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  本文選題：脈沖星　切入點：流量密度　出處：《西南大學(xué)》2017年碩士論文

【摘要】：脈沖星是一種分布在宇宙各處密度極高的高速自轉(zhuǎn)中子星。人們通常用脈沖星流量密度的變化來研究脈沖星的輻射機制以及星際閃爍等問題。脈沖星的流量密度在時域上存在長期變化現(xiàn)象,天文學(xué)家們認為這種現(xiàn)象可能是由于脈沖信號經(jīng)過星際空間到達地球的傳播過程中受到星際介質(zhì)中稀薄等離子體的色散、散射及法拉第旋轉(zhuǎn)等效應(yīng)而導(dǎo)致輻射信號發(fā)生變化,也可能是脈沖星本身的內(nèi)稟屬性引起的,目前大部分人認為這種變化是由星際介質(zhì)的折射式閃爍所引起的。一般情況下,脈沖星的流量密度隨頻率的升高而快速減小,其頻譜呈現(xiàn)冪律譜形式,是一種高能電子同步曲率輻射的非熱輻射譜。但是脈沖星譜指數(shù)的變化及具體范圍并沒有確切的定論。本文通過文獻查閱選取了澳大利亞Parkes望遠鏡所觀測的受衍射式閃爍較小的4顆毫秒脈沖星PSR J1045-4509、PSR J1643-1224、PSR J1824-2452、以及PSR J1939+2134的觀測數(shù)據(jù),經(jīng)過計算處理,首先,得出這4顆毫秒脈沖星分別在10cm、20cm和50cm三個波段處的平均流量密度隨時間的變化關(guān)系,發(fā)現(xiàn)毫秒脈沖星的流量密度在每個頻段上都有長期變化現(xiàn)象,這種現(xiàn)象是由于星際閃爍中的折射式閃爍所導(dǎo)致的,并且其流量密度隨觀測頻率的升高而減小。其次,分別計算了這4顆毫秒脈沖星在10cm、20cm和50cm三個波段處的平均流量密度的結(jié)構(gòu)函數(shù),發(fā)現(xiàn)結(jié)構(gòu)函數(shù)值在每個頻段上都隨時間尺度的增加而增大,隨后出現(xiàn)平臺期。得出了每顆毫秒脈沖星分別在3個波段上結(jié)構(gòu)函數(shù)的結(jié)構(gòu)區(qū)斜率、閃爍時標值以及散射介質(zhì)的kolmogorov譜的譜指數(shù)。研究表明毫秒脈沖星的閃爍時標隨觀測頻率的升高而減小,這與折射式閃爍理論符合的很好。其kolmogorov湍流譜的譜指數(shù)值主要分布在3~4之間,平均值約為為3.68,這與理論的β=11/3符合的很好,表明脈沖星的流量密度的長期變化主要是由大尺度范圍內(nèi)均勻連續(xù)散射介質(zhì)的湍流而引起的。最后,由于前人研究的脈沖星譜指數(shù)都是每顆脈沖星總標準輪廓的平均譜指數(shù),并沒有研究譜指數(shù)隨時間的變化,于是該論文計算了以上4顆毫秒脈沖星分別在3個頻段上每次觀測的譜指數(shù),并給出了譜指數(shù)隨時間的變化關(guān)系、平均值、分布范圍,也計算了同一觀測時間內(nèi)所有頻段上的總譜指數(shù),并給出了總譜指數(shù)的變化及分布范圍。我們發(fā)現(xiàn)毫秒脈沖星的譜指數(shù)在多數(shù)情況下很好的符合冪律譜關(guān)系,譜指數(shù)隨時間變化的規(guī)律性不是很強,計算中還有少數(shù)反轉(zhuǎn)譜出現(xiàn),說明這些觀測中頻譜明顯偏離了冪律譜,這可能是由于觀測誤差所引起的。同時還發(fā)現(xiàn)利用同一時間的所有頻段上的數(shù)據(jù)計算的譜指數(shù)比分波段計算的譜指數(shù)更加集中穩(wěn)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.
【學(xué)位授予單位】：西南大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：P145.6

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本文編號：1714626