1. 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

2. 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

3. 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

4. Cosmic-ray acceleration
Michael Hillas ( )
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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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