High-energy astrophysics with neutrino telescopes

Neutrino astrophysics offers new perspectives on the Universe investigation: high energy neutrinos, produced by the most energetic phenomena in our Galaxy and in the Universe, carry complementary (if not exclusive) information about the cosmos with respect to photons. While the small interaction cross section of neutrinos allows them to come from the core of astrophysical objects, it is also a drawback, as their detection requires a large target mass. This is why it is convenient put huge cosmic neutrino detectors in natural locations, like deep underwater or under-ice sites. In order to supply for such extremely hostile environmental conditions, new frontiers technologies are under development. The aim of this work is to review the motivations for high energy neutrino astrophysics, the present status of experimental results and the technologies used in underwater/ice Cherenkov experiments, with a special focus on the efforts for the construction of a km3 scale detector in the Mediterranean Sea.Comment: 88 pages and 41 figure

The supernova remnant W49B as seen with H.E.S.S. and Fermi-LAT

The supernova remnant (SNR) W49B originated from a core-collapse supernova that occurred between one and four thousand years ago, and subsequently evolved into a mixed-morphology remnant, which is interacting with molecular clouds (MC). γ-ray observations of SNR/MC associations are a powerful tool to constrain the origin of Galactic cosmic-rays, as they can probe the acceleration of hadrons through their interaction with the surrounding medium and subsequent emission of non-thermal photons. The detection of a γ-ray source coincident with W49B at very high energies (VHE; E > 100 GeV) with the H.E.S.S. Cherenkov telescopes is reported together with a study of the source with 5 years of Fermi-LAT high energy γ-ray (0.06 - 300 GeV) data. The smoothly-connected combined source spectrum, measured from 60 MeV to multi-TeV energies, shows two significant spectral breaks at 304±20 MeV and 8.4+2.2−2.5 GeV, the latter being constrained by the joint fit from the two instruments. The detected spectral features are similar to those observed in several other SNR/MC associations and are found to be indicative of γ-ray emission produced through neutral-pion decay

Science with the Cherenkov Telescope Array

The Cherenkov Telescope Array, CTA, will be the major global observatory forvery high energy gamma-ray astronomy over the next decade and beyond. Thescientific potential of CTA is extremely broad: from understanding the role ofrelativistic cosmic particles to the search for dark matter. CTA is an explorerof the extreme universe, probing environments from the immediate neighbourhoodof black holes to cosmic voids on the largest scales. Covering a huge range inphoton energy from 20 GeV to 300 TeV, CTA will improve on all aspects ofperformance with respect to current instruments. The observatory will operate arrays on sites in both hemispheres to providefull sky coverage and will hence maximize the potential for the rarestphenomena such as very nearby supernovae, gamma-ray bursts or gravitationalwave transients. With 99 telescopes on the southern site and 19 telescopes onthe northern site, flexible operation will be possible, with sub-arraysavailable for specific tasks. CTA will have important synergies with many ofthe new generation of major astronomical and astroparticle observatories.Multi-wavelength and multi-messenger approaches combining CTA data with thosefrom other instruments will lead to a deeper understanding of the broad-bandnon-thermal properties of target sources. The CTA Observatory will be operated as an open, proposal-driven observatory,with all data available on a public archive after a pre-defined proprietaryperiod. Scientists from institutions worldwide have combined together to formthe CTA Consortium. This Consortium has prepared a proposal for a CoreProgramme of highly motivated observations. The programme, encompassingapproximately 40% of the available observing time over the first ten years ofCTA operation, is made up of individual Key Science Projects (KSPs), which arepresented in this document

Multi-messenger Observations of a Binary Neutron Star Merger

International audienceOn 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of $\sim 1.7\,{\rm{s}}$ with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg(2) at a luminosity distance of ${40}_{-8}^{+8}$ Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 $\,{M}_{\odot }$. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at $\sim 40\,{\rm{Mpc}}$) less than 11 hours after the merger by the One-Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ∼10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position $\sim 9$ and $\sim 16$ days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC 4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta