An apparent GRBs evolution around us or a sampling of thin GRB beaming jets?

The gamma ray burst apparent average isotropic power versus their red-shift of all known GRB (Sept.2009) is reported. It calls for an unrealistic Gamma Ray Burst Evolution around us or it just probe the need of a very thin gamma precession-jet model. These precessing and spinning jet are originated by Inverse Compton and-or Synchrotron Radiation at pulsars or micro-quasars sources, by ultra-relativistic electrons. These Jets are most powerful at Supernova birth, blazing, once on axis, to us and flashing GRB detector. The trembling of the thin jet (spinning, precessing, bent by magnetic fields) explains naturally the observed erratic multi-explosive structure of different GRBs and its rare re-brightening. The jets are precessing (by binary companion or inner disk asymmetry) and decaying by power law on time scales to a few hours. GRB blazing occurs inside the observer cone of view only a seconds duration times; because relativistic synchrotron (or IC) laws the jet angle is thinner in gamma but wider in X band. Its apparent brightening is so well correlated with its hardness (The Amati correlation). This explain the wider and longer X GRB afterglow duration and the (not so much) rare presence of X-ray precursors well before the apparent main GRB explosion. The jet lepton maybe originated by an inner primary hadron core (as well as pions and muons secondary Jets). The EGRET, AGILE and Fermi few hardest and late GeV gamma might be PeV neutron beta decay in flight observed in-axis under a relativistic shrinkage.

💡 Research Summary

The paper presents an analysis of all gamma‑ray bursts (GRBs) known up to September 2009, focusing on the relationship between the apparent isotropic luminosity and red‑shift. The authors find that the average isotropic power grows roughly as the fourth power of red‑shift, a trend that cannot be reconciled with the standard fireball or magnetar models, which would predict a roughly constant average energy and a monotonic decline of afterglow light curves. Moreover, nearby low‑z GRBs (e.g., GRB 980425, GRB 060218) are systematically under‑luminous and display unusually long, soft X‑ray emission, while the most distant events are extremely bright, hard, and short‑lived.

To explain these contradictions the authors propose a “thin precessing gamma‑jet” model. In this scenario a relativistic jet is launched at the moment of core‑collapse supernova (SN) or compact‑object formation. The jet is powered by ultra‑high‑energy particles (PeV–EeV protons, muons, and neutrons) that generate secondary electron‑positron pairs. These leptons radiate gamma‑rays via inverse‑Compton scattering on ambient infrared photons and via synchrotron emission in magnetic fields. Because the jet’s opening angle is inversely proportional to the Lorentz factor of the primary particles (γ ≈ 10⁹), the beam can be as narrow as 10⁻⁸–10⁻⁹ sr. Only when the beam points directly at Earth does the observer see a classical GRB; otherwise the same event appears as an X‑ray flash (XRF) or an “off‑axis” GRB with much lower apparent luminosity.

The jet is not static. It spins with the central compact object (a pulsar or a black‑hole accretion system) and precesses due to binary companions or asymmetric inner disks. This motion causes the beam to sweep across the line of sight multiple times, naturally producing the multi‑peaked, erratic light curves observed in many GRBs, as well as late re‑brightenings. The jet’s power decays as L ∝ t⁻¹ (α ≈ 1), so the beam widens with time. Consequently, the initial hard gamma‑ray flash is followed by a longer, softer X‑ray afterglow and, occasionally, by a secondary flare when the beam re‑enters the observer’s cone.

A particularly striking feature of the model is its explanation of delayed GeV emission observed by EGRET, AGILE, and Fermi. The authors argue that PeV neutrons produced in the jet escape the dense SN environment and decay in flight. Because of relativistic time contraction (1 − β cos θ ≈ γ⁻² for viewing angles θ ≈ 10⁻³–10⁻⁴ rad), the neutron decay time in the observer frame is reduced from years to seconds‑to‑minutes, matching the observed GeV tails. The decay electrons then radiate GeV photons via synchrotron or inverse‑Compton processes.

The same jet framework is applied to Soft Gamma Repeaters (SGRs), especially the giant flare of SGR 1806‑20 on 27 December 2004. In the conventional magnetar model the flare would consume a large fraction of the star’s magnetic energy, leading to a measurable spin‑down, which was not observed. In the thin‑jet picture, a modest continuous jet power (10³⁶–10³⁸ erg s⁻¹) produces a brief, highly collimated burst whose apparent isotropic energy (≈10⁴⁶ erg) is amplified by the tiny solid angle, while the star’s rotational energy remains essentially unchanged. The model also accounts for the observed pre‑flare X‑ray precursor and the lack of significant change in the spin period after the flare.

Overall, the authors argue that GRBs, XRFs, and SGRs are different observational manifestations of the same underlying phenomenon: a highly collimated, spinning, precessing, and slowly decaying relativistic jet launched during the birth of a compact object. This unified picture explains (1) the red‑shift‑luminosity correlation, (2) the complex temporal structure and re‑brightenings, (3) the presence of X‑ray precursors, (4) delayed high‑energy GeV emission, and (5) the apparent stability of SGR spin parameters during giant flares. The paper concludes that the apparent extreme energetics of GRBs are not intrinsic; they result from extreme geometric beaming, making GRBs the most collimated, not the most energetic, explosions in the universe.