Cosmic rays from multiwavelength observations of the Galactic diffuse emission

Cosmic rays (CRs) generate diffuse emission while interacting with the Galactic magnetic field (B-field), the interstellar gas and the radiation field. This diffuse emission extends from radio, microwaves, through X-rays, to high-energy gamma rays. Diffuse emission has considerably increased the interest of the astrophysical community due to recent detailed observations by Planck, Fermi-LAT, and by very-high-energy Cherenkov telescopes. Observations of this emission and comparison with detailed predictions are used to gain information on the properties of CRs, such as their density, spectra, distribution and propagation in the Galaxy. Unfortunately disentangling and characterizing this diffuse emission strongly depends on uncertainties in the knowledge of unresolved sources, gas, radiation fields, and B-fields, other than CRs throughout the Galaxy. We report here on recent multiwavelength observations of the Galactic diffuse emission, and discuss the diffuse emission produced by CRs and its model uncertainties, comparing observations with predictions. The importance for forthcoming telescopes, especially for the Square Kilometre Array Telescope (SKA) and the Cherenkov Telescope Array (CTA), and for future missions at MeV energies is also addressed.Comment: Proceedings of the TAUP 2015 - XIV International Conference on Topics in Astroparticle and Underground Physics, September 2015 Torino, Ital

Galactic synchrotron emission with cosmic ray propagation models

Cosmic-ray (CR) leptons produce radio synchrotron radiation by gyrating in interstellar magnetic fields (B-field). Details of B-fields, CR electron distributions and propagation are still uncertain. We present developments in our modelling of Galactic radio emission with the GALPROP code. It now includes calculations of radio polarization, absorption, and free-free emission. Total and polarized synchrotron emission are investigated in the context of physical model of CR propagation. Predictions are compared with radio data from 22 MHz to 2.3 GHz, and Wilkinson Microwave Anisotropy Probe data at 23 GHz. Spatial and spectral effects on the synchrotron modelling with different CR distribution, propagation halo size and CR propagation models are presented. We find that all-sky total intensity and polarization maps are reasonably reproduced by including an anisotropic B-field, with comparable intensity to the regular one defined by rotation measures. A halo size of 10 kpc, which is larger than usually assumed, is favoured. This work provides a basis for further studies on foreground emission with the Planck satellite and on interstellar gamma-ray emission with Fermi-Large Area Telescope.Comment: 19 pages, 15 figures, 2 tables. Published in MNRAS. Minor changes to reflect the published versio

Solar gamma rays and modulation of cosmic rays in the inner heliosphere

The first evidence of the gamma-ray emission from the quiescent Sun was found in the archival EGRET data that was later confirmed by Fermi-LAT observations with high significance. This emission is produced by Galactic cosmic rays (CRs) penetrating the inner heliosphere and inter- acting with the solar atmosphere and optical photons. The solar emission is characterized by two spatially and spectrally distinct components: (i) disk emission due to the CR cascades in the solar atmosphere, and (ii) spatially extended inverse Compton (IC) emission due to the CR electrons scattering off of solar photons. The intensity of both components associated with Galactic CRs anti-correlate with the level of the solar activity being the brightest during solar minimum. In this paper we discuss updates of the models of the IC component of the emission based on CR measurements made at different levels of solar activity, and we make predictions for e- ASTROGAM and AMEGO, proposed low-energy gamma-ray missions.Comment: 7 pages, 3 figures, Proceedings of the 35th International Cosmic Ray Conference, ICRC201

Fermi-LAT Observation of Quiet Solar Emission

The Large Area Telescope (LAT) on board Fermi has detected high-energy gamma rays from the quiet Sun produced by interactions of cosmic-ray nucleons with the solar surface and cosmic-ray electrons with solar photons in the heliosphere. Such observations provide a probe of the extreme conditions near the solar atmosphere and photosphere and permit the study of the modulation of cosmic rays over the inner heliosphere. For the first year of Fermi observations the solar modulation was at its minimum corresponding to a maximum cosmic-ray flux and, hence, maximum gamma-ray emission from the Sun. We discuss the study of the quiescent solar emission, including spectral analysis of its two components, disk and inverse Compton, using the first-year data of the mission and models using the electron spectrum measured by Fermi.Comment: 2009 Fermi Symposium; eConf Proceedings C09112

Testing Cosmic-Ray Propagation Scenarios with AMS-02 and Voyager Data

AMS-02 on board the ISS provides precise measurements of Cosmic Rays (CR) near Earth, while Voyager measures CR in the local interstellar medium, beyond the effects of solar modulation. Based on these data, we test and revise various CR propagation scenarios under standard assumptions: pure diffusion, diffusion with convection, diffusion with reacceleration, and diffusion with reacceleration and convection. We report on the scenarios' performance against CR measurements, aiming to limit the number of model parameters as much as possible. For each scenario we find parameters that are able to reproduce Voyager and AMS-02 data for the entire energy band for all the CR species tested. Above several GV we observe a similar injection spectral index for He and C, with He harder than H. Some scenarios previously disfavored are now reconsidered. For example, contrary to usual assumptions, we find that the pure diffusion scenario does not need an upturn in the diffusion coefficient at low energy, while it needs the same number of low-energy breaks in the injection spectrum as diffusive-reacceleration scenarios. We show that scenarios differ in modeled spectra of one order of magnitude for positrons at around 1 GeV and of a factor of 2 for antiprotons at several GV. The force-field approximation describes well the AMS-02 and Voyager spectra analyzed, except antiprotons. We confirm the excess around 10 GeV in the antiproton spectrum for all scenarios. Also, for all scenarios, the resulting solar modulation should be stronger for positrons than for nuclei, with reacceleration models requiring much larger modulation.Comment: Accepted to be published in Ap