5.4 Electromagnetic and neutrino signature modeling

Motivated by the evidence that SGRBs frequently appear in galaxies with very low star formation rates [40, 109], astronomers have suggested that their progenitors are likely to be mergers of either NS-NS and/or BH-NS binaries. While soft-gamma repeaters (SGRs) have been confirmed as an SGRB source from observations of the system SGR 1806–20, they make up no more than approximately 15% of the total observed SGRB fraction according to the leading population estimates [164, 199]. There has been much interest in predicting the EM signatures of NS-NS and BH-NS mergers, along with the associated neutrino emission. The simplest models estimate a local radiation cooling rate for the matter but do not attempt to follow the paths of the photons and/or neutrinos after they are emitted, instead calculating the time-dependent luminosity assuming free streaming. Such models have been used in non-GR simulations of binary mergers going back more than a decade [253Jump To The Next Citation Point, 246Jump To The Next Citation Point], and recently such schemes have been used to perform full GR NS-NS mergers [265Jump To The Next Citation Point], including a self-consistent evolution of the electron fraction of the material Ye, rather than a passive advection approach.

More complicated flux-limited diffusion schemes, in which the neutrino fluxes for given species and energies are given by explicit formulae that limit to the correct values for zero optical depth (free-streaming) and very large optical depth (diffusion), have been used as a post-processing tool to investigate the merger remnants in Newtonian NS-NS mergers [82Jump To The Next Citation Point], but have yet to be applied to full GR simulations. Finally, radiation transport schemes to evolve EM and neutrino fluxes passing through fluid configurations have been implemented in numerical GR codes [80, 103], but have yet to be used in binary merger simulations.

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