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Register a new userA scenario for the anisotropy of galactic cosmic rays related to nearby source and local interstellar magnetic field
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In our recent work, we build a propagation scenario to simultaneously explain the spectra and anisotropy of cosmic rays (CRs) by considering spatially dependent propagation (SDP) model and nearby Geminga supernova remnant (SNR) source. But the phase of anisotropy is still inconsistent with the experimental data. Recent observations of CR anisotropy show that the phase is consistent with local regular magnetic field (LRMF) observed by Interstellar Boundary Explorer (IBEX) below 100 TeV, which indicates that diffusion along LRMF is important. In this work, we further introduce the LRMF and take into account the effect of corresponding anisotropic diffusion to explain the anisotropy of CRs. We find that when the diffusion coefficient perpendicular to the LRMF is much smaller than the parallel one, the phase of anisotropy points to $sim R.A.= 3^h$, which accords with experimental observation below 100 TeV. We also analyze the influence of the ratio of perpendicular and parallel diffusion coefficient on the anisotropy and the energy dependence of the ratio. The results illustrate that with the decrease of perpendicular diffusion, the anisotropic phase changes from the direction of nearby source to the LRMF below 100 TeV, meanwhile it changes from the galactic center (GC) to opposite direction of LRMF above 100 TeV. When the perpendicular diffusion coefficient grows faster than the parallel one with energy, the diffusion approaches to the isotropic at high energy, the phase of anisotropy shifts from the LRMF to the GC above 100 TeV. This could be helpful to ascertain the energy dependence of diffusion coefficients.
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We present the first full-sky analysis of the cosmic ray arrival direction distribution with data collected by the HAWC and IceCube observatories in the Northern and Southern hemispheres at the same median primary particle energy of 10 TeV. The combined sky map and angular power spectrum largely eliminate biases that result from partial sky coverage and holds a key to probe into the propagation properties of TeV cosmic rays through our local interstellar medium and the interaction between the interstellar and heliospheric magnetic fields. From the map we determine the horizontal dipole components of the anisotropy $delta_{0h} = 9.16 times 10^{-4}$ and $delta_{6h} = 7.25 times 10^{-4}~(pm0.04 times 10^{-4})$. In addition, we infer the direction ($229.2pm 3.5^circ$ RA , $11.4pm 3.0^circ$ Dec.) of the interstellar magnetic field from the boundary between large scale excess and deficit regions from which we estimate the missing corresponding vertical dipole component of the large scale anisotropy to be $delta_N sim -3.97 ^{+1.0}_{-2.0} times 10^{-4}$.
In this white paper we introduce the IMAGINE Consortium and its scientific background, goals and structure. Our purpose is to coordinate and facilitate the efforts of a diverse group of researchers in the broad areas of the interstellar medium, Galactic magnetic fields and cosmic rays, and our goal is to develop more comprehensive insights into the structures and roles of interstellar magnetic fields and their interactions with cosmic rays. To achieve a higher level of self-consistency, depth and rigour can only be achieved by the coordinated efforts of experts in diverse areas of astrophysics involved in observational, theoretical and numerical work. We present our view of the present status of this topic, identify its key unsolved problems and suggest a strategy that will underpin our work. The backbone of the consortium is the Interstellar MAGnetic field INference Engine, a publicly available Bayesian platform that employs robust statistical methods to explore the multi-dimensional likelihood space using any number of modular inputs. It provides an interpretation and modelling framework that has the power and flexibility to include a variety of observational, theoretical and numerical lines of evidence into a self-consistent and comprehensive picture of the thermal and non-thermal interstellar media. An important innovation is that a consistent understanding of the phenomena that are directly or indirectly influenced by the Galactic magnetic field, such as the deflection of ultra-high energy cosmic rays or extragalactic backgrounds, is made an integral part of the modelling. The IMAGINE Consortium, which is informal by nature and open to new participants, hereby presents a methodological framework for the modelling and understanding of Galactic magnetic fields that is available to all communities whose research relies on a state-of-the-art solution to this problem. (Abridged.)
We present a method to correct for deflections of ultra-high energy cosmic rays in the galactic magnetic field. We perform these corrections by simulating the expected arrival directions of protons using a parameterization of the field derived from Faraday rotation and synchrotron emission measurements. To evaluate the method we introduce a simulated astrophysical scenario and two observables designed for testing cosmic ray deflections. We show that protons can be identified by taking advantage of the galactic magnetic field pattern. Consequently, cosmic ray deflection in the galactic field can be verified experimentally. The method also enables searches for directional correlations of cosmic rays with source candidates.
The propagation trajectories of ultra-high-energy cosmic rays (UHECRs) are inevitably affected by Galactic magnetic field (GMF). Because of the inevitability, the importance of the studies of the propagation in GMF have increased to interpret the results of recent UHECR experiments. This article reviews the effects of GMF to the propagation and arrival directions of UHECRs and introduces recent studies to constrain UHECR sources.
We report an analysis of the interstellar gamma-ray emission from the Chamaeleon, R Coronae Australis (R CrA), and Cepheus and Polaris flare regions with the Fermi Large Area Telescope. They are among the nearest molecular cloud complexes, within ~300 pc from the solar system. The gamma-ray emission produced by interactions of cosmic-rays (CRs) and interstellar gas in those molecular clouds is useful to study the CR densities and distributions of molecular gas close to the solar system. The obtained gamma-ray emissivities above 250 MeV are (5.9 +/- 0.1(stat) (+0.9/-1.0)(sys)), (10.2 +/- 0.4(stat) (+1.2/-1.7)(sys)), and (9.1 +/- 0.3(stat) (+1.5/-0.6)(sys)) x10^(-27) photons s^(-1) sr^(-1) H-atom^(-1) for the Chamaeleon, R CrA, and Cepheus and Polaris flare regions, respectively. Whereas the energy dependences of the emissivities agree well with that predicted from direct CR observations at the Earth, the measured emissivities from 250 MeV to 10 GeV indicate a variation of the CR density by ~20% in the neighborhood of the solar system, even if we consider systematic uncertainties. The molecular mass calibrating ratio, Xco = N(H2)/Wco, is found to be (0.96 +/- 0.06(stat) (+0.15/-0.12)(sys)), (0.99 +/- 0.08(stat) (+0.18/-0.10)(sys)), and (0.63 +/- 0.02(stat) (+0.09/-0.07)(sys)) x10^20 H2-molecule cm^(-2) (K km s^(-1))^(-1) for the Chamaeleon, R CrA, and Cepheus and Polaris flare regions, respectively, suggesting a variation of Xco in the vicinity of the solar system. From the obtained values of Xco, the masses of molecular gas traced by Wco in the Chamaeleon, R CrA, and Cepheus and Polaris flare regions are estimated to be ~5x10^3, ~10^3, and ~3.3x10^4 Msolar, respectively. A comparable amount of gas not traced well by standard HI and CO surveys is found in the regions investigated.
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