Search for the astrophysical sources of the Fly's Eye event with the highest to date cosmic ray energy E=3.2·10²⁰ eV
Among the registered extremely high energy cosmic rays (EHECR, E > 10²⁰ eV) an event with the highest to date energy of E = 3.2 · 10²⁰ eV was detected by the Fly's Eye experiment (FE event) in 1991. With the use of the back-tracking method for the calculation of the EHECR trajectories in Gal...
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irk-123456789-1199492017-06-11T03:02:49Z Search for the astrophysical sources of the Fly's Eye event with the highest to date cosmic ray energy E=3.2·10²⁰ eV Gnatyk, R.B. Kudrya, Yu.N. Zhdanov, V.I. Among the registered extremely high energy cosmic rays (EHECR, E > 10²⁰ eV) an event with the highest to date energy of E = 3.2 · 10²⁰ eV was detected by the Fly's Eye experiment (FE event) in 1991. With the use of the back-tracking method for the calculation of the EHECR trajectories in Galactic and extragalactic magnetic fields, we show that the galaxies UGC 03574 and UGC 03394 are the most promising candidates among the nearby extragalactic sources for the cases of iron and C-N-O group primary nucleus respectively. The most likely accelerating mechanisms are the newly-born millisecond pulsars, magnetar ares and tidal disruption events in these galaxies. 2016 Article Search for the astrophysical sources of the Fly's Eye event with the highest to date cosmic ray energy E=3.2·10²⁰ eV / R.B. Gnatyk, Yu.N. Kudrya, V.I. Zhdanov // Advances in Astronomy and Space Physics. — 2016. — Т. 6., вип. 1. — С. 41-44. — Бібліогр.: 25 назв. — англ. 2227-1481 DOI:10.17721/2227-1481.6.41-44 http://dspace.nbuv.gov.ua/handle/123456789/119949 en Advances in Astronomy and Space Physics Головна астрономічна обсерваторія НАН України |
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English |
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Among the registered extremely high energy cosmic rays (EHECR, E > 10²⁰ eV) an event with the highest to date energy of E = 3.2 · 10²⁰ eV was detected by the Fly's Eye experiment (FE event) in 1991. With the use of the back-tracking method for the calculation of the EHECR trajectories in Galactic and extragalactic magnetic fields, we show that the galaxies UGC 03574 and UGC 03394 are the most promising candidates among the nearby extragalactic sources for the cases of iron and C-N-O group primary nucleus respectively. The most likely accelerating mechanisms are the newly-born millisecond pulsars, magnetar ares and tidal disruption events in these galaxies. |
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Article |
| author |
Gnatyk, R.B. Kudrya, Yu.N. Zhdanov, V.I. |
| spellingShingle |
Gnatyk, R.B. Kudrya, Yu.N. Zhdanov, V.I. Search for the astrophysical sources of the Fly's Eye event with the highest to date cosmic ray energy E=3.2·10²⁰ eV Advances in Astronomy and Space Physics |
| author_facet |
Gnatyk, R.B. Kudrya, Yu.N. Zhdanov, V.I. |
| author_sort |
Gnatyk, R.B. |
| title |
Search for the astrophysical sources of the Fly's Eye event with the highest to date cosmic ray energy E=3.2·10²⁰ eV |
| title_short |
Search for the astrophysical sources of the Fly's Eye event with the highest to date cosmic ray energy E=3.2·10²⁰ eV |
| title_full |
Search for the astrophysical sources of the Fly's Eye event with the highest to date cosmic ray energy E=3.2·10²⁰ eV |
| title_fullStr |
Search for the astrophysical sources of the Fly's Eye event with the highest to date cosmic ray energy E=3.2·10²⁰ eV |
| title_full_unstemmed |
Search for the astrophysical sources of the Fly's Eye event with the highest to date cosmic ray energy E=3.2·10²⁰ eV |
| title_sort |
search for the astrophysical sources of the fly's eye event with the highest to date cosmic ray energy e=3.2·10²⁰ ev |
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Головна астрономічна обсерваторія НАН України |
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2016 |
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http://dspace.nbuv.gov.ua/handle/123456789/119949 |
| citation_txt |
Search for the astrophysical sources of the Fly's Eye event with the highest to date cosmic ray energy E=3.2·10²⁰ eV / R.B. Gnatyk, Yu.N. Kudrya, V.I. Zhdanov // Advances in Astronomy and Space Physics. — 2016. — Т. 6., вип. 1. — С. 41-44. — Бібліогр.: 25 назв. — англ. |
| series |
Advances in Astronomy and Space Physics |
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2025-07-08T16:58:40Z |
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| fulltext |
Search for the astrophysical sources of the Fly's Eye event
with the highest to date cosmic ray energy E = 3.2 · 1020 eV
R.B.Gnatyk1∗, Yu.N.Kudrya2, V. I. Zhdanov2
Advances in Astronomy and Space Physics, 6, 41-44 (2016) doi: 10.17721/2227-1481.6.41-44
© R.B.Gnatyk, Yu.N.Kudrya, V. I. Zhdanov, 2016
1Faculty of Physics, Taras Shevchenko National University of Kyiv, Glushkova ave., 4, 03127, Kyiv, Ukraine
2Astronomical Observatory, Taras Shevchenko National University of Kyiv, Observatorna str., 3, 04053, Kyiv, Ukraine
Among the registered extremely high energy cosmic rays (EHECR, E > 1020 eV) an event with the highest to
date energy of E = 3.2 · 1020 eV was detected by the Fly's Eye experiment (FE event) in 1991. With the use of the
back-tracking method for the calculation of the EHECR trajectories in Galactic and extragalactic magnetic �elds,
we show that the galaxies UGC03574 and UGC03394 are the most promising candidates among the nearby extra-
galactic sources for the cases of iron and C-N-O group primary nucleus respectively. The most likely accelerating
mechanisms are the newly-born millisecond pulsars, magnetar �ares and tidal disruption events in these galaxies.
Key words: ISM: cosmic rays, magnetic �elds; stars: pulsars, magnetars
introduction
The extremely high-energy cosmic rays (EHECR)
with the energy E > 1020 eV are extremely rare
phenomena in the observed CR �ux: till now two
largest modern detectors registered only six (Pierre
Auger Observatory (PAO, AUGER)) and ten (Tele-
scope Array (TA)) such events [1, 2]. Potential
sources of EHECR are considered to be among the
active galactic nuclei (AGN, especially blazars), cos-
mological gamma-ray bursts, tidal disruptions of
stars in the neighbourhood of the supermassive black
holes, newly-born millisecond pulsars and magnetar
�ares [21]. From the �rst three classes of objects we
expect a certain �ux of light nuclei � protons and
helium (charge Z = 1, 2), whereas from the neutron
stars with an iron crust we can also expect iron nu-
clei (Z = 26) and their decay products, including
the C-N-O group (Z = 6 − 8). The observed nearly
isotropic �ux of UHECR with E > 1018 eV suggests
a signi�cant deviation of UHECR in the Galactic
and intergalactic magnetic �elds [1, 2]. Therefore we
should consider predominantly the EHECR events
with the minimal magnetic de�ection when search-
ing for the correlation of their arrival directions with
the positions of potential sources. Furthermore, the
sources of EHECR should be close enough to the
Earth due to the GZK cut-o�: the GZK horizon for
EHECR protons is smaller than 40Mpc [12]. Sim-
ilar restrictions exist for the propagation length of
the nuclei due to photodisintegration [6]. The most
suitable CR event in this respect is the event with
the highest detected energy. This event was regis-
tered by theFly's Eye (FE) experiment in 1991 with
the following parameters: E = (3.2 ± 0.9) · 1020 eV,
RA = (85.2 ± 0.5)◦, Dec = (48.0+5.2
−6.3)
◦ (the galactic
coordinates are centred at l = 163.4◦ and b = 9.6◦)
and the shower maximum Xmax = 815 g/cm2 [10].
Unfortunately, the nature of the original particle
could not be established, as the observed shower
properties can be accommodated with both the pro-
ton (QGSJETII-03 shower model in the TA collabo-
ration) and an iron nuclei (EPOS-LHC shower model
in the PAO collaboration) [4].
Already in 1995 in [16] it was shown that the
FE event posses a serious problem: interaction of
a CR particle with the cosmic background radiation
restricts its mean free path to less than 50Mpc (a
nucleus with the FE-event energy can not reach the
Earth from the distances beyond 10Mpc [17], the
mean free paths of similar energy protons (against
photomeson losses) and photons (against electron-
positron pair production) are less than 30Mpc [23]),
while the potential astrophysical sources in the sky
region around the CR arrival direction are at con-
siderably larger distances (see also [5, 8]). These
di�culties with the astrophysical sources stimulated
the development of particle physics (especially be-
yond the Standard Model) theories of the FE event,
namely, EHECR from topological defects, from su-
per heavy dark matter decay etc. [9]. The peculiar-
ity of the decaying top-down models is a photon-
dominated �ux [7], however, according to the recent
PAO results on the integral �ux upper limit of the
ultra high-energy photons [11], the top-down models
of UHECR are strongly disfavoured.
In this work we search for the astrophysical
sources of EHECR inside the FE event horizon of 30�
40Mpc (corresponding to the redshift of z < 0.01),
taking into account the favoured transient sources
∗roman_hnatyk@ukr.net
41
Advances in Astronomy and Space Physics R.B.Gnatyk, Yu.N.Kudrya, V. I. Zhdanov
of EHECR in the normal galaxies (newly-born mil-
lisecond pulsars, magnetar �ares, tidal disruption
events) [21] and the recent models of the Galactic
magnetic �eld [19, 20] to recover the trajectory of
the FE cosmic ray and determine the Galactic and
extragalactic objects that could be the sources of the
FE event.
propagation in the galactic and
extragalactic magnetic fields
On their way from the source to the Earth EHE-
CRs are de�ected in the Galactic and extragalac-
tic magnetic �elds. Galactic magnetic �eld can be
presented as a sum of regular and random compo-
nents [14, 19, 20]. Regular magnetic �eld consists of
a spiral disk �eld with a structure that corresponds
to the structure of spiral arms, a toroidal �eld of
the Galactic halo and the X-�eld � the axisymmet-
ric poloidal �eld directed from the southern to the
northern hemisphere of the Galaxy [20]. The trajec-
tory of a cosmic ray with the energy E and charge
q = eZ in a magnetic �eldB is described by the equa-
tion of motion for the radius vector r and velocity v
(for the EHECR Lorentz factor γ ≫ 1 and |v| ≈ c,
neglecting the energy losses only the direction of the
velocity vector is changing):
dr
dt
= v;
dv
dt
=
qc2
E
[v ×B].
A reconstruction of the cosmic ray trajectory can
be achieved via the method of inverse trajectories:
we launch a cosmic ray with the detected energy E,
but with the inverse charge −q, towards the arrival
direction of the EHECR from the position of the ob-
server in the Galaxy (here we take the solar system
coordinates x = −8.5 kpc, y = 0.0 kpc, z = 0.02 kpc
with respect to the Galactic centre). The calculated
in this way trajectory recreates the trajectory of the
detected UHECR.
Now let us consider the role of the random com-
ponents of the Galactic and extragalactic magnetic
�elds. The extragalactic magnetic �eld is usually
simulated in form of cells with the typical size (co-
herence length) of lB = 0.1..1Mpc and a random
distribution of the magnetic �eld amplitude Brms =
10−12..10−9G [14, 24]. EHECR with energy E from
an extragalactic source at a distance D in this �eld
is de�ected at the angle θrms:
θrms(E,D) ≃ 0.08◦ · Z
(
E
1020 eV
)−1
×
×
(
D
10Mpc
) 1
2
(
l
1Mpc
) 1
2
(
Brms
10−10G
)
.
For the FE event θrms ∼ 0.14◦ · Z, and even for the
iron nucleus (Z = 26) deviation is less than 4◦.
For the random component of the Galactic mag-
netic �eld with an amplitude Brms ∼ 10−6G and
coherence length l = 100 pc the trajectory deviation
at the distance d is equal to
θ ∼ 0.3◦Z ·
(
d
10kpc
) 1
2
(
E
1020eV
)−1
,
and even in the case of the iron nuclei does not ex-
ceed 2�5 degrees, depending on the amplitude of the
magnetic �eld.
To summarise, the combined e�ect of the random
Galactic and extragalactic magnetic �elds can be de-
scribed as a spreading with respect to the direction
to the source by up to 6◦ (see also [1, 2, 14, 19, 20]).
The results of the FE event trajectory reconstruc-
tion in the regular Galactic magnetic �eld are pre-
sented in Fig. 1 and 2. Fig. 1 shows the recovered
position of a potential nearby (< 30Mpc) extra-
galactic parent source of the FE event on the sky
map. The calculations made for proton (Z = 1) and
iron nuclei (Z = 26) showed that the regular Galac-
tic magnetic �eld in the FE event arrival direction
(which corresponds nearly to the Galactic anticen-
tre) decreases mainly over the Galactic latitude (b-
coordinate), which results in de�ection at an angle
of 0.35◦ · Z � mainly due to the de�ection in regu-
lar magnetic �elds of the spiral arms (Fig. 2). The
resulting angular bias for a proton � 0.35◦ � is
still within the error of the initially determined po-
sition and therefore is not presented in Fig. 1. For
the C-N-O group particles the bias is approximately
2�3 degrees. The corresponding bias for iron is pre-
sented for two values of the CR energy: the measured
(9◦) and reduced by 1σ (11◦).
search for the potential sources
The FE event is far enough from the Galactic
plane and within the 5◦-circle around its position
(the expected deviation of EHECR in random Galac-
tic and extragalactic magnetic �elds discussed above)
there are no Galactic sources which might be re-
sponsible for its origin [18]. Moreover, even in the
case of the extragalactic sources the nearest poten-
tial standard (blazar) sources of EHECR are much
farther [18, 21].
In Table 1 we show a detailed list of the poten-
tial extragalactic sources of the FE event at the
distances up to 30Mpc, that are no more than 8◦
from the reconstructed extragalactic position of the
event. There are only nine of such galaxies and
all of them are not active. Their characteristics
(name, type, size (diameter), galactic coordinates
l and b, separation from calculated source position
(l = 165.5◦, b = 18.6◦), redshift and distance) are
presented in the columns 2�9 of Table 1. For an iron
nucleus as the UHECR particle, the main source can-
didate is the galaxy UGC03574 because of its prac-
tical coincidence with the corresponding error box
42
Advances in Astronomy and Space Physics R.B.Gnatyk, Yu.N.Kudrya, V. I. Zhdanov
(within the discussed above error in 5 overlapping
with the corresponding error box (extended by the
discussed above 6◦ spreading in random magnetic
�elds, Fig. 1), its large size compared to the other
candidates and therefore a larger number of poten-
tial UHECR sources (e.g. young pulsars, magnetars,
tidal disruption events). For a nucleus from the C-
N-O- group (Z = 6−8) the magnetic deviation error
box is of order of 0.35◦ · Z ∼ 2.5◦ and the best can-
didate is the galaxy UGC03394. It is of smaller size
in comparison with UGC03574, but its advantage
is that the C-N-O-nucleus as the UHECR particle
is in accordance with the recent data about the CR
composition at the highest energies [3, 4, 25]. The
position of these and some other galaxies from Ta-
ble 1 are also shown in Fig. 1.
discussion and conclusions
In the reconstructed FE event area there are no
suitable galactic candidates and, moreover, there are
no nearby AGNs either [18]. Therefore we have per-
formed a search among the ordinary galaxies, in
which millisecond pulsars and magnetars together
with the tidal disruption of stars in the gravitational
�elds of the central supermassive black holes are the
viable sources of EHECR. The supernovae in these
galaxies can give birth to millisecond pulsars or mag-
netars � the neutron stars with enormous magnetic
�elds of the order of 1015G, which appear as anoma-
lous X-ray pulsars (AXPs) or soft gamma repeaters
(SGRs) [13, 15, 21]. Activity of compact objects in
our Galaxy provides evidences in favour of this as-
sumption [22]. The main potential sources of the FE
event are the galaxy UGC03574 (in case of Fe nu-
cleus) and the galaxy UGC03394 (in case of C-N-O
nuclei).
The important point for the interpretation of ob-
servations is the expected transient nature of the
EHECR acceleration in potential sources,as the ac-
celeration occurs during their �aring activity. It may
be realised in a form of an explosive activity of com-
pact stars (like the increase of power of relativistic
jets or the release of magnetised plasmoids in mi-
croquasars, magnetar magnetospheric �ares, strong
wind activity of newly-born millisecond pulsars) or
via the formation of short-lived relativistic jets as a
result of the tidal disruption of stars in the gravi-
tational �eld of a black hole [21]. Such sources of
activity must be accompanied by the �ares of radi-
ation in di�erent bands of the electromagnetic spec-
trum (though one should take into account a time
delay between the EHECR and photon arrival due to
the non-straight-line trajectory in the magnetic �eld,
which in our case is tens to hundreds of years). It is
therefore important to have the multi-wavelength ob-
servations of the potential candidates for additional
veri�cation of the source activities over the right pe-
riod of time.
Small statistics of the detected UHECRs, im-
perfection of the existing Galactic and extragalactic
magnetic �eld models, local inhomogeneity of the ex-
tragalactic magnetic �eld distribution in the vicinity
of the our Galaxy impede the search for Galactic and
extragalactic sources of the UHECR. Nevertheless,
the use of the data on CR of the highest detected en-
ergy to search for the CR sources is the most promis-
ing approach since EHECR experience the small-
est deviations in magnetic �elds. Furthermore, the
EHECR sources must be situated close enough (up
to 50�70Mpc) and their transient acceleration pro-
cess should be accompanied with the bright enough
electromagnetic radiation. Thereby the improving
statistics of EHECR, especially with the commis-
sioning in near future of the orbital UHECR detector
JEM-EUSO, gives hope for the solution of the puzzle
of the UHECR sources.
acknowledgment
The data in Table 1 are taken from the
NASA/IPAC Extragalactic Database1. This pub-
lication is based on the research supported by the
grant of the State Fund For Fundamental Research
of Ukraine (project F64/42-2016).
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43
Advances in Astronomy and Space Physics R.B.Gnatyk, Yu.N.Kudrya, V. I. Zhdanov
Fig. 1: Sky map with the arrival direction of the FE event (thick lines) and the calculated position
of a potential source at the distance of 30Mpc (thin lines) for the iron nucleus (Z = 26) with
E = 3.2 · 1020 eV (left) and the same for its energy reduced by 1 σE = 2.3 · 1020 eV (right). The
possible extragalactic sources of the FE event are also shown. The galactic coordinates are used.
Fig. 2: The increase of the Galactic latitude of the UHECR depicted
in Fig. 1 due to its de�ection in the regular Galactic magnetic �eld as
a function of the distance travelled. The outer edge of the Galaxy in
the FE event direction is at the distance of 12 kpc.
Table 1: Potential candidates of the FE event.
# name l,◦ b, ◦ Type Size, kpc Separation ϕ , min z d, Mpc
1 UGC 03501 166.26 18.24 G Im 2.3 44.6 0.00149 6.2
2 kkh 038 168.54 19.09 G Ir 2.5 173.3 0.0015 6.2
3 NGC 2344 170.25 22.95 G SA(rs) c 7.2 372.9 0.00325 13.3
4 UGC 03574 158.93 22.76 G SA(s) cd 24.9 448.6 0.00481 19.7
5 CGCG 261-017 160.06 24.02 G 5.6 448.8 0.00471 19.2
6 UGC 03647 160.05 24.14 G IBm 8.1 454.3 0.00462 19
7 UGC 03698 172.97 21.62 G Im 2.1 456.9 0.00141 5.8
8 NGC 2337 172.94 21.80 G IBm 4.7 459.7 0.00145 6.0
9 UGC 03394 157.53 16.18 G SB? 13.1 480.6 0.00607 24.9
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44
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