Evidence for an intrinsic luminosity-decay correlation in GRB radio afterglows

TL;DR

This paper discovers a significant correlation between the intrinsic luminosity at 10 days and the decay rate in radio afterglows of gamma-ray bursts, extending known relations across multiple wavebands and supporting models involving viewing geometry and microphysics.

Contribution

It presents the first evidence of a luminosity-decay correlation in radio afterglows, confirming and extending previous multi-wavelength findings.

Findings

A significant negative correlation with Spearman's coefficient of -0.70

The correlation is not due to chance or selection effects, confirmed by Monte Carlo simulations

The radio correlation is consistent with optical, UV, X-ray, and GeV relations

Abstract

We present the discovery of a correlation, in a sample of 16 gamma-ray burst 8.5 GHz radio afterglows, between the intrinsic luminosity measured at 10 days in the rest frame, $L_{\mathrm{Radio,10d}}$, and the average rate of decay past this time, $\alpha_{>10d}$. The correlation has a Spearman's rank coefficient of $-0.70 \pm 0.13$ at a significance of $>3\sigma$ and a linear regression fit of $\alpha_{>10d} = -0.29^{+0.19}_{-0.28} \log \left(L_{\mathrm{Radio,10d}} \right) + 8.12^{+8.86}_{-5.88}$. This finding suggests that more luminous radio afterglows have higher average rates of decay than less luminous ones. We use a Monte Carlo simulation to show the correlation is not produced by chance or selection effects at a confidence level of $>3\sigma$. Previous studies found this relation in optical/UV, X-ray and GeV afterglow light curves, and we have now extended it to radio light curves. The Spearman's rank coefficients and the linear regression slopes for the correlation in each waveband are all consistent within $1\sigma$. We discuss how these new results in the radio band support the effects of observer viewing geometry, and time-varying microphysical parameters, as possible causes of the correlation as suggested in previous works.