长γ暴时域功率密度谱与光度的强相关

提供一个基于光变曲线的长γ暴光度的估计量．对BASTE记录到的12个已知红移的γ暴，利用时域上的时变分析方法计算了各暴的功率密度谱，用功率密度的峰值P表征光变曲线变化的剧烈程度．通过拟合发现在共动坐标系P与γ暴的各向同性峰值光度L之间存在着相关关系．这是继Norris等和Reichart等发现时间延迟与光度、变化率与光度的相关性之后又一个γ暴时变特征量与其光度之间的相关关系．     

Are there cosmological evolution trends on gamma-ray burst features?

The variability of a gamma-ray burst (GRB) is thought to be correlated with its absolute peak luminosity, and this relation had been used to derive an estimate of the redshifts of GRBs. Recently, Amati et al. presented the results of spectral and energetic properties of several GRBs with known redshifts. Here, we analyse the properties of two groups of GRBs: one group with known redshift from afterglow observation and another group with redshift derived from the luminosity–variability relation. We study the redshift dependence of various GRBs features in their cosmological rest frames, including the burst duration, the isotropic luminosity and radiated energy, and the peak energy E_p of ν F _ν spectra. We find that, for these two groups of GRBs, their properties are all redshift-dependent, i.e. their intrinsic duration, luminosity, radiated energy and peak energy E_p are all correlated with the redshift, which means that there are cosmological evolution effects on gamma-ray burst features, and this can provide an interesting clue to the nature of GRBs. If this is true, then the results also imply that the redshift derived from the luminosity–variability relation may be reliable.     

Improved correlation between the variability and peak luminosity of gamma-ray bursts

A new procedure for smoothing a gamma-ray burst (GRB) light curve and calculating its variability is presented. Applying the procedure to a sample of 25 long GRBs, we have obtained a very tight correlation between the variability and the peak luminosity. The only significant outlier in the sample is GRB 030329. With this outlier excluded, the data scatter is reduced by a factor of ∼3 compared to that of Guidorzi et al., measured by the deviation of fit. Possible causes for the outlier are discussed.     

Spectral analysis of Swift long gamma-ray bursts with known redshift

We study the spectral and energetics properties of 47 long-duration gamma-ray bursts (GRBs) with known redshift, all of them detected by the Swift satellite. Due to the narrow energy range (15–150 keV) of the Swift -BAT detector, the spectral fitting is reliable only for fitting models with two or three parameters. As high uncertainty and correlation among the errors is expected, a careful analysis of the errors is necessary. We fit both the power law (PL, two parameters) and cut-off power law (CPL, three parameters) models to the time-integrated spectra of the 47 bursts, and we present the corresponding parameters, their uncertainties and the correlations among the uncertainties. The CPL model is reliable only for 29 bursts for which we estimate the  ν f _ν  peak energy E _pk. For these GRBs, we calculate the energy fluence and the rest-frame isotropic-equivalent radiated energy,   E _γ,iso  , as well as the propagated uncertainties and correlations among them. We explore the distribution of our homogeneous sample of GRBs on the rest-frame diagram   E '_pk  versus   E _γ,iso  . We confirm a significant correlation between these two quantities (the 'Amati' relation) and we verify that, within the uncertainty limits, no outliers are present. We also fit the spectra to a Band model with the high-energy PL index frozen to −2.3, obtaining a rather good agreement with the 'Amati' relation of non- Swift GRBs.     

Testing the gamma-ray burst variability/peak luminosity correlation on a Swift homogeneous sample

We test the gamma-ray burst (GRB) correlation between temporal variability and peak luminosity of the γ-ray profile on a homogeneous sample of 36 Swift /Burst Alert Telescope (BAT) GRBs with firm redshift determination. This is the first time that this correlation can be tested on a homogeneous data sample. The correlation is confirmed, as long as the six GRBs with low luminosity (  <5 × 10⁵⁰   erg s⁻¹  in the rest-frame 100–1000 keV energy band) are ignored. We confirm that the considerable scatter of the correlation already known is not due to the combination of data from different instruments with different energy bands, but it is intrinsic to the correlation itself. Thanks to the unprecedented sensitivity of Swift /BAT, the variability/peak luminosity correlation is tested on low-luminosity GRBs. Our results show that these GRBs are definite outliers.     

Measuring ΩM and ΩΛ with long‐duration gamma‐ray bursts

Gamma‐ray bursts (GRBs) are one of the most luminous events in the Universe. In addition, the Universe itself is almost transparent to γ ‐rays, making GRBs detectable up to very high redshifts. As a result, GRBs are very suitable to probe the cosmological parameters. This work shows the potential of long‐duration GRBs for measuring the cosmological parameters Ω_M and Ω_Λ by comparing the observed log N ‐log P distribution with the theoretical one. Provided that the GRBs rate and luminosity function are well determined, the best values and 1σ confidence intervals obtained are Ω_M = 0.22^+0.05_–0.03 and Ω_Λ = 1.06^+0.05_–0.10. Finally, a set of simulations show the ability of the method to measure Ω_M and Ω_Λ (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Not enough evidence to support the correlation between gamma-ray bursts and foreground galaxy clusters in the Swift Era

The correlation between distant Gamma-Ray Bursts (GRBs) and foreground galaxy clusters is re-examined by using the well localized (with an accuracy down to a few arcsec) Swift/XRT GRBs.The galaxy clusters are compiled from both the X-ray selected ROSAT brightest cluster sample (BCS) and the BCS extension by requiring δ≧ 0° and b ≧ 20°.The Swift/XRT GRBs fulfilling the above selection criteria are cross-correlated with the clusters.Both Nearest-Neighbor analysis and the angular two-point cross-correlation function show that there is not enough evidence supporting the correlation between the GRBs and foreground clusters.We suggest that the non-correlation is probably related to the GRB number-flux relation slope.     

Stellar forensics with the supernova‐GRB connection – Ludwig Biermann Award Lecture 2010

Long‐duration gamma‐ray bursts (GRBs) and type Ib/c supernovae (SNe Ib/c) are amongst nature's most magnificent explosions. While GRBs launch relativistic jets, SNe Ib/c are core‐collapse explosions whose progenitors have been stripped of their hydrogen and helium envelopes. Yet for over a decade, one of the key outstanding questions is what conditions lead to each kind of explosion in massive stars. Determining the fates of massive stars is not only a vibrant topic in itself, but also impacts using GRBs as star formation indicators over distances up to 13 billion light‐years and for mapping the chemical enrichment history of the universe. This article reviews a number of comprehensive observational studies that probe the progenitor environments, their metallicities and the explosion geometries of SN with and without GRBs, as well as the emerging field of SN environmental studies. Furthermore, it discusses SN2008D/XRT 080109 which was discovered serendipitously with the Swift satellite via its X‐ray emission from shock breakout and which generated great interest amongst both observers and theorists while illustrating a novel technique for stellar forensics. The article concludes with an outlook on how the most promising venues of research – with the many existing and upcoming large‐scale surveys such as PTF and LSST – will shed new light on the diverse deaths of massive stars (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Gamma-Ray Bursts and Other Observations: Constraints on Cosmographic Parameters and Dark Energy Models

We use the newly released Union2 SNe Ia dataset to constrain cosmographic parameters, namely the deceleration, jerk and snap parameters (q0, j0 and s0), then calibrate the five luminosity relations of Gamma-ray Bursts (GRBs) at redshift z ≤ 1.4. Assuming that the GRB luminosity relations do not evolve with the redshift, we obtain the distance moduli of 66 high-redshift GRBs. At last, we combine the observational datasets including the observations of the Cosmic Microwave Background (CMB), Baryon Acoustic Oscillation (BAO) and the 116 GRBs with known redshifts to constrain some widely-discussed dark energy models. We find that the ΛCDM model is the best according to the Bayesian Information Criterion (BIC), and the JBP model is the best according to the Akaike Information Criterion (AIC).     

The correlation between the local density of galaxies and the presence of Gamma‐Ray Bursts

In order to explore the characteristics of the environment surrounding Gamma‐Ray Bursts (GRBs), we have studied the correlation between the local density of galaxies and the presence of bursts. Using the Main Galaxy sample of the Sloan Digital Sky Survey Data Release 3 (SDSS DR3) and the Current BATSE GRB Catalog, we calculate the local surface density of galaxies within a radius of <2° surrounding each burst. It turns out that there is no correlation between the local density of galaxies and the presence of GRBs. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Collective Spectra of Resonant Inverse Compton Scattering of Assembly of Relativistic Electrons in Intense Magnetic Fields*

The resonant inverse Compton scattering (RICS) of relativistic electrons in intense magnetic fields is an efficient mechanism for producing the highenergy γ-rays. In our previous work it is suggested that the early-stage γ-ray radiation of γ-ray bursts (GRBs) may be mainly produced by this mechanism. By using this mechanism, some puzzles in the study of GRBs can be clarified, e.g., the origin of the Amati relation obtained from the statistics of observations, the formation of the observed two-segment (broken) power-law spectra, the relevant “deadline problem”, the polarization property, etc. Herein our discussion will be focused on the formation of the broken power-law spectra. Based on the formula of the RICS spectral power of individual fast electrons, we have derived the simplified analytical formula of the collective RICS radiation spectrum (RICS spectral luminosity) produced by the assembly of relativistic electrons in an intense magnetic field when they pass through the ambient low-frequency radiation field, and applied it to several typical low-frequency radiation fields (e.g., the black-body radiation field, power-law radiation field and thermal bremsstrahlung field) around the central neutron star, for the convenience of comparison with the observed spectra. Our calculations indicate that the RICS radiation mechanism has a very high efficiency in the hard X-ray and γ-ray wavebands, if the matching condition (i.e., the condition approximate to resonance) is satisfied, and that independent of the ambient radiation field, the produced spectra are commonly the two-segment power-law spectra. Additionally, it is suggested that the RICS mechanism might be an ideal highly-efficient radiation mechanism for the high-energy emissions (hard X-rays and γ-rays) of the GRBs, soft γ-ray repeated bursts (SGRs) and γ-ray pulsars (GRPs).     

Multi-band observations of gamma ray bursts

This talk focuses on the various aspects we learnt from multiband observations of GRBs both, before and during the afterglow era. A statistical analysis to estimate the probable redshifts of host galaxies using the luminosity function of GRBs compatible with both the afterglow redshift data as well as the overall population of GRBs is discussed. We then address the question whether the observed fields of GRBs with precise localizations from third Inter-Planetary Network (IPN³) contain suitable candidates for their host galaxies.     

Black hole masses from power density spectra: determinations and consequences

We analyse the scaling of the X-ray power density spectra with the mass of the black hole in the examples of Cyg X-1 and the Seyfert 1 galaxy NGC 5548. We show that the high-frequency tail of the power density spectrum can be successfully used for the determination of the black hole mass. We determine the masses of the black holes in six broad-line Seyfert 1 galaxies, five narrow-line Seyfert 1 galaxies and two quasi-stellar objects (QSOs) using the available power density spectra. The proposed scaling is clearly appropriate for other Seyfert galaxies and QSOs. In all but one of the normal Seyferts, the resulting luminosity to Eddington luminosity ratio is smaller than 0.15, with the source MCG -6-15-30 being an exception. The applicability of the same scaling to a narrow-line Seyfert 1 is less clear and there may be a systematic shift between the power spectra of NLS1 and S1 galaxies of the same mass, leading to underestimation of the black hole mass. However, both the method based on variability and the method based on spectral fitting show that those galaxies have relatively low masses and a high luminosity to Eddington luminosity ratio, supporting the view of those objects as analogues of galactic sources in their high, soft or very high state, based on the overall spectral shape. The bulge masses of their host galaxies are similar to that of normal Seyfert galaxies, so they do not follow the black hole mass–bulge mass relation for Seyfert galaxies, being evolutionarily less advanced, as suggested by Mathur. The bulge mass–black hole mass relation in our sample is consistent with being linear, with the black hole to bulge ratio ∼0.03 per cent, similar to Wandel and Laor for low-mass objects, but significantly shifted from the relation of Magorrian et al. and McLure & Dunlop.     

A Study on the Light Curves of GRBs

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.     

Statistics of the Big Blue Bump Feature in a Low Redshift Sample of Active Galactic Nuclei

We present a statistical analysis of the big blue bump (BBB) feature for a large heterogeneous sample of 95 optically selected and soft X-ray bright, low redshift active galactic nuclei (AGNs). This sample covers a sufficiently broad luminosity range, allowing us to test the luminosity dependence of the spectral energy distribution in the BBB region. Following the works of Zheng et al., Laor et al. and Kriss et al., we introduce the broad band spectral index from 1050 Å to0.5 keV (α _UV-SX ), compare its distribution with that of the soft X-ray spectral index (α _SX ) obtained by ROSAT PSPC, and find that the two indices have equal average-values within 1 ～ 2σuncertainties, whether in the whole sample, in luminosity divisions or in subsamples. These equalities also have no obvious luminosity dependence. This indicates that a single power law can describe the overall UV toX-ray spectrum in a statistical sense, or the broad band UV to soft X-ray spectrum is the soft X-ray spectral extension on an average. Thus, our results support Laor et al.'s conjecture about the BBB peak aroundFUV 1050 Å from a statistical viewpoint. As we further test whether the equality holds for individual objects within measure errors, χ₂ test refuse to accept it. In addition, our statistical results, from the luminosity divisions and on the correlation of spectral indices with luminosity (M _B), imply that the luminosity dependence of α _UV and α _UV-SX is mainly due to absorption in low luminosity AGNs.     

Gamma-ray bursts as dark energy–matter probes in the context of the generalized Chaplygin gas model

In this paper we consider the use of gamma-ray bursts (GRBs) as distance markers to study the unification of dark energy and dark matter in the context of the so-called generalized Chaplygin gas (GCG) model. We consider that the GRB luminosity may be estimated from its variability and time-lag, and we also use the so-called Ghirlanda relation. We evaluate the improvements expected once more GRBs and their redshift become available. We show that although GRBs allow for extending the Hubble diagram to higher redshifts, its use as a dark energy probe is limited when compared to Type Ia supernovae. We find that the information from GRBs can provide some bounds on the amount of dark matter and dark energy independently of the equation of state. This is particularly evident for XCDM-type models, which are, for low redshifts  ( z ≤ 2)  , degenerate with the GCG.     

The Kolmogorov-Smirnov test for three redshift distributions of long gamma-ray bursts in the Swift Era

We investigate redshift distributions of three long burst samples, with the first sample containing 131 long bursts with observed redshifts, the second including 220 long bursts with pseudo-redshifts calculated by the variability-luminosity relation, and the third including 1194 long bursts with pseudo-redshifts calculated by the lag-luminosity relation, respectively. In the redshift range 0-1 the Kolmogorov-Smirnov probability of the observed redshift distribution and that of the variability-luminosity relation is large. In the redshift ranges 1-2, 2-3, 3-6.3 and 0-37, the Kolmogorov-Smimov probabilities of the redshift distribution from lag-luminosity relation and the observed redshift distri-bution are also large. For the GRBs, which appear both in the two pseudo-redshift burst samples, the KS probability of the pseudo-redshift distribution from the lag-luminosity relation and the observed reshifi distribution is 0.447, which is very large. Based on these results, some conclusions are drawn: I) the V-Liso relation might be more believable than the τ-Liso relation in low redshift ranges and the τ-Liso relation might be more real than the V-Liso relation in high redshift ranges; ii) if we do not consider the redshift ranges, the τ-Liso relation might be more physical and intrinsical than the V-Liso relation.     

M BH–σ relation in Sloan Digital Sky Survey flat-spectrum radio quasars

The relationship between the black hole mass and velocity dispersion indicated with [O  iii ] linewidth is investigated for a sample of 87 flat-spectrum radio quasars selected from the Sloan Digital Sky Survey Data Release 3 quasar catalogue. We found that the   M _BH−σ_[O III]  relation is different from the Tremaine et al. relation for nearby inactive galaxies, with a larger black hole mass at given velocity dispersion. There is no strong evidence of cosmology evolution in the   M _BH−σ_[O III]  relation up to   z ∼ 0.8  . A significant correlation between the [O  iii ] luminosity and broad-line region (BLR) luminosity is found. When transferring the [O  iii ] luminosity to narrow-line region (NLR) luminosity, the BLR luminosity is, on average, larger than the NLR one by about one order of magnitude. We found a strong correlation between the synchrotron peak luminosity and NLR luminosity, which implies a tight relation between the jet physics and accretion process.     

The Early X-ray Afterglows of Optically Bright and Dark Gamma-Ray Bursts

A systematic study on the early X-ray afterglows of both optically bright and dark gamma-ray bursts (B-GRBs and D-GRBs) observed by Swift is presented. Our sample includes 25 GRBs of which 13 are B-GRBs and 12 are D-GRBs. Our results show that the distributions of the X-ray afterglow fluxes (Fx), the gamma-ray fluxes (5r), and the ratio (Rr,x.) are similar for the two kinds of GRBs, that any observed differences should be simply statistical fluctuation. These results indicate that the progenitors of the two kinds of GRBs are of the same population with comparable total energies of explosion. The suppression of optical emission in the D-GRBs should result from circumburst but not from their central engine.     

Evidence for luminosity evolution of long gamma-ray bursts in Swift data

We compute the luminosity function (LF) and the formation rate of long gamma-ray bursts (GRBs) by fitting the observed differential peak flux distribution obtained by the Burst and Transient Source Experiment (BATSE) in two different scenarios: (i) the GRB luminosity evolves with redshift and (ii) GRBs form preferentially in low-metallicity environments. In both cases, model predictions are consistent with the Swift number counts and with the number of detections at   z > 2.5  and >3.5. To discriminate between the two evolutionary scenarios, we compare the model results with the number of luminous bursts (i.e. with isotropic peak luminosity in excess of 10⁵³ erg s⁻¹) detected by Swift in its first 3 yr of mission. Our sample conservatively contains only bursts with good redshift determination and measured peak energy. We find that pure luminosity evolution models can account for the number of sure identifications. In the case of a pure density evolution scenario, models with   Z _th > 0.3 Z_⊙  are ruled out with high confidence. For lower metallicity thresholds, the model results are still statistically consistent with available lower limits. However, many factors can increase the discrepancy between model results and data, indicating that some luminosity evolution in the GRB LF may be needed also for such low values of Z _th. Finally, using these new constraints, we derive robust upper limits on the bright end of the GRB LF, showing that this cannot be steeper than ∼2.6.