Astroparticle Physics : High Energy
Particles and Non Thermal Radiation
Outline:
Pratik Majumdar
SINP, Kolkata
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Cosmic rays
History and Discovery
Composition and propagation
Non thermal Radiation
How do we see cosmic rays ?
Post MSc Lectures, December, SINP
Reading Materials
Longair : High Energy Astrophysics
• T. Stanev : High Energy Cosmic Rays
• T. Gaisser : Particle Physics and Cosmic rays
• Many review articles on the subject
•
Post MSc Lectures, December, SINP
Astroparticle Physics
Dark matter
Cosmic rays
Solar neutrinos
Gamma ray
astronomy
Neutrino masses
Gravitational
waves
Beyond Standard
Model
Cosmology
Neutrino
astronomy
Post MSc Lectures, December, SINP
What are cosmic rays ?
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High Energy particles
Fully ionised atoms (98%,
mainly Hydrogen and He)
< 1% Electrons and photons
Secondaries : high energy
particles generated by
interactions of cosmic rays in
atmosphere
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Achtung : more than 50,000
of such particles are going
through you in < 30 mins
Particle identification in tracks of emulsion
plates
Development of Geiger counters, Cloud chamber
Birth of Particle Physics in Cosmic
rays ( 1920 to 1940 )
Post MSc Lectures, December, SINP
History of Cosmic rays
Wulf : expt. At Eiffel Tower
• At 330 mts ionization
decreased to 60%
• Millikan named it “cosmic” ->
gamma rays
• Skobeltsyn recorded the first
images in cloud chambers
• Bothe and Kolhoerster
designed the first coincidence
technique to show they are
indeed charged particles.
(1929)
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Post MSc Lectures, December, SINP
History of Cosmic Rays: 1912
1912
Victor Hess
Investigated
sources of
radiation – took balloon up to
5000 meters
Found
radiation increased after
2500 meters
This
could be attributed to the fact
that there was less atmosphere
above to shield him from radiation
Thus
he discovered that
radiation is coming from
space ... “cosmic radiation”
Won
Nobel Prize in 1936
Hess after his flight, which he took
without breathing apparatus in very
cold and thin air!
What are cosmic rays (CRs)?
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As it turns out, these
charged particles are
atomic nuclei zooming
through space
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Called “primary” CRs
Mostly protons or a (He) nuclei
(other elements too, in much
shorter supply)
There are more coming in at
lower than higher energies
When these hit another
nucleus in the atmosphere
and stop, more particles
are knocked downward,
causing a cascading effect
called a “shower”
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Particles in the shower are
called “secondary” CRs
Cosmic Ray “Showers”
Space
“Primary” Cosmic Ray
(Ion, for example a proton)
Earth’s atmosphere
Atmospheric Nucleus
p-
po
g
g
e+ eg
Creating:
g
p+ “Secondary” Cosmic Rays...
(about 50 produced after first collision)
po
g
e-
Electromagnetic
Shower
(mainly g-rays)
p-
p+
nm
m+
muon
neutrino
Hadronic Shower
Plus some:
(mainly muons and neutrinos Neutrons
Carbon-14
reach earth’s surface)
Particle Physics  Cosmic Rays
Electrons and positrons in
cloud chambers
Tracks in Spark Chambers
Post MSc Lectures, December, SINP
Discovering Elementary particles
Anderson and Neddermeyer
discovered muons (1936)
Blackett and others went to
high altitudes, Pic du Midi obs.
Nuclear emulsion plates
Post MSc Lectures, December, SINP
Cosmic rays (1930-1945)
First detection of Air showers
Cosmic rays, gamma rays and neutrinos are all linked
Post MSc Lectures, December, SINP
The Cosmic Ray Spectrum
1 particle per m^2 per sec
solar modulation
E-2.7, mostly protons
1 particle per m^2 per year
Knee
transition to
heavier nuclei
E-3.1
mostly Fe?
1 particle per Km^2 per year
transition to
LHC lighter nuclei ?
Direct Measurements
EAS Detectors
Ankle
?
Power Laws
Shock Acceleration
predicts FSource  E-2
Post MSc Lectures, December, SINP
Open questions after 100 years
 What and where are the sources?
 How do they work?
 How are the particles really accelerated?...
 …or due to new physics at large mass scales?
 And how do cosmic rays manage to reach us?
Post MSc Lectures, December, SINP
Cosmic Rays Composition
Composition
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mainly protons (chemical composition
similar to solar system)
Abundances provide information about
origin and propagation
Nuclei with Z > 1 more abundant in
cosmic rays than solar system
C,N,O, Fe are similar
Overabundance of Li, Be, B in cosmic
rays
Post MSc Lectures, December, SINP
Cosmic Rays Composition
• Primaries : Initially produced from H, He
in stars
• Secondaries : Produced from heavier
nuclei ( C, N, O, Fe)
• Overabundance of Li, Be, B produced due
to Spallation
The existence (and the relative importance)
of the secondary nucleons is an indication
that the cosmic rays have crossed a certain
amount of column density of order
(of 1 interaction length)
X ~ 10 g cm-2
Post MSc Lectures, December, SINP
Post MSc Lectures, December, SINP
Propagation in the Galaxy
Amount of matter traversed decreases as energy
increases ; higher energy CRs spend less time
• CRs propagate freely in containment volume with a
constant probability to escape
• Calculate average matter encountered during their
lifetime in Galaxy
• Taking into account simple Leaky box model
Mean amount of matter λesc = τescρβc
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Confinement time ~ 106 years
Post MSc Lectures, December, SINP
Propagation in the Galaxy Contd…
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If CRs travelled in straight path :
L = t c  L ~ 1016 pc >> 15 Kpc (rgalaxy)
CRs get deflected many
times by the magnetic
field
Confinement in galaxy is a
diffusive process which
takes a long time.
Post MSc Lectures, December, SINP
Diffusion of Cosmic rays
How diffusion occur ?
Random scatterings by irregularities in
magnetic field
Fluctuations in the field.
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Diffusion loss equation :
Exercise : Show this neglecting interactions , where energy loss
-dE/dt = b(E) and Q(E,x,t ) is rate of injection of particles
Post MSc Lectures, December, SINP
Propagation in the Galaxy Contd…
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Leaky Box Model
Cosmic rays injected
Cosmic rays in the Galaxy
Escape Time
Solve for stationary state
Observed Spectrum is different
than Source spectrum
Post MSc Lectures, December, SINP
More on Leaky Box Model
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Consider no injection, spallation, energy
loss/gain terms :
If particles diffuse : exponential,
• If particles remain within confinement
volume with characteristic escape time,
 exponential distribution
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Post MSc Lectures, December, SINP
Number Density of Cosmic Rays
Post MSc Lectures, December, SINP
Post MSc Lectures, December, SINP
Energy Density of Cosmic Rays
Number density is then :
Calculate energy density :
Post MSc Lectures, December, SINP
Post MSc Lectures, December, SINP
Energetics to CR sources
Post MSc Lectures, December, SINP
Possible sources
Typical flares from ordinary stars like
Sun ~ 1034 ergs/sec
• Consider all stars : not enough energy !!!!
Supernova remnants ?
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Explosion rate ~ 1 per 30 yrs in our galaxy
Supernova explosion energy ~ 1051 ergs
Supernova can supply energy to galactic
cosmic rays ???
Post MSc Lectures, December, SINP
apparent
source
direction
Origin of
cosmic rays ?
charged
particle
g, n
nucleus + X -> p + X‘
p0± -> gg
p -> m + n
m -> e + nn
Summer Lectures, DESY, August 26th Berlin
Summer Lectures, DESY, August 26th Berlin
Multiwavelength Astronomy
optical (eV)
Classical Astronomy
“The passive Universe”
Thermal radiation of T=3.000 - 10.000 K
optical view of our Galaxy
December 5th Kolkata
Infrared (10-2eV)
Classical Astronomy
“The passive Universe”
Thermal radiation of T=3.000 - 10.000 K
underlying structure fully revealed in
infrared image
(Spitzer)
December 5th Kolkata
SN1987A
Non-thermal Astronomy
“The revolutionary Universe”
• Violent, non-equilibrium processes in the Universe
=> non-thermal radiation
• Energy stored in non-thermal radiation
similar to energy in thermal radiation or magnetic
fields
=> large contribution to energy balance and
evolution of Cosmos
December 5th Kolkata
Radio (10-6eV)
Radio Astronomy: “First window to violent universe”
Crab
Cyg-A
jets in
radio galaxies
Radio waves emitted by synchrotron radiation of
relativistic electrons gyrating in magnetic fields
Rotation axis
Magnetic axis
Pulsed radio emission
from pulsars
December 5th Kolkata
X-ray (103eV)
X-ray Astronomy: Direct probe of high energy universe
Crab
Cyg-A
hot
intergalactic gas
X-ray emission is bremsstrahlung
of hot gas (T=107-108K)
(Chandra)
Non-thermal
synchrotron radiation
Sources:
pulsars
X-ray
binaries
AGNs
…..
December 5th Kolkata
Very High Energy g-ray Astronomy
TeV Gamma-rays
(1012eV)
• Youngest astronomic discipline
• First significant measurement of TeV
g-ray emission from Crab Nebula by
Whipple telescope in 1989
• Flux Too Low
• Numerous background from charged
particles
December 5th Kolkata
Next Lectures :
We studied Cosmic rays and its propagation
Next lecture : Acceleration of Cosmic rays
What type of sources can accelerate cosmic rays ???
December 4th Berlin
Backup Slides
December 4th Berlin
Post MSc Lectures, December, SINP
SNR Parameters
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Mean ejecta speed : v = (2ESN/Mej)1/2
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Radius swept away : R = (3Mej/4Pr)1/3
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Sweep time : t0 = R/v
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ISM density : r = 1.4mpnh
Post MSc Lectures, December, SINP
Central Question in HE Astrophysics
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Is there unambiguous
evidence for the
acceleration of hadrons
in any or all cosmic
sources?
Victor Hess, 1911
Discovery of the
Cosmic Radiation
Origin still disputed in
2012
Cosmic Rays
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first & most direct evidence of
non-thermal universe
plasma of particles with up to 1020eV
in our own galaxy ???
Post MSc Lectures, December, SINP
1912 discovered
by Victor Hess