Very long time variations of cosmic ray intensity and their origin

Abstract

A large number of sources contribute to cosmic rays in the Galaxy. By studying time profiles of cosmic ray intensity over a very longtime, it is hoped to get some information about a possible source. In this respect, long-lived radioisotopes like 10Be, 14C, produced by cosmic ray interactions in the Earth's atmosphere, carry information on the longtime variations in the local cosmic ray intensity. The record of 10Be concentrations in the Vostok Ice Core in Antartica, over the past 100 Kiloyears(Kyr), displays several steep and relatively brief increases. Out of these, the increase at about 35 Kyr is attributed to increase in cosmic ray intensity arriving at the Earth. This increase is interpreted as due to the arrival of the shock-front from the recently discovered gamma ray and X-ray Pulsar, Geminga. Thus a direct connection between a non-solar cosmic ray source and the resultant increase in the cosmic ray intensity at the Earth is established for the first time. It is suggested that the 26Al intensity in the local interstellar bubble should be doubled as a result of this source.