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Title: A SECOND NEUTRON STAR IN M4?

We show that the optical counterpart of the X-ray source CX 1 in M4 is a {approx}20th magnitude star, located in the color-magnitude diagram on (or very close to) the main sequence of the cluster, and exhibiting sinusoidal variations of the flux. We find the X-ray flux to be also periodically variable, with X-ray and optical minima coinciding. Stability of the optical light curve, lack of UV-excess, and unrealistic mean density resulting from period-density relation for semidetached systems speak against the original identification of CX 1 as a cataclysmic variable. We argue that the X-ray active component of this system is a neutron star (probably a millisecond pulsar).
Authors:
; ; ;  [1] ;  [2]
  1. Nicolaus Copernicus Astronomical Center, Bartycka 18, 00-716 Warsaw (Poland)
  2. Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)
Publication Date:
OSTI Identifier:
22047872
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 750; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTRONOMY; ASTROPHYSICS; COLOR; COSMIC PHOTONS; COSMIC X-RAY SOURCES; DENSITY; DIAGRAMS; MAIN SEQUENCE STARS; NEUTRON STARS; PERIODICITY; PULSARS; STABILITY; VISIBLE RADIATION; X RADIATION