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Testing the anisotropy in the angular distribution of $Fermi$/GBM gamma-ray bursts
High Energy Astrophysical Phenomena · Submitted 9 Dec 2015
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim It is found that short GRBs are distributed anisotropically on the sky, and long ones have an isotropic distribution.
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The abstract, sentence by sentence
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.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | 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. | background 1.00 | 0.06 | 0.03 | asserted 1.00 |
| s1 | This finding was later confirmed with the first redshift, equal to at least $z=0.835$, measured for GRB970508. | background 0.99 | 0.06 | 0.02 | asserted 1.00 |
| s2 | 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. | background 0.93 | 0.12 | 0.16 | hedged possibility 0.75 |
| s3 | $Fermi$/GBM has detected 1669 GRBs up to date, and their sky distribution is examined in this paper. | contribution 0.72 | 0.82 | 0.02 | asserted 0.99 |
| s4 | 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. | method 0.99 | 0.90 | 0.02 | asserted 0.99 |
| s5 | Monte Carlo benchmark testing of each test is performed in order to evaluate its reliability. | method 0.99 | 0.93 | 0.02 | asserted 0.96 |
| s6 | It is found that short GRBs are distributed anisotropically on the sky, and long ones have an isotropic distribution. | result 1.00 | 0.95 | 0.91 | asserted 1.00 |
| s7 | 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. | result 1.00 | 0.94 | 0.28 | asserted 0.98 |
| s8 | The cosmological context of this finding and its relation to large-scale structures is discussed. | interpretation 0.96 | 0.66 | 0.02 | unclear 0.75 |
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The paper
Original 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.
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References
How the literature uses it
7 arXiv papers cite this in 7 sentences
Papers whose main result relates to this one's
States a conflicting result 2 papers
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This result strongly suggests that the set of SGRBs from BATSE are intrinsically isotropic.
On the large-scale angular distribution of short-Gamma ray bursts · 0.83
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Surprisingly, this test gives an anisotropy for the long subgroup on small angular scales.
Anisotropy in the angular distribution of the long gamma-ray bursts? · 0.81
Papers citing it · 6 sentences without a confident label
Uses its method or tool 1 paper
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The statistical uncertainties associated with both $w(θ)$ and $A_j$ are estimated using jackknife [ref] and bootstrap [ref] resampling of the observed catalog.
Testing Statistical Isotropy in the FRB Sky Distribution: A Selection-Function-Aware Framework · Angular Statistics and Uncertainty Estimation · 1.00
What it cites
Cites as background 1 paper
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Gamma-ray bursts (GRBs) are highly energetic events that often are brighter than all other $γ$-ray objects visible on the sky combined, with an emission peak in the 200–500 keV region [ref] .
Gamma Ray Burst Prompt correlations · Introduction · 1.00
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