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29 March 2024
 
  » arxiv » astro-ph/0307125

 Article overview


Low Mass X-ray Binaries and Globular Clusters in Early-Type Galaxies
Craig L. Sarazin ; Arunav Kundu ; Jimmy A. Irwin ; Gregory R. Sivakoff ; Elizabeth L. Blanton ; Scott W. Randall ;
Date 7 Jul 2003
Journal Astrophys.J. 595 (2003) 743-759
Subject astro-ph
AffiliationUVa), Arunav Kundu (MSU), Jimmy A. Irwin (UM), Gregory R. Sivakoff, Elizabeth L. Blanton, Scott W. Randall (UVa
Abstract(Abridged) A high fraction of the Low Mass X-ray Binaries (LMXBs) in early-type galaxies are associated with globular clusters (GCs). Here, we discuss the correlations between LMXBs and GCs in a sample of four early-type galaxies. There is some evidence that the fraction of LMXBs associated with GCs (f_X-GC) increases along the Hubble sequence from spiral bulges to S0s to Es to cDs. On the other hand, the fraction of globular clusters which contain X-ray sources appears to be roughly constant at f_GC-X ~ 4%. There is a strong tendency for the X-ray sources to be associated with the optically more luminous GCs. However, this correlation is consistent with a constant probability of finding a LMXB per unit optical luminosity; it seems to result primarily from the larger number of stars in optically luminous GCs. The probability of finding a bright LMXB per unit optical luminosity in the GCs is about 1.5e-7 LMXBs per L_solar,I for L_X >~ 1e38 erg/s, and rises to about 2.0e-7 LMXBs per L_solar,I at lower X-ray luminosities, L_X >~ 3e37 erg/s. This frequency appears to be roughly constant for different galaxies, including the bulges of the Milky Way and M31. There is a tendency for the X-ray sources to be found preferentially in redder GCs. This seems to indicate that the evolution of X-ray binaries in a GC is affected either by the metallicity or age of the GC, with younger and/or more metal rich GCs having more LMXBs. There is a weak tendency for the brightest LMXBs, whose luminosities exceed the Eddington luminosity for a 1.4 M_solar neutron star, to avoid GCs. That may indicate that black hole X-ray are somewhat less likely to be found in GCs, as seems to be true in our Galaxy.
Source arXiv, astro-ph/0307125
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