arXiv 0807.08112008-07-08astro-ph

DA495 -一个老化的脉冲星风星云

DA495 - an aging pulsar wind nebula

R. Kothes, T. L. Landecker, W. Reich, S. Safi-Harb, Z. Arzoumanian

备注：: 25 pages, accepted by ApJ
DOI：: 10.1086/591653

摘要：

我们提出了一个无线电连续研究的脉冲星风星云（PWN）DA 495（G65.7+1.2），包括图像的总强度和线性偏振从408至10550 MHz的基础上，加拿大银河平面调查和观察与Effelsberg 100米射电望远镜。从叠加的\ion{H}{2}区域和致密河外源中去除通量密度的贡献，揭示了DA 495在1.3 GHz处的光谱中的一个中断，其光谱指数$α={-0.45 \pm 0.20}$低于中断，$α={-0.87 \pm 0.10}$高于中断（${S}_ν\propto{ν^α}$）。频谱中断的频率比在任何其他PWN中检测到的最低中断低三倍以上。光谱的中断可能是同步加速器冷却的结果，而年龄为20，000年的DA 495可能是从一个类似船帆座X星云的天体演化而来，拥有类似的能量脉冲星。我们在星云内部发现了1.3 mG的磁场。在对高内旋测量进行校正后，磁场结构非常简单，类似于投射到天空平面上的偶极场的内部部分，尽管也可能存在环形分量。偶极场轴应该平行于假定的脉冲星的自旋轴，位于北天极以东的${\sim}50\degr$角处，并指向远离我们的西南方向。在DA 495周围的任何壳型超新星遗迹的射电表面亮度上限为$Σ_{1 GHz} \sim 5.4 \times 10^{-23}$ OAWatt m $^{-2}$ Hz $^{-1}$ sr $^{-1}$（假设射电光谱指数为$α= -0.5$），低于迄今已知最暗的壳型遗迹。

英文摘要：

We present a radio continuum study of the pulsar wind nebula (PWN) DA 495 (G65.7+1.2), including images of total intensity and linear polarization from 408 to 10550 MHz based on the Canadian Galactic Plane Survey and observations with the Effelsberg 100-m Radio Telescope. Removal of flux density contributions from a superimposed \ion{H}{2} region and from compact extragalactic sources reveals a break in the spectrum of DA 495 at 1.3 GHz, with a spectral index $α={-0.45 \pm 0.20}$ below the break and $α={-0.87 \pm 0.10}$ above it (${S}_ν\propto{ν^α}$). The spectral break is more than three times lower in frequency than the lowest break detected in any other PWN. The break in the spectrum is likely the result of synchrotron cooling, and DA 495, at an age of $\sim$20,000 yr, may have evolved from an object similar to the Vela X nebula, with a similarly energetic pulsar. We find a magnetic field of $\sim$1.3 mG inside the nebula. After correcting for the resulting high internal rotation measure, the magnetic field structure is quite simple, resembling the inner part of a dipole field projected onto the plane of the sky, although a toroidal component is likely also present. The dipole field axis, which should be parallel to the spin axis of the putative pulsar, lies at an angle of ${\sim}50\degr$ east of the North Celestial Pole and is pointing away from us towards the south-west. The upper limit for the radio surface brightness of any shell-type supernova remnant emission around DA 495 is $Σ_{1 GHz} \sim 5.4 \times 10^{-23}$ OAWatt m$^{-2}$ Hz$^{-1}$ sr$^{-1}$ (assuming a radio spectral index of $α= -0.5$), lower than the faintest shell-type remnant known to date.

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