Multi-GeV Neutrino Emission from Magnetized Gamma Ray Bursts

📝 Abstract

We investigate the expected neutrino emissivity from nuclear collisions in magnetically dominated collisional models of gamma-ray bursts, motivated by recent observational and theoretical developments. The results indicate that significant multi-GeV neutrino fluxes are expected for model parameter values which are typical of electromagnetically detected bursts. We show that for detecting at least one muon event in Icecube and its Deep Core sub-array, a single burst must be near the high end of the luminosity function and at a redshift $z\lesssim 0.2 $. We also calculate the luminosity and distance ranges that can generate $0.01-1$ muon events per GRB in the same detectors, which may be of interest if simultaneously detected electromagnetically, or if measured with future extensions of Icecube or other neutrino detectors with larger effective volume and better sensitivity.

💡 Analysis

We investigate the expected neutrino emissivity from nuclear collisions in magnetically dominated collisional models of gamma-ray bursts, motivated by recent observational and theoretical developments. The results indicate that significant multi-GeV neutrino fluxes are expected for model parameter values which are typical of electromagnetically detected bursts. We show that for detecting at least one muon event in Icecube and its Deep Core sub-array, a single burst must be near the high end of the luminosity function and at a redshift $z\lesssim 0.2 $. We also calculate the luminosity and distance ranges that can generate $0.01-1$ muon events per GRB in the same detectors, which may be of interest if simultaneously detected electromagnetically, or if measured with future extensions of Icecube or other neutrino detectors with larger effective volume and better sensitivity.

📄 Content

Multi-GeV Neutrino Emission from Magnetized Gamma Ray Bursts Shan Gao and Peter Mészáros Department of Physics, Department of Astronomy and Astrophysics, Center for Particle Astrophysics, The Pennsylvania State University, University Park, 16802, USA (Dated: May 16, 2022) We investigate the expected neutrino emissivity from nuclear collisions in a magnetically domi- nated model of gamma-ray bursts motivated by recent observational and theoretical developments. The results indicate that small multi-GeV neutrino fluxes are expected for model parameter values which are typical of electromagnetically detected bursts. We show that for detecting at least one muon event in Icecube and its Deep Core sub-array, a single burst must be near the high end of the luminosity function, and at low redshifts z ≲0.1, where the burst rate is very low. We also calculate the luminosity and distance ranges that can generate 0.01 −1 muon events per GRB in the same detectors, which may be of interest if simultaneously detected electromagnetically, or if measured with future extensions of Icecube or other neutrino detectors with larger effective volume and better sensitivity. I. INTRODUCTION Observations of multi-GeV photons from gamma-ray bursts (GRB) recently accumulated by the Fermi satel- lite (e.g. [1, 2]) have pointed out the need to re-evaluate the type of models used to explain the prompt pho- ton emission mechanisms and the location of the emis- sion regions in these objects (e.g. [3]). In particular, concerns about the radiative efficiency of usual internal shock models, and the larger radii required to avoid two- photon degradation of the spectra have spurred the inves- tigation of baryonic (non-MHD) jet models where the ra- diation arises in a jet photosphere [4–6]. In such baryon- loaded jet models, at a certain radius the timescale of the nuclear elastic collisions (which couple the proton p and neutron n components) becomes longer than the ex- pansion timescale, i.e. the collision optical depth falls below o(1), and the two components decouple from each other [7, 8]. The protons can continue to be accelerated by the radiation, while the neutrons, which have zero electric charge, start to coast with a constant Lorentz factor. Starting at this decoupling radius and for some distance beyond, the longitudinal drift velocity between the n and p becomes ∆v ≳0.5c, and they start to col- lide inelastically. Such large relative velocities between n and p components also can arise in realistic jets where the bulk Lorentz factor Γ depends on the polar angle θ, which also leads to inelastic collisions [6, 9], as neutrons from the outer parts (sheath) of the jet thermally drift into the jet core. In both pictures, pions are created, which in the case of the dynamics being dominated by the baryons results in multi-GeV photons and neutrino production [6, 8]. A different approach towards resolving the radiative ef- ficiency of GRBs involves consideration of magnetically dominated jets [10–12]. Some of these magnetic models assume an almost baryon-free outflow [12–16], while in other cases a substantial but dynamically sub-dominant baryon load is assumed [10, 11, 17–22]. The baryons in such jet models are expected to accelerate at a differ- ent rate than in baryonic (non-MHD) jet models, and the different dynamics leads to quantitatively different predictions for the photon spectrum [23]. Similarly, it should lead to quantitatively different neutrino spectra, which we investigate in this paper. Unlike in the previous investigations cited above, here we consider the neutrino spectra arising from nuclear col- lision effects in magnetically dominated GRB outflows. In this case, both the radial np decoupling radius as well as the photosphere occur at larger radii from the central engine than in the non-magnetic case, and also the transverse drift of neutrons from the periphery of the jet into the jet core becomes important at different radii, where the physical conditions differ from those pre- viously considered. As a consequence, multi-GeV pho- tons are produced at somewhat softer energies and with appreciable time delays [23] respect to the MeV photo- spheric photons, but the detailed neutrino spectrum for such magnetically dominated jets has not been consid- ered so far. In this paper we investigate numerically the neutrino spectrum expected in magnetically dominated baryon-collisional GRB models, taking into account both longitudinal and transverse n, p decoupling and inelastic collisions. These neutrinos are in the energy sensitivity range of Icecube and its DeepCore [24–26] sub-array. In §II we briefly introduce the astrophysical model and present the method of neutrino emission calculation. In §III we present the results for the expected neutrino fluxes and muon events, as well as the detection prospects with Deep Core and IceCube. A discussion and summary of the results is given in §IV. arXiv:1112.5664v3 [astro-ph.HE] 20 Apr 2012 2 II. THE NUCL

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