# Gamma-ray Bursts: 50 Years and Counting!
## 4 The BeppoSAX Era (1996-2000/2004)  
As we have seen, much progress was made during the BATSE era in the investigations of GRBs. Still, regardless of the large amount of data acquired, these were not sufficient to single out a clear model for the production of these signals, and two vastly different classes, galactic and extragalactic models, were discussed in the community. The lack of multiwavelength observations limited the possibilities to understand the underlying mechanism of the production of these signals. At the same time, the poor localization capabilities, together with the impossibility of estimating the distance of the sources, meant that it was not yet possible to understand the energy scales of these phenomena and completely rule out any of the two model paradigms that were proposed. This was aggravated by the no-host problem, i.e., the impossibility of identifying the host galaxies of such signals. In order to move forward and solve these problems, it was therefore necessary to carry out a new type of observation. The key to making multiwavelength observations and estimating distances was to obtain the very precise localizations of the GRBs. BeppoSAX was an Italian-Dutch satellite for X-ray astronomy [25]. Launched from the US space base at Cape Canaveral on 30 April 1996 and built largely by Italian companies,the satellite called SAX (\"Satellite per Astronomia a raggi X\", Italian for \"Satellite for X-ray Astronomy\"), once in orbit, was renamed BeppoSAX, from the nickname of Professor [PERSON], a pioneer of Italian high-energy astrophysics. BeppoSAX hosted five scientific instruments:  
* A Low-Energy Concentrator Spectrometer (LECS);
* A Medium-Energy Concentrator Spectrometer (MECS);
* A High-Pressure Gas-Scintillation-Proportional Counter (HPCSPC);
* A Phoswich Detector System (PDS);
* Two Wide-Field Cameras (WFCs). Of these, the two X-ray focusing telescopes (LECS and MECS), the HPGSPC and the PDS (collectively called Narrow-Field Instruments, NFIs) pointed in the same direction, thus allowing observations in a large energy range, from 0.1 to 300 keV, while the two WFCs pointed orthogonally to the other instruments' axis, covering a large area of the sky. The LECS, MECS, and HPGSPC detectors were all based on gas-scintillation-proportional counters operating in a total energy window from 0.1 keV (LECS) to 120 keV (HPGSPC) with high sensitivity. The PDS detector was a crystal (sodium iodide/cesium iodide) scintillator detector capable of collecting photons from 15 to 300 keV. The PDS detector was covered on its sides by four CsI scintillators that acted as anticoincidence shields for background rejection. With sensitivities from 40 to 700 keV, these panels had large fields of view that were aligned with the two WFCs. It was thus possible to use them to trigger GRB observations, obtaining the first localization with the WFCs in order to then slew the satellite and observe with the NFIs. For this reason, they were referred to as the Gamma-Ray Burst Monitor (GRBM). The WFCs were two units each composed of a proportional counter and a coded mask to obtain excellent angular resolutions covering extended fields of view of \(20^{\circ}\times 20^{\circ}\) in the energy range 2-28 keV. The simultaneous detection of GRBs by the GRBM and WFCs therefore made it possible to obtain the localizations of these signals with excellent precision, reaching accuracies of a few arcminutes. The estimated coordinates were quickly sent to the International Astronomical Union (IAU) and the Gamma-ray burst Coordinate Network Circular. Subsequently, immediate follow-up observations with the onboard NFIs and ground-based optical observatories allowed the accurate localization and detailed observations of GRBs. The BeppoSAX mission achieved a breakthrough in February 1997, within a year of its launch. The gamma-ray burst GRB 970228 was initially detected by BeppoSAX's WFCs, and subsequently, when the X-ray NFIs aboard BeppoSAX were directed toward the source of the burst, they captured a diminishing X-ray emission [26].