GECAM Localization of High Energy Transients and the Systematic Error by Yi Zhao et al. on Wednesday 30 November

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.

arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.15570v1