We investigate the shape of the jet break in within-beam gamma-ray burst (GRB) optical afterglows for various lateral jet structure profiles. We consider cases with and without lateral spreading and a range of inclinations within the jet core half-opening angle, θc. We fit model and observed afterglow light curves with a smoothly-broken power-law function with a free-parameter κ that describes the sharpness of the break. We find that the jet break is sharper (κ is greater) when lateral spreading is included than in the absence of lateral spreading. For profiles with a sharp-edged core, the sharpness parameter has a broad range of 0.1 ≲ κ ≲ 4.6, whereas profiles with a smooth-edged core have a narrower range of 0.1 ≲ κ ≲ 2.2 when models both with and without lateral spreading are included. For sharp-edged jets, the jet break sharpness depends strongly on the inclination of the system within θc, whereas for smooth-edged jets, κ is more strongly dependent on the size of θc. Using a sample of 20 GRBs, we find 9 candidate smooth-edged jet structures and 8 candidate sharp-edged jet structures, while the remaining 3 are consistent with either. The shape of the jet break, as measured by the sharpness parameter κ, can be used as an initial check for the presence of lateral structure in within-beam GRBs where the afterglow is well-sampled at and around the jet-break time.

中文翻译：

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GRB射流结构和射流断裂

我们研究了各种横向射流结构剖面的束内伽马射线爆发 (GRB) 光学余辉中射流破裂的形状。我们考虑有和没有横向扩展的情况，以及射流核心半开角 θc 内的一系列倾斜。我们拟合模型和观察到的余辉光曲线具有平滑破坏的幂律函数，其自由参数 κ 描述了中断的锐度。我们发现，当包括横向扩展时，射流中断更尖锐（κ 更大），而不是在没有横向扩展的情况下。对于边缘锐利的型材，其锐度参数的范围很广，为 0.1 ≲ κ ≲ 4.6，而具有光滑边缘的型材在具有和不具有横向扩展的模型时的范围较窄，为 0.1 ≲ κ ≲ 2.2包括。对于锋利的喷气机，射流断裂的锐度很大程度上取决于系统在 θc 内的倾角，而对于光滑边缘的射流，κ 更强烈地取决于 θc 的大小。使用 20 个 GRB 的样本，我们发现 9 个候选光滑边缘喷流结构和 8 个候选锐边喷流结构，而其余 3 个与任何一个都一致。由锐度参数 κ 测量的射流中断的形状可用作在射流中断时间及其前后对余辉进行良好采样的束内 GRB 中是否存在横向结构的初步检查。