Exploring the cosmic microwave background dipole direction using gamma-ray bursts
Luongo O. Muccino M. Sorrenti F.
1 November 2025EDP Sciences
Astronomy and Astrophysics
2025#703
Context. Cosmic dipole measurements from diverse cosmological probes consistently reveal enhanced dipole amplitudes – and at times even mild directional discrepancies – relative to the cosmic microwave background dipole. Aims. Using gamma-ray burst (GRB) data, we searched for dipole variations in the Hubble constant H 0, as such anisotropies may also shed light on the Hubble tension. Methods. We employed the most recent and reliable GRB catalogs from the E p − E iso and the L 0 − E p − T correlations. Despite their large uncertainties, GRBs are particularly suited for this analysis due to three factors: their redshift coverage up to z ∼ 9; their isotropic sky distribution, which minimizes directional bias; and their strong correlations, whose normalizations act as proxies for H 0. To this aim, a whole sky scan – partitioning GRB data into hemispheres – enabled us to define dipole directions by fitting relevant GRB correlation parameters and cosmological parameters. The statistical significance across the full H 0 dipole maps, one per correlation, was then evaluated through the normalization differences between hemispheres and compared against the cosmic microwave background dipole direction. The method was then validated by simulating directional anisotropies via Markov chain Monte Carlo analyses for the two correlations. Results. Comparison with previous literature confirms the robustness of the method, while no significant dipole evidence is consistently detected with the expected isotropy of GRBs. Conclusions. To confirm this null result, additional studies are needed to understand how much the degree of anisotropy would influence the net dipole and to infer the fundamental properties behind its possible presence.
cosmological parameters , cosmology: miscellaneous , cosmology: theory , gamma-ray burst: general
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Università di Camerino, Divisione di Fisica, Via Madonna delle Carceri 9, Camerino, 62032, Italy
Department of Nanoscale Science and Engineering, University at Albany-SUNY, Albany, 12222, NY, United States
INAF, Osservatorio Astronomico di Brera, Milano, 20121, Italy
INFN, Sezione di Perugia, Perugia, 06123, Italy
Al-Farabi Kazakh National University, Al-Farabi av. 71, Almaty, 050040, Kazakhstan
ICRANet, Piazza della Repubblica 10, Pescara, 65122, Italy
Département de Physique Théorique, Center for Astroparticle Physics, Université de Genève, 24 quai Ernest Ansermet, Genève 4, 1211, Switzerland
Università di Camerino
Department of Nanoscale Science and Engineering
INAF
INFN
Al-Farabi Kazakh National University
ICRANet
Département de Physique Théorique
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