An important concern in the application of gamma-ray bursts (GRBs) to cosmology is that the calibration of GRB luminosity/energy relations depends on the cosmological model, due to the lack of a sufficient low-redshift GRB sample. In this paper, we present a new method to calibrate GRB relations in a cosmology-independent way. Since objects at the same redshift should have the same luminosity distance and since the distance moduli of Type Ia supernovae (SNe Ia) obtained directly from observations are completely cosmology independent, we obtain the distance modulus of a GRB at a given redshift by interpolating from the Hubble diagram of SNe Ia. Then we calibrate seven GRB relations without assuming a particular cosmological model and construct a GRB Hubble diagram to constrain cosmological parameters. From the 42 GRBs at $1.4<z\le6.6$, we obtain $Ω_{\rm M}=0.25_{-0.05}^{+0.04}$, $Ω_Λ=0.75_{-0.04}^{+0.05}$ for the flat $Λ$CDM model, and for the dark energy model with a constant equation of state $w_0=-1.05_{-0.40}^{+0.27}$, which is consistent with the concordance model in a 1-$σ$ confidence region.
We show that, if the long GRBs are produced by the collapse of massive stars, GRBs and their afterglows may provide a powerful probe of cosmology and the early universe.
In a series of articles, we have shown that the newly discovered plasma-redshift cosmology gives a simpler, more accurate and consistent explanation of many cosmological phenomena than the big-bang cosmology. The SNe Ia observations are in better agreement with the magnitude-redshift relation predicted by the plasma redshift than that predicted by the multi-parameter big-bang cosmology. No deceleration or expansion parameters are needed. The plasma-redshift cosmology is flat and quasi-static on a large scale. The Hubble constant is no longer an expansion parameter, but is instead a measure of …
Gamma-ray bursts (GRBs) are tremendous explosions visible across most of the Universe, certainly out to redshifts of z=4.5 and likely out to z~10. Recently, GRBs have been found to have a roughly constant explosive energy as well as to have two luminosity indicators (the spectral lag time and the variability) that can be used to derive the burst's luminosity distance from the gamma-ray light curve alone. There currently exists enough information to calibrate luminosity distances and independent redshifts for nine bursts. From these, a GRB Hubble diagram can be constructed, where the observed s…
We show that, if the long GRBs are produced by the collapse of massive stars, GRBs and their afterglows may provide a powerful probe of cosmology and the early universe.
We show that, if the long GRBs are produced by the collapse of massive stars, GRBs and their afterglows may provide a powerful probe of cosmology and the early universe.
We analyze Hubble's approach to cosmology. In 1929 he accepted a finite expanding universe in order to explain the redshifts of distant galaxies. Later on he turned to an infinite stationary universe due to observational constraints. We show, by quoting his works, that he remained cautiously against the big bang until the end of his life.
The Hubble constant sets the size and age of the Universe, and, together with independent determinations of the age, provides a consistency check of the standard cosmology. The Hubble constant also provides an important test of our most attractive paradigm for extending the standard cosmology, inflation and cold dark matter.
This report is an update and extension of our paper accepted for publication in ApJ (arXiv:0802.4262). Since objects at the same redshift should have the same luminosity distance and the distance moduli of type Ia supernovae (SNe Ia) obtained directly from observations are completely cosmology independent, we obtain the distance modulus of a gamma-ray burst (GRB) at a given redshift by interpolating or iterating from the Hubble diagram of SNe Ia. Then we calibrate five GRB relations without assuming a particular cosmological model, from different regression methods, and construct the GRB Hubbl…
With the understanding that the enigmatic Gamma-Ray Burts (GRBs) are beamed explosions, and with the recently discovered ``Ghirlanda-relation'', the dream of using GRBs as cosmological yardsticks may have come a few steps closer to reality. Assuming the Ghirlanda-relation is real, we have investigated possible constraints on cosmological parameters using a simulated future sample of a large number of GRBs inspired by the ongoing SWIFT mission. Comparing with constraints from a future sample of Type Ia supernovae, we find that GRBs are not efficient in constraining the amount of dark energy or …
Three different methods of measuring cosmology with gamma-ray bursts (GRBs) have been proposed since a relation between the $γ$-ray energy $E_γ $ of a GRB jet and the peak energy $E_p$ of the $νF_ν$ spectrum in the burst frame was reported by Ghirlanda and coauthors. In Method I, to calculate the probability for a favored cosmology, only the contribution of the $E_γ-E_p$ relation that is already best fitted for this cosmology is considered. We apply this method to a sample of 17 GRBs, and obtain the mass density $Ω_M=0.15^{+0.45}_{-0.13}$ ($1σ$) for a flat $Λ$CDM universe. In Method II, to cal…
The luminosity distance vs. redshift law is now measured using supernovae and gamma ray bursts, and the angular size distance is measured at the surface of last scattering by the CMB and at z = 0.35 by baryon acoustic oscillations. In this paper this data is fit to models for the equation of state with w = -1, w = const, and w(z) = w_0+w_a(1-a). The last model is poorly constrained by the distance data, leading to unphysical solutions where the dark energy dominates at early times unless the large scale structure and acoustic scale constraints are modified to allow for early time dark energy e…
Gamma-Ray Bursts (GRBs) offer a potential way to extend the Hubble diagram to very high redshifts and to constrain the nature of dark energy in a way complementary to distant type Ia supernovae. However, gravitational lensing systematically brightens distant GRBs through the magnification bias, in addition to increasing the dispersions of distance measurements. We investigate how the magnification bias limits the cosmological usage of GRBs. We perform Monte-Carlo simulations of Swift GRBs assuming a cosmological constant dominated universe and then constrain the dark energy equation of state n…
The Hubble diagram (HD) of Gamma-Ray Bursts (GRBs) having properly estimated redshifts is compared with the predicted one for the Chaplygin gas (CG), a dark energy candidate. The CG cosmology and that of Friedmann and $Λ$-CDM models are studied and confronted to the GRBs observations. The model-to-sample $χ^2$ statistical analysis indicates the CG model as the best fit. The present GRBs HD plot exhibits a marked trend: as one goes back in time, it gets much closer to the predict HD for a Friedmann universe. This clear trend conclusively demonstrates that a transition from decelerate to acceler…
Gamma Ray Bursts are among the most powerful astrophysical sources and they release up to 1.e54 erg, if isotropic, in less than few hundred seconds. Their detection in the hard X/gamma ray band (at energies >10 keV) and out to very high redshift (z~6.3) makes them a powerful new cosmological tool (a) to study the reionization epoch, (b) to unveil the properties of the IGM, (c) to study the present universe geometry and (d) to investigate the nature and cosmic evolution of the dark energy. While GRBs will surely help to understand the first two issues in the future, the present link between GRB…
Basing on the increasing evidence for the cosmological relevance of the local Hubble flow, we consider a simple analytical cosmological model for the Local Universe. This is a non-Friedmann model with a non-uniform static space-time. The major dynamical factor controlling the local expansion is the antigravity produced by the omnipresent and permanent dark energy of the cosmic vacuum (or the cosmological constant). The antigravity dominates at distances larger than 1-2 Mpc from the center of the Local Group. The model gives a natural explanation of the two key quantitative characteristics of t…
The unrivalled, extreme luminosities of gamma-ray bursts (GRBs) make them the favored beacons for sampling the high redshift Universe. To employ GRBs to study the cosmic terrain -- e.g., star and galaxy formation history -- GRB luminosities must be calibrated, and the luminosity function versus redshift must be measured or inferred. Several nascent relationships between gamma-ray temporal or spectral indicators and luminosity or total energy have been reported. These measures promise to further our understanding of GRBs once the connections between the luminosity indicators and GRB jets and em…
In the sea of super-strong interacting gravitons, non-forehead collisions with gravitons deflect photons, and this deflection may differ for soft and hard radiations. As a result, the Hubble diagram would not be a universal function and it will have a different view for such sources as supernovae in visible light and gamma-ray bursts. Observations of these two kinds are compared here with the limit cases of the Hubble diagram.
Apparently, Gamma-Ray Bursts (GRBs) are all but standard candles. Their emission is collimated into a cone and the received flux depends on the cone aperture angle. Fortunately we can derive the aperture angle through an achromatic steepening of the lightcurve of the afterglow, and thus we can measure the "true" energetics of the prompt emission. Ghirlanda et al. (2004) found that this collimation-corrected energy correlates tightly with thefrequency at which most of the radiation of the prompt is emitted. Through this correlation we can infer the burst energy accurately enough for a cosmologi…
We present a determination of the Hubble constant from measurements of the Sunyaev-Zeldovich Effect (SZE) in an orientation-unbiased sample of 7 z < 0.1 galaxy clusters. With improved X-ray models and a more accurate 32-GHz calibration, we obtain H_O = 64+14-11 +/- 14_sys km/s/Mpc. for a standard CDM cosmology, or 66+14-11 +/- 15_sys km/s/Mpc for a flat LambdaCDM cosmology. In combination with X-ray cluster measurements and the BBN value for Omega_B, we find Omega_M = 0.32 +/- 0.05.
Although more than 2,000 astronomical gamma-ray bursts (GRBs) have been detected, and numerous models proposed to explain their occurrence, they have remained enigmatic owing to the lack of an obvious counterpart at other wavelengths. The recent ground-based detection of a transient source in the vicinity of GRB 970228 may therefore have provided a breakthrough. The optical counterpart appears to be embedded in an extended source which, if a galaxy as has been suggested, would lend weight to those models that place GRBs at cosmological distances. Here we report the observations using the Hubbl…
Spectroscopic and photometric evidence indicates that Type Ia supernovae (SNe Ia) are the thermonuclear explosions of accreting white dwarfs. However, the progenitor binary systems and hydrodynamical models for SNe Ia are still controversial. The relatively uniform light curves and spectral evolution of SNe Ia have led to their use as a standard candle for determining cosmological parameters, such as the Hubble constant, the density parameter, and the cosmological constant. Recent progress includes the calibration of the absolute maximum brightness of SNe Ia with the Hubble Space Telescope, th…
It is well known that a combined analysis of the Sunyaev-Zel'dovich (SZ) effect and the X-ray emission observations can be used to determine the angular diameter distance to galaxy clusters, from which the Hubble constant is derived. The present values of the Hubble constant derived through the SZ/X-ray route have a broad distribution ranging from 30 to 70 km s^-1 Mpc^-1. We show that this broad distribution is primarily due to the projection effect of aspherical clusters, which have been modeled using spherical geometries. The projection effect is also expected to broaden the measured gas mas…
Results from a recent HST survey of field galaxies at wavelengths 1600 Angstroms and 2400 Angstroms are be presented. The data are used to constrain the fraction of Lyman-continuum radiation that escapes from galaxies at redshifts z ~ 1. The combined UV-IR photometry for HDF galaxies is also used to investigate whether low-mass starburst galaxies dominate the field-galaxy population at redshift z ~1. The relative lack of objects with the colors of faded bursts suggests that star-formation is largly quiescent rather than bursty or episodic.
One of the few ways to measure the properties of Dark Energy is to extend the Hubble daigram (HD) to higher redshifts with Gamma-Ray Bursts (GRBs). GRBs have at least five properties (their spectral lag, variability, spectral peak photon energy, time of the jet break, and the minimum rise time) which have correlations to the luminosity of varying quality. In this paper, I construct a GRB HD with 69 GRBs over a redshift range of 0.17 to >6, with half the bursts having a redshift larger than 1.7. This paper uses over 3.6 times as many GRBs and 12.7 times as many luminosity indicators as any prev…
We present a determination of the Hubble constant from measurements of the Sunyaev-Zeldovich Effect (SZE) in an orientation-unbiased sample of 7 z < 0.1 galaxy clusters. With improved X-ray models and a more accurate 32-GHz calibration, we obtain H_O = 64+14-11 +/- 14_sys km/s/Mpc. for a standard CDM cosmology, or 66+14-11 +/- 15_sys km/s/Mpc for a flat LambdaCDM cosmology. The random uncertainty in this result is dominated by intrinsic CMB anisotropies, and the systematic uncertainty is chiefly due to uncertainties in the X-ray spectral models. The implications of this result and future prosp…
In this paper, we use a set of observational $H(z)$ data (OHD) to constrain the $Λ$CDM cosmology. This data set can be derived from the differential ages of the passively evolving galaxies. Meanwhile, the $\mathcal {A}$-parameter, which describes the Baryonic Acoustic Oscillation (BAO) peak, and the newly measured value of the Cosmic Microwave Background (CMB) shift parameter $\mathcal {R}$ are used to present combinational constraints on the same cosmology. The combinational constraints favor an accelerating flat universe while the flat $Λ$CDM cosmology is also analyzed in the same way. We ob…
We present a complete sample of 29 GRBs for which it has been possible to determine temporal breaks (or limits) from their afterglow light curves. We interpret these breaks within the framework of the uniform conical jet model, incorporating realistic estimates of the ambient density and propagating error estimates on the measured quantities. In agreement with our previous analysis of a smaller sample, the derived jet opening angles of those 16 bursts with redshifts result in a narrow clustering of geometrically-corrected gamma-ray energies about E_gamma = 1.33e51 erg; the burst-to-burst varia…
We construct the simplest solution of the Einstein equations that incorporates a shock-wave into a standard Friedmann-Robertson-Walker metric whose equation of state accounts for the Hubble constant and the microwave background radiation temperature. This produces a new solution of the Einstein equations from which we are able to derive estimates for the shock position at present time. We show that the distance from the shock-wave to the center of the explosion at present time is comparable to the Hubble distance. We are motivated by the idea that the expansion of the universe as measured by t…
Gamma-ray bursts (GRBs) being the most luminous among known cosmic objects carry an essential potential for cosmological studies if properly used as standard candles. In this paper we test with GRBs the cosmological predictions of the Gurzadyan-Xue (GX) model of dark energy, a novel theory that predicts, without any free parameters, the current vacuum fluctuation energy density close to the value inferred from the SNIa observations. We also compare the GX results with those predicted by the concordance scenario $Λ$-CDM. According to the statistical approach by Schaefer (2007), the use of sever…
A static non-singular 10-dimensional closed Friedmann universe of Planck size, filled with a perfect fluid with an equation of state with w = -2/3, can arise spontaneously by a quantum fluctuation from nothing in 11-dimensional spacetime. A quantum transition from this state can initiate the inflationary quantum cosmology outlined in Ref. 2 [General Relativity and Gravitation 33, 1415, 2001 - gr-qc/0103021]. With no fine-tuning, that cosmology predicts about 60 e-folds of inflation and a vacuum energy density depending only on the number of extra space dimensions (seven), G, h, c and the ratio…
We construct the Hubble diagram (HD) of Gamma-Ray Bursts (GRBs) with redshifts reaching up to $z \sim 6$, by using five luminosity vs. luminosity indicator relations calibrated with the Cardassian cosmology. This model has a major interesting feature: despite of being matter-dominated and flat, it can explain the present accelerate expansion of the universe. This is the first study of this class of models using high redshift GRBs. We have performed a $χ$-square statistical analysis of the GRBs calibrated with the Cardassian model, and also combined them with both the current Cosmic Microwave B…
We study massive spin-1/2 fermion production in nonsingular superstring cosmology, taking into account one-loop quantum corrections to a superstring effective action with dilaton and modulus fields. While no creation occurs in the massless limit, massive fermions can be produced by the existence of a time-dependent frequency. Due to the increase of the Hubble expansion rate during the modulus-driven phase, the occupation of number of fermions continues to grow until the point of the graceful exit, after which fermion creation ceases with the decrease of the Hubble rate.
Primordial fluctuations in inflationary cosmology acquire classical properties through decoherence when their wavelengths become larger than the Hubble scale. Although decoherence is effective, it is not complete, so a significant part of primordial correlations remains up to the present moment. We address the issue of the pointer states which provide a classical basis for the fluctuations with respect to the influence by an environment (other fields). Applying methods from the quantum theory of open systems (the Lindblad equation), we show that this basis is given by narrow Gaussians that app…
