TY - JOUR
T1 - Can We Reconcile the TA Excess and Hotspot with Auger Observations?
AU - Globus, Noemie
AU - Allard, Denis
AU - Parizot, Etienne
AU - Lachaud, Cyril
AU - Piran, Tsvi
N1 - Publisher Copyright:
© 2017. The American Astronomical Society. All rights reserved..
PY - 2017/2/20
Y1 - 2017/2/20
N2 - The Telescope Array (TA) shows a 20° hotspot as well as an excess of ultra-high-energy cosmic-rays (UHECRs) above 50 EeV when compared with the Auger spectrum. We consider the possibility that both the TA excess and hotspot are due to a dominant source in the northern sky. We carry out detailed simulations of UHECR propagation in both the intergalactic medium and the Galaxy, using different values for the intergalactic magnetic field. We consider two general classes of sources: transients and steady, adopting a mixed UHECR composition that is consistent with the one found by Auger. The spatial location of the sources is drawn randomly. We generate Auger-like and TA-like data sets from which we determine the spectrum, the sky maps, and the level of anisotropy. We find that, while steady sources are favored over transients, it is unlikely to account for all the currently available observational data. While we reproduce fairly well the Auger spectrum for the vast majority of the simulated data sets, most of the simulated data sets with a spectrum compatible with that of TA (at most a few percent depending on density model tested) show a much stronger anisotropy than the one observed. We find that the rare cases in which both the spectrum and the anisotropy are consistent require a steady source within ∼10 Mpc, to account for the flux excess, and a strong extragalactic magnetic field ∼10 nG, to reduce the excessive anisotropy.
AB - The Telescope Array (TA) shows a 20° hotspot as well as an excess of ultra-high-energy cosmic-rays (UHECRs) above 50 EeV when compared with the Auger spectrum. We consider the possibility that both the TA excess and hotspot are due to a dominant source in the northern sky. We carry out detailed simulations of UHECR propagation in both the intergalactic medium and the Galaxy, using different values for the intergalactic magnetic field. We consider two general classes of sources: transients and steady, adopting a mixed UHECR composition that is consistent with the one found by Auger. The spatial location of the sources is drawn randomly. We generate Auger-like and TA-like data sets from which we determine the spectrum, the sky maps, and the level of anisotropy. We find that, while steady sources are favored over transients, it is unlikely to account for all the currently available observational data. While we reproduce fairly well the Auger spectrum for the vast majority of the simulated data sets, most of the simulated data sets with a spectrum compatible with that of TA (at most a few percent depending on density model tested) show a much stronger anisotropy than the one observed. We find that the rare cases in which both the spectrum and the anisotropy are consistent require a steady source within ∼10 Mpc, to account for the flux excess, and a strong extragalactic magnetic field ∼10 nG, to reduce the excessive anisotropy.
KW - cosmic rays
KW - Galaxy: structure
KW - ISM: magnetic fields
UR - http://www.scopus.com/inward/record.url?scp=85014466741&partnerID=8YFLogxK
U2 - 10.3847/1538-4357/836/2/163
DO - 10.3847/1538-4357/836/2/163
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AN - SCOPUS:85014466741
SN - 0004-637X
VL - 836
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 163
ER -