The mystery of the missing GRB redshifts

TL;DR

This paper investigates how optical selection effects bias the observed distribution of gamma-ray burst (GRB) redshifts, highlighting the role of dust extinction and observational limitations in shaping our understanding of GRB host galaxies.

Contribution

It introduces a statistically optimal model quantifying the impact of dust extinction and observational biases on GRB redshift measurements, especially at low to moderate redshifts.

Findings

Dust extinction may cause up to 40% of missing redshifts at z=0-3.

Biases are negligible at very high redshifts.

Observational sensitivity and timing significantly affect high-z redshift detection.

Abstract

It is clear that optical selection effects have distorted the "true" GRB redshift distribution to its presently observed biased distribution. We constrain a statistically optimal model that implies GRB host galaxy dust extinction could account for up to 40% of missing optical afterglows and redshifts in $z = 0-3$, but the bias is negligible at very high-$z$. The limiting sensitivity of the telescopes, and the time to acquire spectroscopic/photometric redshifts, are significant sources of bias for the very high-$z$ sample. We caution on constraining star formation rate and luminosity evolution using the GRB redshift distribution without accounting for these selection effects.