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Register a new userMonopole gravitational waves from relativistic fireballs driving gamma-ray bursts
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Authors
M. Kutschera
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Einsteins general relativity predicts that pressure, in general stresses, play a similar role to energy density in generating gravity. The source of gravitational field, the active gravitational mass density, sometimes referred to as Whittakers mass density, is not conserved, hence its changes can propagate as monopole gravitational waves. Such waves can be generated only by astrophysical sources with varying gravitational mass. Here we show that relativistic fireballs, considered in modelling gamma-ray burst phenomena, are likely to radiate monopole gravitational waves from high-pressure plasma with varying Whittakers mass. Also, ejection of a significant amount of initial mass-energy of the progenitor contributes to the monopole gravitational radiation. We identify monopole waves with h^11+h^22 waves of Eddingtons classification which propagate (in the z-direction) together with the energy carried by massless fields. We show that the monopole waves satisfy Einsteins equations, with a common stress-energy tensor for massless fields. The polarization mode of monopole waves is Phi_22, i.e. these are perpendicular waves which induce changes of the radius of a circle of test particles only (breathing mode). The astrophysical importance of monopole gravitational waves is discussed.
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We consider the interaction between a relativistic fireball and material assumed to be still located just outside the progenitor star. Only a small fraction of the expected mass is sufficient to efficiently decelerate the fireball, leading to dissipation of most of its kinetic energy. Since the scattering optical depths are still large at distances comparable to the progenitor radius, the dissipated energy is trapped in the system, accelerating it to relativistic velocities. The process resembles the birth of another fireball at radii R~1e11 cm, not far from the transparency radius, and with a starting bulk Lorentz factors Gamma_c~10. As seen in the observer frame, this re--generated fireball appears collimated within an angle theta_j=1/Gamma_c. If the central engine works intermittently, the funnel can, at least partially, refill and the process can repeat itself. We discuss how this idea can help solving some open issues of the more conventional internal shock scenario for interpreting the Gamma-Ray Burst properties.
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