Search

We present the results of the most complete ever scan of the parameter space for cosmic ray (CR) injection and propagation. We perform a Bayesian search of the main GALPROP parameters, using the MultiNest nested sampling algorithm, augmented by the BAMBI neural network machine learning package. This is the first such study to separate out low-mass isotopes ($p$, $\bar p$ and He) from the usual light elements (Be, B, C, N, O). We find that the propagation parameters that best fit $p$, $\bar p$, He data are significantly different from those that fit light elements, including the B/C and $^{10}$Be/$^9$Be secondary-to-primary ratios normally used to calibrate propagation parameters. This suggests each set of species is probing a very different interstellar medium, and that the standard approach of calibrating propagation parameters using B/C can lead to incorrect results. We present posterior distributions and best fit parameters for propagation of both sets of nuclei, as well as for the injection abundances of elements from H to Si. The input GALDEF files with these new parameters will be included in an upcoming public GALPROP update., Comment: 20 pages, 10 figures, 5 tables. v2 accepted for publication in ApJ

We review numerical methods for simulations of cosmic ray (CR) propagation on galactic and larger scales. We present the development of algorithms designed for phenomenological and self-consistent models of CR propagation in kinetic description based on numerical solutions of the Fokker-Planck equation. The phenomenological models assume a stationary structure of the galactic interstellar medium and incorporate diffusion of particles in physical and momentum space together with advection, spallation, production of secondaries and various radiation mechanisms. The self-consistent propagation models of CRs include the dynamical coupling of the CR population to the thermal plasma. The CR transport equation is discretized and solved numerically together with the set of magneto-hydrodynamic (MHD) equations in various approaches treating the CR population as a separate relativistic fluid within the two-fluid approach or as a spectrally resolved population of particles evolving in physical and momentum space. The relevant processes incorporated in self-consistent models include advection, diffusion and streaming well as adiabatic compression and several radiative loss mechanisms. We discuss applications of the numerical models for the interpretation of CR data collected by various instruments. We present example models of astrophysical processes influencing galactic evolution such as galactic winds, the amplification of large-scale magnetic fields and instabilities of the interstellar medium., Comment: 99 pages, 13 figures, to be published in the Living Reviews of Computational Astrophysics

The $\gamma$-ray emission from stars is induced by the interaction of cosmic rays with stellar atmospheres and photon fields. This emission is expected to come in two components: a stellar disk emission, where $\gamma$-rays are mainly produced in atmospheric showers generated by hadronic cosmic rays, and an extended halo emission, where the high density of soft photons in the surroundings of stars create a suitable environment for $\gamma$-ray production via inverse Compton (IC) scattering by cosmic-ray electrons. Besides the Sun, no other disk or halo from single stars has ever been detected in $\gamma$-rays. However, by assuming a cosmic-ray spectrum similar to that observed on Earth, the predicted $\gamma$-ray emission of super-luminous stars, like e.g. Betelgeuse and Rigel, could be high enough to be detected by the Fermi Large Area Telescope (LAT) after its first decade of operations. In this work, we use 12 years of Fermi-LAT observations along with IC models to study 9 super-luminous nearby stars, both individually and via stacking analysis. Our results show no significant $\gamma$-ray emission, but allow us to restrict the stellar $\gamma$-ray fluxes to be on average $, Comment: 8 pages, 4 figures

The halo of the Milky Way provides a laboratory to study the properties of the shocked hot gas that is predicted by models of galaxy formation. There is observational evidence of energy injection into the halo from past activity in the nucleus of the Milky Way; however, the origin of this energy (star formation or supermassive-black-hole activity) is uncertain, and the causal connection between nuclear structures and large-scale features has not been established unequivocally. Here we report soft-X-ray-emitting bubbles that extend approximately 14 kiloparsecs above and below the Galactic centre and include a structure in the southern sky analogous to the North Polar Spur. The sharp boundaries of these bubbles trace collisionless and non-radiative shocks, and corroborate the idea that the bubbles are not a remnant of a local supernova but part of a vast Galaxy-scale structure closely related to features seen in gamma-rays. Large energy injections from the Galactic centre are the most likely cause of both the {\gamma}-ray and X-ray bubbles. The latter have an estimated energy of around 10$^{56}$ erg, which is sufficient to perturb the structure, energy content and chemical enrichment of the circumgalactic medium of the Milky Way., Comment: Author's version. 17 pages, 5 figures, Published in Nature 2020, Vol 588

Information on cosmic-ray (CR) composition comes from direct CR measurements while their distribution in the Galaxy is evaluated from observations of their associated diffuse emission in the range from radio to gamma rays. Even though the main interaction processes are identified, more and more precise observations provide an opportunity to study more subtle effects and pose a challenge to the propagation models. GALPROP is a sophisticated CR propagation code that is being developed for about 20 years. It provides a unified framework for interpretations of data from many different types of experiments. It is used for a description of direct CR measurements and associated interstellar emissions (radio to gamma rays), thereby providing important information about CR injection and propagation in the interstellar medium. By accounting for all relevant observables at a time, the GALPROP code brings together theoretical predictions, interpretation of the most recent observations, and helps to reveal the signatures of new phenomena. In this paper we review latest applications of GALPROP and address ongoing and near future improvements. We are discussing effects of different propagation models, and of the transition from cylindrically symmetrical models to a proper 3D description of the components of the interstellar medium and the source distribution., Comment: 6 pages, 5 figures. Proceedings of the Conference "Cosmic Ray Origin - beyond the standard models", San Vito di Cadore (Dolomites, Italy) 18-24 September 2016. Accepted version to be published in Nuclear and Particle Physics (Elsevier)

Some common ideas which are often taken as known or self-evident are put in question: the detection (or not) of the gamma-ray ‘pion bump’, the importance of CR diffusive reacceleration, and the energy range of extragalactic cosmic rays.

The high energy gamma-ray emission from the Sun is due to the interactions of cosmic ray (CR) protons and electrons with matter and photons in the solar environment. Such interactions lead to two component gamma-ray emission: a disk-like emission due to the nuclear interactions of CR protons and nuclei in the solar atmosphere and a space extended emission due to the inverse Compton (IC) scattering of CR electrons off solar photons in the whole heliosphere. The observation of these two solar emission components may give useful information about the evolution of the solar cycle by probing two different CR components (proton and electrons) in regions not directly accessible by direct observations. We present the results of the observations of the Sun with Fermi-LAT in the first 7 years on orbit, with the exception of the flaring periods. Significantly large photon statistics and improved processing performance allow us to explore both components of the emission in greater details and perform better comparisons of data with current models of the IC component. This allows us to probe CR electrons in the inner heliosphere which is not possible by other methods. Moreover, the longer period of observations allows us to study the variations of the emission between the maximum and the minimum of the solar cycle.

International audience; We identify the scientific prospects for studying low-energy cosmic rays, the interstellar medium, and the associated gamma-ray emissions with a next-generation wide-field telescope from 200 keV to ~10 GeV. With improved angular resolution and more than an order of magnitude better sensitivity than previous instruments, the All-sky Medium Energy Gamma-ray Observatory (AMEGO) would allow for the first time to study in detail the low-energy cosmic rays, which play a fundamental role in the formation of stars and in the dynamics of the interstellar medium. It would allow mapping the cosmic-ray distribution in order to understand their propagation in the Galaxy.We discuss the importance of having such a telescope, and we present the predictions for the gamma-ray continuum both at large scale and in individual clouds, and for de-excitation nuclear lines. This paper is based on the Astro2020: Decadal Survey on Astronomy and Astrophysics, science white papers, no. 151; Orlando E. et al. Bulletin of the American Astronomical Society, Vol. 51, Issue 3, id. 151 (2019) ‘Cosmic Rays and Interstellar Medium with Gamma-Ray Observations at MeV Energies’, where more details can be found.

A critical review of the standard paradigm for the origin of Galactic cosmic rays is presented. Recent measurements of local and far-away cosmic rays reveal unexpected behaviours, which challenge the commonly accepted scenario. These recent findings are discussed, together with long-standing open issues. Despite the progress made thanks to ever-improving observational techniques and theoretical investigations, at present our understanding of the origin and of the behaviour of cosmic rays remains incomplete. We believe it is still unclear whether a modification of the standard paradigm, or rather a radical change of the paradigm itself is needed in order to interpret all the available data on cosmic rays within a self-consistent scenario., Review based on a series of discussions that took place at the "The High-Energy Universe: Gamma-Ray, Neutrino, and Cosmic-ray Astronomy" MIAPP workshop in 2018

This review summarizes INTEGRAL results on two topics: the electron-positron annihilation line and X-ray & Gamma-ray diffuse emission of the Milky Way. The electron-positron annihilation line at 511 keV is the most prominent spectral feature in the gamma-ray spectrum of the Milky Way. From the observational perspective, INTEGRAL has already provided constraints on the total flux, morphology of the annihilation line distribution, the spectral shape of the line and the strength of the three-photon annihilation continuum. In particular, the most salient morphological feature in the all-sky map of the annihilation emission based on INTEGRAL data is the so-called ”Bulge” component, with the characteristic size of ∼ 6 − 10 ∘ and the positrons’ annihilation rate of ∼ 10 43 s − 1 . A more extended ”Disc” component is also present, although its total luminosity is model dependent. The brightness of the Bulge component compared to the Disc is in contrast with other multi-wavelength images of the Milky Way. The annihilation spectrum consists of a line centered at 511 keV and the ortho-positronium continuum. The strength of the latter indicates that the majority of annihilations go via the positronium formation channel. The shape of the annihilation spectrum is consistent with the assumption that most of the positrons annihilate in a warm and partly ionized medium, although more complicated scenarios are also possible. From the theoretical point of view, a successful model should answer three main questions: (i) physical mechanism(s) responsible for production of positrons, (ii) positrons spatial migration (if any) from the production sites, and (iii) physics of annihilation. Remarkably, despite significant progress provided by INTEGRAL in the characterization of the Milky Way annihilation emission, the origin of positrons remains an open question. The essence of the problem is the abundance of positron production channels and the uncertainty in the distance positrons can travel before annihilation. The spectral-imaging mapping of the Milky Way by INTEGRAL provides important constraints on the nature of the Galactic diffuse continuum hard X-rays and soft gamma-rays in the 20 keV – 2 MeV band. Below ~ 60 keV, numerous unresolved objects (accreting white dwarfs) dominate the flux, but their contribution fades away at higher energies. Models of cosmic-ray induced emission suggest that the dominant diffuse component above ~ 60 keV (excluding annihilation emission) is inverse Compton scattering from GeV electrons on interstellar radiation fields. Non-thermal bremsstrahlung contributes at a lower level. These models are consistent with the continuum spectrum observed by INTEGRAL and COMPTEL.

We investigate the impact of the recently published ISRF model of the Milky Way by Popescu et al. on the CR electrons and positrons in the context of cosmic-ray transport modelling. We also study predictions for diffuse Galactic gamma radiation and underline the importance of the increased ISRF intensities.We use the PICARD code for solving the CR transport equation to obtain predictions based on Galactic cosmic-ray electron fluxes. We show that the new ISRF yields gamma-ray intensity increases, most particular at the Galactic Center and in the Galactic Plane. The impact is largest at energies around 220 GeV., Comment: 20 pages, 15 figures

Context. The space based γ-ray observatory INTEGRAL of the European Space Agency (ESA) includes the spectrometer instrument “SPI”. This is a coded mask telescope featuring a 19-element Germanium detector array for high-resolution γ-ray spectroscopy, encapsulated in a scintillation detector assembly that provides a veto for background from charged particles. In space, cosmic rays irradiate spacecraft and instruments, which, in spite of the vetoing detectors, results in a large instrumental background from activation of those materials, and leads to deterioration of the charge collection properties of the Ge detectors.Aim. We aim to determine the measurement characteristics of our detectors and their evolution with time, that is, their spectral response and instrumental background. These incur systematic variations in the SPI signal from celestial photons, hence their determination from a broad empirical database enables a reduction of underlying systematics in data analysis. For this, we explore compromises balancing temporal and spectral resolution within statistical limitations. Our goal is to enable modelling of background applicable to spectroscopic studies of the sky, accounting separately for changes of the spectral response and of instrumental background.Methods. We use 13.5 years of INTEGRAL/SPI data, which consist of spectra for each detector and for each pointing of the satellite. Spectral fits to each such spectrum, with independent but coherent treatment of continuum and line backgrounds, provides us with details about separated background components. From the strongest background lines, we first determine how the spectral response changes with time. Applying symmetry and long-term stability tests, we eliminate degeneracies and reduce statistical fluctuations of background parameters, with the aim of providing a self-consistent description of the spectral response for each individual detector. Accounting for this, we then determine how the instrumental background components change in intensities and other characteristics, most-importantly their relative distribution among detectors.Results. Spectral resolution of Ge detectors in space degrades with time, up to 15% within half a year, consistently for all detectors, and across the SPI energy range. Semi-annual annealing operations recover these losses, yet there is a small long-term degradation. The intensity of instrumental background varies anti-correlated to solar activity, in general. There are significant differences among different lines and with respect to continuum. Background lines are found to have a characteristic, well-defined and long-term consistent intensity ratio among detectors. We use this to categorise lines in groups of similar behaviour. The dataset of spectral-response and background parameters as fitted across the INTEGRAL mission allows studies of SPI spectral response and background behaviour in a broad perspective, and efficiently supports precision modelling of instrumental background.

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., 7 pages, 3 figures, Proceedings of the 35th International Cosmic Ray Conference, ICRC2017

We study the impact of possible spiral-arm distributions of Galactic cosmic-ray sources on the flux of various cosmic-ray nuclei throughout our Galaxy. We investigate model cosmic-ray spectra at the nominal position of the sun and at different positions within the Galaxy. The modelling is performed using the recently introduced numerical cosmic ray propagation code \textsc{Picard}. Assuming non-axisymmetric cosmic ray source distributions yields new insights on the behaviour of primary versus secondary nuclei. We find that primary cosmic rays are more strongly confined to the vicinity of the sources, while the distribution of secondary cosmic rays is much more homogeneous compared to the primaries. This leads to stronger spatial variation in secondary to primary ratios when compared to axisymmetric source distribution models. A good fit to the cosmic-ray data at Earth can be accomplished in different spiral-arm models, although leading to decisively different spatial distributions of the cosmic-ray flux. This results in very different cosmic ray anisotropies, where even a good fit to the data becomes possible. Consequently, we advocate directions to seek best fit propagation parameters that take into account the higher complexity introduced by the spiral-arm structure on the cosmic-ray distribution. We specifically investigate whether the flux at Earth is representative for a large fraction of the Galaxy. The variance among possible spiral-arm models allows us to quantify the spatial variation of the cosmic-ray flux within the Galaxy in presence of non-axisymmetric source distributions., 38 pages, 16 figures, accepted for publication in Astroparticle Physics

The Picard code for the numerical solution of the cosmic ray propagation problem is optimised to incorporate the complexity of the 3D structure of our Galaxy down to decaparsec scales. Picard was used to investigate the impact of anisotropic cosmic-ray diffusion on the Galactic cosmic-ray flux distribution. We discuss different magnetic-field models for our Galaxy in the context of a cosmic-ray source distribution aligned with the Galactic spiral arms. With the resulting sets of transport parameters, that can reproduce cosmic-ray observations at Earth for the different magnetic field models, we find restrictions for the spatial diffusion tensor. We show that related variations in the diffusive coupling to the Galactic halo can lead to changes in the cosmic-ray gradients. The most severe changes are found in the Galactic centre where a modification in the magnetic-field topology can change the cosmic-ray proton flux by more than a factor of two.

Cosmic rays (CRs) propagate in the Milky Way and interact with the interstellar medium and magnetic fields. These interactions produce emissions that span the electromagnetic spectrum, and are an invaluable tool for understanding the intensities and spectra of CRs in distant regions, far beyond those probed by direct CR measurements. We present updates on the study of CR properties by combining multi-frequency observations of the interstellar emission and latest CR direct measurements with propagation models., Comment: 8 pages, 4 figures. Proceedings of the 35th International Cosmic Ray Conference, ICRC2017

Recent models for the large-scale Galactic magnetic fields in the literature have been largely constrained by synchrotron emission and Faraday rotation measures. We use three different but representative models to compare their predicted polarized synchrotron and dust emission with that measured by the Planck satellite. We first update these models to match the Planck synchrotron products using a common model for the cosmic-ray leptons. We discuss the impact on this analysis of the ongoing problems of component separation in the Planck microwave bands and of the uncertain cosmic-ray spectrum. In particular, the inferred degree of ordering in the magnetic fields is sensitive to these systematic uncertainties, and we further show the importance of considering the expected variations in the observables in addition to their mean morphology. We then compare the resulting simulated emission to the observed dust polarization and find that the dust predictions do not match the morphology in the Planck data but underpredict the dust polarization away from the plane. We modify one of the models to roughly match both observables at high latitudes by increasing the field ordering in the thin disc near the observer. Though this specific analysis is dependent on the component separation issues, we present the improved model as a proof of concept for how these studies can be advanced in future using complementary information from ongoing and planned observational projects., Comment: 31 pages, 16 figures, updated to match accepted A&A version

We discuss the relation between cosmic-ray induced interstellar gamma-ray and radio emission from our Galaxy, and emphasize the importance of their parallel study. We give an overview of results from Fermi-LAT on the interstellar gamma-ray emission, and then focus on complementary studies of the radio emission from the Galaxy., Proceedings of the 9th Workshop on Science with the New Generation of High Energy Gamma-ray Experiments: From high energy gamma sources to cosmic rays, one century after their discovery (SciNeGHE, 20-22 June 2012, Lecce). Invited talk. Accepted for publication in Nuclear Physics B: Proceedings Supplements

As the next step toward an improved large scale Galactic magnetic field model, we present a simple comparison of polarised synchrotron and thermal dust emission on the Galactic plane. We find that the field configuration in our previous model that reproduces the polarised synchrotron is not compatible with the WMAP 94 GHz polarised emission data. In particular, the high degree of dust polarisation in the outer Galaxy (90deg < l < 270deg) implies that the fields in the dust-emitting regions are more ordered than the average of synchrotron-emitting regions. This new dust information allows us to constrain the spatial mixing of the coherent and random magnetic field components in the outer Galaxy. The inner Galaxy differs in polarisation degree and apparently requires a more complicated scenario than our current model. In the scenario that each interstellar component (including fields and now dust) follows a spiral arm modulation, as observed in external galaxies, the changing degree of ordering of the fields in dust-emitting regions may imply that the dust arms and the field component arms are shifted as a varying function of Galacto-centric radius. We discuss the implications for how the spiral arm compression affects the various components of the magnetised interstellar medium but conclude that improved data such as that expected from the Planck satellite will be required for a thorough analysis., 15 pages, 3 figures, 3 tables, accepted to MNRAS. This research was supported by the Agence Nationale de la Recherche (ANR-08-CEXC-0002-01)

Some recent extensions to the GALPROP cosmic-ray propagation package are described. The enhancements include: an accurate solution option, improved convection formulation, alternative spatial boundary conditions, polarized synchrotron emission, new magnetic field models, updated gamma-ray production cross-sections, free-free radio emission and absorption, primary positrons, additional injection spectral breaks, deuterium production by pp fusion, hadronic energy losses, improved HEALPix skymap format, compatibility with latest HEALPix release, and various bug fixes. The Explanatory Supplement has been extensively updated, including details of these enhancements. A compatible plot package GALPLOT for GALPROP output is also provided, as well as other related software.

We present results obtained from our newly developed Galactic cosmic-ray transport code PICARD, that solves the cosmic-ray transport equation. This code allows for the computation of cosmic-ray spectra and the resulting gamma-ray emission. Relying on contemporary numerical solvers allows for efficient computation of models with deca-parsec resolution. PICARD can handle locally anisotropic spatial diffusion acknowledging a full diffusion tensor. We used this framework to investigate the transition from axisymmetric to spiral-arm cosmic-ray source distributions. Wherever possible we compare model predictions with constraining observables in cosmic-ray astrophysics., 8 pages, 2 figures, presented at the ICRC2015 in Den Haag

We make quantitative estimates of the power supplied to the Galactic cosmic ray population by second-order Fermi acceleration in the interstellar medium, or as it is usually termed in cosmic ray propagation studies, diffusive reacceleration. Using recent results on the local interstellar spectrum from the Voyager missions we show that for parameter values, in particular the Alfv\'en speed, typically used in propagation codes such as Galprop to fit the B/C ratio, the power contributed by diffusive reacceleration is significant and can be of order 50\% of the total Galactic cosmic ray power. The implications for the damping of interstellar turbulence are briefly considered., Comment: Accepted by A&A; discussion of LIS added at suggestions of referee, extra references and minor corrections incorporated

How a galaxy regulates its SNe energy into different interstellar/circumgalactic medium components strongly affects galaxy evolution. Based on the JVLA D-configuration C- (6 GHz) and L-band (1.6 GHz) continuum observations, we perform statistical analysis comparing multi-wavelength properties of the CHANG-ES galaxies. The high-quality JVLA data and edge-on orientation enable us for the first time to include the halo into the energy budget for a complete radio-flux-limited sample. We find tight correlations of $L_{\rm radio}$ with the mid-IR-based SFR. The normalization of our $I_{\rm 1.6GHz}/{\rm W~Hz^{-1}}-{\rm SFR}$ relation is $\sim$2-3 times of those obtained for face-on galaxies, probably a result of enhanced IR extinction at high inclination. We also find tight correlations between $L_{\rm radio}$ and the SNe energy injection rate $\dot{E}_{\rm SN(Ia+CC)}$, indicating the energy loss via synchrotron radio continuum accounts for $\sim0.1\%$ of $\dot{E}_{\rm SN}$, comparable to the energy contained in CR electrons. The integrated C-to-L-band spectral index is $\alpha\sim0.5-1.1$ for non-AGN galaxies, indicating a dominance by the diffuse synchrotron component. The low-scatter $L_{\rm radio}-{\rm SFR}$/$L_{\rm radio}-\dot{E}_{\rm SN (Ia+CC)}$ relationships have super-linear logarithmic slopes at $\sim2~\sigma$ in L-band ($1.132\pm0.067$/$1.175\pm0.102$) while consistent with linear in C-band ($1.057\pm0.075$/$1.100\pm0.123$). The super-linearity could be naturally reproduced with non-calorimeter models for galaxy disks. Using Chandra halo X-ray measurements, we find sub-linear $L_{\rm X}-L_{\rm radio}$ relations. These results indicate that the observed radio halo of a starburst galaxy is close to electron calorimeter, and a galaxy with higher SFR tends to distribute an increased fraction of SNe energy into radio emission (than X-ray)., Comment: 16 pages, 6 figures, 1 table, MNRAS in press

The astrophysical journal / Supplement series 223(2), 26(2016). doi:10.3847/0067-0049/223/2/26, Most of the celestial γ rays detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope originate from the interstellar medium when energetic cosmic rays interact with interstellar nucleons and photons. Conventional point-source and extended-source studies rely on the modeling of this diffuse emission for accurate characterization. Here, we describe the development of the Galactic Interstellar Emission Model (GIEM), which is the standard adopted by the LAT Collaboration and is publicly available. This model is based on a linear combination of maps for interstellar gas column density in Galactocentric annuli and for the inverse-Compton emission produced in the Galaxy. In the GIEM, we also include large-scale structures like Loop I and the Fermi bubbles. The measured gas emissivity spectra confirm that the cosmic-ray proton density decreases with Galactocentric distance beyond 5 kpc from the Galactic Center. The measurements also suggest a softening of the proton spectrum with Galactocentric distance. We observe that the Fermi bubbles have boundaries with a shape similar to a catenary at latitudes below 20° and we observe an enhanced emission toward their base extending in the north and south Galactic directions and located within ~4° of the Galactic Center., Published by Univ. of Chicago Press11033, Chicago, Ill. [u.a.]

The annihilation of positrons in the Galaxy's interstellar medium produces characteristic gamma-rays with a line at 511 keV. This emission has been observed with the spectrometer SPI on INTEGRAL, confirming a puzzling morphology with bright emission from an extended bulge-like region, and faint disk emission. Most plausible sources of positrons are believed to be distributed throughout the disk of the Galaxy. We aim to constrain characteristic spectral shapes for different spatial components in the disk and bulge with the high-resolution gamma-ray spectrometer SPI, based on a new instrumental background method and detailed multi-component sky model fitting. We confirm the detection of the main extended components of characteristic annihilation gamma-ray signatures at 58$\sigma$ significance in the line. The total Galactic line intensity amounts to $(2.7\pm0.3)\times10^{-3}~\mathrm{ph~cm^{-2}~s^{-1}}$ for our assumed spatial model. We derive spectra for the bulge and disk, and a central point-like and at the position of Sgr A*, and discuss spectral differences. The bulge shows a 511 keV line intensity of $(0.96\pm0.07)\times10^{-3}~\mathrm{ph~cm^{-2}~s^{-1}}$ and an ortho-positronium continuum equivalent to a positronium fraction of ($1.08\pm0.03$). The 2D-Gaussian representing the disk has an extent of $60^{+10}_{-5}$ deg in longitude and a latitudinal extent of $10.5^{+2.5}_{-1.5}$ deg; the line intensity is $(1.7\pm0.4)\times10^{-3}~\mathrm{ph~cm^{-2}~s^{-1}}$ with a marginal detection of ortho-positronium and an overall diffuse Galactic continuum of $(5.85\pm1.05)\times10^{-5}~\mathrm{ph~cm^{-2}~s^{-1}~keV^{-1}}$ at 511 keV. The disk shows no flux asymmetry between positive and negative longitudes, although spectral details differ. The flux ratio between bulge and disk is ($0.6\pm0.1$). The central source has an intensity of $(0.8\pm0.2)\times10^{-4}~\mathrm{ph~cm^{-2}~s^{-1}}$., Comment: 16 pages, 29 figures, 10 tables, accepted in A&A

We extend previous work modelling the Galactic magnetic field in the plane using synchrotron emission in total and polarized intensity. In this work, we include a more realistic treatment of the cosmic ray electrons using the galprop propagation code optimized to match the existing high-energy data. This addition reduces the degeneracies in our previous analysis and when combined with an additional observed synchrotron frequency allows us to study the low-energy end of the cosmic ray electron spectrum in a way that has not previously been done. For a pure diffusion propagation, we find a low-energy injection spectrum slightly harder than generally assumed: for J(E) ∝Eα, we find α=−1.34 ± 0.12, implying a very sharp break with the spectrum above a few GeV. This then predicts a synchrotron brightness temperature spectral index, β, on the Galactic plane, that is −2.8 < β < −2.74 below a few GHz and −2.98 < β < −2.91 up to 23 GHz. We find that models including cosmic ray re-acceleration processes appear to be incompatible with the synchrotron data.

We analyze the processes governing cosmic-ray (CR) penetration into molecular clouds and the resulting generation of gamma-ray emission. The density of CRs inside a cloud is depleted at lower energies due to the self-excited MHD turbulence. The depletion depends on the effective gas column density ("size") of the cloud. We consider two different environments where the depletion effect is expected to be observed. For the Central Molecular Zone, the expected range of CR energy depletion is $E\lesssim 10$ GeV, leading to the depletion of gamma-ray flux below $E_\gamma\approx 2$ GeV. This effect can be important for the interpretation of the GeV gamma-ray excess in the Galactic Center, which has been revealed from the standard model of CR propagation (assuming the CR spectrum inside a cloud to be equal to the interstellar spectrum). Furthermore, recent observations of some local molecular clouds suggest the depletion of the gamma-ray emission, indicating possible self-modulation of the penetrating low-energy CRs., Comment: 10 pages, 5 figures, accepted for publication in ApJ

Gamma-ray line emission from the radioactive decay of 26Al reflects nucleosynthesis in massive stars and supernovae. We use INTEGRAL 26Al measurements to characterize the distribution and characteristics of 26Al source regions throughout the Galaxy. We detect the 26Al line from the inner Galaxy at 28\sigma significance. The line appears narrow, and we constrain broadening in the source regions to 5deg.

We have processed the data accumulated with INTEGRAL SPI during 4 years (~ 51 Ms) to study the Galactic ``diffuse'' emission morphology in the 20 keV to 8 MeV energy range. To achieve this objective, we have derived simultaneously an all-sky census of emitting sources and images of the Galactic Ridge (GR) emission. In the central radian, the resolved point source emission amounts to 88%, 91% and 68% of the total emission in the 25-50, 50-100 and 100-300 keV domains respectively. We have compared the GR emission spatial distribution to those obtained from CO and NIR maps, and quantified our results through latitude and longitude profiles. Below 50 keV, the SPI data are better traced by the latter, supporting a stellar origin for this emission. Furthermore, we found that the GR emission spectrum follows a power law with a photon index ~ 1.55 above 50 keV while an additional component is required below this energy. This component shows a cutoff around 30 keV, reinforcing a stellar origin, as proposed by Krivonos et al. (2007). The annihilation diffuse emission component is extracted simultaneously, leading to the determination of the related parameters (positronium flux and fraction). A specific discussion is devoted to the annihilation line distribution since a significant emission is detected over a region as large as ~80 degrees by ~10 degrees potentially associated with the disk or halo surrounding the central regions of our Galaxy., 28 pages, 10 figures. Astrophysical journal (accepted for publication)

In this concluding part of the series of three papers dedicated to the Swift/BAT hard X-ray survey (BXS), we focus on the X-ray spectral analysis and statistical properties of the source sample. Using a dedicated method to extract time-averaged spectra of BAT sources we show that Galactic sources have, generally, softer spectra than extragalactic objects and that Seyfert 2 galaxies are harder than Seyfert 1s. The averaged spectrum of all Seyfert galaxies is consistent with a power-law with photon index of 2.00 (+/-0.07). The cumulative flux-number relation for the extragalactic sources in the 14-170 keV band is best described by a power-law with a slope alpha=1.55 (+/-0.20) and a normalization of 9.6$\pm1.9 \times 10^{-3}$ AGN deg$^{-2}$ (or 396(+/-80) AGN all-sky) above a flux level of 2$\times 10^{-11}$erg cm$^{-2}$ s$^{-1}$ (~0.85 mCrab). The integration of the cumulative flux per unit area indicates that BAT resolves 1-2% of the X-ray background emission in the 14-170 keV band. A sub-sample of 24 extragalactic sources above the 4.5 sigma detection limit is used to study the statistical properties of AGN. This sample comprises local Seyfert galaxies (z=0.026, median value) and ~10% blazars. We find that 55% of the Seyfert galaxies are absorbed by column densities of Log(N_H)>22, but that none is a bona fide Compton-thick. This study shows the capabilities of BAT to probe the hard X-ray sky to the mCrab level.

Cosmic-ray scattering on magnetic turbulence leads to spatial diffusive propagation; if the scattering medium is moving, this will inevitably also cause changes in the momentum of the particles, so-called diffusive reacceleration. This can be described as diffusion in momentum space. Diffusive reacceleration has often been invoked to explain the peak observed in secondary-to-primary ratios at a few GeV, in particular Boron-to-Carbon. This avoids the necessity to postulate an ad-hoc break in the spatial diffusive coefficient, and has become almost a standard in modelling cosmic-ray spectra. However, at the levels invoked, the process implies a significant input of energy from the interstellar medium into cosmic rays, so that in such models interstellar space competes with the usual accelerators like supernova remnants. The questions arise: is reacceleration really occurring at the high level required to explain secondary-to-primary ratios? and are the energy requirements physically plausible? We address this issue using both analytical and numerical models of cosmic-ray propagation., Presented at the ICRC2015 in Den Haag

Observations of the properties of dense molecular clouds are critical in understanding the process of star-formation. One of the most important, but least understood, is the role of the magnetic fields. We discuss the possibility of using high-resolution, high-sensitivity radio observations to measure the in-situ synchrotron radiation from these molecular clouds. If the cosmic-ray (CR) particles penetrate clouds as expected, then we can measure the B-field strength directly using radio data. So far, this signature has never been detected from the collapsing clouds themselves and would be a unique probe of the magnetic field. Dense cores are typically ∼ 0.05 pc in size, corresponding to ∼arcsec at ∼kpc distances, and flux density estimates are ∼ mJy at 1 GHz. They should be detectable, for example with the Square Kilometre Array.

We present the first part of the observations made for the Continuum Halos in Nearby Galaxies, an EVLA Survey (CHANG-ES) project. The aim of the CHANG-ES project is to study and characterize the nature of radio halos, their prevalence as well as their magnetic fields, and the cosmic rays illuminating these fields. This paper reports observations with the compact D configuration of the Karl G. Jansky Very Large Array (VLA) for the sample of 35 nearby edge-on galaxies of CHANG-ES. With the new wide bandwidth capabilities of the VLA, an unprecedented sensitivity was achieved for all polarization products. The beam resolution is an average of 9.6" and 36" with noise levels reaching approximately 6 and 30 microJy per beam for C- and L-bands, respectively (robust weighting). We present intensity maps in these two frequency bands (C and L), with different weightings, as well as spectral index maps, polarization maps, and new measurements of star formation rates (SFRs). The data products described herein are available to the public in the CHANG-ES data release available at www.queensu.ca/changes. We also present evidence of a trend among galaxies with larger halos having higher SFR surface density, and we show, for the first time, a radio continuum image of the median galaxy, taking advantage of the collective signal-to-noise ratio of 30 of our galaxies. This image shows clearly that a typical spiral galaxy is surrounded by a halo of magnetic fields and cosmic rays., Comment: 70 pages, of which 35 pages present the data of each galaxy

The physical processes involved in diffusion of Galactic cosmic rays in the interstellar medium are addressed. We study the possibility that the nonlinear MHD cascade sets the power-law spectrum of turbulence which scatters charged energetic particles. We find that the dissipation of waves due to the resonant interaction with cosmic ray particles may terminate the Kraichnan-type cascade below wavelengths 10^13 cm. The effect of this wave dissipation has been incorporated in the GALPROP numerical propagation code in order to asses the impact on measurable astrophysical data. The energy-dependence of the cosmic-ray diffusion coefficient found in the resulting self-consistent model may explain the peaks in the secondary to primary nuclei ratios observed at about 1 GeV/nucleon., Comment: 15 pages, 20 figures, 1 table, emulateapj.cls; To be published in ApJ 10 May 2006, v.642

We performed a spectroscopic study of the 1809 keV gamma-ray line from 26Al decay in the Galaxy using the SPI imaging spectrometer with its high-resolution Ge detector camera on the INTEGRAL observatory. We analyzed observations of the first two mission years, fitting spectra from all 7130 telescope pointings in narrow energy bins to models of instrumental background and the 26Al sky. Instrumental background is estimated from independent tracers of cosmic-ray activation. The shape of the 26Al signal is compared to the instrumental response to extract the width of the celestial line. We detect the 26Al line at \~16sigma significance. The line is broadened only slightly, if at all; we constrain the width to be below 2.8 keV (FWHM, 2 sigma). The average Doppler velocities of 26Al at the time of its decay in the interstellar medium (decay time~1.04 My) therefore are probably around 100 km/s, in agreement with expectations from Galactic rotation and interstellar turbulence. The flux and spatial distribution of the emission are found consistent with previous observations. The derived amount of 26Al in the Galaxy is 2.8 (+/-0.8) M_solar.

The shape of the γ-ray line from radioactive 26 Al, at 1808.7 keV energy in the frame of the decaying isotope, is determined by its kinematics when it decays, typically 10 6 yr after its ejection into the interstellar medium from its nucleosynthesis source. Three prior measurements of the line width exist: HEAO-C’s 1982 value of (0 + 3) keV FWHM, the GRIS 1996 value of (5.4 ± 1.3) keV FWHM, and the recent RHESSI value of (2.0 ± 0.8) keV FWHM, suggesting either “cold”, “hot”, or “warm” 26 Al in the ISM. We model the line width as expected from Galactic rotation, expanding supernova ejecta, and/or Wolf–Rayet winds, and predict a value below 1 keV (FWHM) with plausible assumptions about 26 Al initial velocities and expansion history. We use this model as an input to a model-fitting approach for INTEGRAL/SPI data analysis in the 1808.7 keV line. Our aim is to detect the signature of Galactic rotation and to constrain the contributions of 26 Al from different regions of the Galaxy to the total emission, such as putting an upper limit on the contribution of local sources.

Recent INTEGRAL observations have confirmed the existence of diffuse sub-MeV radiation from the inner Galaxy. We propose a new explanation for the origin of this diffuse component in terms of electrostatic bremsstrahlung radiation from high-energy electrons. This electrostatic bremsstrahlung interpretation requires a very flat power law energy spectrum of high-energy electrons in the inner Galaxy which is reasonable if many point sources with significant spectral dispersion contribute to the injection of high-energy electrons in the Galaxy. The electrostatic bremsstrahlung interpretation avoids the enormous source power problem that previous explanations by radiation from low-energy electrons have.

The performance of the SPI point-source data analysis system is assessed using a combination of simulations and of observations gathered during the first year of INTEGRAL operations. External error estimates are derived by comparing source positions and fluxes obtained from independent analyses. When the source detection significance provided by the SPIROS imaging reconstruction program increases from ∼10 to ∼100, the errors decrease as the inverse of the detection significance, with values from ∼10 to ∼1 arcmin in positions, and from ∼10 to ∼1 per cent in relative flux. These errors are dominated by Poisson counting noise. Our error estimates are consistent with those provided by the SPIROS program. With higher detection significance, the accuracy is ultimately limited to ∼0.5 arcmin in position and ∼1 per cent in relative flux by other types of errors. In these cases, SPIROS underestimates the true errors as it only takes into account the Poisson counting noise. At the low signal-to-noise ratio end, SPIROS is also too optimistic, and the number of spurious detections is significantly higher than would be expected from statistical noise fluctuations only. The analysis results do not depend significantly on the target off-axis angle, or on the number of pointings considered, provided that this number is larger than ∼15. Realistic source confusion tests are carried out by adding simulated data to the observation of the Crab nebula and pulsar. Reliable flux values can be obtained for sources separated by angles as small as 0.5 deg if their positions are known and kept fixed in the data deconvolution process. However, when SPIROS is searching for best source positions, if two sources are separated by less than ∼2 deg, it may only find a single spurious source located between the real ones (with a flux equal to the sum of the fluxes). Finally, users of the SPIROS program can find a number of important recommendations in the conclusion.

We use the GALPROP model for cosmic-ray propagation to obtain a new estimate of the Galactic component of gamma rays, and show that away from the Galactic plane it gives an accurate prediction of the observed EGRET intensities in the energy range 30 MeV - 50 GeV. On this basis we re-evaluate the extragalactic gamma-ray background. We find that for some energies previous work underestimated the Galactic contribution at high latitudes and hence overestimated the background. Our new background spectrum shows a positive curvature similar to that expected for models of the extragalactic emission based on the blazar population., Comment: Accepted for publication in The Astrophysical Journal; 6 pages, 14 ps-figures, 4 tables emulateapj.sty, natbib.sty, aastex.cls. More details can be found at http://www.gamma.mpe-garching.mpg.de/~aws/aws.html

INTEGRAL's main instruments employ coded apertures to obtain directional information on the incoming radiation. In order to experimentally better determine the imaging capabilities of the spectrometer SPI, the SPI Imaging Test Setup (SPITS) has been built at MPE. It consists of the SPI coded mask and two SPI-identical Ge detectors on an XY-table which allows us to move them to cover the 19 Ge detector positions. The SPI flight model imaging calibration only covered the energy range up to 2.7 MeV and did not include extended emission. SPITS was used to explore the performance of such a coded aperture system - combined with the SPI image analysis software - for higher-energy point sources and extended sources. We find that a 2.4 diameter disk emitting 511 keV emission is reconstructed well. For the high signal-to-noise ratios of laboratory measurements, positions of point sources above 4 MeV could be reconstructed to better than 0.1.

The INTEGRAL Science Data Centre (ISDC) provides the INTEGRAL data and means to analyse them to the scientific community. The ISDC runs a gamma ray burst alert system that provides the position of gamma ray bursts on the sky within seconds to the community. It operates a quick-look analysis of the data within few hours that detects new and unexpected sources as well as it monitors the instruments. The ISDC processes the data through a standard analysis the results of which are provided to the observers together with their data., Comment: 5 pages, 2 figures. Accepted for publication in A&AL (INTEGRAL issue)

The SPI spectrometer on INTEGRAL features a camera system with 19 Ge detector modules, imaging photons through a tungsten coded mask. Background is reduced by an anticoincidence detector system surrounding these. The specifics of this instrument lead to data correction and analysis methods which are described here. Raw data for science analysis are detector event messages and spectra for different categories of detector hits and pulse shapes. Preprocessing combines calibrated spectra from these, which are then interpreted using the imaging and spectral response function for measured spectra where parts of the detector plane are occulted by the mask. Background dominates the overall signal, tailored background estimates and models are based on instrument-specific signatures, their correlations, and trends.

We present a preliminary analysis of the diffuse hard X- and soft γ -ray continuum emission from the inner Galactic ridge using INTEGRAL/SPI data from the first Galactic Plane Deep Exposure and Galactic Plane Scans. The spectrum is consistent with results from previous experiments. These early results demonstrate the potential of the INTEGRAL mission for improving our understanding of this emission.