2001/04/02 by F. E. Bauer, W. N. Brandt, R. M. Sambruna +4 · 4 citations
Physics and Astronomy · #Astrophysical Phenomena and Observations #Astrophysics and Cosmic Phenomena #Black-body radiation #Flux (metallurgy) #Galaxies: Formation, Evolution, Phenomena #Galaxy #Luminosity #Observatory #Point source #Population #Supernova #astro-ph
paper · pdf · doi:10.1086/321123
LaTex using emulateApJ5, 12 pages with 11 embedded figures, AJ in press. Also available at http://www.astro.psu.edu/~fbauer/RESEARCH/Circinus.ps.gz
arxiv created 2001/04/02 · openalex publication_date 2001/07/01 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We have used the Chandra X-Ray Observatory to resolve spatially and spectrally the X-ray emission from the Circinus galaxy. We report here on the nature of the X-ray emission from the off-nuclear point sources associated with the disk of Circinus, which make up ≈34% of the total 0.5–10 keV emission. We find that many of the serendipitous X-ray sources are concentrated along the optical disk of the galaxy, although few have optical counterparts within 1'' of their X-ray positions down to limiting magnitudes of m V = 23–25. At the distance of Circinus (≈3.8 Mpc), their intrinsic 0.5–10 keV luminosities range from ≈2 × 10 37 ergs s -1 to ≈4 × 10 39 ergs s -1 . One-fourth of the sources are variable over the duration of the 67 ks observation, and spectral fitting of these off-nuclear sources shows a diverse range of spectral properties. The overall characteristics of the point sources suggest that most are X-ray binaries and/or ultraluminous supernova remnants within Circinus. We are able to analyze the two strongest off-nuclear sources in greater detail and find both to have remarkable properties. The average X-ray luminosities of the two sources are 3.7 × 10 39 ergs s -1 and 3.4 × 10 39 ergs s -1 . The former displays large and periodic flux variations every 7.5 hr and is well fitted by a multicolor blackbody accretion disk model with T in = 1.35 keV, properties consistent with an eclipsing ≳50 M ⊙ black hole binary. The latter appears to be a young supernova remnant, as it coincides with a nonthermal radio counterpart and an Hα-detected H II region. This source exhibits both long-term (≈4 yr) X-ray variability and a 6.67–6.97 keV iron emission-line blend with a 1.6 keV equivalent width. These two objects further support the notion that super-Eddington X-ray sources in nearby galaxies can be explained by a mixture of intermediate-mass black holes in X-ray binaries and young supernova remnants.