We study the influence of the random part of the galactic magnetic field on the propagation of ultrahigh energy cosmic rays. Within very mild approximations about the properties of the electron ...density fluctuations in the Galaxy, we are able to derive a clear and direct relation between the observed variance of rotation measures and the predicted cosmic ray deflections. Remarkably, this is obtained bypassing entirely the detailed knowledge of the magnetic properties of the turbulent plasma. Depending on the parameters of the electron density spectrum, we can either directly estimate the expected deflection, or constrain it from above. Thanks to the latest observational data on rotation measures, we build a direction-dependent map of such deflections. We find that over most of the sky the random deflections of 40 EeV protons do not exceed 1°-2°, and can be as large as 5° close to the Galactic plane.
A signature of EeV protons of Galactic origin Tinyakov, P. G; Urban, F. R; Ivanov, D ...
Monthly notices of the Royal Astronomical Society,
08/2016, Letnik:
460, Številka:
4
Journal Article
Recenzirano
Odprti dostop
We investigate signatures that would be produced in the spectrum and sky distribution of ultra-high energy cosmic rays (UHECR) by a population of the Galactic sources of high-energy protons in the ...energy range around 1 EeV, i.e. around the diffusive-to-ballistic transition. In this regime, the CR flux has to be calculated numerically. We employ the approach that consists in backtracking anti-protons from Earth through the Galaxy and integrating the source emissivity along the trajectory. This approach makes evident two generic features of the transition region: sharp increase of the total flux as the energy decreases across the transition region, and its strong anisotropy (appearance of a bright compact spot) all the way until the onset of the diffusive regime. We then discuss and compare several methods to experimentally detect or constrain these features. We find that a few per cent admixture of the Galactic protons can in principle be detected by the current UHECR experiments.
We reanalyse the subset of the Faraday rotation measures data from the NRAO VLA Sky Survey catalogue for which redshift and spectral index information is available, in order to better elucidate the ...relations between these observables. We split this subset in two based on their radio luminosity, and find that higher power sources have a systematically higher residual rotation measure, once the regular field of the Milky Way is subtracted. This rotation measure stands well above the variances due to the turbulent field of our Galaxy and measurement errors, contrarily to low-power sources. The effect is more pronounced as the energy threshold becomes more restrictive. If the two sets are merged, one observes an apparent evolution of rotation measure with redshift, but our analysis shows that this can be interpreted as an artefact of the different intrinsic properties of brighter sources that are typically observed at larger distances.
We made use of the two latest sets of rotation measures (RMs) of extragalactic radio sources, namely the NRAO VLA Sky Survey rotation measures catalog and a compilation by Kronberg and Newton-McGee, ...to infer the global structure of the Galactic magnetic field (GMF). We have checked that these two data sets are mutually consistent. Given the existence of clear patterns in the all-sky RM distributions we considered GMF models consisting of two components: disk (spiral or ring) and halo. The parameters of these components were determined by fitting different model field geometries to the observed RMs. We found that the model consisting of a symmetric (with respect to the Galactic plane) spiral disk and antisymmetric halo fits the data best and reproduces the observed distribution of RMs over the sky very well. We confirm that ring disk models are disfavored. Our results favor small pitch angles around ~ -- 5? and an increased vertical scale of electron distribution, in agreement with some recent studies. Based on our fits, we select two benchmark models suitable for studies of cosmic ray propagation, including cosmic rays at ultrahigh energies.
We analyze the gamma-ray halo around stacked AGNs reported by Ando & Kusenko (2010, ApJ, 722, L39). First, we show that the angular distribution of γ-rays around the stacked AGNs is consistent with ...the angular distribution of the γ-rays around the Crab pulsar, which is a point source for Fermi/LAT. This makes it unlikely that the halo is caused by an electromagnetic cascade of TeV photons in the intergalactic space. We then compare the angular distribution of γ-rays around the stacked AGNs with the point-spread function (PSF) of Fermi/LAT and confirm the existence of an excess above the PSF. However, we demonstrate that the magnitude and the angular size of this effect is different for photons converted in the front and back parts of the Fermi/LAT instrument, and thus is an instrumental effect.
PDF
