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

StellarICS: Inverse Compton Emission from the Quiet Sun and Stars from keV to TeV

The study of the quiet Sun in gamma rays started over a decade ago, and rapidly gained a wide interest. Gamma rays from the quiet Sun are produced by Cosmic Rays (CRs) interacting with its surface (disk component) and with its photon field (spatially extended inverse-Compton component, IC). The latter component is maximum close to the Sun and it is above the background even at large angular distances, extending over the whole sky. First detected with EGRET, it is studied now with Fermi-LAT with high statistical significance. Observations of the IC component allow us to obtain information on CR electrons and positrons close to the Sun and in the heliosphere for the various periods of solar activity and polarity. They allow to learn about CR interactions and propagation close to stars, in the heliosphere and on the solar surface, and to understand the Sun itself, its environment, and its activity. Analyses of solar observations are usually model-driven. Hence advances in model calculations and constraints from precise CR measurements are timely and needed. Here we present our StellarICS code to compute the gamma-ray IC emission from the Sun and also from single stars. The code is publicly available and it is extensively used by the scientific community to analyze Fermi-LAT data. It has been used by the Fermi-LAT collaboration to produce the solar models released with the FSSC Fermi Tools. Our modeling provides the basis for analyzing and interpreting high-energy data of the Sun and of stars. After presenting examples of updated solar IC models in the Fermi-LAT energy range that account for the various CR measurements, we extend the models to keV, MeV, and TeV energies for predictions for future possible telescopes such as AMEGO, GECCO, e-ASTROGAM, HAWC, LHAASO, SWGO, and present X-ray telescopes. We also present predictions for some of the closest and most luminous stars.Comment: Updated to reflect the published version. 17 pages, 9 figure