arXiv subjects

Enrico Peretti

Publications and source records attributed to Enrico Peretti.

24 records · Page 2Linked to original sources

arXiv2022

Particle acceleration in galactic wind bubbles

Winds are ubiquitous in galaxies and often feature bubble structures. These wind bubbles are characterized by an external forward shock expanding in the surrounding medium and a wind termination shock separating the cool and fast wind from the hot shocked wind. While the forward shock could not be able to accelerate particles efficiently for a long time, at the wind termination shock the necessary conditions for efficient acceleration may be present. We develop a model for particle acceleration at the termination shock of such bubbles analysing the consequences of different possible engines powering the wind. We finally explore the multi-messenger potential of galactic winds in terms of escaping cosmic rays and high-energy gamma rays and neutrinos produced through hadronic interactions.

astro-ph.HE↗

arXiv2022

Particle acceleration and multimessenger emission from starburst-driven galactic winds

The enhanced star forming activity, typical of starburst galaxies, powers strong galactic winds expanding on kiloparsec (kpc) scales and characterized by bubble structures. Here we discuss the possibility that particle acceleration may take place at the termination shock of such winds. We calculate the spectrum of accelerated particles and their maximum energy, that turns out to range up to a few hundred petaelectronvolt (PeV) for typical values of the parameters. Cosmic rays accelerated at the termination shock are advected towards the edge of the bubble excavated by the wind and eventually escape into extragalactic space. We also calculate the flux of gamma rays and neutrinos produced by hadronic interactions in the bubble as well as the diffuse flux resulting from the superposition of the contribution of starburst galaxies on cosmological scales. Finally, we compute the diffuse flux of cosmic rays from starburst bubbles and compare it with existing data.

astro-ph.HE↗

arXiv2021

Particle acceleration in winds of star clusters

The origin of cosmic rays in our Galaxy remains a subject of active debate. While supernova remnant shocks are often invoked as the sites of acceleration, it is now widely accepted that the difficulties of such sources in reaching PeV energies are daunting and it seems likely that only a subclass of rare remnants can satisfy the necessary conditions. Moreover the spectra of cosmic rays escaping the remnants have a complex shape that is not obviously the same as the spectra observed at the Earth. Here we investigate the process of particle acceleration at the termination shock that develops in the bubble excavated by star clusters' winds in the interstellar medium. While the main limitation to the maximum energy in supernova remnants comes from the need for effective wave excitation upstream so as to confine particles in the near-shock region and speed up the acceleration process, at the termination shock of star clusters the confinement of particles upstream in guaranteed by the geometry of the problem. We develop a theory of diffusive shock acceleration at such shock and we find that the maximum energy may reach the PeV region for powerful clusters in the high end of the luminosity tail for these sources. A crucial role in this problem is played by the dissipation of energy in the wind to magnetic perturbations. Under reasonable conditions the spectrum of the accelerated particles has a power law shape with a slope $4÷4.3$, in agreement with what is required based upon standard models of cosmic ray transport in the Galaxy.

astro-ph.HE↗

arXiv2020

Contribution of starburst nuclei to the diffuse gamma-ray and neutrino flux

In nuclei of starburst galaxies, the combination of an enhanced rate of supernova explosions and a high gas density suggests that cosmic rays can be efficiently produced, and that most of them lose their energy before escaping these regions, resulting in a large flux of secondary products, including neutrinos. Although the flux inferred from an individual starburst region is expected to be well below the sensitivity of current neutrino telescopes, such sources may provide a substantial contribution to the diffuse neutrino flux measured by IceCube. Here we compute the gamma-ray and neutrino flux due to starburst galaxies based on a physical model of cosmic ray transport in a starburst nucleus, and accounting for the redshift evolution of the number density of starburst sources as inferred from recent measurements of the star formation rate. The model accounts for gamma-ray absorption both inside the sources and in the intergalactic medium. The latter process is responsible for electromagnetic cascades, which also contribute to the diffuse gamma-ray background at lower energies. The conditions for acceleration of cosmic ray protons up to energies exceeding $ \sim 10 \, \rm PeV$ in starburst regions, necessary for the production of PeV neutrinos, are investigated in a critical way. We show that starburst nuclei can account for the diffuse neutrino flux above $\sim 200 \, \rm TeV$, thereby producing $\lesssim 40 \%$ of the extragalactic diffuse gamma-ray background. Below $\sim 200 \, \rm TeV$, the flux from starburst appears to be somewhat lower than the observed one, where both the Galactic contribution and the flux of atmospheric neutrinos may account for the difference.

astro-ph.HE↗

arXiv2019

Cosmic ray transport and radiative processes in nuclei of starburst galaxies

The high rate of star formation and supernova explosions of starburst galaxies make them interesting sources of high energy radiation. Depending upon the level of turbulence present in their interstellar medium, the bulk of cosmic rays produced inside starburst galaxies may lose most of their energy before escaping, thereby making these sources behave as calorimeters, at least up to some maximum energy. Contrary to previous studies, here we investigate in detail the conditions under which cosmic ray confinement may be effective for electrons and nuclei and we study the implications of cosmic ray confinement in terms of multifrequency emission from starburst nuclei and production of high energy neutrinos. The general predictions are then specialized to three cases of active starbursts, namely M82, NGC253 and Arp220. Both primary and secondary electrons, as well as electron-positron pairs produced by gamma ray absorption inside starburst galaxies are taken into account. Electrons and positrons produced as secondary products of hadronic interactions are found to be responsible for most of the emission of leptonic origin. In particular, synchrotron emission of very high energy secondary electrons produces an extended emission of hard X-rays that represent a very interesting signature of hadronic process in starburst galaxies, potentially accessible to current and future observations in the X-ray band. A careful understanding of both the production and absorption of gamma rays in starburst galaxies is instrumental to the assessment of the role of these astrophysical sources as sources of high energy astrophysical neutrinos.

astro-ph.HE↗

arXiv2015

Temporal properties of bright BGO GRBs detected by Fermi

We present results of an analysis of a sample of bright Gamma-Ray Bursts (GRBs) detected by Fermi-GBM up to more than 1 MeV, which were collected during six years of Fermi operations. In particular, we focus on the GRB durations over several energy bands of the prompt emission of a subsample of bright GRBs detected up to 10 MeV by GBM and, when possible, up to 1 GeV by Fermi-LAT, thus expanding the Duration-Energy relationship in GRB light curves to high energies for the first time. We find that the relationship for these energetic GRBs is flatter than reported for other samples, suggesting that the high- and low-energy emission mechanisms are closely related.

astro-ph.HE↗