GECAM Localization of High Energy Transients and the Systematic Error

TL;DR

This paper presents a Bayesian localization method for GECAM high-energy transients, including a new systematic error estimation technique, validated through simulations and applied to real burst data to improve localization accuracy.

Contribution

It introduces a Bayesian localization approach tailored for GECAM bursts and a novel systematic error estimation method, enhancing localization reliability for gamma-ray transients.

Findings

The Bayesian method effectively localizes all burst types, especially short ones.

The systematic error of GECAM-B localization is approximately 2.5 degrees.

The approach improves confidence in burst localization and can be applied to other gamma-ray monitors.

Abstract

Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) is a pair of microsatellites (i.e. GECAM-A and GECAM-B) dedicated to monitoring gamma-ray transients including gravitational waves high-energy electromagnetic counterparts, Gamma-ray Bursts, Soft Gamma-ray Repeaters, Solar Flares and Terrestrial Gamma-ray Flashes. Since launch in December 2020, GECAM-B has detected hundreds of astronomical and terrestrial events. For these bursts, localization is the key for burst identification and classification as well as follow-up observations in multi-wavelength. Here, we propose a Bayesian localization method with Poisson data with Gaussian background profile likelihood to localize GECAM bursts based on the burst counts distribution in detectors with different orientations. We demonstrate that this method can work well for all kinds of bursts, especially for extremely short ones. In addition, we propose a new method to estimate the systematic error of localization based on a confidence level test, which can overcome some problems of the existing method in literature. We validate this method by Monte Carlo simulations, and then apply it to a burst sample with accurate location and find that the mean value of the systematic error of GECAM-B localization is $\sim 2.5^{\circ}$. By considering this systematic error, we can obtain a reliable localization probability map for GECAM bursts. Our methods can be applied to other gamma-ray monitors.