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1.
本文简述了1991年5月16日叠加在一个47GB微波大爆发上的快速精细结构(FFS)和spike群的偏振状态.在相隔100MHz的2645、2545MHz两频率上,spike的偏振状态随时间或随频率在50～100ms量级短时标内发生快速交替变化.我们认为这可能与小尺度空间内spike辐射源区的等离子体密度出现短时标的波动及磁场强度的起伏有关.这种波动和起伏使得等离子体频率与磁迴旋频率的比值(ω_p/Q_e)在2~(1/2)附近起伏变化,从而造成电磁波X波模和O波模的电子迴旋脉塞不稳定性增长率交替支配着电磁波的辐射,产生spike 辐射偏振状态的逆转. 相似文献
2.
本文给出了不同能谱指数Γ的非热电子,在不同传播方向的迴旋同步加速辐射的发射因子h_(1,2)(s,θ)的详细结果。其结果表明,对同一谐波数s而言,h_(1,2)(s,θ)随着θ值(波矢量k与磁场方向Η的夹角)的增加或Γ值的下降而增加,而对同一θ和Γ值而言,h_(1,2)(s,θ)还随着s 的增加而迅速下降,而当Γ=1时,h_(1,2)(s,π/2)随着s的增加而下降的程度十分缓慢,表明在横传播条件下,非热电子具有比似纵传播高得多的发射能力,其相应的辐射流量密度要比似纵传播高出几倍。 采用 Sturrock 的耀斑爆发源模型,计算了θ=π/2情况下的迴旋同步加速辐射的射电爆发谱。我们发现对具有Γ=1的非热电子的低次谐波辐射,分别在Ⅳ型爆发的300MHz和9000MHz附近有个峰值,而在他们的高频端的低次谐波的迴旋同步加速辐射遭到强烈的迴旋共振吸收而使辐射迅速下降,从而形成两峰一谷的U型射电爆发谱。 计算表明,1972年8月4日的大爆发,很可能是一团具有能谱指数为1.5,总数为10~(32)—10~(34)的非热电子,在横传播条件下的迴旋同步加速辐射和热电子的迴旋共振吸收机制产生的。 相似文献
3.
本文研究了迴旋共振辐射机制对太阳缓变射电的贡献.我们首先计算出,在单极黑子和双极黑子群上空,迴旋共振辐射的分布,其结果具有一些有意义的特点.最后,我们还计算出太阳缓变射电迴旋共振辐射的流量频谱和偏振频谱,所得结果与观测一致.这表明,迴旋共振辐射机制,是太阳缓变射电的一个主要且重要的辐射机制. 相似文献
4.
在解释天体爆发过程中的短时标相干射电辐射现象方面,非热电子驱动的回旋脉泽辐射得到了广泛应用.在以往的研究中,一个关键条件是非热电子具有各向异性速度分布,从而有效激发回旋脉泽不稳定性.然而,观测显示太阳和其他天体的非热电子经常呈现负幂律谱形式的能量分布.非热电子的这种负幂律能谱特征会严重抑制回旋脉泽不稳定性放大率,因此,进一步研究非热电子的负幂律能谱分布行为,能拓宽电子回旋脉泽辐射机制的适用性,很好地发展天体射电辐射机制理论.最近研究结果显示,负幂律谱电子的低能截止行为可以有效地激发电子回旋脉泽辐射,从而拓宽了其在天体物理研究中的应用范围. 相似文献
5.
本文在Ｔｈｏｒｎｅ工作的基础上讨论了吸积盘中黑洞的有关参量的演化，以及由Ｓｃｈｗａｒｚｓｃｈｉｌｄ黑洞吸积盘向Ｋｅｒｒ黑洞吸积盘演化过程中对吸积盘辐射通量的影响，最后针对几个典型的辐射过程，分别讨论了黑洞吸积盘在牛顿框架中的温度分布方程与广义相对论的温度分布方程的热不稳定性，并给出此类问题的热不稳定性的判据。 相似文献
6.
本文在Ｔｈｏｒｎｅ工作基础上讨论了吸积盘中黑洞的有关参量的演化，以及由Ｓｃｈｗａ－ｒｚｓｃｈｉｌｄ黑洞吸积盘向Ｋｅｒｒ黑洞吸积盘演化过程中对吸积盘辐射通量的影响，最后针对几个典型的辐射过程，分别讨论了黑洞吸积盘在牛顿框架中的温度分布方程与广义相对论的温度分布方程的热不稳定性，并给出此类问题的热不稳定性的判据。 相似文献
7.
在快速粒子流持续注入的条件下,日冕磁流管中离子迴旋不稳定性所引起的快速粒子流演化过程与电子加速过程可以分别考虑.本文详细给出被加速电子的能谱和流强的定量表达式,并讨论这种不稳定性引起的加速过程的一些特性. 相似文献
8.
在磁拱底部非线性等离子体密度波传播期间,损失锥分布的反射电子驱动着电子迴旋maser不稳定性的增长,激励出二次谐频波模,支配着太阳射电毫秒Spike辐射。根据这个理论模型,本文着重研究了太阳射电毫秒Spike辐射的频带宽度问题。对于典型参数,计算结果发现:辐射带宽一般为几MHz到几十MHz,最高为100MHz。而且通常折射出的二次谐频z模辐射带宽较窄,而二次谐频o模辐射带宽较宽。 相似文献
9.
10.
本文给出了改进的一维吸积柱模型,探讨了在大吸积率下吸积柱的结构及物理性质,并理论推导吸积柱内下落物质的温度、密度及速度的变化．计算结果表明,它自上而下可以分为几个部分：冲击区（辐射压减速区）、理想气体压减速区、简并气体压减速区、外流区．作为例证,详细计算了吸积率Ｍ≈１０~１７ｇ／ｓ,极区磁场强度Ｂｍ≈１０~８Ｔ的中子星吸积柱．探讨了吸积柱内的热核反应,认为它可能与低质量Ｘ射线双星的低频ＱＰＯ（准周期振荡）现象有关． 相似文献
11.
Chandreyee Maitra 《Journal of Astrophysics and Astronomy》2017,38(3):50
With forty years since the discovery of the first cyclotron line in Her X-1, there have been remarkable advancements in the field related to the study of the physics of accreting neutron stars – cyclotron lines have been a major torchbearer in this regard, from being the only direct estimator of the magnetic field strength, a tracer of accretion geometry and an indicator of the emission beam in these systems. The main flurry of activities have centred around studying the harmonic separations, luminosity dependence, pulse phase dependence and more recently, the shapes of the line and the trend for long-term evolution in the line energy. This article visits the important results related to cyclotron lines since its discovery and reviews their significance. An emphasis is laid on pulse phase resolved spectroscopy and the important clues a joint timing and spectral study in this context can provide, to build a complete picture for the physics of accretion and hence X-ray emission in accreting neutron stars. 相似文献
12.
黄光力 《紫金山天文台台刊》1999,18(3):343-349
利用北京天文台高时间和高频率分辨率的射电频谱仪对射电尖峰的测量,可以对背景等离子体参数进行的自洽诊断（ 磁场,密度,温度,波矢,及非热电子的性质） 。该诊断基于电子回旋脉塞不稳定性和回旋共振吸收。最后从诊断结果和太阳日冕典型参数的比较以确定尖峰辐射的谐波数。 相似文献
13.
We analyze the observations of the transient X-ray pulsar 4U 0115+63 with the RXTE and INTEGRAL observatories in a wide X-ray (3–100 keV) energy band during its intense outbursts in 1999 and 2004. The energy of the fundamental harmonic of the cyclotron resonance absorption line near the maximum of the X-ray flux from the source (luminosity range 5 × 1037–2 × 1038 erg s?1) is ～11 keV. When the pulsar luminosity falls below ～5 × 1037 erg s?1, the energy of the fundamental harmonic is displaced sharply toward the high energies, up to ～16 keV. Under the assumption of a dipole magnetic field configuration, this change in cyclotron harmonic energy corresponds to a decrease in the height of the emitting region by ～2 km, while other spectral parameters, in particular, the cutoff energy, remain essentially constant. At a luminosity ～7 × 1037 erg s?1, four almost equidistant cyclotron line harmonics are recorded in the spectrum. This suggests that either the region where the emission originates is compact or the emergent spectrum from different (in height) segments of the accretion column is uniform. We have found significant pulse profile variations with energy, luminosity, and time. In particular, we show that the profile variations from pulse to pulse are not reduced to a simple modulation of the accretion rate specified by external conditions. 相似文献
14.
A model is proposed for the nonthermal synchrotron emission from supernova remnants in the uniform interstellar medium. Some characteristics of nonthermal and thermal emission (luminosity and surface brightness distribution) are compared. The conditions when the nonthermal component can be prominent in the X-ray spectrum are specified. We point out some observational tests which will allow a number of parameters characterizing the cosmic ray injection on supernova remnant shocks to be estimated. The cases when electron radiation losses may be neglected are considered. 相似文献
15.
根据不同的发射波模以及偏振态（偏振度与偏振方向）的快速时变特征,对1993年10月2日07：44：34-07：44：52：99UT期间的太阳射电事件进行了证认,认为这是一个由两群、总数约为40个尖峰（spike）结构组成的罕见的宽带事件,它的总带宽＞300MHz、相对带宽■5％．根据它们在2．545GHZ,2．645GHZ;2．695GHZ和2B40GHZ上的流量资料,首次对一些spike结构作了谱分析．发现spike结构谱的峰值频率,第一群呈现为随时间由高频向低频漂移的倾向,第二群基本上位于2．695GHZ上．Spike谱的这些观测特征,可定性地用非热电子束流平均能量的时变特性来解释．对于第二群具有相同峰值频率的spike辐射,可能来自同一电子回旋脉泽不稳定区域． 相似文献
16.
《天文和天体物理学研究(英文版)》2020,(8)
Hercules A(Her A) is one of a rare class of dying and transition-type objects, which has a pair of giant, powerful radio lobes and a weak radio core. We reduce and analyze the radio data of Her A that were observed by the Expanded Very Large Array(EVLA) during 2010-2011 at C band. The intensity distribution is very smooth along the edge of the lobe front and the intensity also sharply decreases at the edge, which supports that magnetic fields may play an important role in radio lobes. The spectrum of the weak core is very steep and the core flux becomes weaker by about ten percent when compared to what was observed twenty years ago, which suggest that the central engine is still dying quickly. Her A deviates a lot from the relation between [O III] luminosity and low-frequency 178 MHz luminosity(LO III-L178 MHz) as defined by other FR I/II sources. However, when only radio core emission is considered, it roughly follows an LO III-L178 MHzcorrelation. This result supports that the black-hole accretion and large-scale jet in Her A did not evolve simultaneously, and indicates that although the large-scale jet is still powerful, the accretion and inner jet have changed into an inactive state. Based on the estimated Bondi accretion rate, we model the spectrum of Her A with a radiatively inefficient accretion flow and jet model. 相似文献
17.
A. L. McNamara Z. Kuncic K. Wu 《Monthly notices of the Royal Astronomical Society》2008,386(4):2167-2172
Compton scattering within the accretion column of magnetic cataclysmic variables (mCVs) can induce a net polarization in the X-ray emission. We investigate this process using Monte Carlo simulations and find that significant polarization can arise as a result of the stratified flow structure in the shock-ionized column. We find that the degree of linear polarization can reach levels up to ∼8 per cent for systems with high accretion rates and low white dwarf masses, when viewed at large inclination angles with respect to the accretion column axis. These levels are substantially higher than previously predicted estimates using an accretion column model with uniform density and temperature. We also find that for systems with a relatively low-mass white dwarf accreting at a high accretion rate, the polarization properties may be insensitive to the magnetic field, since most of the scattering occurs at the base of the accretion column where the density structure is determined mainly by bremsstrahlung cooling instead of cyclotron cooling. 相似文献
18.
Grzegorz Wardzi&#;ski rzej A. Zdziarski 《Monthly notices of the Royal Astronomical Society》2001,325(3):963-971
We investigate how the presence of a non-thermal tail beyond a Maxwellian electron distribution affects the synchrotron process as well as Comptonization in plasmas with parameters typical for accretion flows on to black holes. We find that the presence of the tail can significantly increase the net (after accounting for self-absorption) cyclo-synchrotron emission of the plasma, which then provides seed photons for Compton upscattering. Thus, the luminosity in the thermally Comptonized spectrum is enhanced as well. The importance of these effects increases with both increasing Eddington ratio and black hole mass. The enhancement of the Comptonized synchrotron luminosity can be as large as ∼103 and ∼105 for stellar and supermassive black holes, respectively, when the energy content in the non-thermal tail is 1 per cent.
The presence of the tail only weakly hardens the thermal Comptonization spectrum but it leads to the formation of a high-energy tail beyond the thermal cut-off, which two effects are independent of the nature of the seed photons. Since observations of high-energy tails in Comptonization spectra can constrain the non-thermal tails in the electron distribution and thus the Comptonized synchrotron luminosity, they provide upper limits on the strength of magnetic fields in accretion flows. In particular, the measurement of an MeV tail in the hard state of Cyg X-1 by McConnell et al. implies the magnetic field strength in this source to be at most an order of magnitude below equipartition. 相似文献
The presence of the tail only weakly hardens the thermal Comptonization spectrum but it leads to the formation of a high-energy tail beyond the thermal cut-off, which two effects are independent of the nature of the seed photons. Since observations of high-energy tails in Comptonization spectra can constrain the non-thermal tails in the electron distribution and thus the Comptonized synchrotron luminosity, they provide upper limits on the strength of magnetic fields in accretion flows. In particular, the measurement of an MeV tail in the hard state of Cyg X-1 by McConnell et al. implies the magnetic field strength in this source to be at most an order of magnitude below equipartition. 相似文献
19.
D.K. Galloway † A.B. Giles ‡ K. Wu J.G. Greenhill 《Monthly notices of the Royal Astronomical Society》2001,325(1):419-425
Sharp dips observed in the pulse profiles of three X-ray pulsars (GX 1+4, RX J0812.4−3114 and A 0535+26) have previously been suggested to arise from partial eclipses of the emission region by the accretion column occurring once each rotation period. We present pulse-phase spectroscopy from Rossi X-ray Timing Explorer satellite observations of GX 1+4 and RX J0812.4−3114, which for the first time confirms this interpretation. The dip phase corresponds to the closest approach of the column axis to the line of sight, and the additional optical depth of photons escaping from the column in this direction gives rise to both the decrease in flux and increase in the fitted optical depth measured at this phase. Analysis of the arrival time of individual dips in GX 1+4 provides the first measurement of azimuthal wandering of a neutron star accretion column. The column longitude varies stochastically with a standard deviation ranging between 2° and 6° depending on the source luminosity. Measurements of the phase width of the dip both from mean pulse profiles and from the individual eclipses demonstrate that the dip width is proportional to the flux. The variation is consistent with that expected if the azimuthal extent of the accretion column depends only upon the Keplerian velocity at the inner disc radius, which varies as a consequence of the accretion rate M˙ . 相似文献
20.
We revisit the so-called 'blazar sequence', which connects the observed bolometric luminosity to the shape of the spectral energy distribution (SED) of blazars. We propose that the power of the jet and the SED of its emission are linked to the two main parameters of the accretion process, namely the mass of the black hole and the accretion rate. We assume (i) that the jet kinetic power is proportional to the mass accretion rate; (ii) that most of the jet dissipation takes place at a distance proportional to the black hole mass; (iii) that the broad line region exists only above a critical value of the disc luminosity, in Eddington units, and (iv) that the radius of the broad line region scales as the square root of the ionizing disc luminosity. These assumptions, motivated by existing observations or by reasonable theoretical considerations, are sufficient to uniquely determine the SED of all blazars. This framework accounts for the existence of 'blue quasars', i.e. objects with broad emission lines but with SEDs resembling those of low-luminosity high-energy peaked BL Lacertae (BL Lac) objects, as well as the existence of relatively low-luminosity 'red' quasars. Implications on the possible evolution of blazars are briefly discussed. This scenario can be tested quite easily once the AGILE and especially the GLAST satellite observations, coupled with information in the optical/X-ray band from Swift , will allow the knowledge of the entire SED of hundreds (and possibly thousands) blazars. 相似文献