Analysis of the Arrival Directions of Ultrahigh En

A.A. Mikhailov

Yu.G. Shafer Institute of Cosmophysical Research and Aeronomy, 31 Lenin Ave., 677980 Yakutsk, Russia

mikhailov@ikfia.ysn.ru

Abstract: The arrival directions of ultrahigh energy extensive air showers (EAS) by

Yakutsk, AGASA and SUGAR array data are considered. For the first time, the maps of

equal exposition of celestial sphere for the distribution of particles by AGASA and SUGAR

array data have been constructed. The large-scale anisotropy of E>4.1019 eV cosmic rays

from the side of Input and Output of the Galaxy Local Arm by Yakutsk, AGASA and

SUGAR array data has been detected. The problem of cosmic ray origin is discussed. Introduction

Until there is an opinion, that cosmic rays with energy E>4.1019 eV are isotropic (see for example [1,2]). Here data of array EAS Yakutsk, AGASA, SUGAR with take into account their exposition on celestial sphere are analyzed.

Experimental data and discussion

At first, we have analyzed Yakutsk EAS array data whose shower cores lie inside the array perimeter and the accuracy to determine the arrival angle is ~ 3°. The particle energy is estimated by a new formula according to [3]. Fig.1 presents the distribution of 34 particles with E>4.1019 eV on the map of equal exposition of celestial sphere (the method to construct this map is based on the estimation of the expected number of showers [4,5] and etc.). At the map of equal exposition the equal number of particles from the equal parts of sphere is expected. As seen in Fig.1, the particles practically have isotropic distribution on the celestial sphere. However, the most concentration of particles is observed from the side of Input of Galaxy Local Arm at galactic latitude 3.3°For the distribution of particles with E>4.1019 eV by AGASA array data [6] we construct the map of equal exposition of celestial sphere according to [4,5]. As seen from this map, almost a half of events (25 particles of 58) are within of coordinates toward the side of Input the Local Arm 11.2°be P~0.0003. Thus, the statistically significant particle flux in the case of the AGASA array is

observed from the side of the Input of Local Arm as

data of Yakutsk EAS array.

For the distribution of particles with E>4.1019 eV

of the SUGAR array [7] the map of equal exposition

of celestial sphere is also constructed. In [8] have

shown, that model ‘Hillas” of an estimation of energy

of EAS is more correct, according to this model 80

particles with E>4.1019 eV are registered.

The most concentration 12 of 80 particles [7] is observed toward the Output of Local Arm within

coordinates -28.9°< b <19.3° and 248°We found [9] if the sources of particles are distributed in the Galaxy disc, then the protons with E~1018 eV in main move along the field lines of the

Galaxy Arms. On the basis, it may be suggested that

the observed flux of particles with E>4.1019 eV from

Fig.2. The same as in Fig.1 for the AGASA array data. Dashed quadrangles on the upper a considered region of a celestial sphere.

Fig.1. On the map of equal exposition particles with E>4.1019 eV are shown by the

Y akutsk EAS array data. SGP – Super

Galactic Plane (plane of Local cluster).

Dashed quadrangles on the left – a considered region of a celestial sphere. δ -

declination, RA – right ascension, b, l – galactic latitude and longitude. Big circles – clusters.

v

Fig.3. The same as in Fig.1 for the SUGAR array data. Dashed quadrangles on the right – a considered region of a celestial sphere.

Early by data of arrays EAS Haverah Park and Yakutsk at E~1019 eV the increased flux of particles from the anticenter at latitude b<0° were found [5,12]. We consider the arrival directions of EAS by data Yakutsk, AGASA, SUGAR with E>4.1019 eV for the center in longitude -90°0°)S2/n2(b<0°)S1, where n1, n2 –number of particles at b>0° and b<0°, S1 and S2 are exposure of the celestial sphere to arrays at b>0° and b<0° according [5]. If the cosmic rays are isotropy then R= 1. According to Fig.4a the increased flux of particles is observed from the center of the Galaxy at latitude b>0° and to Fig.4b the increased flux of particles - from the anticenter at latitude b<0°, as predict in galactic model of an origin cosmic rays [11].

It is note, that from northern and southern poles of the Earth at δ ~ ±90° by data of arrays AGASA and SUGAR (Fig.2, 3) concentration of density of distribution of particles is observed.

Conclusion

The large–scale anisotropy of particles at

E>4.1019 eV from the side of the Input and

Output of Galaxy Local Arm has been found.

The particles of ultrahigh energies are most

likely the superheavy nuclei and they have a

galactic origin.

Fig.4. Ratio number of particles R with take into

account exposure of arrays at b>0°/b<0°: a – from

center of Galaxy, b - from the anticenter of Galaxy.References

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