Are long gamma-ray bursts standard candles?

TL;DR

This study examines whether gamma-ray bursts can be used as standard candles by testing the universality of the Amati relation across different redshifts, revealing significant differences between low and high redshift GRBs.

Contribution

The paper provides evidence that the Amati relation varies with redshift, challenging the assumption of its universality and impacting the use of GRBs as cosmological probes.

Findings

Amati relation differs between low and high redshift GRBs at over 3σ confidence

The difference in Amati relation is insensitive to cosmological models

Caution is advised when using Amati relation for Hubble diagram reconstruction

Abstract

Gamma-ray bursts (GRBs) are widely proposed as an effective probe to trace the Hubble diagram of the Universe in high redshift range. However, the calibration of GRBs is not as easy as that of type-Ia supernovae (SNe Ia). Most calibrating methods at present make use one or some of the empirical luminosity correlations, e.g., Amati relation. One of the underlying assumptions of these calibrating methods is that the empirical correlation is universal over all redshifts. In this paper, we check to what extent this assumption holds. Assuming that SNe Ia exactly trace the Hubble diagram of the Universe, we re-investigate the Amati relation for low redshift ($z<1.4$) and high redshift ($z>1.4$) GRBs, respectively. It is found that the Amati relation of low-$z$ GRBs differs from that of high-$z$ GRBs at more than $3\sigma$ confidence level. This result is insensitive to cosmological models. We should be cautious when using Amati relation to reconstruct the Hubble diagram of the Universe.