Searching for the first stars with the Gaia mission

TL;DR

This paper models the potential to detect orphan afterglows from primordial Pop III stars with Gaia, estimating that up to about 5 such events could be observed during its mission, indicating a feasible way to study the first stars.

Contribution

It introduces a semi-analytical model incorporating feedback effects to predict Gaia's capability to observe GRB afterglows from Pop III stars, a novel approach in this context.

Findings

Gaia can observe up to 2.28 off-axis afterglows.

Gaia can observe up to 2.78 on-axis afterglows.

Approximately 10% of observed afterglows could originate from Pop III stars.

Abstract

We construct a theoretical model to predict the number of orphan afterglows (OA) from gamma-ray bursts (GRBs) triggered by primordial metal-free (Pop III) stars expected to be observed by the Gaia mission. In particular, we consider primordial metal-free stars that were affected by radiation from other stars (Pop III.2) as a possible target. We use a semi-analytical approach that includes all relevant feedback effects to construct cosmic star formation history and its connection with the cumulative number of GRBs. The OA events are generated using the Monte Carlo method, and realistic simulations of Gaia's scanning law are performed to derive the observation probability expectation. We show that Gaia can observe up to 2.28 $\pm$ 0.88 off-axis afterglows and 2.78 $\pm$ 1.41 on-axis during the five-year nominal mission. This implies that a nonnegligible percentage of afterglows that may be observed by Gaia ($\sim 10%$) could have Pop III stars as progenitors.