Distribution Of Gamma-ray Bursts Research Articles

The Effect of Weak Gravitational Lensing on the Angular Distribution of Gamma‐Ray Bursts

If Gamma-Ray Bursts (GRBs) are cosmologically distributed standard candles and are associated with the luminous galaxies, then the observed angular distribution of all GRBs is altered due to weak gravitational lensing of bursts by density inhomogeneities. The amplitude of the effect is generally small. For example, if the current catalogs extend to $z_{max}\sim 1$ and we live in a flat $\Omega=1$ Universe, the angular auto-correlation function of GRBs will be enhanced by $\sim 8\%$ due to lensing, on all angular scales. For an extreme case of $z_{max}= 1.5$ and ($\Omega$, $\Lambda$)=(0.2, 0.8), an enhancement of $\sim 33\%$ is predicted. If the observed distribution of GRBs is used in the future to derive power spectra of mass density fluctuations on large angular scales, the effect of weak lensing should probably be taken into account.

Two Different Burster Spatial Distributions of Gamma-Ray Bursts?

By using the first, second and third electronic burst and transcient source experiment catalogs, a joint analysis of spatial and temporal distributions and hardness ratios of gamma-ray bursts is performed. Turning point features at Cmax/Cmin similar 6 are found. This probably indicates the existence of two components of burster population which have distinct spatial distributions.

The Intensity Distribution for Gamma-Ray Bursts Observed with BATSE

The intensity distributions of gamma-ray bursts observed by BATSE from 1991 April 19 to 1994 September 19 are presented. For this data set, <V/V_max_> is 0.329 +/- 0.011, which is 15.5 σ away from the value of 0.5 expected for a homogeneous distribution. Standard cosmological model parameters are obtained by fitting the differentially binned peak flux distribution expressed in units of photons cm^-2^ s^-1^ in the energy range 50-300 keV. The value of z calculated for a peak flux of 1 photon cm^-2^ s^-1^ is 0.8 +/- 0.33. The procedures used to produce the peak flux data and C_p_/C_lim_ data are presented. The differences between the two representations of burst intensity are emphasized so that researchers can determine which type of data is most appropriate for their studies. The sky sensitivity correction as a function of intensity for the peak flux data is also described.

Luminous Galaxies near Gamma-Ray Burst Positions

The isotropic, inhomogeneous distribution of gamma-ray bursts (GRBs) suggests a cosmological origin. We are performing a deep J (1.25 μm), H (1.65 μm), and K' (2.11 μm) imaging survey of the smallest GRB error boxes from the third Interplanetary Network to examine the extragalactic content of these regions. Relatively bright galaxies are seen in each of six GRB error boxes imaged to date. It is shown that the no-host problem does not exist in our sample. In addition, there is an apparent overabundance of brighter galaxies in these fields, which suggests a connection between galaxies and gamma-ray bursts.

Comment on “Analysis of gamma-ray bursts distribution” by Zharkov and Zharkov

A recent statistical analysis of the BATSE gamma ray burst data by Zharkov and Zharkov [Phys. Lett. A 206 (1995) 7] is shown to be flawed. Attention is drawn to a much better statistical analysis of the same data by Efron and Petrosian [Astrophys. J. 449 (1995) 216].

Reply to the comment of Jones on “Analysis of gamma-ray bursts distribution”

We agree with the critical remarks on and corrections of our paper [Phys. Lett. A 206 (1995) 7] made by Jones [Phys. Lett. A 212 (1996) 115]. However, we believe our method to analyse the BATSE data may be useful.

The nu F nu Peak Energy Distributions of Gamma-Ray Bursts Observed by BATSE

view Abstract Citations (156) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The nu F nu Peak Energy Distributions of Gamma-Ray Bursts Observed by BATSE Mallozzi, Robert S. ; Paciesas, William S. ; Pendleton, Geoffrey N. ; Briggs, Michael S. ; Preece, Robert D. ; Meegan, Charles A. ; Fishman, Gerald J. Abstract The majority of gamma-ray bursts exhibit a peak in their νFν photon energy spectra at an energy Ep that is in the range of ∼20-2000 keV available to the Large Area Detectors of the Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory. If gamma-ray burst sources are at cosmological distances (d ≳ 1 Gpc), then the spectra of dim bursts should be redshifted to lower energies relative to those of bright bursts. The magnitude of the shift is a function of the cosmological redshifts z of both the dim and bright burst sources and hence yields the range of redshift available to the bursts; this range is further constrained by considering cosmological model fits to the burst number-intensity distribution. We have produced photon energy spectra for ∼400 bursts using data from BATSE to investigate if this expected shift in the νFν peak is observed. We find that he mean peak energies of the burst spectra are correlated with intensity: lower intensity groups of burst spectra exhibit a lower average peak energy, although the distributions of Ep are quite wide. Denoting the redshift of an event with an observed peak photon flux P (photons cm-2 s-1) by zp, we find that the maximum range consistent with the bursts of our sample is (1 + z1)/(1 + z100) = 1.86+0.36-.24. Publication: The Astrophysical Journal Pub Date: December 1995 DOI: 10.1086/176513 Bibcode: 1995ApJ...454..597M Keywords: GAMMA RAYS: BURSTS; COSMOLOGY: OBSERVATIONS full text sources ADS |

Determination of Distance from Time Dilation of Cosmological Gamma-Ray Bursts

view Abstract Citations (91) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Determination of Distance from Time Dilation of Cosmological Gamma-Ray Bursts Fenimore, E. E. ; Bloom, J. S. Abstract The isotropic distribution of gamma-ray bursts (GRBs) as observed with the Burst and Transient Source Experiment (BATSE) strongly suggests that the bursts are at cosmological distances. At such distances, the expansion of the universe should redshift the spectra and stretch the temporal structure. Indeed, such time dilation has been observed through a variety of analyses and over all observed timescales in gamma-ray bursts. We relate the observed peak intensities, spectral shapes, and time dilation to absolute distance. We include the uncertainties in our knowledge of the intrinsic spectrum and correct for the coupling between the spectral shape and the temporal structure. Assuming a q0 = ½ cosmology, the reported time dilation between the dimmest BATSE bursts and the bright BATSE bursts (a factor of ∼2) requires a standard candle luminosity of ∼1052 ergs-1, which translates into a redshift of >6 for the dimmest BATSE bursts rather than a redshift of 1 or 2, as previously reported. An alternative method to determine the distance to cosmological GRBs is to use the log N-log P distribution. The large luminosity and distance determined from the time dilation is inconsistent with the observed log N-log P distribution (which requires a luminosity of 4.6 × 1050 ergs s-1 and z ∼0.8) unless there is very strong evolution. Cosmologies with q0 ≠ ½ give similar results. The implied distance for the dimmest bursts is beyond where galaxies are thought to form. If true, the gamma-ray bursts would be orphans: no known objects would have the same distance scale. We conclude that either a large fraction (65%) of the observed time dilation between the BATSE bright and dimmest bursts is intrinsic to the bursts or that there are strong evolutionary effects in the log N-log P distribution and that it is only a coincidence that log N-log P shows a -3/2 power law at high intensities. Publication: The Astrophysical Journal Pub Date: November 1995 DOI: 10.1086/176366 arXiv: arXiv:astro-ph/9504063 Bibcode: 1995ApJ...453...25F Keywords: COSMOLOGY: THEORY; GAMMA RAYS: BURSTS; Astrophysics E-Print: 41 pages including figures, uuencoded compressed Postscript. Accepted for publication in the Astrophysical Journal. The preprint can also be found in Postscript form at http://sstcx1.lanl.gov/~jsbloom/ or at ftp://sstcx1.lanl.gov/pub/grb/time_dilation.ps full text sources arXiv | ADS |

Distribution of gamma-ray bursts in halo neutron star-comet models

The motions of comets and neutron stars have been integrated over five billion years in the Galactic potential to determine a gamma-ray burst distribution, presuming that bursts are the result of interactions between these two families of objects. The comets originate in two distinct populations - one from ejection by stars in the Galactic disk, and the other from ejection by stars in globular clusters. No choice of the free parameters resulted in agreement with both the isotropy data and the log(N >F)-log(F) data.

Are galactic GRB models still an option?

The traditional paradigm of a Galactic origin of gamma-ray bursts (GRBs) suffered a major reduction in popularity when BATSE revealed an isotropic but radially inhomogeneous distribution of GRBs. The lack of pronounced galactic anisotropies places severe constraints on models including significant source contributions from the usual disk, bulge, or halo components of the Milky Way. Although models can be designed to preserve the local disk origin, a perhaps more promising approach invokes a very extended Galactic halo. Populating such halos with neutron stars requires very high velocities. Injection of such neutron stars might be restricted to a phase of the early galaxy, or it may continue to the present. We discuss several observational constraints that address the question presented in the title.

Unsteady plasma ejections from hollow accretion columns of galactic neutron stars as a trigger for gamma-ray bursts

We propose a model of gamma-ray bursts (GRBs) based on close Galactic neutron stars with accretion disks. We outline a simple mechanism of unsteady plasma ejections during episodic accretion events. The relative kinetic energy of ejected blobs can be converted into gamma-rays by internal shocks. The beaming of gamma-ray emission can be responsible for the observed isotropic angular distribution of GRBs.

The Brightness Distribution of Bursting Sources in Relativistic Cosmologies

We present analytical solutions for the integral distribution of arbitrary bursting or steady source counts as a function of peak photon count rate within Friedmann cosmological models. We discuss both the standard candle and truncated power-law luminosity function cases with a power-law density evolution. While the analysis is quite general, the specific example discussed here is that of a cosmological gamma-ray burst distribution. These solutions show quantitatively the degree of dependence of the counts on the density and luminosity function parameters, as well as the the weak dependence on the closure parameter and the maximum redshift. An approximate comparison with the publicly available Compton Gamma Ray Observatory data gives an estimate of the maximum source luminosity and an upper limit to the minimum luminosity. We discuss possible ways of further constraining the various parameters.

The Effects of Pure Density Evolution on the Brightness Distribution of Cosmological Gamma-Ray Bursts

In this work, we explore the effects of burst rate density evolution on the observed brightness distribution of cosmological gamma-ray bursts. Although the brightness distribution of gamma-ray bursts observed by the BATSE experiment has been shown to be consistent with a nonevolving source population observed to redshifts of order unity, evolution of some form is likely to be present in the gamma-ray bursts. Additionally, nonevolving models place significant constraints on the range of observed burst luminosities, which are relaxed if evolution of the burst population is present. In this paper, three analytic forms of density evolution are examined. In general, forms of evolution with densities that increase monotonically with redshift require that the BATSE data correspond to bursts at larger redshifts, or to incorporate a wider range of burst luminosities, or both. Independent estimates of the maximum observed redshift in the BATSE data and/or the range of luminosity from which a large fraction of the observed bursts are drawn therefore allow for constraints to be placed on the amount of evolution that may be present in the burst population. Specifically, if recent measurements obtained from analysis of the BATSE duration distribution of the actual limiting redshift in the BATSE data at z(sub lim) = 2 are correct, the BATSE N(P) distribution in a Lambda = 0 universe is inconsistent at a level of approximately 3 alpha with nonevolving gamma-ray bursts and some form of evolution in the population is required. The sense of this required source evolution is to provide a higher density, larger luminosities, or both with increasing redshift.

On the nature of gamma-ray burst time dilations

The recent discovery that faint gamma-ray bursts are stretched in time relative to bright ones has been interpreted as support for cosmological distances: faint bursts have their durations redshifted relative to bright ones. It was pointed out, however, that the relative time stretching can also be produced by an intrinsic correlation bewteen duration and luminosity of gamma-ray bursts in a nearby, bounded distribution. While both models can explain the average amount of time stretching, we find a difference between them in the way the duration distribution of faint bursts deviates from that of bright ones, assuming the luminosity function of gamma-ray bursts is independent of distance. This allows us to distinguish between these two broad classes of model on the basis of the duration distributions of gamma-ray bursts, leading perhaps to an unambiguous determination of the distance scale of gamma-ray bursts. We apply our proposed test to the second Burst and Transient Source Experiment (BATSE) catalog and conclude, with some caution, that the data favor a cosmological interpretation of the time dilation.

Implications of the BATSE data for a helocentric origin of gamma-ray bursts

Several possible models have been suggested to explain the observed distribution of gamma-ray bursts: heliocentric distributions such as the Oort cloud, large galactic halos, and cosmological models. We report here on an investigation into the implications of the Burst and Transient Source Experiment (BATSE) gamma-ray burst distribution (Meegan et al. 1992a) data on the possible helocentric origin of gamma-ray bursts. We find no statistically significant anisotropy in the angular distribution of the bursts in a Sun-referenced coordinate system; there is no dipole moment in the direction of the Sun, and no quardrupole moment associated with the ecliptic plane. We have employed direct analytic calculations and Monte Carlo simulations of sources in the Oort cloud to constrain possible helicentric burst distributions. These can produce distributions consistent with the observed angular isotropy, the meal value of V/V(sub max), and the observed C/C(sub min) distribution of BATSE, and provide limits to burst energy of a few times approximately 10(exp 27) ergs. However, the agreement of the heliocentric C/C(sub min) distributions with the BATSE data is attributable to the relatively limited sampling of strong, nearby bursts. These bursts are known from observation to be homogeneously distributed, yet the density of sources in the Oort cloud is not constant in this region. Integral number-intensity distributions from the Oort cloud for larger numbers of bursts cannot reproduce the known homogeneity of the strong bursts without modification to the computed cometary number density and are therefore unlikely explanations of the gamma-ray burst distribution.

Bookmakers' odds for the sky distribution of gamma-ray bursts

Bookmakers' odds for the sky distribution of gamma-ray bursts

CELESTIAL GAMMA RAY BURSTS DETECTOR DEVELOPMENT AND MODEL SIMULATIONS

CELESTIAL GAMMA RAY BURSTS DETECTOR DEVELOPMENT AND MODEL SIMULATIONS

On the Galactic distribution of gamma-ray bursts

Quashnock and Lamb (1993) defined a sub-sample of Gamma-ray Bursts (GRBs) from the publicly available BATSE database which shows clumping toward the galactic plane, and concluded that all GRBs are galactic in origin. The selection of these bursts (duplicated in this work in Sample 1) involved a peak countrate (in counts s-1) uncorrected for aspect. We assert that the peak flux of a burst is physically more meaningful than peak count-rate. Using, as limits, the corresponding peak fluxes (in photons cm-2 s-1) for the bursts in the QL sample, we find an additional 24 bursts, which we include in a new sample (Sample 2). We find that the significance of anisotropy in Sample 2 is much less than that of Sample 1, which does not support QL's interpretation of the anisotropies as being due to a galactic population. To make meaningful statistical statements regarding isotropy, burst samples must have peak fluxes above a minimum flux, set by the requirement that a burst be detectable from any direction (above the horizon) with respect to GRO, at any detection threshold at which a burst was observed in that sample. We find that a sample of such bursts has a marginal (2.6 sigma) deviation from isotropy, which we consider insufficient to justify the claim that GRBs are galactic in origin.

Effects of location uncertainties on the observed distribution of gamma-ray bursts detected by BATSE

The Burst and Transient Source Experiment (BATSE) on NASA's Compton Gamma-Ray Observatory has shown that the sources of gamma-ray bursts have an angular distribution consistent with isotropy, yet the bursts are spatially inhomogeneous. Detection of a statistically significant deviation from isotropy in the burst distribution would provide a clue to the distance of the burst sources. BATSE's ability to detect slight deviations of the angular distribution from isotropy is, in part, dependent on the accuracy of the computed burst locations. Using bursts whose locations have been determined accurately and independently, we estimate BATSE's location uncertainties and incorporate them into 3D Monte Carlo simulations of the burst distributions to show that, despite individual burst location uncertainties of about 5 deg, the ability of BATSE to place stringent limits on the anisotropy present in the angular distribution of the gamma-ray bursts is not significantly degraded. Observational effects of possible galactic halo distributions of the burst sources are noted.

The distribution of old neutron stars in the galaxy

The distribution of old galactic neutron stars is computed for model galactic potential and initial neutron star velocity distribution following from evolution scenario of binary systems. Neutron stars are supposed to get their initial velocities during (asymmetric) supernova explosion of a single massive (M,, > 10 Ma) star or a massive component of a binary system. Old neutron star population is shown to be capable of filling a torus-like area extending to a few tens kiloparsecs above the galactic plane. Statistical tests related to the spatial distribution of gamma-ray bursts are carried out for the distribution obtained. Recent results from the BATSE device onboard the GRO observatory have shown a full isotropy of gamma-ray burst locations the sky and their inhomogeneous spatial density (( V/V,,,) = 0.33 f 0.02, (sin2 6) = 0.31 f 0.02, (cos 0) = 0.008 f 0.035) (Meegan et al., 1992), where 0 is the angle between the source and the galactic center, b is the galactic latitude and ( ) denotes averaging over the whole sample. In the case of a purely homogeneous, isotropic distribution these quantities would be, respectively 1/2, 1/3 and 0. These observed statistical features of gamma-bursts greatly reinforced interest to the nature of their possible progenitors. An attractive possibility of old galactic neutron stars looses its credibility, especially in view of negative results of searching for any spectral feature in the gamma-burst spectra obtained by BATSE. Some indications appear that gamma-ray bursts can be divided into at least two types: the strong bursts having hard spectra, with (V/Vm,,) > 1/2 and the weaker ones with softer spectra and (V/V,,,) < 1/2 (APEX experiment results, Mitrofanov et al., 1992; see also Lingenfelter & Higdon, 1992). These results might indicate that two populations of gamma-ray burst progenitors having different spatial distributions actually exist, viz. that producing weak bursts and lying outside the galactic disc, and that producing stronger bursts and residing in the galactic disc. Brainerd (1992) has shown that the BATSE results can be reconciliated with the old neutron star paradigm if one considers an extended (2100 kpc) halo consisting of old neutron stars. The question arises, whether there is any mechanism of natural populating such a halo by old neturon stars? The spatial distribution of old galactic neutron stars as putative gamma-ray burst progenitors has been studied earlier (e.g. Paczynski, 1990; Hartmann et al.,