Iris Gebauer

Dark Matter Annihilation in the light of EGRET, HEAT, WMAP, INTEGRAL and ROSAT (15'+5')

The ROSAT Galactic wind observations confirm that our Galaxy launches supernova driven Galactic winds with wind speeds of about 150 km/s in the Galactic plane. Galactic winds of this strength are incompatible with current isotropic models for Cosmic Ray transport. In order to reproduce our local CRs in the presence of Galactic winds, charged CRs are required to be much more localized than in the standard isotropic GALPROP models. This requires that anisotropic diffusion is the dominant diffusion mode in the interstellar medium, particularly that the diffusion in the disk and in the halo are different. In addition small scale phenomena such as trapping by molecular cloud complexes and the structure of our local environment might influence the secondary CR production rate and our local CR density gradients. We introduce an anisotropic convection driven transport model (aCDM) which is consistent with the Galactic wind observations by ROSAT. This also explains the large bulge/disk ratio as observed by INTEGRAL. Furthermore such models predict an increase in the

Supernova explosions of massive stars and cosmic rays

e^+/(e^++e^-)

Study of systematics in anisotropy searches with AMS-02

-fraction as observed by PAMELA and HEAT, if the synchrotron constraints in the 408 MHz and WMAP range are taken into account. No additional contribution from Dark Matter is required. The aCDM is able to explain the absence of a positron annihilation signal from molecular clouds as observed by INTEGRAL by virtue of a mechanism which confines and isotropizes CRs between MCs. We find that the EGRET excess of diffuse

Molecular clouds as the origin of the Fermi gamma-ray GeV-excess

\gamma

Measurement of anisotropies in cosmic ray arrival directions with the Alpha Magnetic Spectrometer on the ISS

-rays currently cannot be explained by astrophysical effects in this type of model and that the interpretation of the EGRET excess as Dark Matter annihilation is perfectly consistent with all observational constraints from local CR fluxes and synchrotron radiation.

Models for cosmic ray transport in the era of AMS-02

Abstract Most cosmic ray particles observed derive from the explosions of massive stars. Massive stars from slightly above about 10 M ⊙ explode as supernovae via a mechanism which we do not know yet: two not mutually exclusive main ideas are an explosion driven by neutrinos, or the magneto-rotational mechanism, in which the magnetic field acts like a conveyor-belt to transport energy outwards for an explosion. Massive stars above about 25 M ⊙ , depending on their heavy element abundance, commonly produce stellar black holes in their supernova explosions. When two such black holes find themselves in a tight binary system they finally merge in a gigantic emission of gravitational waves, events that have now been detected. The radio interferometric data demonstrate that all of these stars have powerful magnetic winds. After an introduction (Section 1) we introduce the basic concept (Section 2): Cosmic rays from exploding massive stars with winds always show two cosmic ray components at the same time: (i) the weaker polar cap component only produced by Diffusive Shock Acceleration, showing a relatively flat spectrum, and cut-off at the knee, and (ii) the stronger 4 π component, which is produced by a combination of Stochastic Shock Drift Acceleration and Diffusive Shock Acceleration, with a down-turn to a steeper power-law spectrum at the knee, and a final cut-off at the ankle. In Section 3 we use the Alpha Magnetic Spectrometer (AMS) data to differentiate these two cosmic ray spectral components; these two cosmic ray components excite magnetic irregularity spectra in the plasma, and the ensuing secondary spectra can explain anti-protons, lower energy positrons, and other secondary particles. Cosmic ray electrons of the polar cap component interact with the surrounding photon field to produce positrons by triplet pair production, and in this manner may explain the higher energy positron AMS data. In Section 4 we test this paradigm with a theory of injection based on a combined effect of first and second ionization potential; this reproduces the ratio of cosmic ray source abundances to source material abundances. We can interpret the abundance data using the relation of the total number of ions enhanced by Q 0 2 A + 2 / 3 , where Q 0 is the initial degree of ionization, and A is the mass number. This interpretation implies the high temperature as observed in the winds of blue super-giant stars; it also requires that cosmic ray injection happens in the shock travelling through such a wind. Most injection happens at the largest radii before slowing down due to interaction with the environment. In Section 5 we interpret the compact radio source 41.9 + 58 in the starburst galaxy M82 as a recent binary black hole merger, with an accompanying gamma ray burst. The tell-tale observational sign is the conical cleaning sweep of the relativistic jet during the merger, observed as an open cone with very low radio emission. This can also explain the Ultra High Energy Cosmic Ray (UHECR) data in the Northern sky. Thus, by studying the cosmic ray particles, their abundances at knee energies, and their spectra, we can learn about what drives these stars to produce the observed cosmic rays.

GALACTIC MODEL UNCERTAINTIES IN INDIRECT DARK MATTER SEARCH

The search for anisotropies in cosmic ray arrival directions with space experiments like the Alpha Magnetic Spectrometer (AMS-02) on the International Space Station is subject to a number of time and energy dependent effects originating from the detector, its environment and the data selection that need to be corrected for. Different approaches to accommodate for these effects are motivated and presented. The impact of these effects on the interpretation of anisotropy is discussed.

An Anisotropic Propagation Model for Galactic Cosmic Rays

The Fermi-LAT data reveal an excess of diffuse gamma-rays at energies of around 2 GeV in the direction of the Galactic center. The excess has been studied by many groups and is observed above the expectation for diffuse gamma-ray emission from cosmic ray interactions with the in- terstellar material (π0 production from cosmic ray protons and bremstrahlung from electrons in the interstellar gas) and the interstellar radiation field (inverse Compton scattering of electrons in the interstellar radiation field). In addition to these standard components in diffuse gamma-rays we find evidence for two additional processes: π 0 production in sources during acceleration and π 0 production in molecular clouds. The first one is characterized by nuclear cosmic rays with a hard E −2 spectrum, expected from diffusive shockwave acceleration and can be traced by the 1.8 MeV gamma-ray line from radioac- tive 26 Al decays, which is synthesized in sources. The second one is characterized by nuclear cosmic rays inside molecular clouds with a sharp cutoff below 6-14 GV, which is most clearly observed in the dense Central Molecular Zone encircling the Galactic center in the Galactic disk. The cutoff leads to a suppression of low energy cosmic ray interactions in molecular clouds, which causes a shift in the maximum of the gamma-ray spectrum to higher energies, the hall-mark of the GeV-excess. This was previously interpreted as a dark matter annihilation signal. No spatial information is provided to our fit. As a result we obtain an uncorrelated and spatially highly resolved distribution of the GeV-excess. We show that a shift in the maximum of the gamma-ray spectrum, or equivalently the GeV-excess, is observed in all directions, where molec- ular clouds are present; these directions are available from the high resolution all-sky CO maps from the Planck satellite.

An alternative Explanation for the Fermi GeV Gamma-Ray Excess

An analysis of anisotropies in the arrival directions of galactic protons, electrons and positrons has been performed with the Alpha Magnetic Spectrometer on the International Space Station using the first five years of data taking. Results on a dipole signal in Galactic coordinates are reported. The positron to proton and positron to electron ratio is consistent with isotropy. For energies above 16 GeV a limit of δ < 0.02 at the 95% confidence level is obtained. The electron to proton ratio is consistent with isotropy. For energies above 16 GeV a limit of δ < 0.004 at the 95% confidence level is obtained. The ratio of high rigidity protons to low rigidity protons is consistent with isotropy. For energies above 80 GV a limit of δ < 0.002 at the 95% confidence level is obtained. Limits on the absolute anisotropies in protons, electrons and positrons are consistent with the limits derived from the relative anisotropies. No indication of any time dependence is observed for all particle species within the present statistics.

Molecular clouds as origin of the Fermi gamma-ray GeV excess

State-of-the-art models for galactic cosmic ray transport as implemented in the DRAGON or GALPROP codes describe a multitude of observations. However, recent measurements of electrons, positrons and protons by AMS-02 and PAMELA challenge our understanding of cosmic ray sources and the subsequent transport processes in the interstellar medium. Here, we use Markov chain Monte Carlo methods to investigate wide ranges of transport parameters. Solutions to the transport equation are numerically obtained by using the DRAGON code. A total amount of more than 15 million solutions was generated. The predictions are compared to measurements of cosmic ray nuclei using data from PAMELA, ACE, CREAM, ISOMAX and HEAO. More than 13,000 models were found to have a maximum deviation from the data of 1 sigma averaged over all data points. We find that even in low dimensional models no definite solution exists. Based on the models found in our analysis, we predict the flux of secondary positrons, produced in proton-gas interactions, and compare our prediction to the AMS-02 data. We determine the local flux of additional energetic positrons necessary to describe the data. We further discuss different transport scenarios, which can explain the change of slope of the proton spectrum at high rigidities, and comment on the discriminating power of future data on B/C. The method described here will be applied to the upcoming AMS-02 data in the future.