[Paper Review] Prospects for the Observation of Primordial Black Hole evaporation with the Southern Wide Field of View Gamma-ray Observatory

R. López-Coto, M. Doro+3 more|arXiv (Cornell University)|Jan 1, 2021

Astrophysics and Cosmic Phenomena33 references12 citations

TL;DR

This paper evaluates the Southern Wide Field of View Gamma-ray Observatory (SWGO) as a next-generation instrument capable of detecting short-duration gamma-ray flashes from evaporating primordial black holes (PBHs). Using simulated sensitivity and combined inner/outer array data, SWGO can constrain PBH burst rates to ∼50 pc⁻³ yr⁻¹ over 0.5–5 s integration windows, improving on current limits by over an order of magnitude, especially for short-duration bursts.

ABSTRACT

Primordial Black Holes (PBHs) are remnants of objects formed in the early Universe. Their lifetime is an increasing function of their mass, so PBHs in the right mass range can end their lives in an evaporation event that is potentially detectable by our instruments now. This evaporation may result in a $\gamma$-ray flash that can be detected by the current generation of Very-High-Energy $\gamma$-ray detectors. The Southern Wide field of view Gamma-ray Observatory (SWGO) will be part of the next generation of these instruments. It will be able to establish limits on PBH evaporations for integration windows between 0.5 and 5 s, in a radius of 0.25 pc around the Earth, being sensitive to a rate of the order of $\sim$50 pc$^{-3}$ yr$^{-1}$, more than one order of magnitude more constraining than the currently established best limits.

Motivation & Objective

• To assess SWGO's sensitivity to short-duration gamma-ray flashes from evaporating primordial black holes (PBHs).
• To improve upon existing observational limits on PBH burst rates using a wide-field-of-view VHE gamma-ray observatory.
• To quantify the impact of detector configuration (inner vs. outer array) and integration time on sensitivity to PBH evaporation signals.
• To provide a robust, background-corrected upper limit on PBH burst rates within 0.25 pc of Earth.

Proposed method

• The study uses the Standard Evaporation Model (SEM) to simulate photon flux from PBHs with masses around 10¹⁵ g, predicting short-duration (0.5–1000 s) gamma-ray bursts.
• Sensitivity is calculated using effective area, energy resolution, and angular resolution from simulations at 20° zenith, with 75% gamma-ray efficiency.
• Background rates are modeled with conservative, fiducial, and optimistic scenarios to bracket uncertainty in detection thresholds.
• Combined likelihood analysis fuses data from SWGO's high-fill-factor inner array and low-fill-factor outer array to optimize sensitivity.
• The post-trial significance is computed using a 5σ threshold to determine the minimum detectable signal and corresponding upper limit on burst rate.
• The analysis accounts for energy-dependent detection efficiency and integrates over time windows to optimize sensitivity for different burst durations.

Experimental results

Research questions

• RQ1 Can SWGO detect gamma-ray flashes from evaporating primordial black holes with durations between 0.5 and 5 seconds?
• RQ2 How does the sensitivity of SWGO's inner and outer arrays compare for short-duration PBH bursts?
• RQ3 What upper limit on the PBH burst rate can SWGO achieve over a 10-year observation period?
• RQ4 How does SWGO's sensitivity compare to existing VHE gamma-ray instruments like HAWC, HESS, and Fermi-LAT?
• RQ5 Can SWGO improve upon the current best limits by more than an order of magnitude for short-duration PBH evaporation events?

Key findings

• SWGO can achieve a PBH burst rate upper limit of approximately 50 pc⁻³ yr⁻¹ for integration windows between 0.5 and 5 seconds.
• For 10 years of observation, SWGO’s sensitivity reaches limits about two orders of magnitude lower than the best current experiments.
• The outer array of SWGO outperforms the inner array for burst durations below 10 seconds due to its larger effective area at high energies.
• The combined sensitivity of both SWGO arrays improves the detection threshold by a factor of 10 compared to the best existing limits from HAWC.
• The study shows that SWGO can constrain PBH burst rates with higher precision than previous instruments, especially for short-duration events.
• The results are robust across different background rate assumptions, with conservative and optimistic scenarios bracketing the final limits.