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Title: Magnetic deflections of ultra-high energy cosmic rays from Centaurus A

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Grant/Contract Number:
0009926; FG02-91-EF0617
Resource Type:
Journal Article: Publisher's Accepted Manuscript
Journal Name:
Astroparticle Physics
Additional Journal Information:
Journal Volume: 61; Journal Issue: C; Related Information: CHORUS Timestamp: 2016-09-04 17:09:44; Journal ID: ISSN 0927-6505
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Citation Formats

Keivani, Azadeh, Farrar, Glennys R., and Sutherland, Michael. Magnetic deflections of ultra-high energy cosmic rays from Centaurus A. Netherlands: N. p., 2015. Web. doi:10.1016/j.astropartphys.2014.07.001.
Keivani, Azadeh, Farrar, Glennys R., & Sutherland, Michael. Magnetic deflections of ultra-high energy cosmic rays from Centaurus A. Netherlands. doi:10.1016/j.astropartphys.2014.07.001.
Keivani, Azadeh, Farrar, Glennys R., and Sutherland, Michael. 2015. "Magnetic deflections of ultra-high energy cosmic rays from Centaurus A". Netherlands. doi:10.1016/j.astropartphys.2014.07.001.
title = {Magnetic deflections of ultra-high energy cosmic rays from Centaurus A},
author = {Keivani, Azadeh and Farrar, Glennys R. and Sutherland, Michael},
abstractNote = {},
doi = {10.1016/j.astropartphys.2014.07.001},
journal = {Astroparticle Physics},
number = C,
volume = 61,
place = {Netherlands},
year = 2015,
month = 2

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1016/j.astropartphys.2014.07.001

Citation Metrics:
Cited by: 10works
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Web of Science

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  • Ultra-high-energy cosmic rays (UHECRs), with energies above {approx}6 x 10{sup 19} eV, seem to show a weak correlation with the distribution of matter relatively near to us in the universe. It has earlier been proposed that UHECRs could be accelerated in either the nucleus or the outer lobes of the nearby radio galaxy Cen A. We show that UHECR production at a spatially intermediate location about 15 kpc northeast from the nucleus, where the jet emerging from the nucleus is observed to strike a large star-forming shell of gas, is a plausible alternative. A relativistic jet is capable of acceleratingmore » lower energy heavy seed cosmic rays (CRs) to UHECRs on timescales comparable to the time it takes the jet to pierce the large gaseous cloud. In this model, many CRs arising from a starburst, with a composition enhanced in heavy elements near the knee region around PeV, are boosted to ultra-high energies by the relativistic shock of a newly oriented jet. This model matches the overall spectrum shown by the Auger data and also makes a prediction for the chemical composition as a function of particle energy. We thus predict an observable anisotropy in the composition at high energy in the sense that lighter nuclei should preferentially be seen toward the general direction of Cen A. Taking into consideration the magnetic field models for the Galactic disk and a Galactic magnetic wind, this scenario may resolve the discrepancy between HiRes and Auger results concerning the chemical composition of UHECRs.« less
  • The Pierre Auger Observatory has associated a few ultra-high energy cosmic rays (UHECRs) with the direction of Centaurus A. This source has been deeply studied in radio, infrared, X-ray, and {gamma}-rays (MeV-TeV) because it is the nearest radio-loud active galactic nucleus. Its spectral energy distribution or spectrum shows two main peaks, the low-energy peak, at an energy of 10{sup -2} eV, and the high-energy peak, at about 150 keV. There is also a faint very high energy (VHE; E {>=} 100 GeV) {gamma}-ray emission fully detected by the High Energy Stereoscopic System experiment. In this work, we describe the entiremore » spectrum: the two main peaks with a synchrotron/synchrotron self-Compton model, and the VHE emission with a hadronic model. We consider p{gamma} and pp interactions. For the p{gamma} interaction, we assume that the target photons are those produced at 150 keV in leptonic processes. On the other hand, for the pp interaction we consider as targets the thermal particle densities in the lobes. Requiring a satisfactory description of the spectra at very high energies with p{gamma} interaction, we obtain an excessive luminosity in UHECRs (even exceeding the Eddington luminosity). However, when considering the pp interaction to describe the {gamma}-spectrum, the number of UHECRs obtained is in agreement with Pierre Auger observations. We also calculate the possible neutrino signal from pp interactions on a Km{sup 3} neutrino telescope using Monte Carlo simulations.« less
  • The full-sky multipole coefficients of the ultra-high energy cosmic ray (UHECR) flux have been measured for the first time by the Pierre Auger and Telescope Array collaborations using a joint data set with E > 10 EeV. We calculate these harmonic coefficients in the model where UHECR are protons and sources trace the local matter distribution, and compare our results with observations. We find that the expected power for low multipoles (dipole and quadrupole, in particular) is sytematically higher than in the data: the observed flux is too isotropic. We then investigate to which degree our predictions are influenced bymore » UHECR deflections in the regular Galactic magnetic field. It turns out that the UHECR power spectrum coefficients C{sub l} are quite insensitive to the effects of the Galactic magnetic field, so it is unlikely that the discordance can be reconciled by tuning the Galactic magnetic field model. On the contrary, a sizeable fraction of uniformly distributed flux (representing for instance an admixture of heavy nuclei with considerably larger deflections) can bring simulations and observations to an accord.« less
  • We evaluate the achievable maximum energy of nuclei diffusively accelerated by shock wave in the jet of Cen A, based on an updated model involving the stochastic magnetic fields that are responsible for recent synchrotron X-ray measurements. For the maximum energy analysis, conceivable energy constraints from spatiotemporal scales are systematically considered for the jet-wide including discrete X-ray knots. We find that in the inner region within approx1 arcmin from galactic core, which includes knots AX and BX, proton and iron nucleus can be accelerated to 10{sup 19}-10{sup 20} and 10{sup 21} eV (10-100 EeV and ZeV) ranges, respectively. The uppermore » cutoff energy of the very energetic neutrinos produced via photopion interaction is also provided. These are essential for identifying the acceleration site of the ultra-high energy cosmic ray detected in the Pierre Auger Observatory, which signifies the arrival from nearby galaxies including Cen A.« less