高能暂现源 · 每日文献综述

Photospheric emission from relativistic gamma-ray burst (GRB) jets is a promising mechanism for producing the Band-like spectra observed in the prompt phase, yet the connections between jet structure, dissipation location, and polarization signatures remain unclear. We investigate time-dependent photospheric radiation transfer in structured relativistic jets by coupling two-dimensional axisymmetric special relativistic hydrodynamic simulations with Monte Carlo photon propagation. Photon escape and subphotospheric dissipation are characterized using the residual line-of-sight optical depth <inline-formula> <mml:math><mml:msub><mml:mrow><mml:mi>τ</mml:mi></mml:mrow><mml:mrow><mml:mi>out</mml:mi></mml:mrow></mml:msub><mml:mo>(</mml:mo><mml:mover><mml:mrow><mml:mi>Ω</mml:mi></mml:mrow><mml:mrow><mml:mo>̂</mml:mo></mml:mrow></mml:mover><mml:mo>)</mml:mo></mml:math> </inline-formula> evaluated along each photon trajectory, allowing a direction-dependent treatment of photon decoupling in structured jets. The radiative transfer includes Klein─Nishina Compton scattering and polarization evolution using the Mueller matrix formalism. We perform a systematic parameter study exploring the effects of viewing angle, electron─positron pair loading (Z<SUB>±</SUB>), and the optical-depth window of subphotospheric dissipation. The model produces time-resolved spectra, peak-energy evolution E<SUB>pk</SUB>(t), Band parameters, polarization degree Π(E, t), and last-scattering statistics. We find that jet angular structure and the geometry of the line-of-sight optical depth strongly regulate spectral evolution and polarization signatures. The dissipation depth and pair loading jointly control the stability of E<SUB>pk</SUB>, the formation of high-energy spectral tails, and the energy dependence of polarization. These results provide quantitative predictions for GRB prompt-emission spectra and polarization that can be tested with current and upcoming high-energy polarimeters.