DIFFUSEGAMMAEMISSION

Sources of cosmic rays and gamma ray emission from the Galaxy

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 Obiettivo del progetto (Objective)

'One hundred years after their discovery by the Austrian physicist Victor Hess, the origin of cosmic rays is still unclear. The detection of TeV gamma rays from supernova remnants (SNRs) by the experiment HESS has strengthened the hypothesis that primary Galactic cosmic-ray electrons are accelerated in SNRs up to the knee energy, where the power-law cosmic ray spectrum changes. Despite this extraordinary recent discovery the question of the origin of cosmic rays is still open, and even if the SNRs prove to be sources of cosmic ray electrons, no compelling evidence for the acceleration of hadrons in SNRs has until now been found. The diffuse gamma radiation arising from the interaction of cosmic-ray particles with matter and radiation in the Galaxy is one of the few probes available to study the origin of cosmic rays. Nevertheless the predictions of the gamma ray flux based upon the measured Galactic matter density and the cosmic-ray spectrum and intensity measured at Earth are in disagreement with the measurements obtained by the EGRET and Milagro detectors. The proposed project aims to investigate the features of the gamma ray spectrum from each direction of the Galaxy and to compare the gamma ray data with the ISM data and use the results as a probe of the cosmic ray flux in the different regions of the galaxy. The regions where the galactic gamma ray flux cannot be explained by interactions of a cosmic ray flux similar to that measured close to the Sun with the passive ISM targets, will be interesting probes of the sites of CR injection.'

Introduzione (Teaser)

Advances in instrumentation, new theories and improved techniques are helping scientists finally understand the mysteries behind cosmic rays in the galaxy.

Descrizione progetto (Article)

About a century ago, Austrian physicist Victor Hess discovered cosmic rays. Today, the origin of these rays is still unclear. Gamma radiation is one way of studying cosmic rays, but has not proven to be very reliable.

The EU-funded project 'Sources of cosmic rays and gamma ray emission from the Galaxy' (DiffuseGammaEmission) studied gamma rays from each direction of the Galaxy. It compared their properties with data on the interstellar medium (ISM), i.e. the matter between star systems. The results were then used to examine cosmic ray flux in certain parts of the galaxy where traditional methods of examination weren't very fruitful.

The project's main objective was to study sources and distribution of cosmic rays by comparing new, detailed gamma ray maps. Team members considered regions of high gas density or molecular clouds (MCs) and supernova remnants (SNRs), recording the multi wavelength spectrum from radio to gamma rays emerging from MCs. It found that some unidentified energy sources may in fact be associated with clouds illuminated by cosmic rays coming from a nearby source.

Exploiting gas data from the surveys of molecular and atomic hydrogen in the galaxy, the project team examined spectral and spatial distributions of the emissions. Different predictions and results from the project are promising to revolutionise the way scientists understand cosmic rays and reveal a better picture of their idiosyncrasies and sources. Finally, a better picture of cosmic rays will emerge.