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1.
We present the long-term light curve of the radio source J1603+1105 and results of the study of its variability on timescales from several days to several weeks. From 2007, a flare with the maximum in 2010 was observed for the object that earlier showed no significant variations of flux density. Three flares with a successively decreasing amplitude were detected at an active phase in the long-term light curve. The characteristic time of the first one was 2.5 yrs. In five sets of daily observations of 95 to 120 days, the flux density variability on scales from 9 to 32 days in 2011, 2012, 2015, and 2016 was detected; in 2015 it was detected at three frequencies simultaneously. In 2011, the variability was found at a single frequency of 4.8 GHz; in 2012—at two frequencies, 4.8 and 7.7 GHz; in 2015—at 4.6, 8.2, and 11.2 GHz.We present instant spectra of the source at different flare phases showing that the dynamics of the flare development is consistent with the model, in which the variability is the result of the shock wave evolution in the radio source jet.  相似文献   

2.
PKS 2155-304 is a well studied BL Lac object in the southern sky. The historical optical data during different periods have been collected and compiled. Light curves spanning 35 yr have been constructed. The R-band light curve has been analyzed by means of three methods: the epoch folding method,the Jurkevich method and the discrete correlation function method. It is derived that there is an evident periodic component of 317 d(i.e. 0.87 yr) superposed on a long-term trend with largeamplitude variation in the light curve. The variability of this source is accompanied by a slight color variation,and the brightness and color index are correlated with each other. On a long-term time scale,PKS 2155-304 exhibits a tendency of bluer-whenbrighter,which means the spectrum becomes flatter when the source brightens.  相似文献   

3.
XTE J1748−288 is a black hole X-ray transient which went into outburst in 1998 June. The X-ray light curves showed canonical morphologies, with minor variations on the 'fast rise exponential decay' profile. The radio source, however, reached an unusually high flux density of over 600 mJy. This high radio flux was accompanied by an exceptional  (>20  per cent)  fractional linear polarization, the variability of which was anticorrelated with the flux density. We use this variability to discuss possible depolarization mechanisms and to predict the underlying behaviour of the (unresolved) core/jet components.  相似文献   

4.
Helium star–compact object binaries, and helium star–neutron star binaries in particular, are widely believed to be the progenitors of the observed double-neutron-star systems. In these, the second neutron star is presumed to be the compact remnant of the helium star supernova. In this paper, the observational implications of such a supernova are discussed, and in particular are explored as a candidate γ-ray burst mechanism. In this scenario, the supernova results in a transient period of rapid accretion on to the compact object, extracting via magnetic torques its rotational energy at highly super-Eddington luminosities in the form of a narrowly beamed, strongly electromagnetically dominated jet. Compton scattering of supernova photons advected within the ejecta, and photons originating at shocks driven into the ejecta by the jet, will cool the jet and can produce the observed prompt emission characteristics, including the peak-inferred isotropic energy relation, X-ray flash characteristics, subpulse light curves, energy-dependent time lags and subpulse broadening, and late time spectral softening. The duration of the burst is limited by the rate of Compton cooling of the jet, eventually creating an optically thick, moderately relativistically expanding fireball that can produce the afterglow emission. If the black hole or neutron star stays bound to a compact remnant, late term light curve variability may be observed as in SN 2003dh.  相似文献   

5.
We present an internal shock model with external characteristics for explaining the complicated light curves of gamma-ray bursts. Shocks produce gamma-rays in the interaction between a precessing beam of relativistic particles and the interstellar medium. Each time the particle beam passes the same line of sight with the observer the interstellar medium is pushed outward. Subsequent interactions between the medium and the beam are delayed by the extra distance to be travelled for the particles before the shock can form. This results in a natural retardation and leads to an intrinsic asymmetry in the light curves produced for gamma-ray bursts. In addition, we account for the cooling of the electron–proton plasma in the shocked region, which gives rise to an exponential decay in the gamma-ray flux. The combination of these effects and the precessing jet of ultrarelativistic particles produces light curves that can be directly compared with observed gamma-ray burst light curves. We illustrate the model by fitting a number of observed gamma-ray bursts that are difficult to explain with only a precessing jet. We develop a genetic algorithm to fit several observed gamma-ray bursts with remarkable accuracy. We find that for different bursts the observed fluence, assuming isotropic emission, easily varies over four orders of magnitude from the energy generated intrinsically.  相似文献   

6.
Multicolor photometric observations of the optical afterglow from GRB 060526 with the Russian-Turkish 1.5-m RTT-150 telescope (Mount Bakyrlytepe, Turkey) are presented. The afterglow light curve was measured in detail starting from about 5 h after the GRB and over five ensuing nights. In addition, upper limits were obtained on the rapid variability of the afterglow on the first night of observations and the history of afterglow color variations was measured in detail. In the time interval from 6 to 16 h after the burst, the flux gradually decreased approximately as a power law with a slope of ?1.14 ± 0.02. Subsequently, variability was observed on a time scale δt < t and the afterglow began to decay much faster. The afterglow color was approximately constant (V?R ≈ 0.5) throughout the observations, despite the flux variability. Variability time scales up to δt/t ≈ 0.0055 were observed at ΔF ν/F ν ≈ 0.3, which violates many constraints on the variability of the observed emission from an ultrarelativistic jet obtained by Ioka et al. (2005). We suggest explaining this variability by the fact that the shell motion is no longer ultrarelativistic at this time.  相似文献   

7.
Nereid is a small irregular moon of Neptune that displays large-, moderate-, and small-amplitude photometric variations on both fast and slow time scales. The central mystery of Nereid is now to explain the physical mechanism of these unique brightness changes and why they change with time. To characterize Nereid's variability, we have been using the SMARTS telescopes on Cerro Tololo for synoptic monitoring from 1999 to 2006. We present a well-sampled photometric time series of 493 magnitudes on 246 nights mostly in the V-band. In combination with our earlier data (for 774 magnitudes over 362 nights), our 20-year data set is the most comprehensive for any small icy body in our Solar System. Our yearly light curves show that Nereid displays various types of behaviors: large amplitude brightenings and fadings (1987 to 1990); moderate-amplitude variation about the average phase curve (1993-1997, 2003, 2005), moderate-amplitude variation and systematically brighter by roughly one-quarter magnitude throughout the entire season (2004); and nearly constant light curves superimposed on a surprisingly large-amplitude opposition surge (1998, 1999, 2000, 2006). Other than in 2004, Nereid's variations were closely centered around a constant phase curve that is well fit with a Hapke model for the coherent backscattering opposition surge mechanism with angular scale of 0.7°±0.1°. In our entire data set from 1987-2006, we find no significant periodicity. We propose that the year-to-year changes in the variability of Nereid are caused by forced precession (caused by tidal forces from Neptune) on the spin axis of a nonspherical Nereid, such that cross-sectional areas and average albedos change as viewed from Earth.  相似文献   

8.
A Fourier series fitting of order 10 to the historical light curve of OJ287 (3648 data points) is presented with correlation coefficient ∼ 0.73. It is found that the Weierstrass function may be used to imitate the short time scale variability of OJ287. A fractal curve constructed by the function possesses the similar correlation coefficient to the light curve as the regression curve. We also calculate the capacity-dimension, information-dimension and correlation-dimension of the light curve. The calculations indicate that their values > 1. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

9.
It is generally believed that the complexity and variability of the light curves of gamma-ray bursts (GRBs) are caused by the internal shocks, which would occur when a rapid shell catches up a slower one and collides with it. The electrons in the shock layer are heated by the shocks and radiate via the mechanisms of synchrotron radiation and inverse Compton scattering. Based on relativistic kinematics, a relation between the photon number of the emission from the rapidly moving shock layer and the number of the photons received by an observer is derived. Then, employing the angular spreading of the internal shock emission, the curve equation and profile of a single pulse are obtained, and the shape is typically in the shape of a fast rise and exponential decline. Furthermore, by using the model of the successive collisions of multiple shells under the condition of reasonable parameters, the observed light curves are fitted with a rather good effect. Therefore, by this means, more different types of light curves of GRBs can be explained.  相似文献   

10.
The light curve of the outburst of Comet P/Metcalf-Brewington (1991 I) is investigated. The parameters of the light curve are quite uncertain as it may be fitted both in terms of variation with heliocentric distance and exponential decay with time however, after maximum a empirical fit ofm 1 = 4.1 + 5 log Delta + 14.8 logr gives a good fit to the data. The absolute magnitude brightened at least 11 magnitudes in outburst. The outburst is most plausibly caused by the release of micron sized grains as, were the outbust due to dust emission, it would imply the expulsion of a large fraction of the total mass of the nucleus.  相似文献   

11.
A new inversion technique for obtaining temperature, pressure, and number density profiles of a planetary atmosphere from an occultation light curve is described. This technique employs an improved boundary condition to begin the numerical inversion and permits the computation of errors in the profiles caused by photon noise in the light curve. We present our assumptions about the atmosphere, optics, and noise and develop the equations for temperature, pressure, and number density and their associated errors. By inverting in equal increments of altitude, Δh, rather than in equal increments of time, Δt, the inversion need not be halted at the first negative point on the light curve as required by previous methods. The importance of the boundary condition is stressed, and a new initial condition is given. Numerical results are presented for the special case of inversion of a noisy isothermal light curve. From these results, simple relations are developed which can be used to predict the noise quality of an occultation. It is found that fractional errors in temperature profiles are comparable to those of pressure and number density profiles. An example of the inversion method is shown. Finally, we discuss the validity of our assumptions. In an appendix we demonstrate that minimum fractional errors in scale height determined from the inversion are comparable to those from an isothermal fit to a noisy isothermal light curve.  相似文献   

12.
Broadband afterglow observations provide a probe of the density structure of the circumburst medium. In the spreading jet model, prompt and intense X-ray/UV radiation from the reverse shock may destroy and clear the dust in the circumburst cloud out to about 30 pc within the initial solid angle of the jet. Asthe jet expands significantly, optical radiation from the high-latitude part of the jet may suffer extinction by dust outside the initial solid angle, while radiation from the part within the initial solid angle can be observed without extinction. In previous studies, it is usually assumed that the extinction is complete. We calculate the extinction effect by taking the optical depth into account. Our numerical results showthat a break appears in the light curve of optical afterglow but it extends over a factor of ～ 80 in time rather than a factor of ～ 10 in time for the case of strong dust extinction and a factor of ～ 60 in time for the case without dust extinction. These results may provide a way to judge how large the number density of the circumburst cloud is. Finally, we carry out a detailed modeling for the afterglow of GRB 000926. Our model can provide a good fit to the multi-color observations of this event.  相似文献   

13.
《New Astronomy》2003,8(5):495-505
We present general analytic expressions for GRB afterglow light curves arising from a variable external density profile and/or a variable energy in the blast wave. The former could arise from a clumpy ISM or a variable stellar wind; The latter could arise from refreshed shocks or from an angular dependent jet structure (patchy shell). Both scenarios would lead to a variable light curve. Our formalism enables us to invert the observed light curve and obtain possible density or energy profiles. The optical afterglow of GRB 021004 was detected 537 s AB (after the burst) [GCN (2002) 1564]. Extensive follow up observations revealed a significant temporal variability. We apply our formalism to the R-band light curve of GRB 021004 and we find that several models provide a good fit to the data. We consider the patchy shell model with p=2.2 as the most likely explanation. According to this model our line of sight was towards a ‘cold spot’ that has lead to a relativity low γ-ray flux and an initially weak afterglow (while the X-ray afterglow flux after a day was above average). Observations above the cooling frequency, νc, could provide the best way to distinguish between our different models.  相似文献   

14.
Whether gamma-ray bursts are highly beamed or not is a very important question, as it has been pointed out that the beaming will lead to a sharp break in the afterglow light curves during the ultrarelativistic phase, with the breaking point determined by  Γ∼1/ θ 0  , where Γ is the bulk Lorentz factor and θ 0 is the initial half opening angle of the ejecta, and such a break is claimed to be present in the light curves of some GRBs. In this paper we will examine whether all the observed breaks in GRB afterglow light curves can be explained by jet effects. Here we present a detailed calculation of the jet evolution and emission, and have obtained a simple formula of bulk Lorentz factor evolution. We show that the light curves are very smoothly steepened by jet effect, and the shape of the light curve is determined by only one parameter –     , where E and n are the fireball energy and surrounding medium density, respectively. We find that for GRB 990123 and GRB 991216, the jet model can approximately fit their light curves, and the values of     are about 0.17 and 0.22, respectively. On the other hand, the light curves of GRB 990510, GRB 000301c, GRB 000926 and GRB 010222 cannot be fitted by the jet model, which suggests that the breaks may be caused by some other reasons, and the jet effect should be not the unique reason.  相似文献   

15.
光变是Blazar最显著的观测特征之一,有的光变呈准周期性. Blazar周期光变可能为其中心黑洞和吸积盘等内部物理结构提供重要信息.因此,周期分析对于讨论Blazar的光变有重要意义.结合经验模态分解(Empirical Mode Decomposition, EMD)和自回归(Auto-regressive, AR)模型谱估计方法的优点,提出了一种基于EMD-AR谱的组合光变周期分析新方法.先对观测数据进行EMD分解,得到各阶模态分量,并计算其与原始光变曲线的相关系数,再取相关度高的分量求和后估算AR谱,最后将此功率谱的周期分析方法用于天体的光变数据分析.讨论了EMD-AR谱方法的原理和应用步骤,并用此方法对类星体3C 273在1887—2016年的观测数据进行了分析,得到3C 273的长时标周期分别为:21.23、13.51、11.02、5.51、4.69、3.79、2.76 yr,与文献中常用方法的分析结果有很好的一致性;短时标周期分别为:(30±1)、(15±0.3)、(7.5±0.2)、(10±0.1)、(5±0.6)、(6±0.4)和(3±0.5) min,此结果未见相关...  相似文献   

16.
Having compared images of a jet of the young star RWAurA obtained with an interval of 21.3 yr, we have found that the outermost knots of the jet have emerged approximately 350 years ago. We come up with arguments that the jet itself has appeared at the same time, and intensive accretion onto the star has begun due to rearrangement of its protoplanetary disk structure caused by the tidal effect of the companion RWAur B. More precisely suppose that intensification of accretion is a response to changing conditions in the outer-disk regions which has followed after the sound wave, generated by these changes, has passed the disk in the radial direction. In our opinion difference in the parameters of blue and red lobes of the RWAurA jet is a result of the asymmetric distribution of the circumstellar matter above and below the disk due to companion’s passage. It was found from the analysis of the RWAur historical light curve that deep and long-term (Δt > 150 days) light attenuations of RWAurA observed after 2010 had no precedents in the previous 110 years.We also associate the change in the character of photometric variability of the star with the rearrangement of the structure of inner (r < 1 AU) regions of its protoplanetary disk, and discuss why these changes have begun only 350 years after the beginning of the active accretion phase.  相似文献   

17.
基于欧文斯谷射电天文台(Owens Valley Radio Observatory,OVRO)40 m望远镜观测数据,收集了耀变体CGRaBS J0835+6835在15 GHz射电波段约12年的数据.利用LSP(Lomb-Scargle Periodogram)方法和加权小波Z变换(Weight Wavelet Z...  相似文献   

18.
We describe the first results of our observations of the exceptionally bright optical afterglow from the cosmic gamma-ray burst (GRB) of March 29, 2003 (030329), with the 1.5-m Russian-Turkish telescope (RTT150) installed at the TUBITAK National Observatory (Turkey) at Mount Bakyrlytepe. RTT150 was one of the first medium-class telescopes pointed at the afterglow. The observations began as early as about six hours after the GRB. During the first five hours of our observations, the BV RI flux fell off exactly as a power law with the same slope ?1.19±0.01. Subsequently, in all of the BV RI bands, we observed the same increase in the power-law slope of the light curve to a value that was later recorded during the observations at observatories in the western hemisphere. The break in the power-law light curve occurs at t ? t 0 ≈ 0.57 days (13.5 h) and lasts for about 0.2 days. Apart from this smooth decrease in the flux, the afterglow exhibited no flux variability. The upper limits on the variability are 10–1% on time scales of 0.1–1000 s, respectively. The BV RI spectral flux distribution during the first night of our observations closely corresponds to a power-law spectrum with a spectral index α=0.66±0.01. The change in the power-law slope of the light curve at the end of our observations is probably attributable to the deceleration of the ultrarelativistic jet to a gamma factor when its structural features begin to show up in the light curve. The radio, optical, and X-ray broadband spectrum is consistent with the assumption about the synchrotron radiation of the ultrarelativistic jet. This unique object continues to be observed with RTT150.  相似文献   

19.
展示活动星系核研究和引力研究中的一些难点,揭示了某些天体的光变存在分形结构的可能性。我们提出了活动星系核的中心黑洞具有某种随机微活动性的假设,该假设可解释活动星系核的一些观测现象。我们发现Ｗｅｉｅｒｓｔｒａｓ函数的分形图形可以用来很好地拟合ＯＪ２８７的短时标光变。一个用Ｗｅｉｅｒｓｔｒａｓ函数构造的分形曲线与ＯＪ２８７的历史光变的线性相关系数达到了０．７３。我们计算了ＯＪ２８７光变曲线的计盒维数,信息维数和关联维数,结果表明,这些维数均大于１。我们研究了两个活动星系核（ＯＪ２８７和３Ｃ３４５）的历史光变,发现在星等和这两个物体滞留在这个星等之下的时间长度的对数之间存在线性关系。这种关系可能源于光变的分形结构。我们提出,空时点及附于该点的一个标架与Ｍｉｎｋｏｗｓｋｉ空间上的一个３阶反对称张量场对应。场中的张量取自于一个固定的张量集合。我们得到了Ｒｉｅｍａｎｎ正则坐标下引力场的一个级数表示式。我们还计算了Ｒｉｃｃｉ张量的线性近似和一级非线性近似。这有利于强引力场下的局部非线性结构分析。期望对于引力的进一步研究,通过非线性科学这门新方法的桥粱,沟通极端天文现象与基本引力相互作用之间的鸿沟  相似文献   

20.
When the axis of a gamma-ray burst (GRB) does not coincide with the spin axis of its source, there may result a ring-shaped jet. Using some refined jet dynamics, we calculate multi-wavelength afterglow light curves for such ring-shaped jets. In the R-band we find an obvious break in the afterglow light curve due to the beaming effect and the break is affected by many parameters, such as the electron energy fraction ξe, the magnetic energy fraction ξ2B, the width of ring A0 and the medium number density n. The overall light curve can be divided into three power-law stages, I.e., an ultra-relativistic stage, an after-break stage and a deep Newtonian stage. For each stage the power-law index is larger in the ring-shaped jet than in the corresponding conical jet.  相似文献   

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