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arXiv 2201.11398astro-ph.HE
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相干曲率辐射引起的脉冲星剖面光谱变化

Spectral variation across Pulsar Profile due to Coherent Curvature Radiation

Rahul Basu, Dipanjan Mitra, George I. Melikidze

摘要:

脉冲星轮廓的特点是两个不同的发射组件,核心和锥。脉冲星无线电发射波束的标准模型源自偶极磁场,将核心置于中心,由内外圆锥组件的同心层包围。与锥体相比,核心发射预期具有更陡的光谱。我们提出了一个详细的分析,在100 MHz和10 GHz之间的宽的频率范围内的核心和conal发射从一个大样本的53颗星的光谱之间的相对差异。可以看出,芯部比锥部陡得多,特别是在100 MHz和1 GHz之间,光谱指数$Δα_{core/cone}\sim$之间的相对差异为-1.0。此外,我们还发现外锥成分的光谱比内锥陡峭,光谱指数$Δα_{in/out}\sim$的相对差异为+0.5。谱从磁轴向开放场线区域边缘的平坦化随场线曲率的增加是带电孤子束的相干曲率辐射的自然结果,并解释了芯和锥之间谱的差异。此外,由于相对论性的光束效应,只有当辐射以窄角度$θ\leq 1/γ$射向观测者时才能看到,其中$γ$是流出等离子体云的洛伦兹因子。这限制了特别是来自外锥的发射,外锥与具有较大曲率的场线相关联,从而使光谱比内锥更陡。

英文摘要:

The pulsar profile is characterised by two distinct emission components, the core and the cone. The standard model of a pulsar radio emission beam originating from dipolar magnetic fields, places the core at the centre surrounded by concentric layers of inner and outer conal components. The core emission is expected to have steeper spectra compared to the cones. We present a detailed analysis of the relative differences in spectra between the core and conal emission from a large sample of 53 pulsars over a wide frequency range between 100 MHz and 10 GHz. The core was seen to be much steeper than the cones particularly between 100 MHz and 1 GHz with a relative difference between the spectral index $Δα_{core/cone}\sim$ -1.0. In addition we also found the spectra of the outer conal components to be steeper than the inner cone with relative difference in the spectral index $Δα_{in/out}\sim$ +0.5. The flattening of the spectra from the magnetic axis towards the edge of the open field line region with increasing curvature of the field lines is a natural outcome of the coherent curvature radiation from charged soliton bunches, and explains the difference in spectra between the core and the cones. In addition due to the relativistic beaming effect, the radiation is only visible when it is directed towards the observer over a narrow angle $θ\leq 1/γ$, where $γ$ is the Lorentz factor of the outflowing plasma clouds. This restricts the emission particularly from outer cones, that are associated with field lines with larger curvature thereby making the spectra steeper than the inner cones.

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