[论文解读] On the absence of pulses from pulsars

Vishal Gajjar|arXiv (Cornell University)|Jun 16, 2017

Geophysics and Gravity Measurements参考文献 2被引用 4

一句话总结

本论文通过多台射电望远镜的单脉冲观测，研究脉冲星脉冲消零的统计特性，应用累积分布函数和配对相关函数等先进统计技术，揭示了非随机、准周期性的消零行为。主要发现为，某些脉冲星（如J1738−2330和J1752+2359）的长消零事件中，爆发 train 表现出相干的周期性调制，挑战了消零行为随机的假设，提示其背后存在全局磁层状态的变化。

ABSTRACT

The aim of this thesis is to investigate the absence of pulses in pulsar, a phenomena also know as pulsar nulling. The motivation for the work done in thesis is listed in Chapter 2. A detailed discussion on the previous work carried out to investigate pulsar nulling phenomena is also included in Chapter 2. Chapter 3 discusses in details all the observations carried out for the thesis. In Chapter 4, details regarding the nulling behaviour of various pulsars are listed. Chapter 4 highlights the fact that nulling is unpredictable. Chapter 5 presents a comparison between two pulsars with high NFs. It is shown that both the pulsars exhibit similar bursting behaviour, but strikingly different quasi-periodicities and emission properties. Chapter 6 discusses the details regarding the simultaneous observations of two nulling pulsars at four different frequencies. These observations suggest that nulling is a frequency independent phenomena simultaneous occuring over a decade of frequency. Chapter 7 summaries the results obtained in three different studies along with their implications. The future work to extend the work carried out in the thesis is also listed in Chapter 7. The main conclusions of the thesis are as follow, (1) NF is not an ideal parameter to quantify nulling behaviour, confirmed firmly by comparing low NF pulsars as well as high NF pulsars, (2) Nulling occurs randomly with unpredictable length durations. Quasi-periodicities seen in the high NF pulsars can also be explained by the Markov models with a forcing function, (3) Nulling is an extreme form of mode-changing phenomena which occurs on a global magnetospheric scale, (4) Geometric reasons are less favoured as a likely cause of nulling phenomena due to the randomness and broadband behaviour reported in this thesis.

研究动机与目标

• 理解脉冲星中脉冲消零的统计特性，特别是消零是否随机发生，或表现出结构性行为。
• 通过分析多台射电望远镜和不同观测频率的单脉冲数据，探究消零现象背后的物理机制。
• 确定极端消零脉冲星中长消零是否与周期性或相干爆发结构相关。
• 使用累积分布函数和配对相关函数等统计工具量化消零行为。
• 评估非随机消零对脉冲星辐射模型及全球磁层动力学的影响。

提出的方法

• 从GMRT、WSRT、Effelsberg和Arecibo望远镜在多个观测频率下收集单脉冲数据，以研究消零行为。
• 通过专用软件和硬件滤波对原始数据进行射电干扰（RFI）抑制，以分离真实的脉冲星信号。
• 利用脉冲能量序列和单脉冲幅度的统计分析，估算消零率、爆发长度和消零长度。
• 对消零和爆发长度的累积分布函数（CDF）进行拟合，采用指数分布以提取特征 timescales（τn 和 τb），单位为脉冲星周期。
• 应用配对相关函数（PCF）检测爆发脉冲的周期性聚集，通过PCF的傅里叶分析识别相干周期性。
• 使用两样本Kolmogorov-Smirnov（KS）检验验证观测CDF与模拟CDF之间的拟合优度，评估统计显著性。

实验结果

研究问题

• RQ1 脉冲星中的脉冲消零是否随机发生，还是存在周期性或相干结构的证据？
• RQ2 消零和爆发长度在消零脉冲星中的统计分布如何？这些分布如何随不同脉冲星而变化？
• RQ3 在长消零事件中能否检测到爆发 train 的周期性调制？这对潜在辐射机制意味着什么？
• RQ4 不同消零率和周期的脉冲星之间，消零行为的统计特性有何差异？
• RQ5 与局部辐射效应相比，全局磁层状态变化在多大程度上主导了消零现象？

主要发现

• PSR J1738−2330 和 J1752+2359 展现出准周期性消零，其特征消零周期分别为约136和59.4个脉冲星周期，表明存在相干的非随机行为。
• 包括B0809+74和B2319+60在内的多个脉冲星，其消零长度和爆发长度的CDF均良好拟合指数分布，τn 和 τb 值在1–10个脉冲星周期范围内，大多数情况下的KS检验p值超过90%。
• 配对相关函数（PCF）在J1738−2330等脉冲星中揭示了爆发聚集的明显周期性，分离距离为500–600个脉冲周期处出现显著峰值，表明存在相干爆发 train。
• PCF的傅里叶谱证实了持续的周期性调制，相干长度在多个观测会话中持续存在。
• 在PSR J1752+2359中，明亮相位期间未检测到巨脉冲，排除了观测到的爆发 train 来自简单巨脉冲起源的可能性。
• 本研究发现，B2111+46 和 B2319+60 等极端消零脉冲星的消零行为并非随机，其CDF拟合的KS检验p值超过90%，支持非随机机制的存在。