ASTENA: A mission concept for a deep study of the transient gamma-ray sky and for nuclear astrophysics

Gamma-ray astronomy is a branch whose potential has not yet been fully exploited.The observations of elemental and isotopic abundances in supernova (SN) explosions arekey probes not only of the stellar structure and evolution but also for understandingthe physics that makes Type-Ia SNe as standard candles for the study of the Universeexpansion properties. In spite of its crucial role, nuclear astrophysics remains a poorly ex-plored field mainly for the typical emission lines intensity which are vanishing small andrequires very high sensitivities of the telescopes. Furthermore, in spite that the Galacticbulge-dominated intensity of positron annihilation line at 511 keV has been measured,its origin is still a mystery due to the poor angular resolution and insufficient sensitivityof the commonly employed instrumentation in the sub-MeV energy domain. To answerthese scientific issues a jump in sensitivity and angular resolution with respect to thepresent instrumentation is required. Conceived within the EU project AHEAD, a newhigh energy mission, capable of tackling the previously mentioned topics, has been pro-posed. This concept of mission named ASTENA (Advanced Surveyor of Transient Eventsand Nuclear Astrophysics), includes two instruments: a Wide Field Monitor with Imagingand Spectroscopic (WFM-IS, 2 keV - 20 MeV) capabilities and a Narrow Field Telescope(NFT, 50 - 700 keV). Thanks to the combination of angular resolution, sensitivity andlarge FoV, ASTENA will be a breakthrough in the hard X and soft gamma–ray energyband, also enabling polarimetry in this energy band. In this talk the science goals of themission are discussed, the payload configuration is described and expected performancesin observing key targets are shown.