本文選題：脈沖星 + 脈沖輪廓��； 參考：《西南大學(xué)》2016年碩士論文

【摘要】：脈沖星是高速自轉(zhuǎn)并具有超強(qiáng)磁場的中子星�？筛鶕�(jù)脈沖星穩(wěn)定的周期性,將一定頻率范圍內(nèi)的幾百個甚至幾千個單脈沖按周期進(jìn)行疊加,會得到一個非常穩(wěn)定的累積脈沖輪廓。脈沖輪廓是可以直接觀測的量,輪廓通常呈現(xiàn)出單峰、雙峰以及多峰等多種結(jié)構(gòu),已有不同類型的脈沖星輻射束模型來解釋脈沖輪廓出現(xiàn)多種形態(tài)的原因。研究脈沖星累積脈沖輪廓的穩(wěn)定性是一個重要的課題,可以為脈沖星輻射機(jī)制和輻射區(qū)結(jié)構(gòu)的研究提供基礎(chǔ),還有助于提高脈沖星計(jì)時精度。前人研究發(fā)現(xiàn)一些脈沖星的累積脈沖輪廓展現(xiàn)出了不穩(wěn)定性。脈沖輪廓會發(fā)生兩種重要的變化現(xiàn)象,都影響著脈沖星的多種觀測特征。其中一種變化是模式變換,即脈沖星具有兩個不同形狀的穩(wěn)定累積脈沖輪廓,分別稱為正常模式和反常模式,兩種模式之間相互轉(zhuǎn)換。模式變換現(xiàn)象通常與脈沖強(qiáng)度的突然變化有關(guān)。另外一種變化稱為消零現(xiàn)象,即脈沖星的射電輻射在連續(xù)的多個周期內(nèi)會突然停止,導(dǎo)致暫時探測不到脈沖星的脈沖信號,一段時間后脈沖星又恢復(fù)到正常的輻射狀態(tài)。通常在消零期結(jié)束后,能觀測到單脈沖的強(qiáng)度和中心相位有明顯的變化。脈沖星累積脈沖輪廓的變化還表現(xiàn)在脈沖寬度以及各脈沖成分之間的相對強(qiáng)度等隨頻率的不同而發(fā)生的變化。正常脈沖星和毫秒脈沖星的脈沖輪廓都會隨著頻率的不同而發(fā)生變化。但是毫秒脈沖星脈沖輪廓的變化相對更加復(fù)雜,脈沖成分的寬度和間距可能隨著頻率的增加而增大,也可能隨著頻率的增加而減小。脈沖星輻射強(qiáng)度發(fā)生變化的原因,可能是脈沖星自身輻射強(qiáng)度的變化,也可能發(fā)生在射電波穿過星際空間的過程中,受到星際介質(zhì)中電子密度不均勻性閃爍引起的不同頻率上流量密度的變化,即脈沖星累積脈沖輪廓的穩(wěn)定性會受星際閃爍的干擾。本文研究了毫秒脈沖星PSR J1022+1001累積脈沖輪廓的穩(wěn)定性問題,該脈沖星呈現(xiàn)雙峰結(jié)構(gòu),在1400MHz觀測頻率附近,具有兩種典型的脈沖輪廓,其峰值比分別是小于1和大于1。研究發(fā)現(xiàn)當(dāng)把總帶寬分成八個子帶寬后,每個子帶寬的脈沖輪廓會隨著頻率的不同而發(fā)生變化,其峰值比隨著頻率的增加而增大。同時由于星際閃爍的影響,各個頻率上的流量密度也會發(fā)生變化。當(dāng)把各個頻率上的脈沖輪廓按照流量密度的大小加權(quán)疊加后,就會形成峰值比小于1和大于1的兩種總輪廓形態(tài)。所以該脈沖星總輪廓呈現(xiàn)變化的主要原因在于脈沖輪廓會隨觀測頻率發(fā)生形態(tài)改變,同時星際閃爍引起各頻率上流量密度變化造成的。但研究還發(fā)現(xiàn),有少數(shù)情況中即使在同一個子頻率上,脈沖星的輪廓也已經(jīng)發(fā)生了改變,因此認(rèn)為部分累積脈沖輪廓表現(xiàn)出的不穩(wěn)定性也可能是脈沖星內(nèi)稟或是其他因素引起的。
[Abstract]:Pulsars are neutron stars with high speed rotation and super magnetic field. According to the stable periodicity of pulsars, a very stable cumulative pulse profile can be obtained by stacking hundreds or even thousands of monopulse pulses in a certain frequency range. Pulse contour is a direct observable quantity, and the contour usually presents a single peak, two peaks and multiple peaks. Different types of pulsar radiation beam models have been developed to explain the reasons for the appearance of various shapes of the pulse profile. It is an important subject to study the stability of pulsar cumulative pulse profile, which can provide a basis for the study of the radiation mechanism and radiation region structure of pulsars, and also help to improve the timing accuracy of pulsars. Previous studies have found that the cumulative pulse profiles of some pulsars exhibit instability. There are two important changes in pulse profile, both of which affect the observation characteristics of pulsars. One of the variations is mode transformation, in which pulsars have two stable cumulative pulse profiles with different shapes, which are called normal mode and anomalous mode respectively, and the two modes are converted to each other. The phenomenon of mode transformation is usually related to the sudden change of pulse intensity. The other change is called zero elimination, that is, the radio radiation of pulsars will stop suddenly for several consecutive periods, which results in the pulsars being unable to detect the pulsars' pulse signals temporarily, and the pulsars return to the normal radiation state after a period of time. At the end of zero elimination period, the intensity and central phase of monopulse can be observed. The variation of pulsar cumulative pulse profile is also reflected in the variation of pulse width and the relative strength of each pulse component with different frequencies. The pulse profiles of both normal pulsars and millisecond pulsars vary with different frequencies. But the variation of pulse profile of millisecond pulsars is more complex. The width and spacing of pulse components may increase with the increase of frequency or decrease with the increase of frequency. The pulsar's radiation intensity may have changed because of the pulsar's own radiation intensity, or in the process of radio waves passing through interstellar space. The variation of flux density at different frequencies caused by the inhomogeneity of electron density in interstellar medium means that the stability of pulsar cumulative pulse profile will be disturbed by interstellar scintillation. The stability of the cumulative pulse profile of millisecond pulsar PSR J1022 1001 is studied in this paper. The pulsar has a bimodal structure. There are two typical pulse profiles near the 1400MHz observation frequency, the peak ratio of which is less than 1 and greater than 1, respectively. It is found that when the total bandwidth is divided into eight sub-bandwidth, the pulse profile of each sub-bandwidth changes with the frequency, and the peak ratio increases with the increase of the frequency. At the same time, due to the influence of interstellar flicker, the flux density on each frequency will also change. When the pulse profiles on each frequency are weighted according to the size of the flow density, two kinds of total contour shapes with peak ratio less than 1 and greater than 1 will be formed. Therefore, the main reason for the variation of the total profile of the pulsar is that the shape of the pulse profile changes with the observed frequency, and the flux density changes at various frequencies caused by interstellar scintillation. But the study also found that in a few cases, even at the same subfrequency, the profile of the pulsar has changed. It is suggested that the instability of partial cumulative pulse profile may also be caused by intrinsic pulsar or other factors.
【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】：2016
【分類號】：P145.6

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