2025/10/24 by Wei, Jun-Jie, Ma, Qing-Bo, Wu, Xue-Feng
#Cosmology and Nongalactic Astrophysics (astro-ph.CO) #FOS: Physical sciences #High Energy Astrophysical Phenomena (astro-ph.HE)
paper · doi:10.48550/arxiv.2510.21097
High-redshift gamma-ray bursts (GRBs), putative counterparts of massive, low-metallicity Population III (Pop III) stars, are a promising probe of the first stars. We assess the detectability of these Pop III GRBs using a metallicity-based progenitor criterion and cosmological N-body/hydrodynamical simulations with three distinct Pop III initial mass functions (IMFs), focusing on the capabilities of the Wide-field X-ray Telescope (WXT) aboard the Einstein Probe (EP) and the coded-mask gamma-ray imager (ECLAIRs) aboard the Space-based multi-band astronomical Variable Objects Monitor (SVOM). Our population synthesis model, calibrated to Swift data, predicts the following Population II/I (Pop II/I) GRB detection rates at z>6: ∼2.4 \mathrmevents yr-1 for EP/WXT and ∼0.9 \mathrmevents yr-1 for SVOM/ECLAIRs. For the IMF with very massive first stars (\mathrm100\textrm--500 M_\odot), we derive upper limits on the Pop III GRB rate at z>6 of <0.06 \mathrmevents yr-1 (EP/WXT) and <0.13 \mathrmevents yr-1 (SVOM/ECLAIRs), based on the absence of confirmed Pop III progenitors in Swift bursts at z>5.5. Our results indicate that while Pop III GRBs are subdominant to Pop II/I GRBs at z<10, their fractional contribution rises significantly with redshift, reaching ∼8% (∼34%) at z>10 and ∼28% (∼68%) at z>16 for EP/WXT (SVOM/ECLAIRs). This trend is systematically enhanced in the other two IMF models, which adopt a lower stellar mass range of [0.1, 100] M_\odot. We conclude that detecting Pop III GRBs at high redshifts is a realistic prospect, and any GRB detected at z>16 is most likely of Pop III origin.