The origin of ultra-high-energy cosmic rays remains one of the key mysteries of particle astrophysics. Observations indicate a transition from a lighter to a heavier composition above an energy of ~$10^{18}$.2 eV, which requires a hard injection spectrum and nearby sources. Gamma-ray bursts are attractive due to their enormous energy release and relativistic outflows, and the detection of multi-TeV gamma-rays from GRB 221009A with a jet opening angle of about 0.8° has revived interest in this connection. Around this work in the archive, there are studies of gamma-ray bursts as sources of cosmic rays, their connection to neutrinos and gamma-rays, and models of internal shocks. This article stands somewhat apart: it is the first to systematically test the hypothesis of a local population of narrow jets, proposed earlier, against the full dataset on spectrum and composition.
The authors use three models of source evolution: a uniform distribution, standard jets that track the star formation rate, and a combination of standard and narrow jets. For each model, they vary the injection parameters—spectral index, maximum rigidity, and nuclear fractions (hydrogen, helium, nitrogen, silicon, iron)—and fit the results to data from the Pierre Auger Observatory on the energy spectrum and depth of shower maximum. Particle propagation is simulated with the CRPropa 3.2 code, accounting for interactions with the cosmic microwave background and extragalactic background light. Then, fluxes of cosmogenic neutrinos and cascade gamma-rays are computed by solving one-dimensional transport equations.
The model with standard and narrow jets describes the data well: the injection spectral index α = -1.6, maximum rigidity $10^{18}$.2 V, composition of 65% protons and 34% helium. At the highest energies, the flux is dominated by narrow jets, limited to redshifts z ≤ 0.36, which reduces propagation losses. The required baryon loading factor for narrow jets is about 10, whereas for standard jets alone it is about 50. Predicted cosmogenic neutrino fluxes lie below current IceCube and Auger limits, and the neutrino flux peak is within an order of magnitude of the estimate for the KM3-230213A event. The cascade gamma-ray flux saturates the Fermi-LAT upper limit at energies around 1 TeV, but leaves room for contributions from other sources, such as blazars.
The work shows that a local population of narrow jets from gamma-ray bursts can explain the observed flux of ultra-high-energy cosmic rays without conflicting with multimessenger data. Unlike previous studies that considered standard jets or a uniform distribution, here a combined model with low redshift for narrow jets is used for the first time, which significantly reduces the predicted cosmogenic neutrino and gamma-ray fluxes. This relieves tension with IceCube and Fermi-LAT constraints and makes the scenario viable.
Future data from AugerPrime and TA×4 will improve measurements of spectrum, composition, and anisotropy, allowing tests of correlations with nearby transients. Next-generation neutrino detectors such as IceCube-Gen2, GRAND, and PUEO will either detect the predicted cosmogenic flux or impose stricter limits. Observations with LHAASO, CTA, and SWGO may resolve the cosmogenic component in gamma-rays from individual gamma-ray bursts.
The results will impact models of particle acceleration in gamma-ray bursts, the interpretation of cosmic-ray observatory data, and strategies for searching for neutrinos and gamma-rays from transients.
More detailed modeling is needed, including realistic distributions of jet opening angles and gamma-ray energies, as well as investigating the influence of magnetic fields on the propagation of secondary particles.
The work is directly related to the unresolved problem of the origin of ultra-high-energy cosmic rays and the question of which astrophysical objects can accelerate particles to energies above 10^18 eV. It also touches on the mystery of the transition from galactic to extragalactic sources and the nature of the spectral feature at an energy of ~5×10^18 eV.
This section is addressed to the author of the paper and their colleagues. Neighbouring works were found by meaning-based search across our archive, not by word overlap. We do not review: we show the field around the work.
What the work does
The authors test the hypothesis that a rare population of long gamma-ray bursts with very narrow jets in the local universe (z ≤ 0.36) explains the flux of ultra-high-energy cosmic rays. They build models of source evolution, fit injection parameters to the Pierre Auger Observatory data on spectrum and composition, and compute the accompanying neutrino and cascade gamma-ray fluxes. The results show that such a population can describe the data without conflicting with current multimessenger constraints.
Where its strength is
The strong point is the systematic approach: for the first time, for the narrow-jet hypothesis, a joint fit of spectrum and composition is performed, taking into account source evolution and particle propagation, which yielded consistent predictions for neutrinos and gamma rays.
Where it could go next
Worth trying
Why this may matter
If narrow jets are indeed the main source of ultra-high-energy cosmic rays, this would link the observed properties of gamma-ray bursts to the particle composition and open a new channel for probing the physics of relativistic outflows and their environments.
Nearby works in our archive
The closest work in the archive sits at 0.62 by meaning — the usual level for our corpus.
The gamma-ray burst GRB 221009A was so bright that it was called the 'Brightest Of All Time' (BOAT). Its jet had an opening angle of just 0.8 degrees, like a flashlight beam from a kilometer away illuminating a coin.
The idea that rare and powerful cosmic explosions could be sources of the most energetic particles resonates with the concept of 'gamma-ray bursts as weapons' in science fiction, for example in Dan Simmons' novel 'Hyperion', where such phenomena are linked to catastrophic events.