Introduction toHigh Energy Astrophysics
Paolo Lipari: INFN Roma “La Sapienza”
XXVI SNFNSN OTRANTO 5-6 giugno 2014
Sources of High Energy Particles in the universe
1. Cosmic Rays 2. Gamma Rays 3. Neutrinos
Viktor HESS (1912)
The beginning of “High Energy Astrophysics” the discovery of Cosmic Rays
First “hint”of the “high energy universe” (beginning of '900)
Existence of “Ionizing Radiation”
Discharge of an electroscope
Effect grows with altitude(and has a maximum soon discovered by Kolhorster )
Source of ionizationis “extraterrrestrial”
Primary Particle
Ground
“Secondaries”
(many absorbed in the atmosphere)
Some secondariesreach the ground
Birth of
Particle Physics
Carl Anderson “Wilson chamber”
march 15, 1933 Discovery of the “positron”
Carl Anderson and Viktor Hess share Nobel prize in 1936
6 mmLead plate
63 MeV
23 MeV
Cosmic Rays are charged particles
Most particles have POSITIVE electric charge:
Protons +ionized nuclei
LATITUDE effect
EAST-WEST effect
LATITUDE EFFECT
East-West effectMost Cosmic Rays havepositive electric charge
Relativistic charged particles. [Latitude effect]
Mostly protons (+ ionized nuclei) [East-West effect]
Extraordinary energy (!) [Extensive Air Showers (electrodynamics) ](1015, 1016 eV) now: 1020eV
Pierre Auger Phys.Rev. 1939
Relativistic charged particles. [Latitude effect]
Mostly protons (+ ionized nuclei) [East-West effect]
Extraordinary energy (!) [Extensive Air Showers (electrodynamics) ]
Power Law energy spectrum(nearly featureless)
(1015, 1016 eV) now: 1020eV
● Where are these relativistic particles coming from ? ● How are they produced ? ● Are they filling the universe (or are more “local”) ?
Relativistic charged particles. [Latitude effect]
Mostly protons (+ ionized nuclei) [East-West effect]
99% nuclei
1% electrons
89% protons
10% Helium
1% Nuclei Z > 2
small quantities : positrons + anti-protons
Power-Law
Energy spectra
Particle Flux: [cm2 s sr GeV]-1
[cm2 s sr GeV/nucleon]-1
Number of particles per [ unit of surface unit of time unit of solid angle unit of energy]
Esponent :
from Tom Gaisser
from Tom Gaisser
Flux *E2Knee
High Energy suppresionor “cutoff”
Ankle
from Tom Gaisser
Knee
High Energy suppresionor “cutoff”
Ankle
electrons
positrons
anti-p
Direct Measurementsof Cosmic Rays
Detectors on satellitesor stratospheric balloons
Kinetic energy
PAMELA
Proton/HeliumCR fluxes1 GV – 1.2 TV
Science in press(march 2011)
Surprising and important result.
Broken power law fits to spectra. Break at same rigidity p/Z
p He
Surprising and important result.
Broken power law fits to spectra. “Ankle” at same rigidity p/Z
p He
Structure
CREAM (calorimeter on balloon) (5 flights in Antartica. Total of 156 days)
Cream 5 trajectory37 days 12/2009-01/2010
SUNSPOTS: signals of solar activity.
Visible lightX-rays
Solar Modulations
NeutronMonitors
Measure the flux of neutronsproduced by the evaporation of Air nuclei by primary cosmic rays
Sunspotnumber
Neutron MonitorCounts
Time of BESS flights:
BESS proton flux MEASUREMENTS
p
e
PAMELA
The SUN as a “laboratory” for CR Acceleration and Transport
PAMELA: Solar Flare 13/dec/2006Ap.J 742 2 2011.
AMS Launch May 16th 2011
ExtragalacticParticle
Particle accelerated in the Milky Way
“Bubble” of cosmic rays generated in the Milky Way and contained by the Galaxy magnetic field
Space extension and properties of this “CR bubble” remain very uncertain
Extragalacticcontribution
GALACTICMAGNETIC FIELDS
“Regular Field”
“Random Field”(turbulent motions)
“Regular Field”(along the spiral Arms) + “Random” (Turbulent) Field
EnergyDensity
25-35 Kpc
0.5 Kpc
8 Kpc
B
Diffusion approximation
Maximum energy for containment
Piece of extragalactic space: Non MilkyWay-like sources
Galaxy
Milky Way
AGN
Injection of cosmic rays
Containment time
Different particles
Galactic Cosmic Rays
Determination of the “confinement time” T(p/Z)
“Cosmic clock” (Beryllium-10)
Nuclear Fragmentation (collisions with the Inter Stellar Medium)
Solar system
v
v
v
proton at rest
(extended halo)
Column density
Escape faster at higher E
Injection of cosmic rays
Containment time
LARGE PowerRequirement
Spectral Shape [Dynamics of acceleration process]
Source Identification
Power Provided by SN is sufficient with a conversion efficiency of 15-20 % in relativistic particles
The cosmic ray acceleratorsinject particles witha power law spectrumof approximately this form
11th june 2008: Launch of GLAST
Gamma rayLargeAreaSpaceTelescope.
NASA press release: 26th august 2008
Enrico Fermi
ELECTRO-WEAK MASS SCALE
The Idea of FERMI acceleration
Why a power law spectrum ?
Origin of the power law spectrum:
Stochastic Process
Gradual acceleration madein many steps
= probability of stopping the iteration
The iterative process results in apopulation of particles with a power law spectrumwith exponent:
Particles that come out of the accelerator
Collision with Moving Plasma Cloudsin the Galaxy
Ei
Ef
MODIFICATION of the original FERMI Model(2nd order Fermi acceleration)
ACCELERATION at SHOCK FRONTS(1st order Fermi acceleration)
Trinity Test (1945)
CAS A(1667)
“Fireball” of an Supernova explosion
Interstellar Gas
Strong Shock
Fermi 1st orderacceleration
SNR
Unshocked material at restPiston
ShockFront
Unshocked material at restPiston
ShockFront
STRONG SHOCK
Unshocked material shocked material
Unshocked material at rest
Compression factor r
For Strong Shocks
Universal exponent for the spectra of acceleration at strong shocks