eXTP对伽马射线暴余辉平台阶段偏振的探测前景
The detection prospects of the polarizations in the plateau phase of GRB afterglow by eXTP
AI总结：
本文研究eXTP对GRB余辉平台阶段偏振的探测前景，发现RWB模型的偏振信号更易被eXTP/PFA探测，可用于检验两种能量注入模型。
AI中文摘要：
约20%-50%的伽马射线暴（GRB）X射线余辉呈现浅衰减特征，目前已提出两种流行的能量注入模型来解释该观测现象：具有坡印廷通量注入的相对论性气泡（RWB）模型，以及具有动力学能量注入的结构喷流（SE）模型。两种模型的偏振预测已被研究，可用于检验这两种模型，但参数对模型预测的影响尚未被研究，也未与即将开展的增强型X射线时变与偏振 mission（eXTP）的探测能力进行对比。我们针对上述问题开展研究，发现模型参数对两种模型预测偏振的影响非常有限。为在平台阶段开展可行的偏振探测，需要优先目标观测（ToO）响应；在优先ToO模式下，一次指向观测对GRB平台阶段的探测概率约为1/3。偏振探测概率取决于坡印廷通量注入与动力学能量注入的比值，该比值目前尚不明确。RWB模型的预测流量密度和偏振度（PD）可远高于eXTP上的偏振聚焦阵列（PFA）的阈值流量和最小可探测偏振度，而SE模型的预测PD则难以被eXTP/PFA探测到。因此，在GRB平台阶段探测到显著偏振信号将更倾向于支持RWB模型，且注入能量为坡印廷通量；若未探测到偏振信号，则表明是SE模型的动力学能量注入。
英文摘要：
Approximately (20-50)$\%$ of the gamma-ray burst (GRB) X-ray afterglows exhibit the shallow decay features. Two popular energy-injection models had been proposed to interpret such observational phenomenons, the relativistic wind bubble (RWB) model with a Poynting-flux injection and the structured ejecta (SE) model with a dynamical energy injection. Polarization predictions of the two models had been investigated and can be used as a test of the two models. However, the impacts of the parameters on the model predictions were not studied and the comparisons with the detection ability of the forthcoming mission, enhanced X-ray Timing and Polarimetry (eXTP), had not been discussed. We considered the above issues and found that influences of the model parameters on the predicted polarizations of the two models are very limited. To perform a feasible polarization detection during the plateau phase, the priority ToO response is required. The detection probability of the GRB plateau phase is about $1/3$ for one pointing under the priority ToO. The polarization detection probability would depend on the ratio between the Poynting-flux injection to the dynamical energy injection, which is unclear currently. The predicted flux density and polarization degree (PD) of the RWB model could be well above the threshold flux and minimal detectable polarization degree of the polarimetry focusing array (PFA) on board eXTP, while the predicted PDs of the SE model would be difficult to be detected by eXTP/PFA. Therefore, a detection of a significant polarization signal during the GRB plateau phase would prefer the RWB model and the injected energy would be in the form of the Poynting flux, while a non detection of the polarized signal would indicate a dynamical energy injection of the SE model.
