Prospects for the Detection of the Prompt Very-high-energy Emission from γ-ray Bursts with the High Altitude Detection of Astronomical Radiation Experiment

Abstract

The observation of very-high-energy (VHE; > 10 GeV) γ-ray emission from γ-ray bursts (GRBs), especially in the prompt phase, will provide critical information for understanding many aspects of their nature including the physical environment, the relativistic bulk motion, the mechanisms of particle acceleration of GRBs, and for studying Lorentz invariance violation, etc. For the afterglow phase, the highest-energy photons detected to date by the imaging atmospheric Cherenkov telescopes extend to the TeV regime. However, for the prompt phase, years of efforts in searching for the VHE emission has yielded no statistically significant detections. A wide field of view and large effective area above tens of GeV are essential for detecting the VHE emissions from GRBs in the prompt phase. The High Altitude Detection of Astronomical Radiation (HADAR) experiment has such merits. In this paper, we report the estimates of its expected annual GRB detection rate, which are obtained by combining the performance of the HADAR instrument with the theoretical calculations based on a phenomenological model to generate the pseudo-GRB population. The expected detectable gamma-ray signal from GRBs above the background is then obtained to give the detection rate. In the spectral model, an extra component is assigned to every GRB event in addition to the Band function. The results indicate that if the energy of the cutoff due to internal absorption is higher than 50 GeV, the detection rate for GRBs for the HADAR experiment is approximately two or three GRBs per year, which varies slightly depending upon the characteristics of the extra component.

Gamma/Hadron Separation Method for the HADAR Experiment

“…Based on Gamma Air Watch (Cusumano et al 2011) and the Fresnel lens telescope in the Joint Experiment Module for the Extreme Universe Space Observatory (Casolino et al 2011), the HADAR experiment is a super wide-angle atmospheric Cherenkov telescope array comprised of four large-aperture, wide-angle water lenses that mimic the structure of the human eye. Figure 1(left) displays a detailed schematic of a single water lens (Xin et al 2021), which consists of a 5 m diameter hemispherical acrylic shell mounted on an 8 m diameter steel tank. The tank consists of, from the outermost layer inwards, an insulation layer (for maintaining a consistent tank temperature), a steel frame (for providing internal structural support) and an absorption layer (which prevents multiple reflections of photons within the tank).…”

“…The PMTs are supported by a steel structure beneath them. The overall layout of the HADAR experiment is illustrated in Figure 1(right) (adopted from Xin et al 2021). The four water lenses are positioned at the vertices of a square with a side length of 100 m. In the figure, the small white squares indicate the scintillation detector array (SA) of the YangBaJing Hybrid array (Feng et al 2019), which can be used for future joint observations.…”

Prospects for Detecting γ-Ray Bursts at Very High Energies with the HADAR Experiment

“…The primary scientific goal of HADAR is to cover γ-ray astronomy in the energy range from 10 GeV to 10 TeV, providing exceptional sensitivity while maintaining a broad FOV. Further details regarding HADARʼs instrument layout, configuration, and performance analysis under different incident rays can be found elsewhere (Xin et al 2021). Our Monte Carlo simulations have yielded some notable outcomes, including the expectation of observing two to three prompt emission GRBs per year (Xin et al 2021).…”

“…Further details regarding HADARʼs instrument layout, configuration, and performance analysis under different incident rays can be found elsewhere (Xin et al 2021). Our Monte Carlo simulations have yielded some notable outcomes, including the expectation of observing two to three prompt emission GRBs per year (Xin et al 2021).…”

“…The performance of the detector, including its effective area (A eff ) at different energy ranges and observation zenith angles (θ), angular resolution (Ω), and proton-γ discrimination capability (η), has been adopted from a previous study (Xin et al 2021).…”