arXiv subjects

Eli Waxman

Publications and source records attributed to Eli Waxman.

At least 127 records · Page 7Linked to original sources

arXiv2003

Neutrino signatures of the supernova - gamma ray burst relationship

We calculate the TeV-PeV neutrino fluxes of gamma-ray bursts associated with supernovae, based on the observed association between GRB 030329 and supernova SN 2003dh. The neutrino spectral flux distributions can test for possible delays between the supernova and the gamma-ray burst events down to much shorter timescales than what can be resolved with photons. As an illustrative example, we calculate the probability of neutrino induced muon and electron cascade events in a km scale under-ice detector at the South Pole, from the GRB 030329. Our calculations demonstrate that km scale neutrino telescopes are expected to detect signals that will allow to constrain supernova-GRB models.

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arXiv2003

Implications of the $γ$-ray Polarization of GRB 021206

We compare two possible scenarios for the producing of high level of polarization within the prompt emission of a GRB: synchrotron emission from a relativistic jet with a uniform (in space and time) magnetic field and synchrotron emission from a jet with a random magnetic field in the plane of the shock. Somewhat surprisingly we find that both scenarios can produce a comparable level of polarization ($\sim 45-50$% for the uniform field and $\sim 30-35$% for a random field). Uniform time independent field most naturally arises by expansion of the field from the compact object. It requires a $10^{12}$G field at the source and a transport of the field as $\propto R^{-1}$. It {\it does not} imply Poynting flux domination of the energy of the wind. There is a serious difficulty however, within this scenario, accounting for particle acceleration (which requires random magnetic fields) both for Poynting flux and non-Poynting flux domination. Significant polarization can also arise from a random field provided that the observer is located within $1/Γ$ orientation from a narrow ($θ_j \sim 1/Γ$) jet. While most jets are wider, the jet of GRB 021206 from which strong polarization was recently observed, was most likely very narrow. GRB 021206 is among the strongest bursts ever. Adopting the energy-angle relation we find an estimated angle of $<1/40$rad or even smaller. Thus, for this particular burst the required geometry is not unusual. We conclude that the RHESSI observations suggest that the prompt emission results from synchrotron radiation. However, in view of the comparable levels of polarizations predicted by both the random field and the homogeneous field scenarios these observations are insufficient to rule out or confirm either one.

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arXiv2003

High Energy Neutrinos from Gamma-Ray Bursts with Precursor Supernovae

The high energy neutrino signature from proton-proton and photo-meson interactions in a supernova remnant shell ejected prior to a gamma-ray burst provides a test for the precursor supernova, or supranova, model of gamma-ray bursts. Protons in the supernova remnant shell, and photons entrapped from a supernova explosion or a pulsar wind from a fast-rotating neutron star remnant provide ample targets for protons escaping the internal shocks of the gamma-ray burst to interact and produce high energy neutrinos. We calculate the expected neutrino fluxes, which can be detected by current and future experiments.

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arXiv2003

Has the GZK suppression been discovered?

The energy spectra of ultra high energy cosmic rays reported by the AGASA, Fly's Eye, Haverah Park, HiRes, and Yakutsk experiments are all shown to be in agreement with each other for energies below 10^{20} eV (after small adjustments, within the known uncertainties, of the absolute energy scales). The data from HiRes, Fly's Eye, and Yakutsk are consistent with the expected flux suppression above 5\times 10^{19} eV due to interactions of cosmic rays with the cosmic microwave background, the Greisen-Zatsepin-Kuzmin (GZK) "supression," and are inconsistent with a smooth extrapolation of the observed cosmic ray energy spectrum to energies > 5\times 10^{19}$ eV. AGASA data show an excess of events above 10^{20} eV, compared to the predicted GZK suppression and to the flux measured by the other experiments.

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arXiv2002

Stability of an Ultra-Relativistic Blast Wave in an External Medium with a Steep Power-Law Density Profile

We examine the stability of self-similar solutions for an accelerating relativistic blast wave which is generated by a point explosion in an external medium with a steep radial density profile of a power-law index > 4.134. These accelerating solutions apply, for example, to the breakout of a gamma-ray burst outflow from the boundary of a massive star, as assumed in the popular collapsar model. We show that short wavelength perturbations may grow but only by a modest factor <~ 10.

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arXiv2002

Gamma-Rays from Intergalactic Shocks

Structure formation in the intergalactic medium (IGM) produces large-scale, collisionless shock waves, where electrons can accelerate to highly relativistic energies. Such electrons can Compton scatter cosmic microwave background photons up to gamma-ray energies. We study the radiation emitted in this process using a hydrodynamic cosmological simulation of a LCDM universe. This radiation, extending beyond TeV energies, has roughly constant energy flux per decade in photon energy, in agreement with the predictions of Loeb & Waxman (2000). Assuming that a fraction xi_e=0.05 of the shock thermal energy is transferred to relativistic electrons, as inferred from collisionless non-relativistic shocks in the interstellar medium, we find that the radiation energy flux, e^2(dJ/de)~ 50-160 eV cm^-2 s^-1 sr^-1, constitutes ~10% of the extragalactic gamma-ray background. The associated point-sources are too faint to account for the ~60 unidentified EGRET gamma-ray sources, but GLAST should resolve several sources associated with large-scale IGM structures for xi_e~0.03, and many more sources for larger xi_e. The intergalactic origin of the radiation can be verified through a cross-correlation with, e.g., the galaxy distribution that traces the same structure. Its shock-origin may be tested by a cross-correlation with radio synchrotron radiation, emitted as the same electrons gyrate in post-shock magnetic fields. We predict that GLAST and Cherenkov telescopes such as MAGIC, VERITAS and HESS should resolve gamma-rays from nearby (redshifts z < 0.01) rich galaxy clusters, perhaps in the form of a \~5-10 Mpc diameter ring-like emission tracing the cluster accretion shock, with luminous peaks at its intersections with galaxy filaments detectable even at z~0.025.

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arXiv2002

Galactic Constraints on the Sources of Ultra-High Energy Cosmic Rays

We show that if the sources of ultra-high energy cosmic rays (UHECRs) with energies E>10^{19}eV are associated with galaxies, then the production of UHECRs must occur in transient events. Our galaxy is currently at a dim state in between transients. The time interval between transients is >3x10^4 years if the minimum Lorentz factor to which protons are accelerated in the transients is between 10^3 and 10^7. This constraint is satisfied by gamma-ray bursts.

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arXiv2002

Orphan GRB radio afterglows: Candidates and constraints on beaming

The number of orphan radio afterglows associated with gamma-ray bursts (GRBs) that should be detected by a flux limited radio survey, is calculated. It is shown that for jetted GRBs this number is smaller for smaller jet opening angle (theta), contrary to naive expectation. For a beaming factor f_b^{-1}=(theta^2/2)^{-1} = 500, roughly the value inferred by Frail et al. (2001) from analysis of afterglow light curves, we predict that between several hundreds to several thousands orphan radio afterglows should be detectable (over all sky) above 1 mJy at GHz frequencies at any given time. This orphan population is dominated by sources lying at distances of a few hundred Mpc, and having an age of ~1 yr. A search for point-like radio transients with flux densities greater than 6 mJy was conducted using the FIRST and NVSS surveys, yielding a list of 25 orphan candidates. We argue that most of the candidates are unlikely to be radio supernovae. However, the possibility that they are radio loud AGNs cannot be ruled out without further observations. Our analysis sets an upper limit for the all sky number of radio orphans, which corresponds to a lower limit f_b^{-1}>10 on the beaming factor. Rejection of all candidates found in our search would imply f_b^{-1}>100. This, and the fact that some candidates may indeed be radio afterglows, strongly motivate further observations of these transients.

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arXiv2002

Collective processes in relativistic plasma and their implications for gamma-ray burst afterglows

We consider the effects of collective plasma processes on synchrotron emission from highly relativistic electrons. We find, in agreement with Sazonov (1970), that strong effects are possible also in the absence of a non-relativistic plasma component, due to the relativistic electrons (and protons) themselves. In contrast with Sazonov, who infers strong effects only in cases where the ratio of plasma frequency to cyclotron frequency is much larger than the square of the characteristic electron Lorentz factor, nu_p/nu_B >> gamma^2, we find strong effects also for 1 << nu_p/nu_B << gamma^2. The modification of the spectrum is prominent at frequencies nu < nu_{R*} = nu_p min[gamma, (nu_p/nu_B)^(1/2)], where nu_{R*} generalizes the Razin-Tsytovich frequency, nu_R = gamma nu_p, to the regime nu_p/nu_B << gamma^2. Applying our results to gamma-ray burst (GRB) plasmas, we predict a strong modification of the radio spectrum on minute time scale following the GRB, at the onset of fireball interaction with its surrounding medium, in cases where the ratio of the energy carried by the relativistic electrons to the energy carried by the magnetic field exceeds ~ 10^5. Plausible electron distribution functions may lead to negative synchrotron reabsorption, i.e to coherent radio emission, which is characterized by a low degree of circular polarization. Detection of these effects would constrain the fraction of energy in the magnetic field, which is currently poorly determined by observations, and, moreover, would provide a novel handle on the properties of the environment into which the fireball expands.

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arXiv2001

Stability of the Forward/Reverse Shock System Formed by the Impact of a Relativistic Fireball on an Ambient Medium

We analyze the stability of a relativistic double (forward/reverse) shock system which forms when the fireball of a Gamma-Ray Burst (GRB) impacts on the surrounding medium. We find this shock system to be stable to linear global perturbations for either a uniform or a wind (r^{-2}) density profile of the ambient medium. For the wind case, we calculate analytically the frequencies of the normal modes which could modulate the early short-term variability of GRB afterglows. We find that perturbations in the double shock system could induce oscillatory fluctuations in the observed flux on short (down to seconds) time scales during the early phase of an afterglow.

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arXiv2001

Probing Micro-quasars with TeV Neutrinos

The jets associated with Galactic micro-quasars are believed to be ejected by accreting stellar mass black-holes or neutron stars. We show that if the energy content of the jets in the transient sources is dominated by electron-proton plasma, then a several hour outburst of 1--100 TeV neutrinos produced by photo- meson interactions should precede the radio flares associated with major ejection events. Several neutrinos may be detected during a single outburst by a 1km^2 detector, thereby providing a powerful probe of micro-quasars jet physics.

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arXiv2001

High energy particles from gamma-ray bursts

A review is presented of the fireball model of gamma-ray bursts (GRBs), and of the production in GRB fireballs of high energy protons and neutrinos. Constraints imposed on the model by recent afterglow observations, which support the association of GRB and ultra-high energy cosmic-ray (UHECR) sources, are discussed. Predictions of the GRB model for UHECR production, which can be tested with planned large area UHECR detectors and with planned high energy neutrino telescopes, are reviewed.

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arXiv2001

TeV Neutrinos and GeV Photons from Shock Breakout in Supernovae

We show that as a Type II supernova shock breaks out of its progenitor star, it becomes collisionless and may accelerate protons to energies >10 TeV. Inelastic nuclear collisions of these protons produce a ~1 hr long flash of TeV neutrinos and 10 GeV photons, about 10 hr after the thermal (10 MeV) neutrino burst from the cooling neutron star. A Galactic supernova in a red supergiant star would produce a photon and neutrino flux of ~10^{-4} erg/cm^2 s. A km^2 neutrino detector will detect ~100 muons, thus allowing to constrain both supernova models and neutrino properties.

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arXiv2000

High Energy Astrophysical Neutrinos: the Upper Bound is Robust

We elucidate the physical basis for the upper bound on high energy neutrino fluxes implied by the observed cosmic ray flux. We stress that the bound is valid for neutrinos produced either by p,gamma reactions or by p-p(n) reactions in sources which are optically thin for high energy protons to photo-meson and nucleon-meson interactions. We show that the upper bound is robust and conservative. The Waxman-Bahcall bound overestimates the most likely neutrino flux by a factor ~ 5/tau, for small optical depths tau. The upper limit cannot be plausibly evaded by invoking magnetic fields, optically thick AGNs, or large hidden fluxes of extragalactic protons. We describe the implications of the bound for future experiments including the AMANDA, ANTARES, Auger, ICECUBE, NESTOR, and OWL/AIRWATCH detectors.

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arXiv2000

High Energy Neutrinos from Gamma-Ray Bursts

Observations suggest that gamma-ray bursts (GRBs) are produced by the dissipation of the kinetic energy of a relativistic fireball. In this talk, recent work on the production of high energy neutrinos by GRB fireballs is reviewed. A significant fraction of GRB energy is expected to be converted to an accompanying burst of high energy neutrinos. Photomeson interactions produce a burst of ~100 TeV neutrinos in coincidence with the GRB, and a burst of \~10^18 eV neutrinos following the GRB on a time scale of 10 s. Inelastic p-n nuclear collisions result in the production of a burst of ~10 GeV neutrinos in coincidence with the GRB. Planned 1 km^3 neutrino telescopes are expected to detect tens of 100 TeV neutrino events, and several 10^18 eV events, correlated with GRBs per year. A suitably densely spaced detector may allow the detection of several 10 GeV events per year. The detection of high-energy neutrino events correlated with GRBs will allow to constrain GRB progenitor models and to test the suggestion that GRBs accelerate protons to >10^20 eV. Moreover, such detection will allow to test for neutrino properties, e.g. flavor oscillations (for which upward moving tau's would be a unique signature) and coupling to gravity, with an accuracy many orders of magnitude better than is currently possible.

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arXiv2000

Fluctuations in the Radio Background from Intergalactic Synchrotron Emission

The shocks produced in the intergalactic medium during large-scale structure formation accelerate a population of highly relativistic electrons which emit synchrotron radiation due to intergalactic magnetic fields. In a previous paper (Loeb & Waxman 2000) we have shown that these electrons cool primarily by inverse-Compton scattering of the microwave background photons and can thereby produce the observed intensity and spectrum of the diffuse gamma-ray background. Here we calculate the intensity and angular fluctuations of the radio synchrotron background that results from the same high-energy electrons, as well as the expected angular fluctuations in the gamma-ray background. On angular scales smaller than a degree, the predicted fluctuations in the microwave background temperature are of order 40micro-K*(xi_B/0.01)(nu/10 GHz)^{-3}, where xi_B is the magnetic fraction of the post-shock energy density. This foreground might have already dominated the anisotropy signal detected in existing low-frequency CMB experiments, and can be identified with confidence through multi-frequency observations. Detection of the synchrotron fluctuations would allow to determine the strength of the intergalactic magnetic field. We predict a strong correlation between high-resolution maps taken at low-frequency radio waves and at high-energy gamma-rays. Young X-ray clusters may also appear as radio or gamma-ray clusters. The detailed study of this correlation will become easily accessible with the future launch of GLAST.

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arXiv2000

Ultra-high energy cosmic rays may come from clustered sources

Clustering of cosmic-ray sources affects the flux observed beyond the cutoff imposed by the cosmic microwave background and may be important in interpreting the AGASA, Fly's Eye, and HiRes data. The standard deviation, sigma, in the predicted number, N, of events above 10^{20} eV is sigma/N = 0.9(r_0/10 Mpc)^{0.9}, where r_0 is the unknown scale length of the correlation function (r_0 = 10 Mpc for field galaxies). Future experiments will allow the determination of r_0 through the detection of anisotropies in arrival directions of ~ 10^{20} eV cosmic-rays over angular scales of Theta ~ r_0/30 Mpc.

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arXiv2000

Neutrino afterglow from Gamma-Ray Bursts: ~10^{18} eV

We show that a significant fraction of the energy of a gamma-ray burst(GRB) is probably converted to a burst of 10^{17}-10^{19} eV neutrinos and multiple GeV gammas that follow the GRB by > 10 s . If, as previously suggested, GRB's accelerate protons to ~10^{20} eV, then both the neutrinos and the gammas may be detectable.

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