Cyg X-1高态和转换态的X射线短时标爆发

分析ＲＸＴＥ卫星ＰＣＡ探测器对ＣｙｇＸ－１的观测数据,得到了其处于高态及高低态转换时的Ｘ射线短时标爆发（Ｓｈｏｔ）结构．在所观测到的三种态中是不对称的,并且不同的状态中Ｓｈｏｔ的结构有明显差异．Ｓｈｏｔ前后沿可分别由双指数函数近似拟合．Ｓｈｏｔ中的快时变过程是由慢的上升前沿和快的下降后沿构成．在所观测态中Ｓｈｏｔ平均宽度约为０．１１秒（ＦＷＨＭ）,比低态时的宽度窄．同一状态中高能段的Ｓｈｏｔ宽度较低能段窄,且更加不对称．转换态的硬度在Ｓｈｏｔ峰前有明显下降,之后迅速上升,Ｓｈｏｔ期间的平均硬度低于非Ｓｈｏｔ期平均值;而高态时峰前硬度没有明显下降,Ｓｈｏｔ期间的平均硬度高于非Ｓｈｏｔ期间的平均值．本文还就Ｓｈｏｔ的产生机制进行了讨论．     

Properties of X-ray shots of Cyg X-1 in high state

Temporal variations in the high-energy radiation of Cyg X-1 can be represented by the properties of its X-ray short bursts (shots). The properties of the X-ray shots of Cyg X-1 have been studied extensively, especially for the Cyg X-1 in its typical low/hard state. In this paper, we study the shot properties when Cyg X-1 is in its high/soft state, using direct superposition of shots and the autocorrelation function. Our result shows that when Cyg X-1 is in the high state, the shot structure is qualitatively similar to that of the low state, and that the full-width at half-maximum (FWHM) of the shot decreases with increasing energy, which is inconsistent with the prediction of the Comptonization model. In addition, the evolution of the shot energy spectrum and the asymmetry of the shot structure can explain the observed time lag in Cyg X-1.     

Cyg X-1高态中短暴性质的研究

CygX-1高能辐射的时变特征可以通过短暴(shot)的性质反映．因此CygX-1的短暴性质，特别是处于低态时的性质曾被广泛研究,利用直接叠加短暴和自相关函数，对CygX-1高态时短暴的性质进行了研究．结果表明，当CygX-1处于高态时，其短暴的结构类似于低态时所具有的性质，短暴的半高宽随能量的增加按指数下降．此结果和康普顿化模型不一致．另外，短暴的能谱演化及结构的非对称性可以解释CygX-1中的时延现象．     

Multicolour Photometry of AM Her During 1994–96

Multicolour photometry of the polar AM Her was obtained during 3 observational seasons (1994/95/96). The star was in its high state for most of the observations. It was in its low state in '96 April. It was established that these two states differ not only in the average light level but in the larger amplitudes of variations at low state than at high state. Moreover the energy distributions of the two states differ in the stronger dependence of the flux on ν at high state than at low state. The Fourier analysis of the photometric data shows variability with the spectroscopic (orbital) period. The amplitudes of this variability in all colours are about two times bigger at low state than at high state. An attempt to explain the photometric behaviour of AM Her by a model of dominant emission of two hot spots at the magnetic poles of the white dwarf was made and the spot parameters were determined. This revised version was published online in August 2006 with corrections to the Cover Date.     

Geminid Meteor shower activity 2003–2005 as observed by Gadanki radar

The distribution of meteor signals reflected from a backscatter radar is considered according to their duration. This duration time (T) is used to classify the meteor echoes and to calculate the mass index (S) of different meteoroids of shower plus sporadic background. Observational data on particle size distribution of the Geminid meteor shower are very scarce, particularly at low latitudes. In this paper the observational data from Gadanki radar (13.46°N, 79.18°E) have been used to determine the particle size distribution and the number density of meteoroids inside the stream of the Geminid meteor shower. The mean variation of meteor number density across the stream has been determined for three echo duration classes, T<0.4, T=0.4–1 and T>1 s. We are more interested in the appearance of echoes of various durations and therefore meteors of various masses in order to understand more on the filamentary structure of the stream. It is observed that the faint particle flux peaks earlier than the larger particles. We found a decreasing trend in the mass index values from the day of peak activity to the next observation days. The mass index profile was found to be U-shaped with a minimum value near the time of peak activity. The observed minimum s values are 1.64±0.05 and 1.65±0.04 in the years 2003 and 2005, respectively. The activity of the shower indicates the mass segregation of meteoroids inside the stream. Our results are best comparable with the “scissors” structure model of the meteoroid stream formation of Ryabova [2007. Mathematical modeling of the Geminid meteoroid stream. Mon. Not. R. Astron. Soc. 375, 1371–1380] by considering the asteroid 3200 Phaethon as an extinct comet.     

Optical Measurements in an Exploding Wire Experiment

We present optical measurements (Shadow and Schlieren pictures) of a 12.5 Joule exploding wire experiment. After performing a large number of shots some sort of time evolution can be reconstructed from the pictures. The pictures were taken during the dark phase (zero current) and the plasma phase. Although the electrical signals are quite reproducible from shot to shot (allowing a good time correlation and indicating that the global dynamics is reproducible) we observed that the individual details are quite different, probably due to the non-uniformity of the wire. We observed a uniform expansion (the volume increases almost linearly with time) with the presence of surface instabilities and there is no evident difference in the density distribution between the dark and the plasma phases. Finally, we derive a mean radius and velocity evolution with time and an approximate energy balance.     

Long-term INTEGRAL and RXTE observations of the X-ray pulsar LMC X-4

We analyze the observations of the X-ray pulsar LMCX-4 performed by the INTEGRAL observatory and the All-Sky Monitor (ASM) of the RXTE observatory over a wide energy range. The observed hard X-ray flux from the source is shown to change by more than a factor of 50 (from ～70 mCrab in the high state to ～1.3 mCrab in the low state) on the time scale of the accretion-disk precession period, whose mean value for 1996–2004 was determined with a high accuracy, P_prec = 30.275 ± 0.004 days. In the low state, a flare about 10 h in duration was detected from the source; the flux from the source increased by more than a factor of 4 during this flare. The shape of the pulsar’s broadband spectrum is essentially invariable with its intensity; no statistically significant features associated with the possible resonance cyclotron absorption line were found in the spectrum of the source.     

Seasonal monsoon forecast for the years 1987 and 1988

The results of several seasonal integrations with an atmospheric global circulation model with prescribed “perfect” sea surface temperatures are presented. These experiments illustrate the results of seasonal simulations for the years 1987 and 1988. These were a dry and a wet monsson year, respectively, when compared to the average. The integrations cover the period from June 1 through August 31 for both years and were carried out at two horizontal resolutions, T42 and T106, of a global model containing two different parameterizations of surface hydrology. The seasonal differences of the motion fields, divergent circulations and rainfall distributions for these respective experiments are compared with the corresponding observed fields.The sensitivity of seasonal simulations to the initial state is explored with integrations starting on two successive dates. In these experiments we diagnose differences of the simulated time mean states from residue free budgets of the complete vorticity equation.     

Long-Term Variability Of The Optical Emission Lines In The Nuclear Spectrum Of The Seyfert Galaxy Ngc 3227

Fifty-three spectrograms in the optical region (3700–7300 Å) with the spectral resolution ～8 Å have been obtained for the Seyfert nucleus of the galaxy NGC 3227 with the 6-m telescope on January 1977, while the nucleus was in the historically important epoch of its extreme maximum brightness. Width of the slit was 1″, length of the box during the spectra measurements was 1.5″. Data obtained by us and those compiled from literature showed that profiles of the Balmer lines H_α, H_β and H_γ are different, evidencing that the gas emitting these lines is highly self-absorbed. It was shown that narrow components of the profiles revealed by Rubin and Ford kept their positions (radial velocities) over 25 years. The components showed intensity variations compared to the central one from minimum to maximum of the nucleus brightness. The same variations were observed by us earlier in the emission line profiles of the NGC 7469 nucleus spectrum. Narrow profile components can reflect long-lived flows or jets in the broad line region (BLR). Obtained facts evidenced that long-lived gas streams and flows causing narrow components of broad line profiles presented not only when BLR of accretion disc is strong but when BLR of accretion disc declined. Blue bump at radial velocity of ?5000 km/s in H_γ profile was revealed in spectra of high states of the nucleus, which disappeared in low state. One of the interpretations of this event can be in the framework of a model of one-sided or two-sided gas ejection during the high state of the nucleus, positive radial velocities of which being screened out by a circumnuclear disk.     

Indirect imaging of the accretion stream in eclipsing polars – III. HU Aquarii low state

We apply our technique for indirect imaging of the accretion stream to the polar HU Aqr, using eclipse profiles observed when the system was in a low-accretion state. The eclipse profile is different from that in the high state, and more variable from cycle to cycle. We find that the stream maps are brightest near the white dwarf and there is no significant brightening in the threading region. In the low state the stream threads on to the magnetic field closer to the L₁ point than in the high state, with a footpoint of the accreting field line at high latitude. We then produce maps of the accretion region from polarimetry using Stokes imaging. These show that the majority of the accretion occurs near the equator. The difference between the maps may be explained if most of the stream material is not emitting significantly in the low state. If so, neither the stream eclipse mapping nor Doppler tomography techniques will trace the bulk of the accretion flow between the two stars.     

Variability of η Carinae – III

Spectra (1951–78) of the central object in η Car, taken by A. D. Thackeray, reveal three previously unrecorded epochs of low excitation. Since 1948, at least, these states have occurred regularly in the 2020-d cycle proposed by Damineli et al. They last about 10 per cent of each cycle. Early slit spectra (1899–1919) suggest that at that time the object was always in a low state. JHKL photometry is reported for the period 1994–2000. This shows that the secular increase in brightness found in 1972–94 has continued and its rate has increased at the shorter wavelengths. Modulation of the infrared brightness in a period near 2020 d continues. There is a dip in the JHKL light curves near 1998.0, coincident with a dip in the X-ray light curve. Evidence is given that this dip in the infrared repeats in the 2020-d cycle. As suggested by Whitelock & Laney, the dip is best interpreted as an eclipse phenomenon in an interacting binary system; the object eclipsed being a bright region ('hotspot'), possibly on a circumstellar disc or produced by interacting stellar winds. The eclipse coincides in phase and duration with the state of low excitation. It is presumably caused by a plasma column and/or by one of the stars in the system.     

Long-term flux variations in Cen X-3: clues from flux-dependent orbital modulation and pulsed fraction

We have investigated the long-term flux variation in Cen X-3 using orbital modulation and pulsed fraction in different flux states using observations made with the All-Sky Monitor and the Proportional Counter Array on board the Rossi X-ray Timing Explorer . In the high state, the eclipse ingress and egress are found to be sharp whereas in the intermediate state the transitions are more gradual. In the low state, instead of eclipse ingress and egress, the light curve shows a smooth flux variation with orbital phase. The orbital modulation of the X-ray light curve in the low state shows that the X-ray emission observed in this state is from an extended object. The flux-dependent orbital modulations indicate that the different flux states of Cen X-3 are primarily due to varying degree of obscuration. Measurement of the pulsed fraction in different flux states is consistent with the X-ray emission of Cen X-3 having one highly varying component with a constant pulsed fraction and an unpulsed component and in the low state, the unpulsed component becomes dominant. The observed X-ray emission in the low state is likely to be due to scattering of X-rays from the stellar wind of the companion star. Though we cannot ascertain the origin and nature of the obscuring material that causes the aperiodic long-term flux variation, we point out that a precessing accretion disc driven by radiative forces is a distinct possibility.     

High time resolution observations of solar radio emission at four frequencies: evidence for energy release in microflares

As evidence for energy release in microflares, high time resolution observations of solar radio emission obtained with our “synchronous observation system of solar radio radiation with high time resolution at four frequencies (1.42, 2.13, 2.84 and 4.26 GHz)” from December 1989 to April 1993 are presented in this paper. The observed events include weak ms spikes, “spike-likes”, fast pulsations as well as two kinds of newly discovered fast fine structures, i.e., microwave type III bursts and microwave patch-like structures. A statistical study of the duration of fast fine structures has been made and on its basis the various types of phenomena are illustrated with actual examples.     

Cyg X-1频谱的细微结构

利用线性状态空间模型（Ｌｉｎｅａｒ Ｓｔａｔｅ Ｓｐａｃｅ Ｍｏｄｅｌ－ＬＳＳＭ）,将 Ｃｙｇ Ｘ－１的功率谱分解为ＬＳＳＭ产生的模型功率谱和剩余功率谱两部分．集中分析剩余功率谱,结果显示, Ｃｙｇ Ｘ－１在低／硬态、转换态和高／软态三种状态的剩余功率谱有着不同的结构特征．其中高／软态和低／硬态的剩余功率谱存在一个宽峰结构,中心频率分别为～ ８ Ｈｚ和～ ５ Ｈｚ,低／硬态的剩余功率诺在～ ０．０７ Ｈｚ达到极大;转换态的剩余功率谱有双峰结构,其中心频率分别在～０．５—４Ｈｚ和～５—１１Ｈｚ,与我们以前分析的 ＱＰＯ的中心频率很接近,说明 ＱＰＯ与线性状态空间所要求的自回归模型可能属于不同的物理过程．与总功率谱比较,剩余功率谱对谱的变化部分（例如ＱＰＯ、截断频率等）更为敏感,本文对剩余功率谱中谱峰变化的原因做了初步的探讨．     

黑洞候选体MAXI J1535-571爆发期间的时变现象

利用“慧眼”(Hard X-ray Modulation Telescope, Insight-HXMT)卫星在2017年9月对黑洞候选体MAXI J1535-571的观测数据,研究了该源在爆发期内的时变现象.当源处于不同的爆发谱态时,功率密度谱的谱型存在明显差异.在硬中间态,有明显的限带噪声(band-limited noise)成分和QPO (Quasi-Periodic Oscillation)成分.分析结果表明:低频限带噪声的特征频率随能量的变化呈现正相关,即软能段光子的特征频率小于硬能段光子的特征频率. 0.1–0.5 Hz频率区间的限带噪声RMS (Root Mean Square)谱在硬中间态和软中间态均出现峰值,且在高能端存在差异,可能是主导噪声RMS的能谱成分占比不同.当谱态由硬中间态过渡到软中间态时, C型QPO的RMS谱保持相似趋势,但限带噪声RMS谱存在谱态依赖现象,暗示着噪声和QPO有不同的起源机制.     

A Study of the γ-ray and X-ray Radiations of BL Lac Objects

The X-ray and γ-ray flux densities of 18 γ-loud BL Lac objects as well as their average spectral indices of X-ray wave band (1 keV) and γ-ray wave band (>100 MeV) are collected, and the correlations among the various quantities are examined. The results indicate: (1) The X-ray flux density and the γ-ray flux density exhibit rather strong correlations in all the states, high, low or mediate. (2) Between the mean spectral indices in X-ray and γ-ray wave bands there is a comparatively intense anti-correlation. (3) Between the average spectral indices and the X-ray and γ- flux densities there is no evident correlation either in the high or the mediate state. (4) Between the average spectral index of γ-ray wave band and the flux density of X-rays in low state there is a rather strong anticorrelation. Between the mean spectral index of X-ray wave band and the γ-flux density in low state there also exists a weak correlation. The results of our analysis support the viewpoint that both the X-ray and γ-ray emissions of BL Lac objects come from the synchrotron radiation and synchrotron self Compton (SSC) radiation with one and the same distribution of relativistic electrons.     

Magnetic field and flares of the large sunspot group of April–May 1978

From magnetograms of the active region 15266 obtained at Yunnan observatory we found that 1) an inverted field configuration and a twisted neutral line are both closely correlated with high-energy flare eruptions. After the flares, the field configuration and the neutral line revert to more stable states. 2) Most of the flares of the present region occurred away from the neutral line; those near the line occurred either in regions of high field gradient or in the vicinity of Severny's “neutral points”.     

Luminosity dependent study of the high mass X-ray binary pulsar 4U 0114 + 65 with ASCA

Here we report the spectral characteristics of the high and low states of the pulsar 4U 0114 + 65 and examine the change in the parameters of the spectral model. A power law and a photoelectric absorption by material along the line of sight together with a high energy cut-off suffice to describe the continuum spectrum in both the states. A fluorescence iron line at ∼6.4 keV is present in the high as well as in the low state, though it is less intense in the latter. The photon index, cut-off energy and e-folding energy values hardly show any discernible change over the states. We compare these spectral characteristics as observed with ASCA with those of other satellites. We also compare the spectral characteristics of 4U 0114 + 650 with other X-ray sources which show intensity variation at different time scales.     

Variability of the extreme z = 4.72 blazar, GB 1428+4217

On 1998 May 9–11, the highly variable, low-luminosity Seyfert 1 galaxy NGC 4051 was observed in an unusual low-flux state by BeppoSAX , RXTE and EUVE . We present fits of the 4–15 keV RXTE spectrum and BeppoSAX MECS spectrum obtained during this observation, which are consistent with the interpretation that the source had switched off, leaving only the spectrum of pure reflection from distant cold matter. We place this result in context by showing the X-ray light curve of NGC 4051 obtained by our RXTE monitoring campaign over the past two and a half years, which shows that the low state lasted for ∼150 d before the May observations (implying that the reflecting material is >10¹⁷ cm from the continuum source) and forms part of a light curve showing distinct variations in long-term average flux over time-scales > months. We show that the long-time-scale component to X-ray variability is intrinsic to the primary continuum and is probably distinct from the variability at shorter time-scales. The long-time-scale component to variability maybe associated with variations in the accretion flow of matter on to the central black hole . As the source approaches the low state, the variability process becomes non-linear. NGC 4051 may represent a microcosm of all X-ray variability in radio-quiet active galactic nuclei (AGNs), displaying in a few years a variety of flux states and variability properties which more luminous AGNs may pass through on time-scales of decades to thousands of years.     

Type II Radio Bursts with High and Low Starting Frequencies

We report on the detailed analysis of i) differences between the properties of type IIs with various starting frequencies (high: ≥100 MHz; low: ≤50 MHz; mid: 50 MHz ≤f≤ 100 MHz) and ii) the properties of CMEs and flares associated with them. For this study, we considered a sample of type II radio bursts observed by Culgoora radio spectrograph from January 1998 to December 2000. The X-ray flares and CMEs associated with these events are identified using GOES and SOHO/LASCO data. The secondary aim is to study the frequency dependence on other properties of type IIs, flares, and CMEs. We found that the type IIs with high starting frequencies have larger drift rate, relative drift rate, and shock speed than the type IIs with low starting frequencies. The flares associated with high frequency type IIs are of impulsive in nature with shorter rise time, duration and delay between the flare start and type II start times than the low frequency type IIs. There is a distinct power – law relationship between the flare parameters and the starting frequencies of type II bursts, whereas the trend in the CME parameters shows low correlation. While the mean speed of CMEs is larger for the mid-frequency group, it is nearly the same for the high and low frequency groups. On the other hand, the percentage of CME association (90%) is larger for low frequency type IIs than for the high frequency type IIs (75%).