1B Catalog Research Articles

Correlations among Gamma‐Ray Burst Properties

Gamma-ray bursts are mysterious flashes of gamma radiation the properties of which have shown virtually no significant, nondefinitional correlations or bimodalities. The physical processes which relate burst properties to one another could be revealed by finding significant relations. In the past, searches for correlations and bimodalities in the data have been made for a relatively small set of properties. We present the results of a systematic search for statistically significant correlations and bimodalities from a set of 49 burst properties, with particular attention paid to the establishment and inclusion of light-curve characteristics. We have used the database of the 260 bursts in the 1B catalog of BATSE. No unpublished, significant, nondefinitional correlations correlations were found, nor were any original, nonsystematic bimodalities observed. Our method recovered the known correlation between the log of duration and spectral hardness with a probability that the result is a random fluctuation of 9.3 × 10-5. The previously reported bimodality in the logarithm of duration was recovered.

Further Evidence for Some Gamma‐Ray Bursts Consistent with Primordial Black Hole Evaporation

Previously we identified some short burst events from the BATSE 1B catalog that were consistent with an origin of primordial black hole evaporation at the quark-gluon phase transition. We showed that these events are also consistent with arising from a homogeneous spatial distribution. Recently the PHEBUS group has also indicated that the short bursts are consistent with V/Vmax ~ 1/2. In this paper we describe the results of the study of the BATSE 3B catalog shape that confirm the results from BATSE 1B.

The Superiority of the Two‐Point Correlation Function over the Nearest Neighbor Analysis as a Test for Gamma‐Ray Burst Repetition

The locations of most gamma-ray bursts are known only to several degrees. As a consequence, to detect repeated outbursts from gamma-ray burst sources in the largest gamma-ray burst catalogs, one must apply statistical tests for clustering. I show that the two-point correlation function is superior to the nearest neighbor test for detecting repetition whenever the average angle of separation between bursts in the sample is larger than the location error. The two-point correlation function is particularly sensitive to repeating sources that each produce a large number of observed gamma-ray bursts. The effects of Earth blockage and the disabling of the burst trigger are examined, and the ability of different repetition models to produce an observable repetition signal is calculated. I show that only a large number of repetitions per source can produce an observable signal, which underscores the strength of the two-point correlation function as a test of burst repetition. From these results, one must conclude that the deviation from isotropy found in the BATSE 1B catalog with the nearest neighbor test is a statistical fluctuation, and not a manifestation of burst repetition.

Repeating of gamma-ray bursts in light of the BATSE 2B catalog

We examine the evidence for repeating of ϒ-ray bursts in light of the BATSE 2B catalog. The temporal coverage of the 2B-1B (non-MAXBC) data set is ≈ 1/3 smaller than that of the 1B catalog. We find evidence that the distributions of the burst statistical positional errors and of the burst fluences also differ. Assuming that the bursts in the 1B catalog form a “fair sample” and taking these observational selection effects into account, we simulate the 2B-1B (less MAXBC) data set. We find that a repeating signal like that seen in the nearest neighbor distribution of the bursts in the 1B catalog would not be detectable in the 2B-1B (non-MAXBC) and 2B (non-MAXBC) data sets, because of the differences in the temporal coverage and in the distribution of positional errors.

Selection effects and tests of repetition (clustering) in the BATSE 1B catalog

A “repeater statistic” (derived from the two-point angular correlation function and accounting for location errors) is used to identify constraints on the rate of burst repetition from the BATSE 1B catalog. Because of the anisotropic sky exposure, repeating sources should create additional effects in the large-scale distribution of close burst pairs.

Testing Isotropy versus Clustering of Gamma-Ray Bursts

view Abstract Citations (9) References (11) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Testing Isotropy versus Clustering of Gamma-Ray Bursts Efron, Bradley ; Petrosian, Vahe Abstract The cosmological origin for gamma-ray bursts has been gaining popularity primarily because they manifest nearly isotropic angular distribution. Analyses of the data using different statistical tests have claimed contradictory results on the degree and significance of deviation of the angular distribution from isotropy. In this paper we apply several tests, which we believe are more powerful than those applied previously, to the BATSE 1B and 2B catalogs. In the 1B catalog we find that the excess of sources at small angles claimed by Quashnock & Lamb (1993b) is significant and can be interpreted as evidence that 15 sources have repeated twice. We also find some weak evidence for clustering of sources on a scale of about 30°. These features, however, are absent in the 2B catalog. We also investigate dependence of the angular distribution on burst intensity and find no strong correlation or deviation from isotropy. In a separate paper (Petrosian & Efron 1995) we search for a correlation between temporal and angular distribution of the bursts and find some marginal evidence for repeaters in both the 1B and 2B catalogs. Publication: The Astrophysical Journal Pub Date: August 1995 DOI: 10.1086/176048 Bibcode: 1995ApJ...449..216E Keywords: GAMMA RAYS: BURSTS; METHODS: STATISTICAL full text sources ADS |

On the correlation of angular position with time of occurrence of gamma-ray bursts

Evidence indicating that a large fraction of gamma-ray bursts are repeaters would provide strong support for noncosmological origin of these sources. Wang & Lingenfelter have claimed existance of a correlation between angular position and time of occurrence of bursts. We perform statistical tests and find a marginal evidence for nearby bursts occurring within 4 to 5 days of each other in the BATSE 1B catalog. This evidence is present also in the 2B catalogs, which in addition, shows some marginal evidence for bursts repetition at longer time delays up to the total length of the observations.

Inferring the spatial and energy distribution of gamma-ray burst sources. 1: Methodology

We describe Bayesian methods for analyzing the distribution of gamma- ray burst peak photon fluxes and directions. These methods fit the differential distribution, and have the following advantages over rival methods: (1) they do not destroy information by binning or averaging the data (as do, say, x^2^, <V/V_max_>, and angular moment analyses); (2) they straightforwardly handle uncertainties in the measured quantities; (3) they analyze the strength and direction information jointly; (4) they use information available about nondetections; and (5) they automatically identify and account for biases and selection effects given a precise description of the experiment. In these methods, the most important information needed about the instrument threshold is not its value at the times of burst triggers, as is used in <V/V_max_> analyses, but rather the value of the threshold at times when no trigger occurred. We show that this information can be summarized as an average detection efficiency that is similar to the product of the exposure and efficiency reported in the First BATSE Burst (1B) Catalog, but significantly different from it at low fluxes. We also quantify an important bias that results from estimating the peak flux by scanning the burst to find the peak number of counts in a window of specified duration, as was done for the LB Catalog. When the duration of the peak of the light curve is longer than the window duration, a simple flux estimate based on the peak counts significantly overestimates the peak flux in a nonlinear fashion that distorts the shape of the log (N)-log (P) distribution. This distortion also corrupts analyses of the V/V_max_ distribution that use ratios of counts above background to estimate V/V_max_. The Bayesian calculation specifies how to account for this bias. Implementation of the Bayesian approach requires some changes in the way burst data are reported that we describe in detail. Subsequent papers will report analyses of the 1B Catalog data using the methods described here.