Neutron star atmosphere composition: the quiescent, low-mass X-ray binary in the globular cluster M28

Understand

Using deep Chandra observations of the globular cluster M28, we study the quiescent X-ray emission of a neutron star in a low-mass X-ray binary in order to constrain the chemical composition of the neutron star atmosphere and the equation of state of dense matter.

• We fit the spectrum with different neutron star atmosphere models composed of hydrogen, helium or carbon.
• The parameter values obtained with the carbon model are unphysical and such a model can be ruled out.
• Hydrogen and helium models give realistic parameter values for a neutron star, and the derived mass and radius are clearly distinct depending on the composition of the atmosphere.