Journal
ASTROPHYSICAL JOURNAL
Volume 766, Issue 2, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/766/2/88
Keywords
black hole physics; galaxies: elliptical and lenticular, cD; galaxies: individual (Centaurus A, NGC 5128); X-rays: binaries; X-rays: galaxies
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Funding
- NASA [NAS8-03060]
- University of Birmingham
- NWO Vidi grant [016.093.305]
- NSERC Discovery
- STFC [ST/J001414/1, ST/J001600/1, ST/J001333/1] Funding Source: UKRI
- Grants-in-Aid for Scientific Research [12F02321] Funding Source: KAKEN
- Science and Technology Facilities Council [ST/J001600/1, ST/J001333/1, ST/J001414/1] Funding Source: researchfish
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We present a spectral investigation of X-ray binaries (XBs) in NGC 5128 (Cen A), using six 100 ks Chandra observations taken over two months in 2007. We divide our sample into thermally and non-thermally dominated states based on the behavior of the fitted absorption column N-H, and present the spectral parameters of sources with L-x greater than or similar to 2 x 10(37) erg s(-1). The majority of sources are consistent with being neutron star low-mass X-ray binaries (NS LMXBs) and we identify three transient black hole (BH) LMXB candidates coincident with the dust lane, which is the remnant of a small late-type galaxy. Our results also provide tentative support for the apparent gap in the mass distribution of compact objects between similar to 2-5M(circle dot). We propose that BH LMXBs are preferentially found in the dust lane, and suggest this is because of the younger stellar population. The majority (similar to 70%-80%) of potential Roche lobe filling donors in the Cen A halo are greater than or similar to 12 Gyr old, while BH LMXBs require donors greater than or similar to 1 M-circle dot to produce the observed peak luminosities. This requirement for more massive donors may also explain recent results that claim a steepening of the X-ray luminosity function with age at L-x >= 5 x 10(38) erg s(-1) for the XB population of early-type galaxies; for older stellar populations, there are fewer stars greater than or similar to 1 M-circle dot, which are required to form the more luminous sources.
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