Timing techniques applied to distributed modular high-energy astronomy: the H.E.R.M.E.S. project

The association of GW170817 with GRB170817A proved that electromagnetic counterparts of gravitational wave events are the key to deeply understand the physics of NS-NS merges. Upgrades of the existing GW antennas and the construction of new ones will allow to increase sensitivity down to several hundred Mpc vastly increasing the number of possible electromagnetic counterparts. Monitoring of the hard X-ray/soft gamma-ray sky with good localisation capabilities will help to effectively tackle this problem allowing to fully exploit multi-messenger astronomy. However, building a high energy all-sky monitor with large collective area might be particularly challenging due to the need to place the detectors onboard satellites of limited size. Distributed astronomy is a simple and cheap solution to overcome this difficulty. Here we discuss in detail dedicated timing techniques that allow to precisely locate an astronomical event in the sky taking advantage of the spatial distribution of a swarm of detectors orbiting Earth.