TY - JOUR
T1 - Spectral properties of X-ray binaries in Centaurus a
AU - Burke, M.J.
AU - Raychaudhury, S.
AU - Kraft, R.P.
AU - Forman, W.R.
AU - Jones, C.
AU - Murray, S.S.
AU - Birkinshaw, M.
AU - Evans, D.A.
AU - Jordán, A.
AU - Worrall, D.M.
AU - Maccarone, T.J.
AU - Croston, J.H.
AU - Brassington, N.J.
AU - Hardcastle, M.J.
AU - Goodger, J.L.
AU - Kainulainen, J.
AU - Woodley, K.A.
AU - Sivakoff, G.R.
AU - Gilfanov, M.
AU - Zhang, Z.
AU - Sarazin, C.L.
AU - Voss, R.
PY - 2013/4/1
Y1 - 2013/4/1
N2 - 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 , and present the spectral parameters of sources with L ≳ 2 × 10 erg s. 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 ∼2-5 M . We propose that BH LMXBs are preferentially found in the dust lane, and suggest this is because of the younger stellar population. The majority (∼70%-80%) of potential Roche lobe filling donors in the Cen A halo are ≳ 12 Gyr old, while BH LMXBs require donors ≳ 1 M 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 ≥ 5 × 10 erg s for the XB population of early-type galaxies; for older stellar populations, there are fewer stars ≳ 1 M , which are required to form the more luminous sources.
AB - 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 , and present the spectral parameters of sources with L ≳ 2 × 10 erg s. 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 ∼2-5 M . We propose that BH LMXBs are preferentially found in the dust lane, and suggest this is because of the younger stellar population. The majority (∼70%-80%) of potential Roche lobe filling donors in the Cen A halo are ≳ 12 Gyr old, while BH LMXBs require donors ≳ 1 M 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 ≥ 5 × 10 erg s for the XB population of early-type galaxies; for older stellar populations, there are fewer stars ≳ 1 M , which are required to form the more luminous sources.
UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84875465181&partnerID=8YFLogxK
U2 - 10.1088/0004-637X/766/2/88
DO - 10.1088/0004-637X/766/2/88
M3 - Article
AN - SCOPUS:84875465181
SN - 0004-637X
VL - 766
SP - n/a
JO - The Astrophysical Journal
JF - The Astrophysical Journal
IS - 2
M1 - 88
ER -