arXiv subjects

Jörg R. Hörandel

Publications and source records attributed to Jörg R. Hörandel.

21 records · Page 2Linked to original sources

arXiv2011

Nearby supernova remnants and the cosmic-ray spectral hardening at high energies

Recent measurements of cosmic-ray spectra of several individual nuclear species by the CREAM, TRACER, and ATIC experiments indicate a change in the spectral index of the power laws at TeV energies. Possible explanations among others include non linear diffusive shock acceleration of cosmic-rays, different cosmic-ray propagation properties at higher and lower energies in the Galaxy and the presence of nearby sources. In this paper, we show that if supernova remnants are the main sources of cosmic rays in our Galaxy, the effect of the nearby remnants can be responsible for the observed spectral changes. Using a rigidity dependent escape of cosmic-rays from the supernova remnants, we explain the apparent observed property that the hardening of the helium spectrum occurs at relatively lower energies as compared to the protons and also that the spectral hardening does not persist beyond $\sim (20-30)$ TeV energies.

astro-ph.HE↗

arXiv2011

On the point source approximation of nearby cosmic-ray sources

In this paper, we check in detail the validity of the widely adopted point source approximation for nearby cosmic-ray (CR) sources. Under an energy independent escape model for CRs from the sources, we show that for young nearby sources, the point source approximation breaks down at lower energies and the CR spectrum depends on the size and the morphology of the source. When applied to the nearby supernova remnants (SNRs), we find that the approximation breaks down for some of the individual remnants like the Vela, but interestingly it still holds good for their combined total spectrum at the Earth. Moreover, we also find that the results obtained under this simple approximation are quite different from those calculated under an energy dependent escape model which is favored by diffusive shock acceleration models inside SNRs. Our study suggests that if SNRs are the main sources of CRs in our Galaxy, then the commonly adopted point source model (with an energy independent escape scenario) appears flawed for CR studies from the nearby SNRs.

astro-ph.GA↗

arXiv2011

A possible correlation between the high energy electron spectrum and the cosmic-ray secondary-to-primary ratios

Recent observations of high energy cosmic-ray electrons by the Fermi-LAT and the HESS experiments between $20$ GeV and $5$ TeV have found that the energy spectrum closely follow a broken power-law with a break at around $1$ TeV. On the other hand, measurements of cosmic-ray secondary-to-primary ratios like the boron-to-carbon ratio seem to indicate a possible change in the slope at energies around $100$ GeV/n. In this paper, we discuss one possible explanation for the observed break in the electron spectrum and its possible correlation with the flattening in the secondary-to-primary ratios at higher energies. In our model, we assume that cosmic-rays after acceleration by supernova remnant shock waves, escape downstream of the shock and remain confined within the remnant until the shock slows down. During this time, the high-energy electrons suffer from radiative energy losses and the cosmic-ray nuclei undergo nuclear fragmentations due to their interactions with the matter. Once the cosmic-rays are released from the supernova remnants, they follow diffusive propagation in the Galaxy where they further suffer from radiative or fragmentation losses.

astro-ph.HE↗