The redshift distribution of gamma-ray bursts revisited

Abstract

In this letter, we calculate the redshift distribution of gamma-ray bursts assuming that they trace (i) the globally averaged star formation rate or (ii) the average metallicity in the Universe. While at redshifts 5 and below, both the star formation rate and metallicity are observationally determined modulo some uncertainties, at higher redshifts there are few constraints. We extrapolate the star formation rate and metallicity to higher redshifts and explore models that are broadly consistent with bounds on the optical depth from WMAP results. In addition, we also include parametric descriptions of the luminosity function, and the typical spectrum for GRBs. With these essential ingredients included in the modeling, we find that a substantial fraction 75% of GRBs are expected to originate at redshifts below 4, in variance with some previous estimates. Conversely, if we assume as expected for the collapsar model that gamma-ray bursts favour a low metallicity environment and therefore, relate the GRB rate to a simple model of the average metallicity as a function of redshift, we find that a higher fraction of bursts, about 40% originate from redshifts greater than 4. We conclude with the implications of SWIFT GRB detections.Comment: 5 pages, 2 figures, revised version, MNRAS pink pages in press, error in y-axis label in Fig.2 (bottom panel) correcte

Enhanced cosmological GRB rates and implications for cosmogenic neutrinos

“…At higher redshifts, the Universe is less metal-enriched than at the present [49], resulting in an increase in the expected evolution of the GRB rate density (compared to the SFH), as shown by Langer and Norman [28] (see also Refs. [50,51]). Accounting for stellar evolution effects, Yoon, Langer, and Norman calculated the expected ratio of GRBs to corecollapse supernovae as a function of redshift, as seen in Fig.…”

Observations of GRBs at high redshift

“…Notable recent attempts include the following: Guetta et al (2005) explore a variety of different star-formation rate histories and GRB luminosity functions; Natarajan et al (2005) additionally incorporate a simple prescription for a lowmetallicity preference for GRBs; Yoon & Langer (2005) take a more sophisticated approach to the metallicity question by explicitly identifying stellar evolution models, which naturally lead to collapsar progenitors; and Bromm & Loeb (2006) further consider the possibility of a population III contribution to the high-z GRB rate.…”

GRB 050904 at redshift 6.3: observations of the oldest cosmic explosion after the Big Bang

“…A significant fraction of GRBs has been predicted to occur even at higher redshifts (e.g. Lamb & Reichart 2000;Gorosabel et al 2004;Natarajan et al 2005;Mesinger et al 2005), during the re-ionization epoch (6 < ∼ z < ∼ 20, Gnedin & Ostriker 1997;Fan et al 2002;Spergel et al 2003). Since the progenitors of long-duration GRBs are thought to be short-lived massive stars (Galama et al 1998;Stanek et al 2003;Hjorth et al 2003;Malesani et al 2004), their detection at large redshifts provides a direct measurement of the star formation rate in the early Universe.…”