# Distributed Architectures and Constellations for \(\gamma\)-ray Burst Science
## 4 The Role of Distributed Architectures in Tomorrow's Multi-Messenger Astrophysics
### A Constellation of Nano-Satellites for High-Energy Transient Detection and Localization
Modularity can allow us to (a) avoid single (or even multiple) point failures (if one or several units are lost the constellation and the experiment can still be operative); (b) fully test the hardware in orbit with the first launches and then improve it, if needed, with the following launches (iterative development, used in the context of gamma-ray flashes and GRBs early on by the VELA satellites. The second generation included gamma-ray detectors with much better timing capabilities, strongly improving the localization capabilities of the constellation); (c) to build the final mission step by step, gradually increasing its performance while diluting costs and risks. An all-sky monitor, capable of monitoring the whole sky, or a large fraction of the sky, at all times, requires either a distributed infrastructure on LEO or a dedicated spacecraft far from the Earth. Given the advantages of miniaturized instrumentation hosted by CubeSats, it is relatively natural to propose building a sensitive all-sky monitor based on a constellation of nano-satellites. In the previous section, in the context of multi-messenger astrophysics, we discussed the scientific relevance of even simple high-energy transient detections at the time of GWEs. Of course, their accurate localization would multiply the scientific return, prompting multi-wavelength (and even multi-messenger) follow-ups. In the context of multi-wavelength astrophysics, it must be considered that, in a few years, the Vera Rubin Observatory (VRO) and the Cerenkov Array Telescope (CTA) will come online. VRO will have the ability to cover \(\sim\)1/4 of the sky every night, finding millions of transients per night down to a magnitude r < 24.5 using real-time data analysis. On the one hand, optical counterparts of GRBs and GWEs will likely be serendipitously found in VRO images (covering each about 10 deg\({}^{2}\)), providing arcsec positions and immediately prompting multiwavelength follow-up. On the other hand, the detection of X-ray and gamma-ray emission will promptly characterize the VRO transients (magnetars, soft gamma ray repeaters, tidal disruption events, thermonuclear bursts from accreting NS, novae, AGN jets, etc., in addition to GRBs), thus better focusing the multiwavelength follow-up. CTA will boost the study of the 20 GeV-300 TeV energy range. Only three GRBs have been detected at TeV energies so far: one by MAGIC [18] and two by HESS [19]. The CTA's fast re-positioning capabilities (20 s) and the improved sensitivity, due to the larger collecting area and lower energy threshold (~20 GeV) compared to MAGIC and HESS, will aid the study of GRB high-energy radiation routine, opening the possibility to accurately derive the jet Lorentz factor, assessing the role of synchrotron and inverse Compton radiation, and constraining the magnetic field strength and configuration. Given the limited field of view (FoV) of CTA at GeV energies (4.3\({}^{\circ}\)), an instrument operating during the 20 s and providing the localization of GRBs with errors smaller than the CTA FoV is of paramount importance for triggering CTA follow-up observations.