Searching for the first stars with the Gaia mission
  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.
