1. Astroparticle Physics : High Energy Particles and Non Thermal Radiation
Outline:
Cosmic rays
History and Discovery
Composition and propagation
Non thermal Radiation
How do we see cosmic rays ?
Pratik Majumdar
SINP, Kolkata
Parlero’ telescopio MAGIC come esempio di “ground based experiment” per la gamma-astronomia.
Da quando fu osservata la prima sorgente nel 1989 (wipple) i Ttelescopi cherenkov hanno raffinato tecnologie e metodologie. Ora gli IACT sono un maturo strumento di misura e osservazione per l’astronomia gamma delle alte energie
Siamo giunti alla realizzazione di telescopi cherenkov di seconda generazione. Magic tra questi sara’ quello con la piu’ bassa soglia in energia
Esistono altri progetti di esperimento “ground based” non imaging cherenkov telescopes come solar array (celeste) o rivelatori di particelle in alta quota (ARGO) ma, almenno finora, non hanno dimostrato di avere un ottimale strategia di reiezione del fondo.
Post MSc Lectures, December, SINP
M. Mariotti Padova

2. 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
M. Mariotti Padova

3. Astroparticle Physics
Dark matter
Cosmic rays
Solar neutrinos
Gamma ray astronomy
Neutrino masses
Gravitational waves
Beyond Standard Model
Neutrino astronomy
Cosmology
Post MSc Lectures, December, SINP
M. Mariotti Padova

4. What are cosmic rays ? 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
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
M. Mariotti Padova

5. 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)
Post MSc Lectures, December, SINP
M. Mariotti Padova

6. 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
Scientists who, in 1909, 1910 and 1911, made balloon ascents to record ionization were not given credit since their instruments developed defects. Hess figured out that radiation was coming from space by showing that radiation increased as he ascended into the atmosphere (in a balloon) and was the first to be credited for this discovery.
Hess after his flight, which he took without breathing apparatus in very cold and thin air!

7. What are cosmic rays (CRs)?
As it turns out, these charged particles are atomic nuclei zooming through space
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”
Particles in the shower are called “secondary” CRs

8. Cosmic Ray “Showers” p+ po p- po p+ p- e+ e- m+ nm e- g g g g neutrino
Space
“Primary” Cosmic Ray
(Ion, for example a proton)
Earth’s atmosphere
Atmospheric Nucleus p+ po p-
“Secondary” Cosmic Rays...
(about 50 produced after first collision) po g g p+ p-
When primary rays reach our atmosphere, they run into other atomic nuclei and cause showers of particles. One primary “ray” can cause 50 secondary “rays”, a cascading effect that eventually gets down to the ground. The shower of secondaries can spread over a large area. You are constantly being bombarded by these particles. e+ e- g g m+
muon nm
neutrino g e-
Creating:
Electromagnetic Shower
Hadronic Shower
Plus some: Neutrons
Carbon-14
(mainly muons and neutrinos
reach earth’s surface)
(mainly g-rays)

9. Particle Physics  Cosmic Rays
Electrons and positrons in
cloud chambers
Tracks in Spark Chambers
Post MSc Lectures, December, SINP

10. 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

11. Cosmic rays (1930-1945) First detection of Air showers
Cosmic rays, gamma rays and neutrinos are all linked
Post MSc Lectures, December, SINP

12. The Cosmic Ray Spectrum
solar modulation
transition to
heavier nuclei
E3.1
mostly Fe?
Knee ?
EAS Detectors
Direct Measurements
lighter nuclei ?
E2.7, mostly protons
1 particle per m^2 per sec
1 particle per m^2 per year
Ankle
1 particle per Km^2 per year
Power Laws
Shock Acceleration
predicts FSource  E2
LHC
Post MSc Lectures, December, SINP
M. Mariotti Padova

13. 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
M. Mariotti Padova

14. Cosmic Rays Composition
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
M. Mariotti Padova

15. 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
M. Mariotti Padova

16. Post MSc Lectures, December, SINP

17. 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
Confinement time ~ 106 years
Post MSc Lectures, December, SINP
M. Mariotti Padova

18. Propagation in the Galaxy Contd…
If CRs travelled in straight path :
L = t c  L ~ 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
M. Mariotti Padova

19. Diffusion of Cosmic rays
How diffusion occur ?
Random scatterings by irregularities in magnetic field
Fluctuations in the field.
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

20. Propagation in the Galaxy Contd…
Cosmic rays in the Galaxy
Leaky Box Model
Cosmic rays injected
Escape Time
Solve for stationary state
Observed Spectrum is different than Source spectrum
Post MSc Lectures, December, SINP
M. Mariotti Padova

21. More on Leaky Box Model
Consider no injection, spallation, energy loss/gain terms :
If particles diffuse : exponential,
If particles remain within confinement volume with characteristic escape time,
 exponential distribution
Post MSc Lectures, December, SINP

22. Number Density of Cosmic Rays
Post MSc Lectures, December, SINP
M. Mariotti Padova

23. Post MSc Lectures, December, SINP

24. Energy Density of Cosmic Rays
Number density is then :
Calculate energy density :
Post MSc Lectures, December, SINP
M. Mariotti Padova

25. Post MSc Lectures, December, SINP

26. Energetics to CR sources
Post MSc Lectures, December, SINP
M. Mariotti Padova

27. Possible sources Explosion rate ~ 1 per 30 yrs in our galaxy
Typical flares from ordinary stars like Sun ~ ergs/sec
Consider all stars : not enough energy !!!!
Supernova remnants ?
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
M. Mariotti Padova

28. ,  Origin of cosmic rays ? 0 ->  ± ->  +   -> e + 
apparent
source
direction
Origin of
cosmic rays ?
charged
particle
, 
0 -> 
± ->  + 
nucleus + X ->  + X‘
 -> e + 
Summer Lectures, DESY, August 26th Berlin

29. Summer Lectures, DESY, August 26th Berlin
M. Mariotti Padova

30. Multiwavelength Astronomy
M. Mariotti Padova

31. optical view of our Galaxy
optical (eV)
Classical Astronomy
“The passive Universe”
Thermal radiation of T= K
optical view of our Galaxy
December 5th Kolkata

32. “The passive Universe”
Infrared (10-2eV)
Classical Astronomy
“The passive Universe”
Thermal radiation of T= K
(Spitzer)
underlying structure fully revealed in infrared image
December 5th Kolkata

33. Non-thermal Astronomy “The revolutionary Universe”
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

34. Radio Astronomy: “First window to violent universe”
Radio (10-6eV)
Radio Astronomy: “First window to violent universe”
Cyg-A
Crab
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

35. X-ray Astronomy: Direct probe of high energy universe
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= K)
Non-thermal synchrotron radiation
Sources:
pulsars
X-ray binaries AGNs
…..
(Chandra)
December 5th Kolkata

36. Very High Energy -ray Astronomy
TeV Gamma-rays
(1012eV)
Very High Energy -ray Astronomy
Youngest astronomic discipline
First significant measurement of TeV -ray emission from Crab Nebula by Whipple telescope in 1989
Flux Too Low
Numerous background from charged particles
December 5th Kolkata

37. 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

38. Backup Slides
December 4th Berlin

39. Post MSc Lectures, December, SINP
M. Mariotti Padova

40. SNR Parameters Mean ejecta speed : v = (2ESN/Mej)1/2
Radius swept away : R = (3Mej/4Pr)1/3
Sweep time : t0 = R/v
ISM density : r = 1.4mpnh
Post MSc Lectures, December, SINP
M. Mariotti Padova

41. Central Question in HE Astrophysics
Victor Hess, 1911
Discovery of the
Cosmic Radiation
Origin still disputed in 2012
Is there unambiguous evidence for the acceleration of hadrons in any or all cosmic sources?
Cosmic Rays
first & most direct evidence of non-thermal universe
plasma of particles with up to 1020eV in our own galaxy ???
1912 discovered by Victor Hess
Post MSc Lectures, December, SINP
M. Mariotti Padova