Dust sublimation by GRBs and its implications

The prompt optical flash recently detected accompanying GRB990123 suggests that, for at least some GRBs, gamma-ray emission is accompanied by prompt optical-UV emission with luminosity L(1-7.5eV)=10^{49}(\Delta\Omega/4\pi)erg/s, where \Delta\Omega is the solid angle into which gamma-ray and optical-UV emission is beamed. Such an optical-UV flash can destroy dust in the beam by sublimation out to an appreciable distance, approximately 10 pc, and may clear the dust out of as much as 10^7(\Delta\Omega/4\pi)M_sun of molecular cloud material on an apparent time scale of 10 seconds. Detection of time dependent extinction on this time scale would therefore provide strong constraints on the GRB source environment. Dust destruction implies that existing, or future, observations of not-heavily-reddened fireballs are not inconsistent with GRBs being associated with star forming regions. In this case, however, if gamma-ray emission is highly beamed, the expanding fireball would become reddened on a 1 week time scale. If the optical depth due to dust beyond approximately 8 pc from the GRB is 0.2<\tau_V<2, most of the UV flash energy is converted to infra-red, \lambda \sim 1 micron, radiation with luminosity \sim 10^{41} erg/s extending over an apparent duration of \sim 20(1+z)(\Delta\Omega/0.01) day. Dust infra-red emission may already have been observed in GRB970228 and GRB980326, and may possibly explain their unusual late time behavior.Comment: 16 pages, including 1 figure, submitted to Ap

TeV Neutrinos from Successful and Choked Gamma-Ray Bursts

Core collapse of massive stars resulting in a relativistic fireball jet which breaks through the stellar envelope is a widely discussed scenario for gamma-ray burst production. For very extended or slow rotating stars, the fireball may be unable to break through the envelope. Both penetrating and choked jets will produce, by photo-meson interactions of accelerated protons, a burst of neutrinos with energies in excess of 5 TeV while propagating in the envelope. The predicted flux, from both penetrating and chocked fireballs, should be easily detectable by planned cubic kilometer neutrino telescopes.Comment: Phys.Rev.Letters, in press, final version accepted 8/31/01 (orig. 3/17/01

GeV Photons from Ultra High Energy Cosmic Rays accelerated in Gamma Ray Bursts

Gamma-ray bursts are produced by the dissipation of the kinetic energy of a highly relativistic fireball, via the formation of a collisionless shock. When this happens, Ultra High Energy Cosmic Rays up to 10^20 eV are produced. I show in this paper that these particles produce, via synchrotron emission as they cross the acceleration region, photons up to 300 GeV which carry away a small, ~0.01, but non-negligible fraction of the total burst energy. I show that, when the shock occurs with the interstellar medium, the optical depth to photon-photon scattering, which might cause energy degradation of the photons, is small. The burst thusly produced would be detected at Earth simultaneoulsy with the parent gamma-ray burst, although its duration may differ significantly from that of the lower energy photons. The expected fluences, ~10^{-5}-10^{-6} erg/cm^2 are well within the range of planned detectors. A new explanation for the exceptional burst GRB 940217 is discussed.Comment: Accepted for publication in The Physical Review Letters. 4 pages, RevTeX needed, no figure

Enhance synchronizability by structural perturbations

In this paper, we investigate the collective synchronization of system of coupled oscillators on Barab\'{a}si-Albert scale-free network. We propose an approach of structural perturbations aiming at those nodes with maximal betweenness. This method can markedly enhance the network synchronizability, and is easy to be realized. The simulation results show that the eigenratio will sharply decrease to its half when only 0.6% of those hub nodes are under 3-division processes when network size N=2000. In addition, the present study also provides a theoretical evidence that the maximal betweenness plays a main role in network synchronization.Comment: 4 pages, 3 eps figure

High Energy Neutrinos from Cosmological Gamma-Ray Burst Fireballs

Observations suggest that $\gamma$-ray bursts (GRBs) are produced by the dissipation of the kinetic energy of a relativistic fireball. We show that a large fraction, $\ge 10$, of the fireball energy is expected to be converted by photo-meson production to a burst of $\sim10^{14} eV$ neutrinos. A km^2 neutrino detector would observe at least several tens of events per year correlated with GRBs, and 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.Comment: Submitted to PRL (4 pages, LaTeX

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.Comment: Accepted ApJ; added sentence re: sterile neutrinos; related material at http://www.sns.ias.edu/~jn

High energy neutrinos from magnetars

Magnetars can accelerate cosmic rays to high energies through the unipolar effect, and are also copious soft photon emitters. We show that young, fast-rotating magnetars whose spin and magnetic moment point in opposite directions emit high energy neutrinos from their polar caps through photomeson interactions. We identify a neutrino cut-off band in the magnetar period-magnetic field strength phase diagram, corresponding to the photomeson interaction threshold. Within uncertainties, we point out four possible neutrino emission candidates among the currently known magnetars, the brightest of which may be detectable for a chance on-beam alignment. Young magnetars in the universe would also contribute to a weak diffuse neutrino background, whose detectability is marginal, depending on the typical neutrino energy.Comment: emulateapj style, 6 pages, 1 figure, ApJ, v595, in press. Important contributions from Dr. Harding added. Major revisions made. More conservative and realistic estimates about the neutrino threshold condition and emission efficiency performed. More realistic typical beaming angle and magnetar birth rate adopte

High Energy Neutrinos from Astrophysical Sources: An Upper Bound

We show that cosmic-ray observations set a model-independent upper bound to the flux of high-energy, > 10^14 eV, neutrinos produced by photo-meson (or p-p) interactions in sources of size not much larger than the proton photo-meson (or pp) mean-free-path. The bound applies, in particular, to neutrino production by either AGN jets or GRBs. This upper limit is two orders of magnitude below the flux predicted in some popular AGN jet models, but is consistent with our predictions from GRB models. We discuss the implications of these results for future km^2 high-energy neutrino detectors.Comment: Added discussion showing bound cannot be evaded by invoking magnetic fields. Accepted Phys Rev

Evolutionary branching in a stochastic population model with discrete mutational steps

Evolutionary branching is analysed in a stochastic, individual-based population model under mutation and selection. In such models, the common assumption is that individual reproduction and life career are characterised by values of a trait, and also by population sizes, and that mutations lead to small changes in trait value. Then, traditionally, the evolutionary dynamics is studied in the limit of vanishing mutational step sizes. In the present approach, small but non-negligible mutational steps are considered. By means of theoretical analysis in the limit of infinitely large populations, as well as computer simulations, we demonstrate how discrete mutational steps affect the patterns of evolutionary branching. We also argue that the average time to the first branching depends in a sensitive way on both mutational step size and population size.Comment: 12 pages, 8 figures. Revised versio

Gamma-Ray Bursts: The Underlying Model

A pedagogical derivation is presented of the ``fireball'' model of gamma-ray bursts, according to which the observable effects are due to the dissipation of the kinetic energy of a relativistically expanding wind, a ``fireball.'' The main open questions are emphasized, and key afterglow observations, that provide support for this model, are briefly discussed. The relativistic outflow is, most likely, driven by the accretion of a fraction of a solar mass onto a newly born (few) solar mass black hole. The observed radiation is produced once the plasma has expanded to a scale much larger than that of the underlying ``engine,'' and is therefore largely independent of the details of the progenitor, whose gravitational collapse leads to fireball formation. Several progenitor scenarios, and the prospects for discrimination among them using future observations, are discussed. The production in gamma- ray burst fireballs of high energy protons and neutrinos, and the implications of burst neutrino detection by kilometer-scale telescopes under construction, are briefly discussed.Comment: In "Supernovae and Gamma Ray Bursters", ed. K. W. Weiler, Lecture Notes in Physics, Springer-Verlag (in press); 26 pages, 2 figure