Speaker
Dr
Anna Uryson
(Lebedev Physical Institute, RAS)
Description
The main problem of ultra-high energy cosmic rays (UHECRs) is where they come from. Point UHECR sources seem to be appropriate but they are not discovered. Information about UHECR origin is obtained from particle energy spectrum. In space, particles lose energy in interaction with cosmic microwave background. This results in a lack of particles at E>10^20 eV at the Earth (GZK-effect) if UHECRs come from distances of more than ~100 Mpc. The spectrum of UHECRs collected from nearer distances have no GZK-suppression. Experimental data indicate that UHECR energy spectrum is suppressed. However, there may be one more reason for spectrum suppression along with GZK-effect. Particles are accelerated to the maximum energy of ~10^21 eV due to conditions in possible UHECR sources. As sources are still unknown, the acceleration energy limit cannot be ruled out. So the reason for the spectrum suppression is not clear.
Another effect of UHECR interaction with cosmic microwave background is electromagnetic cascades that particles initiate in extragalactic space (Hayakawa (1966), Prilutski&Rozental (1970)). In cascade, transverse distances between particles are gigantic (in spite of small angle distances) due to large lengths at which cascades develop. Therefore intensity of cascade particles is low. However we demonstrate that it is possible to study source remoteness and initial particle energy spectra by studying cascades.
We have calculated intensity of cascade quanta at E≈10^14 eV and found that it depends on above mentioned source characteristics. As in the Earth atmosphere cosmic rays initiate air showers, selecting quanta-initiated showers (and excluding those from the galactic plane, gamma-ray sources, etc.) makes it possible to obtain UHECR-source parameters. The statistics of showers registered at 10^14 eV being ~10^8, the number of quanta-initiated showers is 0 or ~1000 depending on source characteristics. This difference is large enough to use this method for studying UHECR sources.
| Registration number following "ICRC2015-I/" | 1042 |
|---|---|
| Collaboration | -- not specified -- |
Author
Dr
Anna Uryson
(Lebedev Physical Institute, RAS)
