Open AccessX‐Ray Sources and Their Optical Counterparts in the Globular Cluster M4
Author(s) -
C. Bassa,
D. Pooley,
Lee Homer,
F. Verbunt,
B. M. Gaensler,
W. H. G. Lewin,
Scott F. Anderson,
B. Margon,
V. M. Kaspi,
M. van der Klis
Publication year - 2004
Publication title -
the astrophysical journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.376
H-Index - 489
eISSN - 1538-4357
pISSN - 0004-637X
DOI - 10.1086/421259
Subject(s) - globular cluster , physics , astrophysics , millisecond pulsar , rosat , observatory , astronomy , luminosity , cluster (spacecraft) , hubble space telescope , astrometry , radius , mass segregation , pulsar , stars , galaxy , computer security , computer science , programming language
We report on the Chandra X-ray Observatory ACIS-S3 imaging observation of theGalactic globular cluster M4 (NGC 6121). We detect 12 X-ray sources inside thecore and 19 more within the cluster half-mass radius. The limiting luminosityof this observation is Lx~10e29 erg/sec for sources associated with thecluster, the deepest X-ray observation of a globular cluster to date. Weidentify 6 X-ray sources with known objects and use ROSAT observations to showthat the brightest X-ray source is variable. Archival data from the HubbleSpace Telescope allow us to identify optical counterparts to 16 X-ray sources.Based on the X-ray and optical properties of the identifications and theinformation from the literature, we classify two (possibly three) sources ascataclysmic variables, one X-ray source as a millisecond pulsar and 12 sourcesas chromospherically active binaries. Comparison of M4 with 47 Tuc and NGC 6397suggests a scaling of the number of active binaries in these clusters with thecluster (core) mass.
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