The interactions of cosmic rays with the solar atmosphere produce secondary particles which can reach the Earth. In this work, we present a comprehensive calculation of the yields of secondary ...particles such as gamma-rays, electrons, positrons, neutrons, and neutrinos performed with the fluka code. We also estimate the intensity at the Sun and the fluxes at the Earth of these secondary particles by folding their yields with the intensities of cosmic rays impinging on the solar surface. The results are sensitive to the assumptions on the magnetic field nearby the Sun and to the cosmic-ray transport in the magnetic field in the inner Solar System.
ABSTRACT
According to radiative models, radio galaxies and quasars are predicted to produce gamma rays from the earliest stages of their evolution. Exploring their high-energy emission is crucial for ...providing information on the most energetic processes, the origin and the structure of the newly born radio jets. Taking advantage of more than 11 yr of Fermi-LAT data, we investigate the gamma-ray emission of 162 young radio sources (103 galaxies and 59 quasars), the largest sample of young radio sources used so far for such a gamma-ray study. We separately analyse each source and perform the first stacking analysis of this class of sources to investigate the gamma-ray emission of the undetected sources. We detect significant gamma-ray emission from 11 young radio sources, 4 galaxies, and 7 quasars, including the discovery of significant gamma-ray emission from the compact radio galaxy PKS 1007+142 (z = 0.213). The cumulative signal of below-threshold young radio sources is not significantly detected. However, it is about one order of magnitude lower than those derived from the individual sources, providing stringent upper limits on the gamma-ray emission from young radio galaxies (Fγ < 4.6 × 10−11 ph cm−2 s−1) and quasars (Fγ < 10.1 × 10−11 ph cm−2 s−1), and enabling a comparison with the models proposed. With this analysis of more than a decade of Fermi-LAT observations, we can conclude that while individual young radio sources can be bright gamma-ray emitters, the collective gamma-ray emission of this class of sources is not bright enough to be detected by Fermi-LAT.
Dark matter particles from the galactic halo can be gravitationally trapped in the solar core or in external orbits. The enhanced density of dark matter particles either in the solar core or in ...external orbits can result in the annihilation of these particles producing gamma rays via long-lived intermediate states or directly outside the Sun, respectively. These processes would yield characteristic features in the energy spectrum of the subsequent gamma rays, i.e., a boxlike or linelike shaped feature, respectively. We have performed a dedicated analysis using a 10-year sample of gamma-ray events from the Sun collected by the Fermi Large Area Telescope searching for spectral features in the energy spectrum as a signature of dark matter annihilation. In the scenario of gamma-ray production via long-lived mediators, we have also evaluated the dark matter-nucleon spin-dependent and spin-independent scattering cross section constraints from the flux limits in a dark matter mass range from 3 GeV/c2 up to about 1.8 TeV /c2. In the mass range up to about 150 GeV/c2, the limits are in the range 10−46 – 10−45 cm2 for the spin-dependent scattering and in the range 10−48 – 10−47 cm2 for the spin-independent case. The range of variation depends on the decay length of the mediator.
The fourth catalog of active galactic nuclei (AGNs) detected by the Fermi Gamma-ray Space Telescope Large Area Telescope (4LAC) between 2008 August 4 and 2016 August 2 contains objects located at ...high Galactic latitudes ( ). It includes 85% more sources than the previous 3LAC catalog based on 4 yr of data. AGNs represent at least 79% of the high-latitude sources in the fourth Fermi-Large Area Telescope Source Catalog (4FGL), which covers the energy range from 50 MeV to 1 TeV. In addition, gamma-ray AGNs are found at low Galactic latitudes. Most of the 4LAC AGNs are blazars (98%), while the remainder are other types of AGNs. The blazar population consists of 24% Flat Spectrum Radio Quasars (FSRQs), 38% BL Lac-type objects, and 38% blazar candidates of unknown types (BCUs). On average, FSRQs display softer spectra and stronger variability in the gamma-ray band than BL Lacs do, confirming previous findings. All AGNs detected by ground-based atmospheric Cerenkov telescopes are also found in the 4LAC.
We use 7 years of electron and positron Fermi-LAT data to search for a possible excess in the direction of the Sun in the energy range from 42 GeV to 2 TeV. In the absence of a positive signal we ...derive flux upper limits which we use to constrain two different dark matter (DM) models producing e+e− fluxes from the Sun. In the first case we consider DM model being captured by the Sun due to elastic scattering and annihilation into e+e− pairs via a long-lived light mediator that can escape the Sun. In the second case we consider instead a model where DM density is enhanced around the Sun through inelastic scattering and the DM annihilates directly into e+e− pairs. In both cases we perform an optimal analysis, searching specifically for the energy spectrum expected in each case, i.e., a boxlike shaped and linelike shaped spectrum respectively. No significant signal is found and we can place limits on the spin-independent cross section in the range from 10−46 cm2 to 10−44 cm2 and on the spin-dependent cross section in the range from 10−43 cm2 to 10−41 cm2. In the case of inelastic scattering the limits on the cross section are in the range from 10−43 cm2 to 10−41 cm2. The limits depend on the life time of the mediator (elastic case) and on the mass splitting value (inelastic case), as well as on the assumptions made for the size of the deflections of electrons and positrons in the interplanetary magnetic field.
The Large Area Telescope onboard the Fermi Gamma-ray Space Telescope has collected the largest ever sample of high-energy cosmic-ray electron and positron events. Possible features in their energy ...spectrum could be a signature of the presence of nearby astrophysical sources or of more exotic sources, such as annihilation or decay of dark matter (DM) particles in the Galaxy. In this paper, for the first time we search for a deltalike line feature in the cosmic-ray electron and positron spectrum. We also search for a possible feature originating from DM particles annihilating into electron-positron pairs. Both searches yield negative results, but we are able to set constraints on the line intensity and on the velocity-averaged DM annihilation cross section. Our limits extend up to DM masses of 1.7 TeV/c2 and exclude the thermal value of the annihilation cross section for DM lighter than 150 GeV/c2.
We present a measurement of the cosmic-ray electron+positron spectrum between 7 GeV and 2 TeV performed with almost seven years of data collected with the Fermi Large Area Telescope. We find that the ...spectrum is well fit by a broken power law with a break energy at about 50 GeV. Above 50 GeV, the spectrum is well described by a single power law with a spectral index of 3.07±0.02(stat+syst)±0.04(energy measurement). An exponential cutoff lower than 1.8 TeV is excluded at 95% CL.
Abstract
Current measurements of cosmic-ray fluxes have reached
unprecedented accuracy thanks to the new generation of experiments,
and in particular the AMS-02 mission. At the same time, significant
...progress has been made in the propagation models of galactic cosmic
rays. These models include several propagation parameters, which are
usually inferred from the ratios of secondary to primary cosmic
rays, and which depend on the cross sections describing the
collisions among the various species of cosmic-ray nuclei. At
present, our knowledge of these cross sections in the energy range
where cosmic-ray interactions occur is limited, and this is a source
of uncertainties in the predicted fluxes of secondary cosmic-ray
nuclei. In this work we study the impact of the cross section
uncertainties on the fluxes of light secondary nuclei (Li, Be, B)
using a preliminary version of the upcoming DRAGON2 code. We
first present a detailed comparison of the secondary fluxes computed
by implementing different parameterizations for the network of
spallation cross sections. Then, we discuss the use of
secondary-over-secondary cosmic-ray flux ratios as a tool to improve
the consistency of cross sections parameterizations and give insight
of the overall uncertainties coming from the cross sections
parametrisations. We show that the uncertainties inferred from the
cross section data are enough to explain the discrepancies in the Be
and Li fluxes with respect to the AMS-02 data, with no need of a
primary component in their spectra. In addition, we show that the
fluxes of B, Be and Li can be simultaneously reproduced by rescaling
their cross sections within the experimental uncertainty. Finally,
we also revisit the diffusive estimation of the halo size, obtaining
good agreement with previous works and a best fit value of
6.8 ± 1 kpc from the most updated cross sections
parametrisations.
Abstract
Recent cosmic-ray measurements are challenging our models of propagation in the Galaxy. A good characterization of the secondary cosmic rays (B, Be, Li and sub-iron species) is crucial to ...constrain these models and exploit the precision of modern CR experiments. In this work, a Markov chain Monte Carlo analysis has been implemented to fit the experimental flux ratios between B, Be and Li and their flux ratios to the primary cosmic-ray nuclei C and O. We have fitted the data using two different parametrizations for the spallation cross sections. The uncertainties in the evaluation of the spectra of these secondary cosmic rays, due to spallation cross sections, have been taken into account by introducing scale factors as nuisance parameters in the fits, assuming that this uncertainty is mostly due to the normalization of the cross sections parametrizations. We have also tested two different formulations for the diffusion coefficient, which differ in the origin of the high energy hardening (∼ 200 GeV/n) of cosmic rays. Additionally, two different approaches are used to scale the cross sections, one based on a combined analysis of all the species (“combined” analysis) and the other reproducing the high energy spectra of the secondary-to-secondary flux ratios of Be/B, Li/B, Li/Be (“scaled” analysis). This allows us to make a better comparison between the propagation parameters inferred from the cross sections parametrizations tested in this work. This novel analysis has been successfully implemented using the numerical code DRAGON2 dedicated to cosmic-ray propagation to reproduce the cosmic-ray nuclei data up to Z=14 from the AMS-02 experiment.
In general, it is found that the ratios of Li favor a harder spectral index of the diffusion coefficient, but compatible with the other ratios inside the observed 2σ uncertainties. In addition, it is shown that, including these scale factors, the secondary-to-primary flux ratios can be simultaneously reproduced, obtaining that the scale factor associated to the cross sections of boron production is the lowest one, whereas that associated to Li production is the largest one.
Abstract
All known small solar system bodies have diameters between a few meters and a few thousands of kilometers. Based on the collisional evolution of solar system bodies, a larger number of ...asteroids with diameters down to ∼2 m is thought to exist. As all solar system bodies, small bodies can be passive sources of high-energy gamma-rays, produced by the interaction of energetic cosmic rays impinging on their surfaces. Since the majority of known asteroids are in orbits between Mars and Jupiter (in a region known as the Main Belt), we expect them to produce a diffuse emission close to the ecliptic plane. In this work, we have studied the gamma-ray emission coming from the ecliptic using the data collected by the Large Area Telescope (LAT) onboard the Fermi satellite. We have fit the results with simulations of the gamma-ray intensity at the source level (calculated with the software
FLUKA
) to constrain the small solar system bodies population. Finally, we have proposed a model describing the distribution of asteroid sizes and we have used the LAT data to constrain the gamma-ray emission expected from this model and, in turn, on the model itself.
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