Abstract
We compute the expected neutrino fluence from SGRB 170817A, associated with the gravitational wave event GW 170817, directly based on Fermi observations in two scenarios: structured jet and off-axis (observed) top-hat jet. While the expected neutrino fluence for the structured jet case is very small, large off-axis angles imply high radiation densities in the jet, which can enhance the neutrino production efficiency. In the most optimistic allowed scenario, the neutrino fluence can reach only $10^{-4}$ of the sensitivity of the neutrino telescopes. We furthermore demonstrate that the fact that gamma-rays can escape limits the baryonic loading (energy in protons versus photons) and the off-axis angle for the internal shock scenario. In particular, for a baryonic loading of ten, the off-axis angle is more strongly constrained by the baryonic loading than by the time delay between the gravitational wave event and the onset of the gamma-ray emission.
Highlights
The gravitational wave event GW170817 [1] has recently been drawing a lot of attention because it was accompanied by electromagnetic counterparts, first in gamma-rays [2], and later in the X-ray [3, 4] and radio [5, 6] bands.The UV, optical, and near-infrared observations have been interpreted as kilonova [7,8,9], with evidence for the synthesis of heavy r-process elements [10, 11]
Since the observed gamma-ray fluence has to be de-boosted by the Doppler factor, the photon density in the jet frame will be much higher compared to the structured jet case, and as a consequence the neutrino production efficiency; the boost back into the observer’s frame cannot compensate for that, which means that the expected neutrino flux will be higher for large off-axis angles due to this simple re-scaling
The expected maximal neutrino fluence is at most about four orders of magnitude below the neutrino telescope sensitivities, which means that the detection of a neutrino coming from this short Gamma-Ray Burst (SGRB) was extremely unlikely in the structured jet scenario
Summary
The gravitational wave event GW170817 [1] has recently been drawing a lot of attention because it was accompanied by electromagnetic counterparts, first in gamma-rays [2], and later in the X-ray [3, 4] and radio [5, 6] bands. A detailed overview of the many multi-wavelength and multi-messenger observations can be found in Ref. [12] and references therein; for a theoretical interpretational overview, see e.g. Ref. The results have been interpreted in terms of models predicting neutrinos from neutron star-neutron star mergers [15, 16], re-scaled to the observed distance. No direct prediction for this short Gamma-Ray Burst (SGRB) event 170818A has been derived. We use the information on the spectral energy distribution (SED) from Fermi-GBM [17] together with the inferred parameters of the SGRB jet directly to predict the expected neutrino fluence for this event. We consider two different jet models, a structured jet and a uniform top-hat jet observed off-axis. We discuss the relevance of the photospheric constraint in the off-axis scenario
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