The radius of the quiescent neutron star in the globular cluster M13

Understand

X-ray spectra of quiescent low-mass X-ray binaries containing neutron stars can be fit with atmosphere models to constrain the mass and the radius.

• Mass-radius constraints can be used to place limits on the equation of state of dense matter.
• We perform fits to the X-ray spectrum of a quiescent neutron star in the globular cluster M13, utilizing data from ROSAT, Chandra and XMM-Newton, and constrain the mass-radius relation.
• Assuming an atmosphere composed of hydrogen and a 1.4${\rm M}_{\odot}$ neutron star, we find the radius to be $R_{\rm NS}=12.2^{+1.5}_{-1.1}$ km, a significant improvement in precision over previous measurements.