Thermal Radiation from Neutron Stars: Chandra Results

The outstanding capabilities of the Chandra X-ray observatory have greatly increased our potential to observe and analyze thermal radiation from the surfaces of neutron stars (NSs). Such observations allow one to measure the surface temperatures and confront them with the predictions of the NS cooling models. Detection of gravitationally redshifted spectral lines can yield the NS mass-to-radius ratio. In rare cases when the distance is known, one can measure the NS radius, which is particularly important to constrain the equation of state of the superdense matter in the NS interiors. Finally, one can infer the chemical composition of the NS surface layers, which provides information about formation of NSs and their interaction with the environment. We overview the recent Chandra results on the thermal radiation from various types of NSs -- active pulsars, young radio-quiet neutron stars in supernova remnants, old radio-silent ``dim'' neutron stars -- and discuss their implications.