
The temporal and spectral properties of ultraluminous X-ray sources (ULXs, L X > 2 × 10 39 ergs s -1 ) and bright X-ray sources ( L X > 3 × 10 38 ergs s -1 ) are examined and compared in two extremely different host environments: the old elliptical galaxy NGC 1399 and the young, star-forming Antennae galaxies (NGC 4038/4039). ULXs in NGC 1399 show little variability on either long or short timescales. Only 1 of 8 ULXs and 10 of 63 bright sources in NGC 1399 are variable at a confidence level of 90%. On long timescales, the NGC 1399 sources are steadier than most Galactic black hole X-ray binaries, but are similar to GRS 1915+105. The outburst duration of the NGC 1399 sources is about 20 yr, again, similar to that of GRS 1915+105. The bright X-ray sources in NGC 1399 may be black hole X-ray binaries with giant-star companions similar to GRS 1915+105. The brightest ULX (PSX-1) in NGC 1399 is coincident with a globular cluster, shows a hard spectrum with a photon index around 1.5, and has a nearly constant luminosity around 5 × 10 39 ergs s -1 . It may be an intermediate-mass black hole (IMBH) in a hard spectral state. In contrast to NGC 1399, the ULXs in the Antennae are all variable, and a large fraction of the bright sources (9 of 15) are also variable. The variability and luminosity of ULXs in the Antennae suggest that they are black hole high-mass X-ray binaries accreting via Roche lobe overflow. A flare with a duration of about 5 ks is found from Antennae X-42. The most luminous ULX, X-16, with a very hard spectrum (Γ = 1.0-1.3) and a luminosity that varies by a factor of 10, could be an IMBH candidate.