毫秒脉冲星流量密度及谱指数的变化研究

发布时间：2018-04-05 11:45

本文选题：脉冲星　切入点：流量密度　出处：《西南大学》2017年硕士论文

【摘要】：脉冲星是一种分布在宇宙各处密度极高的高速自转中子星。人们通常用脉冲星流量密度的变化来研究脉冲星的辐射机制以及星际闪烁等问题。脉冲星的流量密度在时域上存在长期变化现象,天文学家们认为这种现象可能是由于脉冲信号经过星际空间到达地球的传播过程中受到星际介质中稀薄等离子体的色散、散射及法拉第旋转等效应而导致辐射信号发生变化,也可能是脉冲星本身的内禀属性引起的,目前大部分人认为这种变化是由星际介质的折射式闪烁所引起的。一般情况下,脉冲星的流量密度随频率的升高而快速减小,其频谱呈现幂律谱形式,是一种高能电子同步曲率辐射的非热辐射谱。但是脉冲星谱指数的变化及具体范围并没有确切的定论。本文通过文献查阅选取了澳大利亚Parkes望远镜所观测的受衍射式闪烁较小的4颗毫秒脉冲星PSR J1045-4509、PSR J1643-1224、PSR J1824-2452、以及PSR J1939+2134的观测数据,经过计算处理,首先,得出这4颗毫秒脉冲星分别在10cm、20cm和50cm三个波段处的平均流量密度随时间的变化关系,发现毫秒脉冲星的流量密度在每个频段上都有长期变化现象,这种现象是由于星际闪烁中的折射式闪烁所导致的,并且其流量密度随观测频率的升高而减小。其次,分别计算了这4颗毫秒脉冲星在10cm、20cm和50cm三个波段处的平均流量密度的结构函数,发现结构函数值在每个频段上都随时间尺度的增加而增大,随后出现平台期。得出了每颗毫秒脉冲星分别在3个波段上结构函数的结构区斜率、闪烁时标值以及散射介质的kolmogorov谱的谱指数。研究表明毫秒脉冲星的闪烁时标随观测频率的升高而减小,这与折射式闪烁理论符合的很好。其kolmogorov湍流谱的谱指数值主要分布在3~4之间,平均值约为为3.68,这与理论的β=11/3符合的很好,表明脉冲星的流量密度的长期变化主要是由大尺度范围内均匀连续散射介质的湍流而引起的。最后,由于前人研究的脉冲星谱指数都是每颗脉冲星总标准轮廓的平均谱指数,并没有研究谱指数随时间的变化,于是该论文计算了以上4颗毫秒脉冲星分别在3个频段上每次观测的谱指数,并给出了谱指数随时间的变化关系、平均值、分布范围,也计算了同一观测时间内所有频段上的总谱指数,并给出了总谱指数的变化及分布范围。我们发现毫秒脉冲星的谱指数在多数情况下很好的符合幂律谱关系,谱指数随时间变化的规律性不是很强,计算中还有少数反转谱出现,说明这些观测中频谱明显偏离了幂律谱,这可能是由于观测误差所引起的。同时还发现利用同一时间的所有频段上的数据计算的谱指数比分波段计算的谱指数更加集中稳定。
[Abstract]:Pulsar is a high-speed rotating neutron star distributed throughout the universe with high density.The radiative mechanism of pulsars and interstellar scintillation are usually studied by using the variation of pulsar flux density.There is a long-term variation in the flux density of pulsars in time domain, which astronomers believe may be due to the dispersion of the pulse signal in the interstellar medium as it travels through interstellar space to Earth.The effects of scattering and Faraday rotation may also be caused by the intrinsic properties of the pulsar itself. At present, most people think that this change is caused by the refraction flicker of interstellar medium.In general, the flux density of pulsars decreases rapidly with the increase of frequency, and the frequency spectrum of pulsars is in the form of power law spectrum, which is a non-thermal radiation spectrum of high energy electron synchrotron curvature radiation.However, there is no definite conclusion on the variation of pulsar spectral index and its specific range.In this paper, four millisecond pulsars, PSR J1045-4509 and PSR J1939 2134, which are observed by the Australian Parkes Telescope, are selected. The data of J1643-1224 PSR J1824-2452 and PSR J1939 2134 are selected.The relationship between the average flux density of the four millisecond pulsars at the wavelength of 10 cm ~ (-1) 20cm and the 50cm band is obtained. It is found that the flux density of the four millisecond pulsars has a long-term variation in each band.This phenomenon is caused by refraction scintillation in interstellar scintillation and its flux density decreases with the increase of observed frequency.Secondly, the structure functions of the average flux density of the four millisecond pulsars at the wavelength of 10 cm ~ (-1) 20cm and 50cm are calculated, respectively. It is found that the structural function values increase with the increase of time scale, and then the plateau period occurs.The structural slope of the structure function of each millisecond pulsar at three bands, the scintillation scale and the spectral exponent of the kolmogorov spectrum of the scattering medium are obtained.It is shown that the scintillation time scale of millisecond pulsars decreases with the increase of observed frequency, which is in good agreement with the refraction scintillation theory.The kolmogorov spectra are mainly distributed in the range of 3 ~ 4, with an average value of 3.68, which is in good agreement with the theoretical 尾 ~ (11 / 3).It is shown that the long term variation of pulsar flow density is mainly caused by the turbulence of homogeneous and continuous scattering medium in large scale.Finally, since the spectral indices of pulsars studied by previous studies are the average spectral indices of the total standard profile of each pulsar, the variation of spectral indices with time is not studied.In this paper, the spectral exponents of the four millisecond pulsars observed at each time in three frequency bands are calculated, and the variation of the spectral exponents with time, the average value and the distribution range are given.The total spectral exponents on all frequency bands in the same observation time are also calculated, and the variation and distribution range of the total spectral indices are given.We find that the spectral exponent of millisecond pulsars is in good agreement with the power law spectral relationship in most cases, the variation of spectral exponents with time is not very strong, and a few inversion spectra appear in the calculation.It is suggested that the spectrum deviates from the power law spectrum obviously, which may be caused by the observation error.At the same time, it is found that the spectral exponent band calculated by using the data of all frequency bands at the same time is more concentrated and stable.
【学位授予单位】：西南大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P145.6

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