Faraday Rotation Measure Gradients from a Helical Magnetic Field in 3C 273
Faraday Rotation Measure Gradients from a Helical Magnetic Field in 3C 273
复制标题
DOI：
10.1086/431901
复制
发表时间：
2005-05
期刊：
影响因子：
--
通讯作者：
R. Zavala;G. Observatory;Nrao;Kavli Institute for Astrophysics;Cosmology
中科院分区：
文献类型：
--
作者：
R. Zavala;G. Observatory;Nrao;Kavli Institute for Astrophysics;Cosmology
使用高频（12-22 GHz）VLBA观测，我们确认存在一个法拉第旋转测量梯度~500拉德m-2 mas-1横向喷流轴的类星体3C 273。梯度是在两个时期间隔约6个月。这种稳定的横向旋转测量梯度是预期的，如果一个螺旋磁场缠绕周围的射流。内部投影40 pc中磁场的总体顺序与螺旋场一致。然而，我们发现一个意想不到的增加，分数极化沿着边缘的来源，相反的预期。这种高分数极化排除了内部法拉第旋转，但不容易用螺旋场解释。在对旋转测量进行校正后，3C 273喷流中的内禀磁场方向在两个位置处从平行于投影喷流运动变为几乎垂直于投影喷流运动。如果一个螺旋磁场导致所观察到的旋转测量梯度，那么同步辐射发射电子必须从螺旋场区域分离。本文还讨论了其他源中存在或不存在横向旋转测量梯度的问题。
Using high-frequency (12-22 GHz) VLBA observations, we confirm the existence of a Faraday rotation measure gradient of ~500 rad m-2 mas-1 transverse to the jet axis in the quasar 3C 273. The gradient is seen in two epochs spaced roughly 6 months apart. This stable transverse rotation-measure gradient is expected if a helical magnetic field wraps around the jet. The overall order to the magnetic field in the inner projected 40 pc is consistent with a helical field. However, we find an unexpected increase in fractional polarization along the edges of the source, contrary to expectations. This high fractional polarization rules out internal Faraday rotation but is not readily explained by a helical field. After correcting for the rotation measure, the intrinsic magnetic field direction in the jet of 3C 273 changes from parallel to nearly perpendicular to the projected jet motion at two locations. If a helical magnetic field causes the observed rotation measure gradient, then the synchrotron-emitting electrons must be separate from the helical field region. The presence or absence of transverse rotation-measure gradients in other sources is also discussed.