Testing the anisotropy in the angular distribution of $Fermi$/GBM gamma-ray bursts

Abstract

Gamma-ray bursts (GRBs) were confirmed to be of extragalactic origin due to their isotropic angular distribution, combined with the fact that they exhibited an intensity distribution that deviated strongly from the $-3/2$ power law. This finding was later confirmed with the first redshift, equal to at least $z=0.835$, measured for GRB970508. Despite this result, the data from $CGRO$/BATSE and $Swift$/BAT indicate that long GRBs are indeed distributed isotropically, but the distribution of short GRBs is anisotropic. $Fermi$/GBM has detected 1669 GRBs up to date, and their sky distribution is examined in this paper. A number of statistical tests is applied: nearest neighbour analysis, fractal dimension, dipole and quadrupole moments of the distribution function decomposed into spherical harmonics, binomial test, and the two point angular correlation function. Monte Carlo benchmark testing of each test is performed in order to evaluate its reliability. It is found that short GRBs are distributed anisotropically on the sky, and long ones have an isotropic distribution. The probability that these results are not a chance occurence is equal to at least 99.98\% and 30.68\% for short and long GRBs, respectively. The cosmological context of this finding and its relation to large-scale structures is discussed.

14 pages, 5 figures; accepted in MNRAS

References in corpus (27)

• The Eleventh and Twelfth Data Releases of the Sloan Digital Sky Survey: Final Data from SDSS-III
• The Supernova -- Gamma-Ray Burst Connection
• Discerning the physical origins of cosmological Gamma-ray bursts based on multiple observational criteria: the cases of z=6.7 GRB 080913, z=8.3 GRB 090423, and some short/hard GRBs
• Planck intermediate results. XLVI. Reduction of large-scale systematic effects in HFI polarization maps and estimation of the reionization optical depth
• Revisiting the Long/Soft-Short/Hard Classification of Gamma-Ray Bursts in the Fermi Era
• Gamma Ray Bursts in the Swift-Fermi Era
• Further Study of the Gamma-Ray Bursts Duration Distribution
• Classification of Swift's gamma-ray bursts
• A Comparative Study of Long and Short GRBs. I. Overlapping Properties
• A giant ring-like structure at 0.78<z<0.86 displayed by GRBs
• An analysis of the durations of Swift Gamma-Ray Bursts
• New data support the existence of the Hercules-Corona Borealis Great Wall
• Statistical Study of Observed and Intrinsic Durations among BATSE and Swift/BAT GRBs
• Testing the Randomness in the Sky-Distribution of Gamma-Ray Bursts
• Analysis of Fermi gamma-ray burst duration distribution
• Classification of BeppoSAX's Gamma-Ray Bursts
• Analysis of gamma-ray burst duration distribution using mixtures of skewed distributions
• GRB 090227B: the missing link between the genuine short and long GRBs
• Investigation of Redshift- and Duration-Dependent Clustering of Gamma-ray Bursts
• On the large-scale angular distribution of short-Gamma ray bursts
• Testing the homogeneity of the Universe using gamma-ray bursts
• On the limit between short and long GRBs
• Analysis of the observed and intrinsic durations of gamma-ray bursts with known redshift
• Redshift distribution of gamma-ray bursts and star formation rate
• Analysis of the observed and intrinsic durations of $Swift$/BAT gamma-ray bursts
• On the Connection of Gamma-Ray Bursts and X-Ray Flashes in the BATSE and RHESSI Databases
• A new class of gamma-ray bursts from stellar disruptions by intermediate mass black holes

Cited by in corpus (16)

• Gamma Ray Burst Prompt correlations
• Testing Isotropic Universe Using the Gamma-Ray Burst Data of Fermi / GBM
• The scale of homogeneity in the local Universe with the ALFALFA catalogue
• The angular scale of homogeneity in the Local Universe with the SDSS blue galaxies
• The homogeneity scale and the growth rate of cosmic structures
• The clustering of gamma-ray bursts in the Hercules-Corona Borealis Great Wall: the largest structure in the Universe?
• Revisiting the statistical isotropy of GRB sky distribution
• Isotropy analyses of the Planck convergence map
• Update on Testing the Isotropy of the Properties of Gamma-Ray Bursts
• On Spectral Peak Energy of Swift Gamma-Ray Bursts
• Does the GRB Duration Depend on Redshift?
• Re-Examining the Evidence of the Hercules-Corona-Borealis Great Wall
• Influence of a second satellite on the rotational dynamics of an oblate moon
• An Independent Measure of the Kinematic Dipole from SDSS
• Dipolar fluence distribution of statistically isotropic FERMI gamma-ray bursts
• Probing dipole and quadrupole anisotropy in Gamma-ray bursts from Swift dataset