Very High Energy Phenomena in the Universe Rencontres du Vietnam 2018 Jean Ballet AIM, CEA Saclay, France Thank you for establishing conference center here, my first time in Vietnam. Honored to give this introduction Very High Energy Phenomena in the Universe August 13-18, 2018

Cosmic rays at the Earth Credit: IceCube masterclass Knee Galactic Ankle Extragal 1 Joule Human accelerators Cosmic rays at the Earth Observed in the atmosphere since Victor Hess (1912) Charged particles (mostly protons) Pervade our Galaxy Spectrum peaks at a few GeV (dangerous for astronauts) But extends to much higher energies (mystery for astrophysicists) Relativistic charged particles in space, observed directly near the Earth, but coming from outside solar system Peak of the spectrum (where most of the power is) relatively easy to explain but highest energies more enigmatic VHEPU 2018

Cosmic-ray propagation Charged particles are deflected by magnetic fields They move more or less randomly and are confined in our Galaxy At the highest energies, cosmic-rays can cross galaxies freely Their sources can be traced in γ-rays Complex plot simply means that CRs do not propagate in straight line so we can’t know easily where they come from But radiation (X, gamma or neutrinos) emitted at their source propagates in straight line. Look for gamma-ray sources VHEPU 2018 Credit: Strong, Moskalenko & Reimer

Cosmic-ray acceleration Michael Hillas (1932-2017) 1984 plot Cosmic-ray acceleration requires very large magnetic fields or very large sizes Zoo of astrophysical accelerators Hillas plot tells which astrophysical objects could be the source of the highest energy cosmic rays Range from very small (neutron stars) to very large (clusters of galaxies) Credit: Juan Aguilar, ULB VHEPU 2018

Thousands of gamma-ray sources Fermi LAT since 2008 8 years > 1 GeV Galactic coordinates. Diffuse gamma-ray emission proves that cosmic rays pervade entire Galaxy Many individual sources (my main personal occupation) Diffuse emission from cosmic rays hitting interstellar gas in the Galaxy Thousands of gamma-ray sources VHEPU 2018

Pulsars artist’s view of a pulsar End product of massive stars radio End product of massive stars Neutron-stars (10 km radius) Fast rotating (< 1 second) Huge magnetic fields Direct acceleration by electric fields 100s of Fermi sources γ-ray Start with the smallest. Fast rotating magnetic field  strong electric field  accelerated particles  gamma-rays Probably not the source of cosmic rays, but very interesting systems VHEPU 2018 Credit: NASA/Fermi/Cruz de Wilde

Pulsar wind nebulae Crab nebula X-rays Created by electromagnetic emission of the pulsars Filled by electron – positron pairs Could be the source of cosmic-ray electrons and positrons Larger (a light year). Relativistic wind from the central pulsar. Expanding nebula. No indication that protons are accelerated in large quantities Credit: NASA/CXC/ASU/J. Hester VHEPU 2018

Supernova remnants Explosion of massive star (supernova) in our Galaxy SN 1006 X-rays Supernova remnants Explosion of massive star (supernova) in our Galaxy This one is well documented in Arab and Chinese records Fast shock wave (several 1000 km/s) accelerates particles Thought to be the main source of Galactic protons 100s in our Galaxy Yet larger (100 light years). Blast wave in interstellar space. Protons accelerated at the rim. VHEPU 2018 Credit: NASA/CXC/Middlebury College/F.Winkler

γ-ray bursts and gravitational waves LIGO End product of binary system of two massive stars Merging generates mostly gravitational waves First observed in 2016 (binary black-hole system) by LIGO (km-length interferometer) 17 August 2017 event coincided with γ-ray burst Lasts only a few seconds, but could be the source of highest energy cosmic rays Very small again (neutron stars) but observed only in faraway galaxies (very rare). Gamma-ray bursts observed often. Gravitational waves (recent discovery) measures mass, distance. Both together excellent diagnostics (more to come) artist’s view of two merging neutron stars VHEPU 2018 Credit: NSF/LIGO/Sonoma State University/A. Simonnet

Jets of active galactic nuclei Hercules A radio map on top of optical image Jets of active galactic nuclei Huge black holes swallowing gas at the center of galaxies Enormous jets much larger than the galaxy Very bright in γ rays when seen face-on 1000s of Fermi sources Could be the source of highest energy cosmic rays Gas falling on supermassive black holes at the center of many galaxies. Powerful relativistic jets (this one is seen from the side). Lobes much larger than galaxy. Very variable but persistent sources. VHEPU 2018 Credit: NASA/Hubble and NRAO/VLA

Neutrinos from active galactic nuclei Credit: IceCube collaboration Neutrinos from active galactic nuclei Neutrinos can probe deeper than γ rays Telltale sign of proton acceleration (not only electrons) Detected since 2013 by IceCube km-size detector in Antarctica ice First spatial coincidence this year between a high-energy neutrino and a flaring Fermi blazar Neutrinos are very light elementary particles emitted in nuclear interactions and propagating like photons Very hard to detect. Not clear yet that they come from individual relatively nearby sources. Coincidence to be confirmed. VHEPU 2018

Immediate future CTA Next-generation γ-ray telescope CTA North Canary islands Immediate future CTA Next-generation γ-ray telescope Higher energy than Fermi Atmosphere as a detector World-wide effort to build two arrays of Cerenkov telescopes in order to cover the full sky Construction has started First results at the next VHEPU! After spectacular progress on neutrinos and gravitational waves, back to gamma rays. Very powerful instrument aimed at observing as many sources as Fermi at higher energy. VHEPU 2018 Photo: Daniel Mazin, ICRR Tokyo

Very High Energy Phenomena in the Universe Rencontres du Vietnam 2018 Since the last high-energy meeting in 2014, multi-messenger astronomy (cosmic-rays, γ rays, neutrinos, gravitational waves) has taken off ! Will hear about all this here, and more. High-energy astronomy is richer than I could depict in 20 mn. Very High Energy Phenomena in the Universe August 13-18, 2018