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Probing the X-Ray Binary Populations of the Ring Galaxy NGC 1291
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Author and Affiliation:
Luo, B.(Harvard Univ., Smithsonian Center for Astrophysics, Cambridge, MA, United States);
Fabbiano, G.(Harvard Univ., Smithsonian Center for Astrophysics, Cambridge, MA, United States);
Fragos, T.(Harvard Univ., Smithsonian Center for Astrophysics, Cambridge, MA, United States);
Kim, D. W.(Harvard Univ., Smithsonian Center for Astrophysics, Cambridge, MA, United States);
Belczynski, K.(Warsaw Univ., Astronomical Observatory, Warsaw, Poland);
Brassington, N. J.(Hertfordshire Univ., Hatfield, United Kingdom);
Pellegrini, S.(Bologna Univ., Dipartimento di Astronomia, Italy);
Tzanavaris, P.(Johns Hopkins Univ., Baltimore, MD, United States);
Wang, J.(Harvard Univ., Smithsonian Center for Astrophysics, Cambridge, MA, United States);
Zezas, A.(Crete Univ., Crete, Greece)
Abstract: We present Chandra studies of the X-ray binary (XRB) populations in the bulge and ring regions of the ring galaxy NGC 1291. We detect 169 X-ray point sources in the galaxy, 75 in the bulge and 71 in the ring, utilizing the four available Chandra observations totaling an effective exposure of 179 ks. We report photometric properties of these sources in a point-source catalog. There are approx. 40% of the bulge sources and approx. 25% of the ring sources showing > 3(sigma) long-term variability in their X-ray count rate. The X-ray colors suggest that a significant fraction of the bulge (approx. 75%) and ring (approx. 65%) sources are likely low-mass X-ray binaries (LMXBs). The spectra of the nuclear source indicate that it is a low-luminosity AGN with moderate obscuration; spectral variability is observed between individual observations. We construct 0.3-8.0 keV X-ray luminosity functions (XLFs) for the bulge and ring XRB populations, taking into account the detection incompleteness and background AGN contamination. We reach 90% completeness limits of approx.1.5 x 10(exp 37) and approx. 2.2 x 10(exp 37) erg/s for the bulge and ring populations, respectively. Both XLFs can be fit with a broken power-law model, and the shapes are consistent with those expected for populations dominated by LMXBs. We perform detailed population synthesis modeling of the XRB populations in NGC 1291 , which suggests that the observed combined XLF is dominated by aD old LMXB population. We compare the bulge and ring XRB populations, and argue that the ring XRBs are associated with a younger stellar population than the bulge sources, based on the relative over-density of X-ray sources in the ring, the generally harder X-ray color of the ring sources, the overabundance of luminous sources in the combined XLF, and the flatter shape of the ring XLF.
Publication Date: Feb 14, 2012
Document ID:
20120015664
(Acquired Nov 15, 2012)
Subject Category: ASTROPHYSICS
Report/Patent Number: GSFC.JA.7094.2012
Document Type: Preprint
Contract/Grant/Task Num: NAS8-03060; GO0-11104X; ASI/INAF I/009/10/0
Financial Sponsor: NASA Goddard Space Flight Center; Greenbelt, MD, United States
Organization Source: Harvard Univ.; Smithsonian Center for Astrophysics; Cambridge, MA, United States
Description: 15p; In English; Original contains color and black and white illustrations
Distribution Limits: Unclassified; Publicly available; Unlimited
Rights: Copyright; Distribution under U.S. Government purpose rights
NASA Terms: X RAY ASTROPHYSICS FACILITY; X RAY BINARIES; POINT SOURCES; GALACTIC BULGE; X RAY SOURCES; LUMINOSITY; VARIABILITY; STARS
Miscellaneous Notes: To be published in The Astrophysical Journal
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