Context.
The study of nonthermal processes such as synchrotron emission, inverse Compton scattering, bremsstrahlung, and pion production is crucial to understanding the properties of the Galactic ...cosmic-ray population, to shed light on their origin and confinement mechanisms, and to assess the significance of exotic signals possibly associated to new physics.
Aims.
We present a public code called
HERMES
which is designed generate sky maps associated to a variety of multi-messenger and multi-wavelength radiative processes, spanning from the radio domain all the way up to high-energy gamma-ray and neutrino production.
Methods.
We describe the physical processes under consideration, the code concept and structure, and the user interface, with particular focus on the
python
-based interactive mode. In particular, present the modular and flexible design that allows the user to easily extend the numerical package according to their needs.
Results.
In order to demonstrate the capabilities of the code, we describe the details of a comprehensive set of sky maps and spectra associated to all physical processes included in the code. We comment in particular on the radio, gamma-ray, and neutrino maps, and mention the possibility of studying signals stemming from dark matter annihilation.
Conclusions.
HERMES
can be successfully applied to constrain the properties of the Galactic cosmic-ray population, improve our understanding of the diffuse Galactic radio, gamma-ray, and neutrino emission, and search for signals associated to particle dark matter annihilation or decay.
Abstract
Cosmic rays (CRs) govern the energetics of present-day galaxies and might have also played a pivotal role during the Epoch of Reionization. In particular, energy deposition by low-energy (E ...≲ 10 MeV) CRs, accelerated by the first supernovae, might have heated and ionized the neutral intergalactic medium (IGM) well before (z ≈ 20) it was reionized, significantly adding to the similar effect by X-rays or dark matter annihilations. Using a simple, but physically motivated reionization model, and a thorough implementation of CR energy losses, we show that CRs contribute negligibly to IGM ionization, but heat it substantially, raising its temperature by ΔT = 10–200 K by z = 10, depending on the CR injection spectrum. Whether this IGM pre-heating is uniform or clustered around the first galaxies depends on CR diffusion, which, in turn, is governed by the efficiency of self-confinement due to plasma streaming instabilities that we discuss in detail. This aspect is crucial to interpret future H i 21-cm observations, which can be used to gain unique information on the strength and structure of early intergalactic magnetic fields, and the efficiency of CR acceleration by the first supernovae.
We study the imprint of dark matter (DM) annihilation on the global 21 cm signal from the Dark Ages to Cosmic Reionization. Motivated by recent observations, we focus on three DM candidates: (i) a 10 ...GeV Bino-like neutralino; (ii) a 200 GeV Wino and (iii) a 1 TeV heavier particle annihilating into leptons. For each DM candidate we assume two values for the thermally averaged annihilation cross-section 〈σv〉, the standard thermal value 〈σv〉th = 3 × 10−26 cm3 s−1 and the maximum value allowed by WMAP7 data, 〈σv〉max. We include the enhancement of DM annihilations due to collapsed structures, detailed estimates of energy deposition into the intergalactic medium (IGM), as well realistic prescriptions for astrophysical sources of UV and X-ray radiation. In these models, the additional heat input from DM annihilation suppresses the mean 21 cm brightness temperature offset by δT
b ∼ a few-100 mK. In particular, the very deep δT
b ∼ −150 mK absorption feature at ∼20 z 25 predicted by popular models of the first galaxies is considerably reduced or totally erased by some of the considered DM candidates. Such an enhancement in IGM heating could come from either DM annihilations or a stronger-than-expected astrophysical component (i.e. abundant early X-ray sources). However, we find that the two signatures are not degenerate, since the DM heating is dominated by haloes several orders of magnitude smaller than those hosting galaxies, whose fractional abundance evolves more slowly resulting in a smaller gradient: dδT
b/dν 4 mK MHz−1 in the range ν ∼ 60-80 MHz. The detection of such signals by future radio telescopes would be clear evidence of DM energy injection at high redshifts.
Context.
The Tibet AS
γ
and LHAASO collaborations recently reported the observation of a
γ
-ray diffuse emission with energy up to the PeV level from the Galactic plane.
Aims.
We discuss the ...relevance of non-uniform cosmic-ray transport scenarios and the implications of these results for cosmic-ray physics.
Methods.
We used the
DRAGON
and
HERMES
codes to build high-resolution maps and spectral distributions of that emission for several representative models under the condition that they reproduce a wide set of local cosmic-ray data up to 100 PeV.
Results.
We show that the energy spectra measured by Tibet AS
γ
, LHAASO, ARGO-YBJ, and
Fermi
-LAT in several regions of interest in the sky can all be reasonably described in terms of the emission arising by the Galactic cosmic-ray “sea”. We also show that all our models are compatible with IceTop
γ
-ray upper limits.
Conclusions.
We compare the predictions of conventional and space-dependent transport models with those data sets. Although the
Fermi
-LAT, ARGO-YBJ, and LHAASO preliminary data slightly favor this scenario, due to the still large experimental errors, the poorly known source spectral shape at the highest energies, the potential role of spatial fluctuations in the leptonic component, and a possible larger-than-expected contamination due to unresolved sources, a solid confirmation requires further investigations. We discuss which measurements will be most relevant in order to resolve the remaining degeneracy.
We present results obtained with the updated version of our code medea2, which includes all physical processes necessary to study the energy deposition in the surrounding environment from primary ...photons and fast leptons produced by dark matter (DM) particle decay/annihilation. Such interactions now include also Compton scattering of primary photons off electrons and pair creation of photons on atoms. Our ultimate aim is a thorough study of the impact of DM annihilations on the thermal and ionization history of the high-redshift intergalactic medium (IGM) during the dark ages. In addition, a precise determination of the effects of DM decays/annihilations can help constrain its nature. We present the results for some selected DM candidates: (i) a 10-GeV bino-like neutralino; (ii) a heavy DM candidate of rest mass 1 TeV that pair annihilates into muons; and (iii) a 200-GeV wino-like neutralino with a pair annihilation into W+W− pairs. An interface to darksusy allows us to use the computed annihilation spectra in input for our code and follow the complete secondary cascade. The fractional energy depositions into the IGM depend strongly on the DM particle rest mass: whereas for the 10-GeV particle the absorbed energy fraction, in the redshift range 10 < z < 1000, is ≳50 per cent, higher mass candidates deposit their energy less efficiently (∼1-10 per cent), making their impact on the high-z IGM considerably weaker. Noticeably, our approach allows us to consistently follow the low-energy deposition of the cascade products, which can be of interest for a broad range of applications. Finally, we provide both tabulated results and analytical fits that can be readily implemented in theoretical studies of the effects and detectability of the most popular DM candidates.
We study the development of high-energy (Ein≤ 1 TeV) cascades produced by a primary electron of energy Ein injected into the intergalactic medium (IGM). To this aim we have developed the new code ...medea (Monte Carlo Energy Deposition Analysis) which includes Bremsstrahlung and inverse Compton (IC) processes, along with H/He collisional ionizations and excitations, and electron–electron collisions. The cascade energy partition into heating, excitations and ionizations depends primarily not only on the IGM ionized fraction, xe, but also on redshift, z, due to IC on cosmic microwave background (CMB) photons. While Bremsstrahlung is unimportant under most conditions, IC becomes largely dominant at energies Ein≥ 1 MeV. The main effect of IC at injection energies Ein≤ 100 MeV is a significant boost of the fraction of energy converted into low-energy photons (hν < 10.2 eV) which do not further interact with the IGM. For energies Ein≥ 1 GeV CMB photons are preferentially upscattered within the X-ray spectrum (hν > 104 eV) and can free stream to the observer. Complete tables of the fractional energy depositions as a function of redshift, Ein and ionized fraction are given. Our results can be used in many astrophysical contexts, with an obvious application related to the study of decaying/annihilating dark matter (DM) candidates in the high-z Universe.
Unveiling the nature of cosmic dark matter (DM) is an urgent issue in cosmology. Here we make use of a strategy based on the search for the imprints left on the cosmic microwave background ...temperature and polarization spectra by the energy deposition due to annihilations of the most promising DM candidate, a stable weakly interacting massive particle (WIMP) of mass m
χ = 1-20 GeV. A major improvement with respect to previous similar studies is a detailed treatment of the annihilation cascade and its energy deposition in the cosmic gas. This is vital as this quantity is degenerate with the annihilation cross-section 〈σv〉. The strongest constraints are obtained from Monte Carlo Markov chain analysis of the combined Wilkinson Microwave Anisotropy Probe 7 and South Pole Telescope (SPT) data sets up to max = 3100. If annihilation occurs via the e
+ − e
− channel, a light WIMP can be excluded at the 2σ confidence level as a viable DM candidate in the above mass range. However, if annihilation occurs via μ+ − μ− or τ+ − τ− channel instead, we find that WIMPs with m
χ > 5 GeV might represent a viable cosmological DM candidate.
We compare the results obtained in this work with those obtained adopting an analytical simplified model for the energy deposition process widely used in the literature, and we found that realistic energy deposition descriptions can influence the resulting constraints up to 60 per cent.
Simulating intergalactic quasar scintillation Pallottini, A; Ferrara, A; Evoli, C
Monthly notices of the Royal Astronomical Society,
10/2013, Letnik:
434, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Intergalactic scintillation of distant quasars is sensitive to free electrons and therefore complements Lyα absorption-line experiments probing the neutral intergalactic medium (IGM). We present a ...new scheme to compute IGM refractive scintillation effects on distant sources in combination with adaptive mesh refinement cosmological simulations. First, we validate our model by reproducing the well-known interstellar scintillation (ISS) of Galactic sources. The simulated cosmic density field is then used to infer the statistical properties of intergalactic scintillation. Contrary to previous claims, we find that the scattering measure of the simulated IGM at z < 2 is 〈SMequ〉 = 3.879, i.e. almost 40 times larger than that for the usually assumed smooth IGM. This yields an average modulation index ranging from 0.01 (ν
s
= 5 GHz) up to 0.2 (ν
s
= 50 GHz); above ν
s
30 GHz the IGM contribution dominates over ISS modulation. We compare our model with data from a 0.3 ≤ z ≤ 2 quasar sample observed at νobs = 8.4 GHz. For this high-frequency (10.92 ≤ ν
s
≤ 25.2), high-galactic-latitude sample ISS is negligible, and IGM scintillation can reproduce the observed modulation with a 4 per cent accuracy, without invoking intrinsic source variability. We conclude by discussing the possibility of using IGM scintillation as a tool to pinpoint the presence of intervening high-z groups/clusters along the line of sight, thus making it a probe suitably complementing Sunyaev-Zel'dovich data recently obtained by Planck.
Abstract
The Outreach Cosmic Ray Activities (OCRA) project was created in 2018 within the Italian Istituto Nazionale di Fisica Nucleare (INFN) to offer a platform for all outreach activities focusing ...on cosmic rays within the institute. OCRA now counts 22 of the institute’s divisions all over Italy as members. The project offers activities both for students and teachers. The one activity common to all local groups is the participation in the yearly International Cosmic Day, organized by DESY, inviting high school students to carry out hands-on measurements of the cosmic ray flux and learn about the related physics background. Two students from each division are then selected to participate in the annual OCRA science camp, a three-day full immersion into the life of a physicist. For both teachers and students, the OCRA website https://web.infn.it/OCRA/, offers a series of online laboratories designed both to be used by students individually but also to be offered in the classroom by teachers. A section dedicated to teachers provides ample material to help bring these laboratories to the classroom. The online materials were presented in a course for teachers in spring 2021. In addition to the national efforts, there are also local initiatives of the OCRA member groups: workshops and secondments, science competitions and the development of new detectors for outreach activities offer a multitude of possibilities for students to engage with our researchers and to explore the world of cosmic rays. This article provides an overview on all activities offered by OCRA with a particular focus on the 2022 science camp.
We propose a new method to constrain the warm dark matter (WDM) particle mass, m
χ, based on the counts of multiply imaged, distant supernovae (SN) produced by strong lensing by intervening ...cosmological matter fluctuations. The counts are very sensitive to the WDM particle mass, assumed here to be m
χ = 1, 1.5, 2 keV. We use the analytic approach developed by Das & Ostriker to compute the probability density function of the cold dark matter (CDM) convergence (κ) on the lens plane; such method has been extensively tested against numerical simulations. We have extended this method generalizing it to the WDM case, after testing it against WDM N-body simulations. Using the observed cosmic star formation history, we compute the probability for a distant SN to undergo a strong lensing event in different cosmologies. A minimum observing time of 2 yr (5 yr) is required for a future 100 square degrees survey reaching z ≈ 4 (z ≈ 3) to disentangle at 2σ a WDM (m
χ = 1 keV) model from the standard CDM scenario. Our method is not affected by any astrophysical uncertainty (such as baryonic physics effects), and, in principle, it does not require any particular dedicated survey strategy, as it may come as a byproduct of a future SN survey.
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