ArXiv: 1712.09984

Abstract

We suggest that the low-luminosity (LL) gamma-ray bursts (GRBs) can be the sources of UHECR nuclei. LL GRBs are a subclass of GRBs which have lower luminosity ($L_\gamma \leq 10^{49}\rm~erg~s^{-1}$) and higher event rate ($\sim 300 \rm~Gpc~yr^{-1}$) compared to the classical high-luminosity (HL) GRBs. As have been shown in the left panel of the figure, the nuclear component in the interior of the progenitors can be loaded into the relativistic outflow. We found that the intrajet nuclear component can be divided into two groups depending on the mass fraction of Silicon nuclei, Si-free and Si-rich. In addition, we also consider the hypernova ejecta composition under the case that the jet maybe launched later than the hypernova. We found the Si-rich model or hypernova ejecta model can match the Auger data well, while the Si-free models have more difficulty in fitting the spectrum, as we have shown in the right panel of the figure for nuclear composition model Si-R 2.