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J.A. Pons, F.W. Walter, J.M. Lattimer, M. Prakash (SUNY at Stony Brook)
We present an investigation of the mass (M) and radius (R) determination of the isolated Neutron Star RX J185635-3754. We compute non-magnetized model atmospheres and emergent spectra for different compositions and gravities, and discuss model fits to ROSAT, EUVE and HST/optical data. The spectral energy distribution is consistent with a heavy element (Iron, Silicon) atmosphere, while light element atmospheres seem difficult to reconcile with the data, even with the presence of a strong magnetic field. Our fits allow us to determine the effective temperature and the M/R and R/D ratios. These ratios, together with recent parallax measurements which give a distance to the object of D\approx 60 pc, result in the first direct measurement of the mass and radius of a Neutron Star. The implications on the equation of state of dense matter and the possible presence of exotic phases at several times nuclear saturation density are outlined.
The author(s) of this abstract have provided an email address for comments about the abstract: jpons@neutrino.ess.sunsyb.edu