Cosmological Tests Using GRBs, the Star Formation Rate and Possible Abundance Evolution

Understand

The principal goal of this paper is to use attempts at reconciling the Swift long gamma-ray bursts (LGRBs) with the star formation history (SFH) to compare the predictions of $\Lambda$CDM with those in the $R_{\rm h}=ct$ Universe.

• In the context of the former, we confirm that the latest Swift sample of GRBs reveals an increasing evolution in the GRB rate relative to the star formation rate (SFR) at high redshifts.
• The observed discrepancy between the GRB rate and the SFR may be eliminated by assuming a modest evolution parameterized as $(1+z)^{0.8}$---perhaps indicating a cosmic evolution in metallicity.
• However, we find a higher metallicity cut of $Z=0.52Z_{\odot}$ than was seen in previous studies, which suggested that LGRBs occur preferentially in metal poor environments, i.e., $Z\sim0.1-0.3Z_{\odot}$.