BEGIN:VCALENDAR VERSION:2.0 PRODID:-//CERN//INDICO//EN BEGIN:VEVENT SUMMARY:Transition from galactic to extragalactic cosmic rays DTSTART;VALUE=DATE-TIME:20070709T213000Z DTEND;VALUE=DATE-TIME:20070709T222500Z DTSTAMP;VALUE=DATE-TIME:20260718T151320Z UID:indico-contribution-37-0-1320@cern.ch DESCRIPTION:Speakers: Dr. BEREZINSKY\, Veniamin (INFN\, Laboratori Naziona li del Gran Sasso)\nDespite the radical change of origin\, the transition from galactic \nto extragalactic cosmic rays (CR) is not well established and not \nwell understood. In principle three important characteristics of CR\, \nspectrum\, chemical composition and anisotropy\, must change at\ne nergy of transition. The spectrum is naturally changing from steep \nto fl at component. The end of galactic CR is characterised by steep\nspectrum w ith exponent \\gamma ~ 3.1. If transition is natural\, \nthe extragalactic spectrum must be flatter. For rigidity-acceleration \nor rigidity-propaga tion models the end of galactic CR must be presented \nby the heaviest nu clei\, most probably by iron. The transition should\nbe characterised by c hanging the mass composition from heaviest to\nthe light nuclei\, like pr oton and helium. In the end of galactic CR \nspectrum the anisotropy shoul d be noticeable\, while for extragalactic \nCR isotropic distribution is m ore natural. There are two features in \nthe observed spectrum\, where th e transition may occur: the ankle\, \nthe flattening of the spectrum at en ergy ~10 EeV\, and the \nsecond knee at energy 0.4 - 08~EeV. Two classes of models describing \ntransition at these two energies will be reviewed. \n\nhttps://indico.nucleares.unam.mx/event/4/session/37/contribution/1320 LOCATION:Merida\, Mexico Gran Salon Yucatan (Fiesta Americana) URL:https://indico.nucleares.unam.mx/event/4/session/37/contribution/1320 END:VEVENT BEGIN:VEVENT SUMMARY:Voyager Observations of Galactic and Anomalous Cosmic Rays at the Termination Shock and in the \nHeliosheath DTSTART;VALUE=DATE-TIME:20070709T222500Z DTEND;VALUE=DATE-TIME:20070709T225500Z DTSTAMP;VALUE=DATE-TIME:20260718T151320Z UID:indico-contribution-37-0-1314@cern.ch DESCRIPTION:Speakers: Prof. MCDONALD\, Frank B. (University of Maryland)\n On December 16\, 2004 Voyager 1 at 94 AU crossed the heliospheric terminat ion\nshock and began the exploration of the vast region of the heliosheath . At the\ntermination shock the observed intensity of anomalous cosmic ray s > 4 MeV/n was\nmuch below that expected at what was generally believed t o be their acceleration site\nwhile the galactic cosmic ray intensity (150 -380 MeV/n He) was close to its solar\nmaximum value. Based on the observa tions of Voyager 1 and Voyager 2 in the immediate\nforeshock region and of the initial 2.2 years of Voyager 1 in the\nheliosheath we propose that th ere were 3 major temporal effects that collectively\nproduced the low anom alous cosmic ray intensity at the time of the termination shock\ncrossing: \n(a) The passage of the large interplanetary transients associated with t he intense\nOctober/November 2003 solar events and subsequent solar activi ty played a major\nrole in reducing the energetic particles over the ~4 mo nth period prior to the\ntermination shock crossing.\n(b) The close correl ation between the anomalous and galactic cosmic rays over cycle 23\nsugges ts a long-term solar cycle modulation of the anomalous cosmic rays at the\ ntermination shock.\n(c) There is a variation of the anomalous cosmic ray intensity associated with the\nreversal of the interplanetary magnetic fie ld at the termination shock over the\ncycle 23 solar maximum.\nIn early 20 07 the GCR He is approaching its expected solar minimum value at Voyager 1 \nand Voyager 2\, and the effects of cosmic ray modulation in the helioshe ath can be\ndetermined directly.\nIn addition\, there has been a significa nt increase in the intensity of 2.5-140 MeV\nelectrons\nstarting in the im mediate foreshock region. These electrons are especially sensitive\nto the passage of transients through the heliosheath. It should also be possible \nto estimate their local interstellar intensity.\n\nhttps://indico.nuclea res.unam.mx/event/4/session/37/contribution/1314 LOCATION:Merida\, Mexico Gran Salon Yucatan (Fiesta Americana) URL:https://indico.nucleares.unam.mx/event/4/session/37/contribution/1314 END:VEVENT BEGIN:VEVENT SUMMARY:Gamma-ray absorption and photon archeology DTSTART;VALUE=DATE-TIME:20070709T225500Z DTEND;VALUE=DATE-TIME:20070709T232500Z DTSTAMP;VALUE=DATE-TIME:20260718T151320Z UID:indico-contribution-37-0-1318@cern.ch DESCRIPTION:Speakers: Dr. STECKER\, F. W. (NASA\, Goddard\, Space Flight C enter)\nOngoing deep surveys of galaxy luminosity functions\, spectral e nergy\ndistributions and backwards evolution models of star formation ra tes\ncan be used to calculate the past history of intergalactic photo n\ndensities and\, from them\, the present and past optical depth of th e\nuniverse to gamma-rays. Stecker\, Malkan & Scully have recently done \nthis calculation for pair-production interactions of gamma-rays with\n intergalactic background light (IBL) photons of energies from 0.03 eV\nto the Lyman limit at 13.6 eV and for redshifts 0 < z < 6. This\nproc eedure can also be reversed by looking for sharp cutoffs in the\nspectr a of extragalactic gamma-ray sources such as blazars at high\nredshift s in the multi-GeV energy range with GLAST. Determining the\ncutoff ene rgies of sources with known redshifts and little intrinsic\nabsorption m ay enable a more precise determination of the IBL photon\ndensities in t he past\, i.e.\, the "archeo-IBL"\, and therefore allow a\nbetter measur e of the past history of the total star formation rate\,\nincluding that from galaxies too faint to be observed. Conversely\,\nobservations of sharp high energy cutoffs in the gamma-ray spectra of\nsources at unknow n redshifts can be used instead of spectral lines to\ngive a measure of t heir redshifts.\n\nhttps://indico.nucleares.unam.mx/event/4/session/37/con tribution/1318 LOCATION:Merida\, Mexico Gran Salon Yucatan (Fiesta Americana) URL:https://indico.nucleares.unam.mx/event/4/session/37/contribution/1318 END:VEVENT END:VCALENDAR