Populations III.1 and III.2 gamma-ray bursts: constraints on the event rate for future radio and X-ray surveys

¹ IAG, Universidade de São Paulo, Rua do Matão 1226, Cidade Universitária, CEP 05508-900 São Paulo SP Brazil
² Institute for the Physics and Mathematics of the Universe, Todai Institutes for Advanced Study, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8583, Japan
e-mail: rafael.desouza@ipmu.jp
³ KEK Theory Center and the Graduate University for Advanced Studies (Sokendai), Tsukuba 305-0801, Japan

Received: 12 May 2011
Accepted: 20 July 2011

Abstract

Aims. We calculate the theoretical event rate of gamma-ray bursts (GRBs) from the collapse of massive first-generation (Population III; Pop III) stars. The Pop III GRBs could be super-energetic with the isotropic energy up to E_iso ≳ 10⁵⁵⁻⁵⁷ erg, providing a unique probe of the high-redshift Universe.

Methods. We consider both the so-called Pop III.1 stars (primordial) and Pop III.2 stars (primordial but affected by radiation from other stars). We employ a semi-analytical approach that considers inhomogeneous hydrogen reionization and chemical evolution of the intergalactic medium.

Results. We show that Pop III.2 GRBs occur more than 100 times more frequently than Pop III.1 GRBs, and thus should be suitable targets for future GRB missions. Interestingly, our optimistic model predicts an event rate that is already constrained by the current radio transient searches. We expect  ~10−10⁴ radio afterglows above  ~0.3 mJy on the sky with  ~1 year variability and mostly without GRBs (orphans), which are detectable by ALMA, EVLA, LOFAR, and SKA, while we expect to observe maximum of N < 20 GRBs per year integrated over at z > 6 for Pop III.2 and N < 0.08 per year integrated over at z > 10 for Pop III.1 with EXIST, and N < 0.2 for Pop III.2 GRBs per year integrated over at z > 6 with Swift.