How can we explain last UHERC anisotropies D. Fargion1 P.G. De Sanctis Lucentini2

2025-05-06 0 0 1.59MB 9 页 10玖币

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How can we explain last UHERC anisotropies?

D. Fargion1, P.G. De Sanctis Lucentini2, M.Y. Khlopov3,4,5

1Physics Department, Rome University 1, P.le A. Moro 2, 00185, Rome, Italy

2Gubkin University, Leninskiy prospekt 65, Moscow, 119991, Russia

3Center for Cosmoparticle physics Cosmion, National Research Nuclear University ”MEPHI”,

Moscow 115409, Russia

4Institute of Physics, Southern Federal University, Stachki 194 Rostov on Don 344090, Russia

5Virtual Institute of Astroparticle Physics, Paris 75018, France

E-mail: daniele.fargion@fondazione.uniroma1.it

Abstract. We consider the recent results on UHECR (Ultra High Energy Cosmic Ray),

clustering, composition, distribution in the sky, from the energy of several EeV with the dipole

anisotropy up to the highest ones. We have suggested since 2008 and we reconﬁrm here that

UHECR at 40 −70 EeV are mostly made by light and lightest nuclei. The remarkable Virgo

absence and the few localized nearby extragalactic sources as CenA, NG 253, and M82 may be

well understood by the lightest nuclei fragility and opacity within Mpc distances. We comment

also on the role of a few galactic UHECR sources at ten EeV that may be partially feeding the

Auger dipole UHECR anisotropy. The recent anisotropy in the UHECR spectral composition of

lightest and heavy nuclei, outside and along the galactic plane, could also be a ﬁrst conﬁrmation

of our previous claims (2012). The interplay of the heavier and most energetic UHECR galactic

nuclei with the mainly local (Mpcs) extragalactic signals ruled by lightest nuclei, seems to ﬁt

the main pieces of UHECR puzzle.

1. Introduction: The Virgo Absence and the two Hot Spots

The Ultra High Energy Cosmic Rays (UHECR) after two decades of data are, probably, at a

ﬁrst stage of understanding. Because of their nature, the hadron charged Cosmic Rays (CR) are

bent and smeared by magnetic ﬁelds both from near, galactic, and by far cosmic distances. The

lepton CR, electron pairs, instead, lose very fast their energy and have a very local (parsecs)

origin, bounded within lowest energy (TeVs-PeVs) ones. However, the highest energetic CR,

nucleon or light nuclei, should be able to point back to their source with a good directionality

thanks to their high rigidity. Their heavier nuclei directionality may unfortunately be anyway

smeared by their largest charges. Therefore the understanding of UHECR is a hard combined

puzzle of energy, composition, magnetic ﬁelds and volumetric source distribution and nature.

Anisotropy maps, event rates, UHECR compositions and the wide astrophysical data maps have

to be all tuned at once.

In last two decades, largest area detectors for UHECR after Fly’s Eye, as the AGASA [1], the

High Resolution Fly’s Eye (HiRes), the Telescope Array (TA), the Pierre Auger Observatory

(Auger), they were able to record several hundreds above 6 ·1019 eV UHECR events, near or

well above the GZK cutoﬀ [2, 3].

Moreover, the nucleon or the light nuclei UHECR disruption and fragmentation (due to the

photo pion,the GZK cut oﬀ, or to the photo nuclear dissociation, both caused by the cosmic

arXiv:2210.14365v1 [astro-ph.HE] 25 Oct 2022

radiation interaction) make the UHECR proton conﬁned into a small (hundred Mpc, the GZK

cut oﬀ) or even, lightest nuclei, within a very local (few Mpcs) Universe. The heaviest CR like

iron, Ni, Co are much bent by their large charges and cannot be easly disentangled in the sky.

Heaviest ones, may be even turn in spirals, possibly captured inside the galaxy. Proton, the most

popular courier for last decades, may ﬂy nearly straight (clustering within a few degrees,'3◦

at 6 ·1019 eV). But since a decade there are not in AUGER, in terrestrial South, or in TA

(Telescope Array), in the North, such characteristic narrow clusterings of observed UHECR.

Lightest UHECR nuclei (He,D,Li,Be..) directions are little smeared, still enough collimated, up

to '10◦at 6 ·1019. That is a typical size as the ﬁrst observed UHECR anisotropy (the twin Hot

Spot) in AUGER and later in TA. Moreover lightest UHECR nuclei (He like) are constrained

much within a few Mpc Universe by photonuclear distruption and fragmentation. This opacity

is avoding any ten-tens Mpcs distance: this is an the ideal ﬁlter or an opacity toward the Virgo

cluster, explaing its amazing and puzzling absence both in AUGER and TA sky. Additional

role of few heaviest nuclei at highest UHECR energy had been also considered [4]. Most of the

frame and details of the present article, are included in an earlier contribute [5] and references

therein.

Let us remind ﬁrst that the charged nuclei or nucleon in CR are easily deﬂected by the

astrophysical (galactic and intergalactic) magnetic ﬁelds via Lorentz forces. Therefore, heavy

charged nuclei (A >> 4) CR are soon bent and turn, loosing their primordial directionality.

However, the CR of the highest energies above 1019 eV (tens EeV), if protons, suﬀer less and

less from deﬂection promising a geometrical connection with their original sources. Eventual

Ultra High Energy Cosmic Ray (UHECR) neutrons (born by photopion interactions) being

neutral are un-deﬂected but they are bounded by their instability within a very narrow cosmic

radius: 'Mpc En

1020eV . Many bounds exist on EeVs neutrons, but they might also play a very

minor galactic role.

First we noted the remarkable absence of Virgo in the UHECR clustering since 2007 [6]

discover, a clustering expected for UHECR proton composition. A ﬁrst low clustering rised also

around Cen A nearest AGN. The heavy iron nuclei (considered by most as ideal courier) could

not cluster as a narrow angle as this ﬁrst Auger Hot spot size. Therefore we considered the

lightest nuclei as the solving candidate, being well ﬁltered and opaque from far Virgo distances,

but transparent from Cen A, bent by a needed size angle. Five years later it became quite

agreed that UHECR at such energies are mainly light nuclei (or lightest ones), [7] (see also

therein, the note at page 26, and their references 83 −87), by their average slanth depth of

the shower maximum. We noted the characteristic bending (or deﬂection) angle expected by

random or coherent deﬂection by Lorentz forces [8], mainly due to galactic magnetic ﬁelds.

These angles agree well with hot spot smeared angle size. We remind our consequent foreseen

lightest nuclei fragmentation from Cen A UHECR above 40 −60 EeV, into fragment around

twenty EeV ones [8]. Two years later Auger observed such fragments in multiplet tails near 20

EeV energy. These twin tails around Cen A had been observed as well as a similar one along

LMC and SMC multiplet published in a later article [9]. This multiplet near LMC and SMC

suggest a minor galactic role of UHECR. The same conclusion arised from the UHECR dipole

anisotropy discussed later.

Incidentally and historically, let us also to remind the earliest Fly’s Eye 300 EeV event from

1995. Its huge energy, over GZK cut oﬀ [2, 3], its arrival direction out of any known important

nearby source, led us to consider an UHE neutrino courier scattering onto relic light (about eV

mass) ones. These ZeV UHE neutrino might overcome the GZK cut oﬀ, a very severe one for

any nucleon or nuclei. These UHE neutrino scattering (by resonant Z boson production) onto

the relic cosmic warm ones (at eV mass) could allow its secondariy hadron fragments to reach

us from unexpected distances, overcoming any GZK cut oﬀ and explaining earliest and also

recent puzzling correlations with very far AGN sources. Indeed recent mild UHECR clustering

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摘要：

HowcanweexplainlastUHERCanisotropies?D.Fargion1,P.G.DeSanctisLucentini2,M.Y.Khlopov3;4;51PhysicsDepartment,RomeUniversity1,P.leA.Moro2,00185,Rome,Italy2GubkinUniversity,Leninskiyprospekt65,Moscow,119991,Russia3CenterforCosmoparticlephysicsCosmion,NationalResearchNuclearUniversity"MEPHI",Moscow115409...

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How can we explain last UHERC anisotropies D. Fargion1 P.G. De Sanctis Lucentini2

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