共查询到19条相似文献，搜索用时 187 毫秒
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本文报导光学选类星体样本的光变研究结果。利用ＣＣＤ 测光资料,本文研究中等亮类星体样本的长期光变行为。结果表明,大约４０ ％ 的光学选类星体在１８ 年的研究期间内有光变;变光类星体的光变同光度负相关,即愈亮的类星体的光变愈小;光变同红移也可能存在负相关。 相似文献
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《天文学报》2017,(3)
伽玛暴νfν谱的峰值能量E_p是伽玛暴的一个很重要的观测物理量,观测系中伽玛暴νf_ν谱的峰值能量Ep分布很宽.根据各向同性光度L_(iso)、初始洛伦兹因子Γ_0和暴源系中峰值能量E_p,z之间的关系式估算伽玛暴的初始洛伦兹因子Γ_0,再把伽玛暴νf_ν谱的峰值能量E_p和光度L_(iso)修正到共动坐标系,发现共动系中峰值能量的分布还是很宽.这意味着观测系中E_p的宽分布可能是伽玛暴的真实物理分布.检验了共动坐标系中光度和峰值能量之间的关系,发现它们之间仍然存在相关性.最后,进一步对伽玛暴的辐射物理进行限制,认为共动坐标系中峰值能量分布很宽可能是由于辐射电子的洛伦兹因子γ_e分布很宽. 相似文献
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《天文研究与技术》2015,(4)
使用活动星系核射电喷流的VLBA监测实验(Monitoring Of Jets in Active galactic nuclei with VLBA Experiments,MOJAVE)的15.3 GHz超长基线阵列(Very Long Baseline Array,VLBA)观测数据,利用功率谱密度函数方法对59个耀变体的光变曲线进行了周期分析,结果表明这59个耀变体的光变曲线显示了从2.6年到11.1年的可能的光变周期。分析了59个光变周期与其红移的关系,结果表明二者没有相关性,进一步搜集了14.5 GHz波段上的110个活动星系核的周期并分析了它们的周期与红移的关系,结果表明二者没有相关性。 相似文献
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利用Union2 557个Ia型超新星数据限制宇宙学参数qo、jo和so,在红移z≤1.4范围内校准5个γ暴(gamma-ray burst,GRB)光度关系.假设γ暴光度关系不随红移演化,得到66个高红移γ暴的距离模数.最后综合利用宇宙微波背景(Cosmic Microwave Background,CMB)辐射观测数据、重子声波震荡(Baryon AcousticOscillations,BAO)观测数据与116个具有红移的γ暴数据限制几个常见的暗能量模型.根据贝叶斯判据(Bayesian Information Criterion,BIC),发现ACDM模型是最好的模型;根据Akaike判据(Akaike Information Criterion,AIC),发现JBP模型是最好的模型. 相似文献
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在活动星系核的标准模型中,中心有一个超大质量黑洞,黑洞周围是一个吸积盘,喷流处在垂直于吸积盘的平面上。理论研究表明,喷流和吸积盘之间存在一定的联系,许多学者利用射电(或伽马)辐射与发射线辐射之间的相关性研究这种关系。然而,耀变体的射电或伽马辐射具有强烈的成束效应,使得在讨论喷流-吸积盘的联系时,应该考虑成束效应。收集了202个FERMI/LAT耀变体的宽发射线数据研究喷流与吸积的关系。202个源中,66个具有多普勒因子。对整个样本和平谱射电类星体与蝎虎座BL型天体2个子样本,分别研究了去除红移影响和成束放大效应时,伽马射线与宽发射线以及射电波段与宽发射线的相关关系,得到整个样本202个源的伽马射线与宽发射线以及射电波段与宽发射线之间存在强的正相关,而且这种相关性在去除红移效应之后仍然存在。对于66个有多普勒因子的源,在去除多普勒因子的影响之后,伽马射线与宽发射线以及射电波段与宽发射线之间仍然存在正相关。分析结果表明:(1)整个样本和各个子类的伽马射线与宽发射线之间都存在强相关。这些相关性在红移效应去除后仍然存在,并且证实了文献中他们所研究的结果。(2)对于66个有多普勒因子的耀变体,宽发射线与多普勒因子之间存在强的相关性,伽马射线与宽发射线在去除多普勒因子的影响之后存在相关性。在射电和宽发射线之间也得到了类似的结果。(3)吸积过程与喷流之间存在强关联性。 相似文献
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伴随着引力波事件GW170817的短暴GRB (Gamma-Ray Burst) 170817A首次提供了双中子星并合与短暴相联系的直接证据.但是短暴GRB 170817A具有非常弱的光度,意味着观测的视线方向可能偏离喷流轴方向.根据短暴静止系的峰值能量E_(p,i)和各向同性光度L_(iso)。之间的关系以及洛伦兹因子Γ和L_(iso)。之间的关系估算了短暴GRB 170817A以及长短暴GRB 060614观测角与喷流边缘的夹角θ'_(obs)和洛伦兹因子Γ,结果表明GRB 170817A的Γ=45±27,θ'_(obs)=2.2±0.5°,而GRB 060614的Γ=214±93,θ'_(obs)=0.5±0.1°.这个结果相当于GRB 170817A的正轴各向同性光度L_(iso,on)=(2.1±0.7)×10~(49) erg·s~(-1),比典型的短暴少2-3个数量级.GRB 060614的L_(iso,on)=(5.12±1.91)×10~(51) erg·s~(-1)与典型短暴相当.这意味着GRB 060614可能属于短暴类型,而GRB 170817A可能本质上就是一个弱暴. 相似文献
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Zhao-yu Yang Li-ming Song Rong-feng Shen Zhuo Li Yu-sheng Lu 《Chinese Astronomy and Astrophysics》2005,29(4):361-369
This work presents a possible luminosity estimator for long γ-ray bursts (GRBs) based on their light curves. We use the method of variability analysis in the time domain to calculate the power density spectrum (PDS) for each of the 12 GRBs with known redshifts observed by CGRO/BATSE. The peak of the power density spectrum P is a measure of the intensity of variability of the given light curve and a strong correlation is found between P and the isotropic peak luminosity L of the GRB. It is a successor to the lag-luminosity relation of Norris et al. (2000) and the variability-luminosity relation of Reichart et al. (2001). 相似文献
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Gamma-ray burst remnants become trans-relativistic typically in days to tens of days, and they enter the deep Newtonian phase in tens of days to months, during which the majority of shock-accelerated electrons will no longer be highly relativistic. However, a small portion of electrons are still accelerated to ultra-relativistic speeds and are capable of emitting synchrotron radiation. The distribution function for electrons is re-derived here so that synchrotron emission from these relativistic electrons can be calculated. Based on the revised model, optical afterglows from both isotropic fireballs and highly collimated jets are studied numerically, and compared to analytical results. In the beamed cases, it is found that, in addition to the steepening due to the edge effect and the lateral expansion effect, the light curves are universally characterized by a flattening during the deep Newtonian phase. 相似文献
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The BATSE (Compton Gamma-ray Observatory/Bursts and Transient Source Experiment), Swift (Swift Gamma-ray Burst Explorer) and Fermi (Fermi Gamma-ray Space Telescope) satellites have provided us with a large amount of GRB sample. After a systematical study and comparison of the properties of the GRBs detected by these 3 kinds of instruments, it is found that although significant differences exist in the number of red-shifted bursts, the proportion of long bursts in total bursts and the photon flux distribution (lgN − lg P), but no significant difference exists in the duration time, the total flux of Gamma-ray radiation and the spectral hardness ratio. Considering that the observational energy bands of the Swift- and Fermi-detected bursts are different, after making corrections the difference in the lgN − lg P distribution can be basically eliminated. The differences in the number of red-shifted bursts and the proportion of long bursts in total bursts are caused by the different sensitivities of instruments. Namely, various instruments give different observed characteristics of GRBs, but they are consistent in nature. 相似文献
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If X-ray flashes (XRFs) and X-ray rich Gamma-ray Bursts (XRRGs) have the same origin as the Gamma-ray bursts (GRBs) but are viewed off-center from structured jets,their early afterglows may differ from those of GRBs,and when the ultra-relativistic outflow inter-acts with the surrounding medium,there are two shocks formed,a forward shock (FS),and a reverse shock (RS). We calculate numerically the early afterglow powered by uniform jets,Gaussian jets and power-law jets in the forward-reverse shock scenario. A set of differen-tial equations govern the dynamical evolution. The synchrotron self-Compton effect has been taken into account in the calculation. In the uniform jets,the very early afterglows of XRRGs and XRFs are significantly lower than the GRBs and the observed peak times of RS emission are later in the interstellar medium environment. The RS components in XRRGs and XRFs are difficult to detect,but in the stellar wind environment,the reduction of the very early flux and the delay of the RS peak time are not so remarkable. In nonuniform jets (Gaussian and power-law jets),where there are emission materials on the line of sight,the very early light curve resembles equivalent isotropic ejecta in general although the RS flux decay index shows notable deviations if the RS is relativistic (in stellar wind). 相似文献
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P. A. Curran A. J. van der Horst R. A. M. J. Wijers 《Monthly notices of the Royal Astronomical Society》2008,386(2):859-863
Gamma-ray burst (GRB) afterglow observations in the Swift era have a perceived lack of achromatic jet breaks compared to the BeppoSAX or pre- Swift era. Specifically, relatively few breaks, consistent with jet breaks, are observed in the X-ray light curves of these bursts. If these breaks are truly missing, it has serious consequences on the interpretation of GRB jet collimation and energy requirements, and the use of GRBs as cosmological tools. Here, we address the issue of X-ray breaks that are possibly 'hidden' and hence the light curves are misinterpreted as being single power laws. We do so by synthesizing X-ray telescope (XRT) light curves and fitting both single and broken power laws, and comparing the relative goodness of each fit via Monte Carlo analysis. Even with the well-sampled light curves of the Swift era, these breaks may be left misidentified, hence caution is required when making definite statements on the absence of achromatic breaks. 相似文献
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采用一个简单的激波模型来讨论了珈玛射线爆光变曲线的轮廓。根据激波理论,爆炸产生压力脉冲并以压力波的形式传播,既有压缩波也有膨胀波。压缩波的合并产生激波,它的强度被随后并入的压缩波或膨胀波分别增强或减弱。该模型能自然地描述珈玛爆光变曲线和光变曲线具有的"快速上升指数下降"的轮廓特征。我们认为这一特征是压缩波和膨胀波的传播特性导致的。 相似文献
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定义了一个新的量,曲率宽度,去检查同步模型与伽玛射线暴(GRB)光谱的一致性.此量用于测量GRB中辐射能谱(νFν,ν和Fν分别是频率和随频率变化的能量流量)峰值处的光谱拐折锐度.然后使用它检查了理论同步模型与观测到的GRB光谱之间的一致性.首先计算几种典型的同步模型的曲率宽度,包括单能、单幂律和拐折幂律电子同步模型.其次从Fermi/GBM (Gamma-ray Burst Monitor)长GRB时间分辨光谱目录中选择包含1198个光谱的GRB样本,将光谱与常用的经验模型拟合,并计算最佳拟合模型的光谱曲率宽度.通过比较两个曲率宽度,发现大多数样本与同步模型不一致,因为同步模型的光谱拐折比数据的光谱拐折更加平滑.结果表明同步模型很难适合大多数观测到的GRB光谱.此外,在暴脉冲中发现光子流量和曲率宽度之间存在强的反相关性,这表明流量越高,光谱拐折越尖锐,或者与同步模型的偏差就越大. 相似文献
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S. A. Farrell D. Barret G. K. Skinner 《Monthly notices of the Royal Astronomical Society》2009,393(1):139-156
We present the results of a study with the Swift Burst Alert Telescope in the 14–195 keV range of the long-term variability of five low-mass X-ray binaries with reported or suspected superorbital periods – 4U 1636−536, 4U 1820−303, 4U 1916−053, Cyg X-2 and Sco X-1. No significant persistent periodic modulation was detected around the previously reported periods in the 4U 1916−053, Cyg X-2 or Sco X-1 light curves. The ∼170-d period of 4U 1820−303 was detected up to 24 keV, consistent with variable accretion due to the previously proposed triple system model. The ∼46-d period in 4U 1636−536 was detected up to 100 keV, with the modulation in the low- and high-energy bands found to be phase shifted by ∼180° with respect to each other. This phase shift, when taken together with the near-coincident onset of the ∼46-d modulation and the low/hard X-ray state, leads us to speculate that the modulation could herald transient jet formation. 相似文献
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We introduce a new physical parameter, the optical variability amplitude, to the well-established Eigenvector 1 space of quasars and test a sample of long-term B-band light curves of 42 Palomar-Green quasars monitored by Giveon et al. We find that the optical variability amplitude strongly correlates with the intensity ratio of Fell to Hβ,Hβwidth and peak luminosity at 5007A. We briefly discuss the physical meaning of our findings and suggest that the Eddington ratio may be a key factor in determining a quasar's variability. 相似文献