``Local'' Explanation for Cosmic Ray Conundrum

``However, if the cosmic rays of 10¹⁸−10¹⁹ eV are nuclei, the turbulent Galactic micro-Gauss magnetic fields [2] can retain them in the Galaxy and isotropize their directions sufficiently to show no disagreement with the data. Moreover, since the diffusion times depend on the rigidity, the observed composition can be altered by diffusion [3]. Since the heavier nuclei spend more time in the Galaxy than the lighter nuclei and protons, they have the higher number density and flux. Thus, diffusion alone can alter the composition of UHECRs produced by the Galactic sources and increase the observed fraction of nuclei.''

``A cluster of several UHECRs around Cen A detected by PAO may be the result of such a fluctuation due to one GRB that happens to coincide with Cen A. Alternatively, since we expect the high-energy protons to escape from our Galaxy and from other galaxies, the cluster around Cen A may be due to extragalactic protons. Unlike protons, UHE nuclei from the last GRB do not introduce a large degree of anisotropy, as one can see form Fig. 2 based on a semi-realistic Monte Carlo simulation.''

``We have shown that effects of rigidity-dependent diffusion of UHECRs from possible Galactic sources, such as past GRBs (or rare types of supernovae), in the Milky Way can produce the energy-dependent composition as observed by PAO [1]. The simplest two-component model including protons and iron nuclei from the Galactic sources gives a good fit to composition [1] and spectrum [24] for reasonable values of the Galactic magnetic fields.''

Taken from arXiv .

The Pierre Auger Observatory (PAO) is a new type of particle detector. If Calvez, Kusenko, and Nagataki are right, this huge object is a sort of ``microscope'' for our galaxy.

Imagine you are humongous being looking down through the eyepiece of a huge microscope. You will see stars, like we see cells.

The lights, showing up here and there in your microscope/telescope, are Gamma Ray Bursts (GRBs). Inside those lightning phenomena our Galaxy is not like outside them. In this micro/macro analogy I am making here, you'll find intense forces, just ask anybody stricken by lightning.

Calvez et al., propose that inside the Galaxy (``local''), these fields are strong, albeit rare, to affect cosmic ray paths coming from outside the Galaxy; thus explaining the ultra high energy cosmic rays (UHECRs) conundrum.

The problem that needed explanation, as expressed in the quote above ``Since the heavier nuclei spend more time in the Galaxy than the lighter nuclei and protons, they have the higher number density and flux.'' Mass number dependence with energy was not expected from extragalactic objects getting to Earth unimpeded. These scientists claim, they are impeded, a little bit, here and there, and voilá, they can explain the data.

Again if they are right. Now we know our Galaxy better, because we have this microscope/telescope in the Argentinean plains.

The Cen A anomaly brought my attention to this problem. These authors have something to say about it.

I hope so :-)