The mass and the radius of the neutron star in the transient low-mass x-ray binary SAX J1748.9-2021

Tolga Güver, Feryal Ozel

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We use time-resolved spectroscopy of thermonuclear X-ray bursts observed from SAX J1748.9-2021 to infer the mass and the radius of the neutron star in the binary. Four X-ray bursts observed from the source with the Rossi X-ray Timing Explorer enable us to measure the angular size and the Eddington limit on the neutron star surface. Combined with a distance measurement to the globular cluster NGC 6440, in which SAX J1748.9-2021 resides, we obtain two solutions for the neutron star radius and mass, R = 8.18 ± 1.62 km and M = 1.78 ± 0.3 M or R = 10.93 ± 2.09 km and M = 1.33 ± 0.33 M.

Original languageEnglish (US)
Article numberL1
JournalAstrophysical Journal Letters
Issue number1
Publication statusPublished - Mar 1 2013



  • stars: neutron
  • X-rays: binaries
  • X-rays: individual (SAX J1748-2021)

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

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