General Relativistic Spectra of Accretion Disks around Rotating Neutron Stars

General relativistic spectra from accretion disks around rotating neutronstars in the appropriate space-time geometry for several different equation ofstate, spin rates and mass of the compact object have been computed. Theanalysis involves the computation of the relativistically corrected radialtemperature profiles and the effect of Doppler and gravitational red-shifts onthe spectra. Light bending effects have been omitted for simplicity. Therelativistic spectrum is compared with the Newtonian one and it is shown thatthe difference between the two is primarily due to the different radialtemperature profile for the relativistic and Newtonian disk solutions. To facilitate direct comparison with observations, a simple empiricalfunction has been presented which describes the numerically computedrelativistic spectra well. This empirical function (which has three parametersincluding normalization) also describes the Newtonian spectrum adequately. Thusthe function can in principle be used to distinguish between the two. Inparticular, the best fit value of one of the parameters ($\beta$-parameter)$\approx 0.4$ for the Newtonian case, while it ranges from 0.1 to 0.35 forrelativistic case depending upon the inclination angle, EOS, spin rate and massof the neutron star. Constraining this parameter by fits to futureobservational data of X-ray binaries will indicate the effect of strong gravityin the observed spectrum.Comment: 11 pages, 7 figures, uses psbox.tex and emulateapj5.sty. Accepted for publication in Ap