Cosmic Ray Origin: beyond the Standard Model(s). The case of Pulsar Wind Nebulae and Unidentified very high energy gamma-ray sources

TL;DR

This paper reviews the current understanding of cosmic ray origins, emphasizing the role of pulsar wind nebulae and unidentified gamma-ray sources, highlighting recent observational and theoretical advances in high-energy astrophysics.

Contribution

It introduces the Ancient Pulsar Wind Nebulae scenario and discusses its significance in explaining unidentified gamma-ray sources related to cosmic ray acceleration.

Findings

Many high-energy gamma-ray sources remain unidentified, especially at TeV energies.

The Ancient Pulsar Wind Nebulae scenario offers a promising explanation for dark sources.

Observational evidence supports hadronic acceleration in supernova remnants.

Abstract

The riddle of the origin of Cosmic Rays is open since one century. Recently we got the experimental proof of hadronic acceleration in Supernovae Remnants, however new questions rised and no final answer has been provided so far. Gamma ray observations above 100 MeV reveal the sites of cosmic ray acceleration to energies where they are unaffected by solar modulation. In the last years the knowledge in this field of research widely increased, however almost 50% of the TeV (> 10^12 eV) Galactic sources are still unidentified, at GeV (> 10^9 eV) energies, 67% of EGRET sources were unidentified and also with the newer generation of gamma-ray satellites we have the same result: in fact, at low Galactic latitudes (b<10 deg), 62% of the Fermi LAT detected sources have no formal counterpart. Hence understanding the high energy unidentified sources will be a crucial brick in solving the whole riddle of Cosmic Rays origin. Several examples will be shown, underlining the importance of the so-called "dark sources". Both theoretical aspects (with particular emphasis to the so-called Ancient Pulsar Wind Nebulae scenario) and their observational proofs will be discussed.