Luminosity function and jet structure of Gamma Ray Bursts

TL;DR

This paper investigates the luminosity function of Gamma Ray Bursts to infer their jet structures, finding that both uniform and strongly structured jets can explain observed luminosity distributions, with certain structured models being favored.

Contribution

It provides analytical models for GRB luminosity functions under uniform and structured jet assumptions and compares them with observational data.

Findings

Both low and high luminosity GRBs follow a unified luminosity function.

Uniform jets can reproduce the entire luminosity function with reasonable parameters.

A strongly structured jet model with E ∝ θ^{-k} (k > 4) fits the data, unlike the classical E ∝ θ^{-2} model.

Abstract

The structure of Gamma Ray Burst (GRB) jets impacts on their prompt and afterglow emission properties. The jet of GRBs could be uniform, with constant energy per unit solid angle within the jet aperture, or it could instead be structured, namely with energy and velocity that depend on the angular distance from the axis of the jet. We try to get some insight about the still unknown structure of GRBs by studying their luminosity function. We show that low (1e46-1e48 erg/s) and high (i.e. with L > 1e50 erg/s) luminosity GRBs can be described by a unique luminosity function, which is also consistent with current lower limits in the intermediate luminosity range (1e48-1e50} erg/s). We derive analytical expressions for the luminosity function of GRBs in uniform and structured jet models and compare them with the data. Uniform jets can reproduce the entire luminosity function with reasonable values of the free parameters. A structured jet can also fit adequately the current data, provided that the energy within the jet is relatively strongly structured, i.e. E propto theta^{-k} with k > 4. The classical E propto theta^{-2} structured jet model is excluded by the current data.