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arXiv 1502.06897astro-ph.HE
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脉冲星射电辐射中的极化准周期结构反映了非定常等离子体流的时间调制

Polarized quasiperiodic structures in pulsar radio emission reflect temporal modulations of non-stationary plasma flow

Dipanjan Mitra, Mihir Arjunwadkar, Joanna M. Rankin

摘要:

当用几十微秒的时间分辨率观察时,许多射电望远镜的明亮单脉冲显示出快速的强度波动(称为微观结构)。在这里,我们报告的Arecibo 59.5 $μ$秒分辨率极化观测的11个P波段和32个L波段的周期范围从150毫秒到3.7秒的分析。这些高频率的观测为详细的微观结构研究提供了最可靠的基础。对单个脉冲的仔细检查表明,大多数脉冲表现出具有明确定义的周期性时间尺度($P_μ$)的准周期性。虽然我们发现一些脉冲具有深度调制的微观结构,但大多数脉冲在宽平滑的子脉冲特征之上显示出低幅度调制,从而难以推断周期性。我们已经开发了一种用于这种低幅度波动的方法,其中从每个去噪子脉冲中减去平滑子脉冲包络;然后使用每个子脉冲的波动部分通过自相关分析来估计$P_μ$。我们发现,微观结构的时间尺度$P_μ$是共同的偏振脉冲星信号的所有斯托克斯参数。此外,在高分辨微结构中没有发现真空中曲率辐射的明显特征,我们的分析进一步显示了$P_μ$与脉冲星周期$P$之间的强相关性。我们讨论了这一结果的影响方面的相干辐射模型,其中无线电发射出现由于形成和加速的电子-正电子对在内部真空间隙超过磁极帽,和一个子脉冲对应于一系列的非稳态火花放电。我们认为,在这个模型中,$P_μ$反映了非稳态等离子体流的时间调制。

英文摘要:

Bright single pulses of many radio pulsars show rapid intensity fluctuations (called microstructure) when observed with time resolutions of tens of microseconds. Here, we report an analysis of Arecibo 59.5 $μ$sec-resolution polarimetric observations of 11 P-band and 32 L-band pulsars with periods ranging from 150 msec to 3.7 sec. These higher frequency observations forms the most reliable basis for detailed microstructure studies. Close inspection of individual pulses reveals that most pulses exhibit quasiperiodicities with a well-defined periodicity timescale ($P_μ$). While we find some pulses with deeply modulating microstructure, most pulses show low-amplitude modulations on top of broad smooth subpulses features, thereby making it difficult to infer periodicities. We have developed a method for such low-amplitude fluctuations wherein a smooth subpulse envelope is subtracted from each de-noised subpulse; the fluctuating portion of each subpulse is then used to estimate $P_μ$ via autocorrelation analysis. We find that the microstructure timescale $P_μ$ is common across all Stokes parameters of polarized pulsar signals. Moreover, no clear signature of curvature radiation in vacuum in highly resolved microstructures was found. Our analysis further shows strong correlation between $P_μ$ and the pulsar period $P$. We discuss implications of this result in terms of a coherent radiation model wherein radio emission arises due to formation and acceleration of electron-positron pairs in an inner vacuum gap over magnetic polar cap, and a subpulse corresponds to a series of non-stationary sparking discharges. We argue that in this model, $P_μ$ reflects the temporal modulation of non-stationary plasma flow.

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