Structure of Pair Winds from Compact Objects with Application to Emission from Hot Bare Strange Stars

Abstract

We consider a stationary, spherically outflowing wind consisting of electron-positron pairs and photons. We do not assume thermal equilibrium and include the two-body processes that occur in such a wind, Møller and Bhaba scattering of pairs, Compton scattering, two-photon pair annihilation, and two-photon pair production, together with their radiative three-body variants: bremsstrahlung, double Compton scattering, and three-photon pair annihilation, with their inverse processes. In the concrete example described here, the wind injection source is a hot, bare, strange star. Such stars are thought to be powerful sources of pairs created by the Coulomb barrier at the quark surface. We present a new, finite difference scheme for solving the relativistic kinetic Boltzmann equations for pairs and photons. Using this method, we study the kinetics of the wind particles and the emerging emission for total luminosities of L = 1034-1042 ergs s-1 (the upper limit being set, at the moment, by computational limitations). We find the rates of particle number and energy outflows, outflow velocities, number densities, energy spectra, and other parameters for both photons and pairs as functions of the distance. We find that for L > 2 × 1035 ergs s-1, photons dominate the emerging emission. For all values of L the number rate of emerging pairs is bounded: e ≲ ≃ 1043 s-1. As L increases from ~1034 to 1042 ergs s-1, the mean energy of emergent photons decreases from ~400-500 to 40 keV, as the spectrum changes in shape from that of a wide annihilation line to nearly a blackbody spectrum with a high-energy (>100 keV) tail. These results are pertinent to the deduction of the outside appearance of hot bare strange stars, which might help discern them from neutron stars.