脉冲星参数的取值对γ暴火球余辉的影响

用中心有脉冲星的γ射线暴的火球模型计算出GRB970228和GRB000301c两个γ射线暴的余辉辐射流，计算结果与观测结果相比较，符合的很好，解释了GRB970228和GRB000301c光学R波段余辉的光变曲线带‘拐折’的特征，讨论了中心脉冲星参数的取值对余辉的光曲线起的重要作用。     

Fermi伽玛暴时间分辨谱拐折幂率拟合的模型限制

使用平滑拐折幂率(Smoothly Broken Power Law, SBPL)模型、折线幂率(Broken Power Law, BPL)模型和波段函数(Band)模型拟合8个费米(Fermi)亮暴,得到165个最佳模型拟合谱,然后根据这165个谱的能量流量得出3个模型拟合数据的范围和一些结论。折线幂率模型能很好地拟合较暗的暴(F_e5×10~(-5)erg·cm~(-2)),而较亮的暴用波段函数模型(5×10~(-5)erg·cm~(-2)F_e2.0×10~(-4)erg·cm~(-2))和平滑拐折幂率模型(2.0×10~(-4)erg·cm~(-2)F_e3.8×10~(-4)erg·cm~(-2))可以得到更好的拟合结果。样本中大约一半的谱用折线幂率模型拟合较好,表明有些较暗的暴的谱形接近折线形状,即谱拐折比较尖锐。虽然多数光谱中最佳拟合模型是折线幂率模型,但波段函数模型和平滑拐折幂率模型拟合也能得到可以接受的结果,并且高能光子少以至于现有的数据不能很好地排除一些能谱模型。另外,目前的拟合结果可能受到仪器响应矩阵的影响,不能很好地确定真实的物理模型,也就是说伽玛暴谱看似能被模型解释,但可能不是真实的。     

不同仪器GRB观测数据的一致性分析

BATSE(Compton Gamma-Ray Observatory/Bursts and Transient SourceExperiment)、Swift(Swift Gamma-ray Burst Explorer)和Fermi卫星(Fermi GammaraySpace Telescope)提供了大量的GRB样本.研究比较3种仪器观测的暴的特征,发现虽然有红移暴的数目、所有暴中长暴的比例以及光子流量分布(lgN-lgP分布)等有显著差异,但是暴的持续时间、伽玛辐射总流量、谱硬度比等均没有显著差异.考虑Swift和Fermi暴的观测能段不同,进行修正以后,发现lgN-lgP分布的差异也基本消除.有红移暴的数目、长暴占总暴数的比例是由仪器本身的灵敏度决定的,即不同仪器决定不同GRB的观测特征,但是它们的本质是一致的.     

Fermi耀变体的能谱分布研究

从SSDC (Italian Space Agency Science Data Center)搜集了68个Fermi耀变体的射电至X射线波段的观测数据,用对数抛物线拟合计算了其同步辐射峰的参数.研究了有效谱指数、同步辐射峰值频率和曲率的关系并用有效谱指数估算同步峰频.主要结果有:(1)研究同步峰频和曲率的线性关系发现,对于全部的蝎虎天体(BL Lac),结果与能量依赖加速概率模型的预测一致.但是,如果仅仅考虑高峰频BL Lac,即同步峰频lg (ν_p/Hz) 15.3的BL Lac,其结果却与分数变换加速增益模型的预测结果一致.(2)对于同步峰频相同的源,射电-光学的有效谱指数αro与曲率间有显著的负相关,而光学-X射线的有效谱指数α_(ox)与曲率无关.通过α_(ro)可以确定一个同步峰频与曲率的关系.     

非均匀喷流模型及其在BL Lac天体中的应用

在非均匀锥形喷流模型中,电子数密度、磁场强度随着到喷流顶点的距离呈幂律分布.该模型能成功解释活动星系核喷流核心区域的平谱射电辐射,但已有的模型计算只适用于喷流运动方向与视线夹角很大的情况,所以需要建立适用于任何视角情况的非均匀锥形喷流辐射计算公式.普遍认为BL Lac天体中喷流的运动方向与视线夹角很小,推广后的非均匀喷流模型拟合了3个BL Lac天体的射电观测谱,确定了它们喷流中电子数密度、磁场强度等物理参数.研究结果表明观测辐射谱拐折频率确定出锥形喷流离黑洞最近距离,对于这3个BL Lac天体,它们的锥形喷流离黑洞最近距离约为Schwarzschild半径.     

不同卫星伽玛νF_ν暴谱的峰值能量分布

伽玛暴是宇宙中最剧烈的爆发现象之一,观测伽玛暴预警和暂现源实验卫星(Compton Gamma-Ray Observatory/Bursts and Transient Source Experiment,BATSE)、高能暂现源探测卫星(High Energy Transient Explorer,HETE)和Fermi提供了大量的伽玛暴样本,对这些数据进行分析,用统计的方法寻找其中蕴含的伽玛暴辐射物理信息是必要的。伽玛暴能谱νFν的峰值能量Ep是伽玛暴一个很重要的物理量,并且每个暴的峰值能量不同。研究比较不同仪器观测的伽玛暴νFν谱的峰值能量Ep分布,发现伽玛暴的峰值能量Ep分布很宽,不同仪器的Ep分布相似,BATSE样本Ep分布的峰值比HETE-2和Fermi样本的Ep峰值要大一些,这可能是由于选取的BATSE样本都是亮暴造成的。3种仪器观测的Log N-Log Ep分布也没有显著差异。即从统计学的角度上讲,3种暴的Ep分布没有本质不同,不同仪器观测到的伽玛暴的辐射物理信息应该是一致的。     

重构Ly-α线丛的功率谱约束对数正态(LN)模型参数

选择3个类星体Keck观测样本,使用Gauss化方法重构宇宙质量密度扰动场,并计算相应的小波功率谱．同时,设定对数正态(LN)模型中的形状因子Γ和平滑因子r为自由参数,并通过数值模拟生成模拟样本,与观测样本的统计结果做拟合,来确定Γ和r．结合观测的辐射流量功率谱和数值模拟的结果可以唯一确定Γ的值,最后得到Γ≈0．50,r≈0．0g．类星体的辐射流量是非Gauss的,使用传统的Gauss化方法无法消除非Gauss特征．但是观测样本和数值模拟样本的偏斜谱、峰度谱以及尺度-尺度相关等非Gauss特征的表征量在研究的尺度(>100kpc)上表现一致,这就支持了拟合的结果．     

Seyfert星系核大蓝包特征

借助HST高分辨率观测图像所分离的Seyfert星系核的光学光度,以及IUE观测的紫外流量,来推算Seyfert星系核的大蓝包特征谱指数(α)(Fν～ν-α)并进行统计。发现样本的平均谱指数是-0.55,比Sloan数字天空巡天(SDSS)类星体合成谱幂律拟合谱指数(0.46)要小,更接近于经典吸积盘理论所预测的光学—紫外谱指数(-0.3)。尽管谱指数分布仍然较宽,但与星系总辐射所推测的大蓝包谱指数αT相比,大多数天体都有所降低。另外发现,相比Ⅰ型来说,SeyfertⅡ型星系核大蓝包特征谱指数的降低有异常的大,可能与星系盘上紫外辐射在Ⅱ型总辐射中占有相当大的份额有关。     

耀变体3C 273在2～10keV的光变特性研究

从RXTE(Rossi X-ray timing explorer)观测原始数据出发,分析了耀变体3C 273在X射线波段2～10 keV从1996年2月2日(MJD 50115)到2007年8月27日(MJD 54339)的数据.一共得到了1 010次观测数据的光子谱指数和相应的流量,平均每次观测时间为1 666.76 s.通过分析3C 273在观测期间2～10 keV硬X射线的能谱变化及光变行为,发现在2000年2月,2003年3、4月,2004年2、3、7月,2006年及2007年,其光子谱指数Γ与流量lgF_(2～10 keV)存在显著反相关.在1999年和2000～2007年观测期间,Γ与lgF_(2～10 keV)月平均行为也同样存在显著反相关.对整个观测期间的光变行为作定量的分析,发现几次较大的光变,并在部分光谱拟合中发现Fe发射线存在的证据,其平均宽度为93.85±21.49 eV.通过分析光变强度与Fe发射线特性,发现3C 273同时具有耀变体与Seyfert星系的一些性质.     

蝎虎类星体Mrk 421的宽带能谱光变特性分析

搜集了Mrk 421的光变宽带光谱能量分布(Spectral Energy Distributions, SEDs)数据,共有73个态作为研究样本,使用电子能谱为稳态拐折幂律谱的单区轻子模型进行拟合,进而研究Mrk 421在光变时喷流的物理性质。主要结果如下：(1)样本中磁场B和多普勒因子δ之间显著反相关,说明B和δ在汤姆逊(Thomson)区相互依赖。(2)电子谱指数p₁支持Mrk 421光变时的激波解释或磁重联等解释。(3)同步峰值频率logν_syn^pk和峰值光度logν_syn^pkL_syn^pk之间存在正相关关系,意味着Mrk 421在光变时存在反耀变体序列。(4)根据均分参数ε=U_e/U_B(相对论电子能量密度与磁场能量密度的比值),有26%的态电子能量和磁场能量接近均分,63%的态电子能量比磁场能量大一个数量级,11%的态电子能量远大于磁场能量,这说明Mrk 421在光变过程中更可能出现...     

Relationships between Relative Spectral Lags and Relative Widths of Gamma-ray Bursts

The phenomenon of gamma-ray burst (GRB) spectral lags is very common, but a definitive explanation has not yet been given. From a sample of 82 GRB pulses we find that the spectral lags are correlated with the pulse widths, however, there is no correlation be- tween the relative spectral lags and the relative pulse widths. We suspect that the correlations between spectral lags and pulse widths might be caused by the Lorentz factor of the GRBs concerned. Our analysis on the relative quantities suggests that the intrinsic spectral lag might reflect other aspect of pulses than the aspect associated with the dynamical time of shocks or that associated with the time delay due to the curvature effect.     

Important Property of GRB Pulse: Power-Law Indices of Time Properties on Energy

The dependence of pulse temporal properties (pulse width, pulse rise width and pulse decay width) on energy is power-law function. Some correlated relationships between the power-law indices of the pulse time properties on energy and the spectral lags, relative spectral lags, spectral parameters of band function, and photon flux using a well-separated long-duration γ-ray burst (GRB) pulse sample is demonstrated here. We argue that the curvature effect can explain the correlated properties.     

Broadening of the thermal component of the prompt GRB emission due to rapid temperature evolution

The observations of the prompt emission of gamma ray bursts (GRB) by GLAST Burst Monitor (GBM), on board Fermi Gamma-ray Space Telescope, suggest the presence of a significant thermal spectral component, whose origin is not well understood. Recently, it has been shown that for long duration GRBs, the spectral width as defined as the logarithm of the ratio of the energies at which the spectrum falls to half its peak value, lie in the range of 0.84–1.3 with a median value of 1.07. Thus, while most of the GRB spectra are found to be too narrow to be explained by synchrotron emission from an electron distribution, they are also significantly broader than a blackbody spectrum whose width should be 0.54. Here, we consider the possibility that an intrinsic thermal spectrum from a fire-ball like model, may be observed to be broadened if the system undergoes a rapid temperature evolution. We construct a toy-model to show that for bursts with durations in the range 5–70 s, the widths of their 1 second time-averaged spectra can be at the most ≲ 0.557. Thus, while rapid temperature variation can broaden the detected spectral shape, the observed median value of ∼ 1.07 requires that there must be significant sub-photospheric emission and/or an anisotropic explosion to explain the broadening for most GRB spectra.     

Millimetric properties of gamma-ray burst host galaxies

We present millimetre (mm) and submillimetre (submm) photometry of a sample of five host galaxies of gamma-ray bursts (GRBs), obtained using the Max Planck Millimetre Bolometer (MAMBO2) array and Submillimetre Common-User Bolometer Array (SCUBA). These observations were obtained as part of an ongoing project to investigate the status of GRBs as indicators of star formation. Our targets include two of the most unusual GRB host galaxies, selected as likely candidate submm galaxies: the extremely red  ( R − K ≈ 5)  host of GRB 030115, and the extremely faint  ( R > 29.5)  host of GRB 020124. Neither of these galaxies is detected, but the deep upper limits for GRB 030115 impose constraints on its spectral energy distribution, requiring a warmer dust temperature than is commonly adopted for submillimetre galaxies (SMGs).
As a framework for interpreting these data, and for predicting the results of forthcoming submm surveys of Swift -derived host samples, we model the expected flux and redshift distributions based on luminosity functions of both submm galaxies and GRBs, assuming a direct proportionality between the GRB rate density and the global star formation rate density. We derive the effects of possible sources of uncertainty in these assumptions, including (1) introducing an anticorrelation between GRB rate and the global average metallicity, and (2) varying the dust temperature.     

Time-resolved spectral analysis of prompt emission from long gamma-ray bursts with GeV emission

We performed detailed time-resolved spectroscopy of bright long gammaray bursts(GRBs)which show significant GeV emissions(GRB 080916C,GRB090902B and GRB 090926A).In addition to the standard Band model,we also use a model consisting of a black body and a power law to fit the spectra.We find that for the latter model there are indications of an additional soft component in the spectra.While previous studies have shown that such models are required for GRB 090902B,here we find that a composite spectral model consisting of two blackbodies and a power law adequately fits the data of all the three bright GRBs.We investigate the evolution of the spectral parameters and find several interesting features that appear in all three GRBs,like(a)temperatures of the blackbodies are strongly correlated with each other,(b)fluxes in the black body components are strongly correlated with each other,(c)the temperatures of the black body trace the profile of the individual pulses of the GRBs,and(d)the characteristics of power law components like the spectral index and the delayed onset bear a close similarity to the emission characteristics in the GeV regions.We discuss the implications of these results and the possibility of identifying the radiation mechanisms during the prompt emission of GRBs.     

Precise Synchrotron Radiation Spectrum of Fast-cooling Electrons and the Prompt GRB Emission

It is generally believed that the synchrotron radiation of electrons from the internal shock is the main radiation mechanism of the prompt GRB (gamma-ray burst) emission. However, what this model predicts can not explain observations well. In this paper, we confirm that electrons are quickly cooled due to radiation losses and also point out that the synchrotron radiation spectrum presented in previous papers is a relatively rough estimation. We get the precise synchrotron radiation spectrum of fast-cooling electrons by carrying out a numerical calculation, and thereby reasonably explain the observed distribution of low-energy spectral index (α) of long GRBs based on a unified model. In addition, we fit the correlation between α and the peak energy of the νFν spectrum (E_p).     

Evidence for chromatic X-ray light-curve breaks in Swift gamma-ray burst afterglows and their theoretical implications

The power-law decay of the X-ray emission of gamma-ray burst (GRB) afterglows 050319, 050401, 050607, 050713A, 050802 and 050922C exhibits a steepening at about 1–4 h after the burst which, surprisingly, is not accompanied by a break in the optical emission. If it is assumed that both the optical and X-ray afterglows arise from the same outflow then, in the framework of the standard forward shock model, the chromaticity of the X-ray light-curve breaks indicates that they do not arise solely from a mechanism related to the outflow dynamics (e.g. energy injection) or the angular distribution of the blast-wave kinetic energy (structured outflows or jets). The lack of a spectral evolution accompanying the X-ray light-curve break shows that these breaks do not arise from the passage of a spectral break (e.g. the cooling frequency) either. Under these circumstances, the decoupling of the X-ray and optical decays requires that the microphysical parameters for the electron and magnetic energies in the forward shock evolve in time, whether the X-ray afterglow is synchrotron or inverse-Compton emission. For a steady evolution of these parameters with the Lorentz factor of the forward shock and an X-ray light curve arising cessation of energy injection into the blast wave, the optical and X-ray properties of the above six Swift afterglows require a circumburst medium with a r ⁻² radial stratification, as expected for a massive star origin for long GRBs. Alternatively, the chromatic X-ray light-curve breaks may indicate that the optical and X-ray emissions arise from different outflows. Neither feature (evolution of microphysical parameters or the different origin of the optical and X-ray emissions) was clearly required by pre-Swift afterglows.     

γ射线暴X射线耀发的研究进展

γ射线暴是宇宙中恒星尺度的最剧烈爆发现象。γ射线暴瞬时辐射结束后,进入余辉辐射阶段。X射线耀发是γ射线暴X射线辐射衰减过程中出现的短时标闪耀现象。X射线耀发的脉冲轮廓具有不对称性,其上升时标小于下降时标。在部分γ射线暴中,X射线耀发的亮度达到瞬时辐射的亮度。X射线耀发的持续时间与峰值时间具有线性关系。X射线耀发的光谱比X射线余辉的光谱硬。早期X射线耀发与晚期X射线耀发相比,其脉冲轮廓较窄,光谱较硬。X射线耀发产生的物理过程类似于γ射线暴瞬时辐射的物理过程。在火球(fireball)模型中,内部壳层之间发生碰撞,产生的内激波加速电子,电子的同步辐射产生X射线耀发。当火球扫过星际介质,外激波加速电子时,电子的同步辐射也可产生X射线耀发。在光球(photospere)模型中,能量耗散发生在光学厚的区域,热辐射的光谱峰值落在X射线能段附近,γ射线暴的喷流在光球半径处会产生X射线耀发。如果射线暴喷流由坡印亭能流主导,喷流就会与星际介质相互作用,磁场的不稳定性使磁场发生耗散,产生的能量形成X射线耀发。γ射线暴的喷流具有几何效应。一部分同步辐射可能发生在喷流辐射面的高纬度处。由于曲率效应(curvature effect),各向异性辐射与各向同性辐射相比,X射线耀发的峰值出现较晚。此外,在γ射线暴发生后,黑洞会间歇性地吸积外部介质。在吸积过程中,黑洞周围的磁场会调节吸积的速率和喷流中的能量,这是出现多个X射线耀发的原因。     

Jet breaks at the end of the slow decline phase of Swift GRB light curves

The Swift mission has discovered an intriguing feature of gamma-ray burst (GRBs) afterglows, a phase of shallow decline of the flux in the X-ray and optical light curves. This behaviour is typically attributed to energy injection into the burst ejecta. At some point this phase ends, resulting in a break in the light curve, which is commonly interpreted as the cessation of the energy injection. In a few cases, however, while breaks in the X-ray light curve are observed, optical emission continues its slow flux decline. This behaviour suggests a more complex scenario. In this paper, we present a model that invokes a double component outflow, in which narrowly collimated ejecta are responsible for the X-ray emission while a broad outflow is responsible for the optical emission. The narrow component can produce a jet break in the X-ray light curve at relatively early times, while the optical emission does not break due to its lower degree of collimation. In our model both components are subject to energy injection for the whole duration of the follow-up observations. We apply this model to GRBs with chromatic breaks, and we show how it might change the interpretation of the GRBs canonical light curve. We also study our model from a theoretical point of view, investigating the possible configurations of frequencies and the values of GRB physical parameters allowed in our model.     

Methods and results of an automatic analysis of a complete sample of Swift-XRT observations of GRBs

We present a homogeneous X-ray analysis of all 318 gamma-ray bursts detected by the X-ray telescope (XRT) on the Swift satellite up to 2008 July 23; this represents the largest sample of X-ray GRB data published to date. In Sections 2–3 , we detail the methods which the Swift -XRT team has developed to produce the enhanced positions, light curves, hardness ratios and spectra presented in this paper. Software using these methods continues to create such products for all new GRBs observed by the Swift -XRT. We also detail web-based tools allowing users to create these products for any object observed by the XRT, not just GRBs. In Sections 4–6 , we present the results of our analysis of GRBs, including probability distribution functions of the temporal and spectral properties of the sample. We demonstrate evidence for a consistent underlying behaviour which can produce a range of light-curve morphologies, and attempt to interpret this behaviour in the framework of external forward shock emission. We find several difficulties, in particular that reconciliation of our data with the forward shock model requires energy injection to continue for days to weeks.