On the Redshift Distribution of Gamma‐Ray Bursts in theSwiftEra

Abstract

A simple physical model for long-duration gamma-ray bursts (GRBs) is used to fit the redshift (z) and the jet opening angle distributions measured with earlier GRB missions and with Swift. The effect of different sensitivities for GRB triggering is sufficient to explain the difference in the z distributions of the pre-Swift and Swift samples, with mean redshifts of hzi ffi 1:5 and hzi ffi 2:7, respectively. Assuming that the emission properties of GRBs do not change with time, we find that the data can only be fitted if the comoving rate density of GRB sources exhibits positive evolution to z k 3Y5. The mean intrinsic beaming factor of GRBs is found to range from %34 to 42, with the Swift average opening half-angle h j i $ 10 , compared to the pre-Swift average of h j i $ 7 . Within the uniform jet model, the GRB luminosity function is /L À3:25 Ã , as inferred from our best fit to the opening angle distribution. Because of the unlikely detection of several GRBs with z P 0:25, our analysis indicates that low-redshift GRBs represent a different population of GRBs than those detected at higher redshifts. Neglecting possible metallicity effects on GRB host galaxies, we find that %1 GRB occurs every 600,000 yr in a local L Ã spiral galaxy like the Milky Way. The fraction of high-redshift GRBs is estimated at 8% Y12% and 2.5%Y6% at z ! 5 and z ! 7, respectively, assuming continued positive evolution of the GRB rate density to high redshifts.

The high-redshift star formation rate derived from gamma-ray bursts: possible origin and cosmic reionization

“…Observations also show that GRBs are associated with Type Ib/c supernovae (Stanek et al 2003;Hjorth et al 2003), so GRBs provide a complementary technique for measuring the SFR history (Totani 1997;Wijers et al 1998;Porciani & Madau 2001). Recent studies have shown that Swift GRBs do not trace the star formation history measured by traditional means exactly, but include an additional evolution (Le & Dermer 2007;Salvaterra & Chincarini 2007;Kistler et al 2008;Yüksel et al 2008;Wang & Dai 2009;Wanderman & Piran 2010;Qin et al 2010;Cao et al 2011;Robertson & Ellis 2012; but see Elliott et al 2012). The SFR inferred from the high-redshift (z > 6) GRBs seems to be too high in comparison with the one obtained from some high-redshift galaxy surveys (Kistler et al 2009;Bouwens et al 2009).…”

Limits on the Lorentz Invariance Violation from UHECR Astrophysics

“…• R 5 : Sources follow the GRB rate evolution from reference Le & Dermer (2007). The evolution is proportional to (1 + 11z)/[1 + (z/3) 0.5 ].…”

GRBs and Fundamental Physics

“…Recent studies show that the rate of GRBs does not strictly follow the SFH but is actually enhanced by some mechanism at high redshift (Le & Dermer 2007;Salvaterra & Chincarini 2007;Kistler et al 2008;Yüksel et al 2008;Robertson & Ellis 2012;Wang 2013). The SFR inferred from the highredshift (z > 6) GRBs seems to be too high in comparison with the SFR obtained from some high-redshift galaxy surveys (Bouwens et al 2009(Bouwens et al , 2011.…”

“…Because the lifetimes of massive stars are short, the formation rate can be treated as their death rate. Surprisingly, the Swift data reveals that long GRBs are not tracing the SFR directly, instead implying some kind of additional evolution (Daigne et al 2006;Le & Dermer 2007;Yüksel & Kistler 2007;Salvaterra & Chincarini 2007;Guetta & Piran 2007;Kistler et al 2008;Campisi et al 2010;Salvaterra et al 2012). But the conversion factor between GRB rate and SFR is hard to determine.…”