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one of the outstanding questions in contemporary astronomy is the origin of hecrs ranging from below the knee of the cosmic - ray spectrum at @xmath4 ev to the highest energies exceeding @xmath5 ev . ultra - high energy cosmic rays ( uhecrs ) , defined here as cosmic rays ( crs ) with energies greater than the ankle energy at @xmath6 ev , are probably extragalactic protons in view of their large gyroradii , lack of enhancements of arrival directions toward the galactic plane , the observed flattening of the cosmic - ray spectrum at the ankle ( which could result from photopair energy - loss processes on cosmic - ray protons @xcite ) , and suggestions of a composition change from heavy to light nuclear composition above @xmath7 ev @xcite ( see @xcite for a review ) . because high - energy protons will radiate @xmath1-ray photons from hadronic and leptonic processes at the site where they are produced , the most likely candidate sources of uhecrs are extragalactic nonthermal @xmath1-ray emitters , specifically grbs and blazar agns . models for these sources involve jets of relativistic plasma that are ejected by accreting black holes . the paucity of blazar sources within tens of mpc that could account for the near isotropy of cosmic rays at energies @xmath8 ev suggest that grbs are the sources of uhecrs . grbs in the galaxy will also accelerate hecrs , and could form most of the cosmic rays with energies between @xmath9 ev and @xmath10 ev .    several types of observations can test this hypothesis . detection of high - energy neutrinos from a grb , which would requires an ultra - relativistic hadronic component that is much more powerful than the nonthermal electron component that produces the hard x - ray and soft @xmath1-ray emissions from grbs @xcite , is predicted by this model . another prediction is the detection of hadronic emission components in the spectra of grbs . the unusual @xmath1-ray emission component observed @xcite in grb 941017 , which could be caused by ultra - relativistic hadron acceleration and photopion processes in the inner jets of grbs @xcite , could be the first example of such a signature . a third observation that would implicate grbs as the sources of hecrs is the detection of high - energy neutron @xmath2-decay halos around star - forming galaxies @xcite , including @xmath2-decay emission from grbs in the milky way @xcite . a fourth observation is the absence of @xmath11 ev cosmic - ray _ point - source _ excesses , such as the source claimed to be detected with the sugar array . this is opposite to the conclusion arrived by @xcite , as explained below , and will soon be tested with the auger experiment , which is now taking data . we have recently proposed a model for hecrs from galactic and extragalactic grbs @xcite , building on previous suggestions that uhecrs are accelerated by extragalactic grbs @xcite . in our model , relativistic outflows in grbs are assumed to inject power - law distributions of cosmic rays to the highest ( @xmath12 ev ) energies . a diffusive propagation model for hecrs from a single recent grb within @xmath13  kpc from earth that took place within the last 0.5 million years can explain the kascade data for the cr ion spectra near and above the knee . the cr spectrum at energies @xmath11  ev is fit with crs from extragalactic grbs . uhecrs produced by extragalactic grbs lose energy from momentum redshifting and photo - pair and photo - pion production on the cmbr during propagation through a flat @xmath14cdm universe ( we take @xmath15 and @xmath16 in our calculations ) . attenuation produces features in the uhecr flux at characteristic energies @xmath17  ev and @xmath18  ev due to photo - pair and photo - pion energy - loss processes , respectively , from distant sources at @xmath19 . the grb rate - density evolution is assumed to follow the sfr history derived from the blue and uv luminosity density of distant galaxies . to accommodate uncertainty in the sfr evolution , we take two models , one based on optical / uv measurements without extinction corrections ( lower sfr ) , and the other with extinction corrections ( upper sfr ) . the upper sfr is roughly a factor of 3(10 ) greater than the lower sfr at red - shift @xmath20 for @xmath21  ev crs , both evolution models give the same flux , but the upper sfr contributes a factor @xmath22 more cr flux over the lower sfr at energies @xmath23  ev . ev and using the upper limit to the sfr evolution . we also show the agasa data ( triangles ) , but do not include these in our fits ( see @xcite for references to the data ) . the cutoff energy for the galactic - halo component is @xmath24  ev and @xmath25 the fit implies that the transition from galactic to extragalactic crs occurs near the second knee and that the ankle is associated with photo - pair production . ] the combined kascade , hires - i and hires - ii monocular data between @xmath26  ev to @xmath27  ev are fit in fig.1 which shows our best case , with cosmic - ray number injection index @xmath28 , @xmath29  ev , and the upper sfr . a @xmath30 spectrum provides a worse fit than the @xmath31 case , although the cr energy demand is less in this case because crs are injected equally per unit decade in particle energy . the transition between galactic and extragalactic crs is found in the vicinity of the second knee at @xmath32  ev , consistent with a heavy - to - light composition change @xcite . the ankle , at @xmath33  ev , is interpreted as a suppression from photo - pair losses , analogous to the gzk suppression . by normalizing the energy injection rate to that required to produce the cr flux from extragalactic sources observed locally , we determine the amount of energy a typical grb must release in the form of nonthermal hadrons . our results imply that grb blast waves are baryon - loaded by a factor @xmath34 compared to the primary electron energy that is inferred from the fluxes of hard x - rays and soft @xmath1 rays measured from grbs .    in fig . 2 we show the neutrino fluences expected in the collapsar grb scenario from a burst with photon fluence @xmath35 . the neutrino fluences are calculated for 3 values of the doppler factor @xmath36 from a grb at redshift @xmath37 ( we take a hubble constant of 65 km s@xmath38 mpc@xmath38 in the calcuations ) . in order to demonstrate the dependence of the neutrino fluxes on @xmath36 , we consider 3 values of @xmath36 and set @xmath39 in this calculation . we assume that the prompt emission is contributed by @xmath40 spikes with characteristic timescales @xmath41 each , which defines the characteristic size ( in the proper frame ) of the emitting region associated with each individual spike through the relation @xmath42 . the numbers of muon neutrinos that would be detected from a single grb with these parameters with icecube for @xmath43 and 300 are @xmath44 and 0.016 , respectively . we should note , however , that for the assumed value of @xmath45 , the calculated total fluence of neutrinos ( both @xmath46 and @xmath47 ) produced when @xmath48 is @xmath49 erg @xmath50 , i.e. , by a factor @xmath51 _ larger _ than the assumed radiation fluence . this means that the maximum value of the baryon loading that could be allowed if the high - energy radiation fluence is less than the x/@xmath1 fluence for this particular case should be about 8  10 , instead of 20 , in order that the hadronic cascade @xmath1-ray flux is guaranteed not to exceed the measured photon flux . consequently , the expected number of neutrinos for @xmath52 should be reduced to @xmath53 . on the other hand , the neutrino fluence for the case @xmath54 is equal to @xmath55 , so this accommodates an increased baryon - loading from @xmath56 up to @xmath57 , with the expected number of neutrinos observed by icecube being @xmath58 . if the radiation fluence at mev gev energies is allowed to exceed the x/@xmath1 fluence by an order of magnitude , a possibility that glast will resolve , then the expected number of detected neutrinos could be increased correspondingly .     with x - ray / mev @xmath1-ray fluence of @xmath59 ergs @xmath50 and doppler factors @xmath48 , 200 and 300 , and a nonthermal baryon - loading factor @xmath60 . ]    for the large baryon load required for the proposed model of hecrs , calculations show that 100 tev 100 pev neutrinos could be detected several times per year from all grbs with kilometer - scale neutrino detectors such as icecube @xcite . detection of even 1 or 2 neutrinos from grbs with icecube or a northern hemisphere neutrino detector will provide compelling support for this scenario for the origin of high - energy and uhe cosmic rays . based on joint analysis of batse large area detector and the egret total absorption shower counter data , gonzlez et al.@xcite reported the detection of an anomalous mev emission component in the spectrum of grb 941017 that decays more slowly than the prompt emission detected with the lad in the @xmath61 kev  1 mev range . the multi - mev component lasts for @xmath62 seconds ( the @xmath63 duration of the lower - energy prompt component is 77 sec ) , and is detected with the batse lad near 1 mev and with the egret tasc between @xmath13 and 200 mev . the spectrum is very hard , with a photon number flux @xmath64 , where @xmath65 is the observed photon energy . this component is not predicted or easily explained within the standard leptonic model for grb blast waves , though it possibly could be related to comptonization of reverse - shock emission by the forward shock electrons @xcite , including self - absorbed reverse - shock optical synchrotron radiation @xcite . another possibility is that hadronic acceleration in grb blast waves could be responsible for this component . we have argued @xcite that this component could be a consequence of the acceleration of hadrons at the relativistic shocks of grbs . a pair - photon cascade initiated by photohadronic processes between high - energy hadrons accelerated in the grb blast wave and the internal synchrotron radiation field produces an emission component that appears during the prompt phase , as shown in fig .  3 . photomeson interactions in the relativistic blast wave also produce a beam of uhe neutrons , as proposed for blazar jets @xcite . subsequent photopion production of these neutrons with photons outside the blast wave will produce a directed hyper - relativistic electron - positron beam in the process of charged pion decay and the conversion of high - energy photons formed in @xmath66 decay . these energetic leptons produce a synchrotron spectrum in the radiation reaction - limited regime extending to @xmath67 gev energies , with properties in the 1  200 mev range similar to that measured from grb 941017 . grbs displaying these anomalous @xmath1-ray components are most likely to be detected as sources of high - energy neutrinos @xcite . if grbs are the sources of hecrs , then high - energy neutrons will be formed at the burst site through photo - pion processes and , being neutral , can escape to intergalactic space . indeed , it is possible that charged ultra - high energy protons and ions are trapped by ambient magnetic field and lose energy adiabatically near the acceleration site , so that uhecrs are made primarily of neutron - decay protons .    the decay of the neutrons far from the grb through the process @xmath68 leads to @xmath2-decay electrons that make synchrotron and compton radiation . the best prospect for discovering neutron - decay halos is to search for diffuse optical synchrotron halos surrounding field galaxies that display active star formation @xcite . grbs that have recently taken place in our galaxy will produce compton radiation at tev energies that could be detected by the _ hess _ and _ veritas _ imaging air cherenkov telescopes @xcite . the emission of nonthermal synchrotron and compton radiation from photopion processes by uhecrs traveling through intergalactic space will also produce a nonthermal component of the diffuse radiation background , which can be used to determine the magnetic field of intergalactic space . because the milky way is actively making young high - mass stars , grbs will also occur in our galaxy . the rate of grbs in the milky way is very uncertain because of lack of precise knowledge about the opening angle of grb jets , but could be as frequent as once every 10,000 years . over the age of the galaxy , there is a good chance that a nearby powerful grb with a jet oriented towards earth could have lethal consequences for life . it has recently been argued @xcite that such an event contributed to the ordovician extinction event 440 myrs ago . to assess cosmic ray transport from a grb , we @xcite developed a 3d propagation model to simulate the sequence of irradiation events that occurs when a grb jet is pointed towards earth . the cosmic rays move in response to a large - scale magnetic field that traces the spiral arm structure of the galaxy , and they diffuse through pitch - angle scattering with magnetic turbulence . the magnetic field of the galaxy is modeled as a bi - symmetric spiral for the galaxy s disk , and a dipole magnetic field for the galaxy s halo @xcite . the evolution of the particle momentum is found by solving the lorentz force equation . a monte carlo simulation of pitch - angle scattering and diffusion was developed that takes into account the energy dependence of the cosmic - ray mean free path . 4 displays the cosmic - ray halo that surrounds a grb source 14,000 years after the grb event . the geometry of the system is modeled by twin radial jets of cosmic rays with a jet - opening half - angle of 0.1 radian . a conical shell forms as a result of protons and neutron - decay protons with energies @xmath11 ev . @xmath69 ev . ]    the hypothesis @xcite that the @xmath11 ev cosmic - ray excesses detected with the agasa ( akeno giant air shower array ) and sugar arrays @xcite are cosmic - ray neutrons from a grb is not , however , supported by our simulations . the relativistic blast waves in a grb accelerate the highest energy cosmic rays over timescales of weeks or less @xcite , and the high - energy neutrons therefore arrive on this same timescale . cosmic ray protons with energies @xmath70 ev are delayed over a timescale @xmath71 years from a source at the distance of the galactic center . for the sugar excess , which is coincident on the sub - degree angular scale with a point source , a grb would have to take place within weeks of the observation for cosmic - ray protons to maintain their direction to the source . including the requirement that the grb jet was also pointed towards earth means that an impulsive grb origin is excluded because such an event is so improbable . the greater ( @xmath72 ) extent of the agasa excess does not conclusively exclude a grb origin , but here the diffuse excess could simply reflect the greater pathlength for cosmic - ray proton collisions with spiral arm gas along the cygnus arm .    because the sugar point source does not admit an impulsive grb solution , only cosmic rays from a persistent source , such as a microquasar , could make such an excess . the hypothesis @xcite that grbs are sources of @xmath0 ev cosmic rays is therefore incompatible with such a source . our cosmic - ray origin hypothesis will soon be tested by results from the auger observatory to confirm or refute the existence of the sugar source . if the source is real , then our grb / cosmic - ray model is incomplete . we have summarized a complete model @xcite for hecrs from galactic and extragalactic grbs . our interpretation of the hecr spectrum requires that grbs are hadronically dominated , which is necessary @xcite for neutrinos from grbs to be detectable with a km - scale neutrino telescope . detection of high - energy neutrinos from grbs will provide strong support for this model . searches for anomalous @xmath1-ray emission components with _ glast _ , as already observed form grb 941017 with batse and egret , will give additional support for cosmic - ray acceleration in grbs , provided that these components can be attributed to hadronic cascade radiation @xcite . observations of neutron @xmath2-decay radiation from recent grbs in the galaxy @xcite and around galaxies that host grbs @xcite provide further tests of the hypothesis that high - energy cosmic rays are accelerated by grbs . the ground - based auger experiment , which will measure air showers and nitrogen fluorescence from the uhecr interactions in the atmosphere , is now taking data . this experiment will greatly expand our knowledge of high - energy cosmic rays , for example , by measuring with high quality statistics and checks on calibration the spectrum of @xmath12 ev cosmic rays which produce high - energy neutrinos at their source and as they propagate through intergalactic space . detection of @xmath73 ev cosmic - ray point sources is incompatible with an origin from impulsive grbs , so that if the sugar source is confirmed , this cosmic - ray origin model is incomplete . i am pleased to acknowledge my collaboration with armen atoyan , jeremy holmes , and stuart wick . this work was supported by the office of naval research and a nasa _ gamma ray large area space telescope _ grant .
a complete model for the origin of high - energy ( @xmath0 ev ) cosmic rays from gamma - ray bursts ( grbs ) and implications of this hypothesis are described . 
 detection of high - energy neutrinos from grbs provide an unambiguous test of the model . 
 evidence for cosmic - ray acceleration in grbs is suggested by the detection of anomalous @xmath1-ray components such as that observed from grb 941017 . 
 neutron @xmath2-decay halos around star - forming galaxies such as the milky way are formed as a consequence of this model . 
 cosmic rays from grbs in the galaxy are unlikely to account for the @xmath3 ev cosmic - ray excess reported by the sydney university giant air shower recorder ( sugar ) , but could contribute to past extinction events . 
 [ 1999/12/01 v1.4c il nuovo cimento ]