论文标题
具有多极磁场的磁场相干无线电发射的角度依赖性
Angular Dependence of Coherent Radio Emission from Magnetars with Multipolar Magnetic Fields
论文作者
论文摘要
最近从银河磁铁中检测到快速无线电爆发（FRB）的事实确保了具有超强磁场的中子星（NSS）能够产生这些非常明亮的相干无线电爆发。解释这种相干无线电发射起源的主要机制之一是偶极磁场结构内的曲率辐射过程。但是，已经证明磁铁可能具有更复杂的磁场拓扑结构。在这里，我们在存在倾斜的偶极和四极（“四极”）磁场的情况下进行严格研究曲率无线电发射，并表明其角度特性在其角度特性与纯粹的偶极情况有所不同。我们在分析上表明，可以显着修改开放线的形状，具体取决于四极与偶极场强度的比率及其在NS表面的倾斜角度的比率。这会沿每个磁场线创建多个点，与观察者的视线一致，并可以解释观察到的FRB的复杂光谱和时间结构。我们还发现，在Quadrudipole中，无线电梁可以采用更大的角范围，并且梁宽度可以比纯偶极子宽。这可以解释为什么磁铁的瞬时无线电脉动的脉冲宽度与普通无线电脉冲星的脉冲宽度大。
The recent detection of a Fast Radio Burst (FRB) from a Galactic magnetar secured the fact that neutron stars (NSs) with super-strong magnetic fields are capable of producing these extremely bright coherent radio bursts. One of the leading mechanisms to explain the origin of such coherent radio emission is the curvature radiation process within the dipolar magnetic field structure. It has, however, already been demonstrated that magnetars likely have a more complex magnetic field topology. Here we critically investigate curvature radio emission in the presence of inclined dipolar and quadrupolar ("quadrudipolar") magnetic fields and show that such field structures differ in their angular characteristics from a purely dipolar case. We analytically show that the shape of open field lines can be modified significantly depending on both the ratio of quadrupole to dipole field strength and their inclination angle at the NS surface. This creates multiple points along each magnetic field line that coincides with the observer's line of sight and may explain the complex spectral and temporal structure of the observed FRBs. We also find that in quadrudipole, the radio beam can take a wider angular range and the beam width can be wider than in pure dipole. This may explain why the pulse width of the transient radio pulsation from magnetars is as large as that of ordinary radio pulsars.
