The afterglow emission from gamma-ray bursts (GRBs) is believed to originate from a relativistic blast wave driven into the circumburst medium. Although the afterglow emission from radio up to X-ray frequencies is thought to originate from synchrotron radiation emitted by relativistic, non-thermal electrons accelerated by the blast wave, the origin of the emission at high energies (HE; $\gtrsim$GeV) remains uncertain. The recent detection of sub-TeV emission from GRB 190114C by MAGIC raises further debate on what powers the very high-energy (VHE; $\gtrsim 300$GeV) emission. Here, we explore the inverse Compton scenario as a candidate for the HE and VHE emissions and consider two sources of seed photons for scattering: synchrotron photons from the blast wave (synchrotron self-Compton or SSC) and isotropic photon fields external to the blast wave (external Compton). For each case, we compute the multi-wavelength afterglow spectra and light curves. We find that SSC will dominate particle cooling and the GeV emission, unless a dense ambient infrared photon field, typical of star-forming regions, is present. Additionally, considering the extragalactic background light attenuation, we discuss the detectability of VHE afterglows by existing and future gamma-ray instruments for a wide range of model parameters. Studying GRB 190114C, we find that its afterglow emission in the Fermi-LAT band is synchrotron-dominated for $t\lesssim10^3$ s, but it later becomes SSC-dominated. The late-time Fermi-LAT measurement (i.e., $t\sim 10^4$ s) also sets an upper limit on the energy density of a putative external infrared photon field (i.e., $\lesssim 7.5\times 10^{-8}\, {\rm erg\,cm^{-3}}$). Finally, we predict that the VHE flux at $10^4$ s, which is still SSC dominated, is $ 3\times 10^{-11}$ ${\rm erg\,cm^{-2}\,s^{-1}}$.

中文翻译：

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伽马射线爆发余辉的逆康普顿特征

伽马射线暴 (GRB) 的余辉发射被认为源自驱动到环爆介质中的相对论性爆炸波。虽然从无线电发射到 X 射线频率的余辉发射被认为源自由爆炸波加速的相对论性非热电子发射的同步加速器辐射，但高能发射的起源 (HE; $\gtrsim$GeV)仍然不确定。最近由 MAGIC 检测到 GRB 190114C 的亚 TeV 发射引发了关于是什么为超高能 (VHE; $\gtrsim 300$GeV) 发射提供动力的进一步辩论。在这里，我们探索了逆康普顿场景作为 HE 和 VHE 发射的候选者，并考虑了两种用于散射的种子光子源：来自冲击波的同步加速器光子（同步加速器自康普顿或 SSC）和冲击波外部的各向同性光子场（外部康普顿）。对于每种情况，我们计算多波长余辉光谱和光变曲线。我们发现 SSC 将主导粒子冷却和 GeV 发射，除非存在密集的环境红外光子场，这是典型的恒星形成区域。此外，考虑到河外背景光衰减，我们讨论了现有和未来伽马射线仪器对各种模型参数的 VHE 余辉的可探测性。研究 GRB 190114C，我们发现它在 Fermi-LAT 波段的余辉发射在 $t\lesssim10^3$ s 内以同步加速器为主，但后来变为以 SSC 为主。后期 Fermi-LAT 测量（即，$t\sim 10^4$ s) 还为假定的外部红外光子场的能量密度设置了上限（即 $\lesssim 7.5\times 10^{-8}\, {\rm erg\,cm ^{-3}}$）。最后，我们预测 $10^4$ s 处的 VHE 通量，仍为 SSC 主导，为 $ 3\times 10^{-11}$ ${\rm erg\,cm^{-2}\,s^ {-1}}$。