论文标题
伽马射线爆发中衰减磁场的同步加速器极化
The Synchrotron Polarization in Decaying Magnetic Field in Gamma-Ray Bursts
论文作者
论文摘要
极化可以用作伽马射线爆发（GRB）中辐射机理和磁场（MF）构型的探针。在恒定MF的情况下，已广泛研究了GRB的及时阶段中的同步偏振。在本文中，我们考虑了腐烂的MF的情况。我们计算了脉冲中的时间平均和瞬时同步加速器极化，用于不同的视角和大规模衰减的MF模型，这可以解释所谓的带谱。我们发现，用于衰减的大规模MF模型（典型参数的$ \ sim 0.6 $）在50-500 keV的能量带中的轴上时间平均极化度（PD）高于常数MF模型（$ \ \ sim 0.5 $）。一个有趣的结果是，离轴案例中的瞬时PD会经历失误，即PD将从正值演变为负值。这表明极化角度（PA）的变化为$ 90^\ Circ $。这样的结果与在某些脉冲中的发现中发现PA演变的结果大致一致，例如GRB 170114a和GRB 160821a。我们的结果意味着至少一部分突发（离轴爆发）应在脉冲中具有PA演化。
Polarization can serve as a probe of the radiation mechanism and magnetic field (MF) configuration in gamma-ray bursts (GRBs). In the case of constant MF, the synchrotron polarization in the prompt phase of GRBs has been widely studied. In this paper, we consider the case of the decaying MF. We calculate the time-averaged and instantaneous synchrotron polarizations in a pulse for different viewing angles and for the large-scale decaying MF model, which can explain the so-called Band spectrum. We find that the on-axis time-averaged polarization degree (PD) in the energy band of 50-500 keV for the decaying large-scale MF model ($\sim 0.6$ for typical parameters) is higher than that in the constant MF model ($\sim 0.5$). An interesting result is the instantaneous PD in the off-axis case will experience a turnover, i.e., the PD will evolve from a positive value to a negative one. This suggests the polarization angle (PA) change by an angle of $90^\circ$. Such a result is roughly consistent with the discovery of the PA evolution within a pulse in some bursts, such as GRB 170114A and GRB 160821A. Our result implies at least a part of bursts (off-axis bursts) should have the PA evolution in a pulse.
