SNR G156 .2+5.7在λ 6cm处的偏振观测
Polarization observations of SNR G156.2+5.7 at lambda 6cm
摘要：
G156.2+5.7是在ROSAT X射线巡天中首次发现的大型超新星遗迹（SNR），但由于其表面亮度低和体积大，无线电观测很少。无线电连续谱和偏振图像的SNR G156.2+5.7在λ 6厘米的第一次被讨论的背景下，与现有的数据，以调查其物理特性。我们得到了G156.2+5.7的积分通量密度为S_6cm = 2.5+-0.5Jy。在λ 74 cm和6 cm之间，不包括致密射电源，综合发射的光谱指数为α =-0.48+-0.08。我们还得到了一个光谱指数图，它显示了壳和SNR的中心区域之间的变化很小。这与恒定积分通量密度谱是一致的。高极化无线电发射已被检测到从SNR壳，但也从一个中央补丁，这可能是起源于前部分的球形SNR壳。我们从11 cm和6 cm处的偏振数据导出了旋转测量的分布，并在SNR壳层中发现了相反方向的RM梯度。SNR G156.2+5.7是不寻常的，因为它在射电范围内具有极高的X射线亮度和极低的表面亮度。磁场沿髋臼杯外围非常有序，与压缩环境磁场的预期一致。环形磁场分量由RM分布表示。（节略）
英文摘要：
G156.2+5.7 is a large supernova remnant (SNR) first discovered in the ROSAT X-ray survey but radio observations are rare because of its low surface brightness and large size. Radio continuum and polarization images of the SNR G156.2+5.7 at lambda 6 cm are presented for the first time to be discussed in the context with available data to investigate its physical properties. We obtained an integrated flux density for G156.2+5.7 of S6cm= 2.5+-0.5Jy. The spectral index of the integrated emission is alpha=-0.48+-0.08 between lambda 74 cm and 6 cm excluding compact radio sources. We also obtained a spectral index map, which shows little variation between the shells and the central area of the SNR. This is consistent with the constant integrated flux density spectrum. Highly polarized radio emission has been detected from the SNR shell, but also from a central patch, which probably originates in the front part of the spherical SNR shell. We derived the distribution of rotation measure from polarization data at 11 cm and 6 cm and found RM gradients of opposite direction in the SNR shell. The SNR G156.2+5.7 is unusual by its exceptionally high X-ray brightness and very low surface-brightness in the radio range. The magnetic field is very well ordered along the shell periphery as expected for a compressed ambient magnetic field. A toroidal magnetic field component is indicated by the RM distribution. (abridged)
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