Post MSc Lectures, December, SINP Pratik Majumdar SINP, Kolkata Outline: Cosmic rays History and...
-
Upload
rudolf-hall -
Category
Documents
-
view
217 -
download
0
Transcript of Post MSc Lectures, December, SINP Pratik Majumdar SINP, Kolkata Outline: Cosmic rays History and...
Post MSc Lectures, December, SINP
Pratik MajumdarSINP, Kolkata
Outline: Cosmic rays History and Discovery Composition and
propagation Non thermal Radiation How do we see cosmic
rays ?
Astroparticle Physics : High Energy Particles and Non Thermal Radiation
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
Cosmic rays
Gamma ray astronomy
Gravitational waves
Neutrino astronomy
Dark matter
Solar neutrinos
Neutrino masses
Cosmology
Beyond Standard Model
Post MSc Lectures, December, SINP
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
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)
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)? 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
“Primary” Cosmic Ray (Ion, for example a proton)
Atmospheric Nucleus
po p- p+
g g
e+ e-
g e-
Electromagnetic Shower
po
p- p+
(mainly g-rays)
m+
muonnm
neutrino
Hadronic Shower
(mainly muons and neutrinos reach earth’s surface)
“Secondary” Cosmic Rays...(about 50 produced after first collision)
Cosmic Ray “Showers”Space
Earth’s atmosphere
Plus some:NeutronsCarbon-14
g g
Creating:
Post MSc Lectures, December, SINP
Particle Physics Cosmic Rays
Tracks in Spark Chambers
Electrons and positrons in cloud chambers
Post MSc Lectures, December, SINP
Discovering Elementary particles
Anderson and Neddermeyer discovered muons (1936)
Nuclear emulsion plates
Blackett and others went to high altitudes, Pic du Midi
obs.
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
Power Laws Shock Accelerationpredicts FSource E2
E2.7, mostly protons
Ankle
sola
r m
odul
atio
n
transition toheavier nuclei E3.1
mostly Fe?
Knee
?EAS DetectorsDirect Measurements
transition tolighter nuclei ?LHC
1 particle per m^2 per sec
1 particle per m^2 per year
1 particle per Km^2 per year
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• 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 indicationthat the cosmic rays have crossed a certainamount 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
Confinement time ~ 106 years
Post MSc Lectures, December, SINP
Propagation in the Galaxy Contd…
• 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.
Exercise : Show this neglecting interactions , where energy loss-dE/dt = b(E) and Q(E,x,t ) is rate of injection of particles
Diffusion loss equation :
Post MSc Lectures, December, SINP
Propagation in the Galaxy Contd…
• Leaky Box Model Cosmic rays in the Galaxy
Escape TimeCosmic rays injected
Observed Spectrum is different than Source spectrum
Solve for stationary state
Post MSc Lectures, December, SINP
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
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 ?
Explosion rate ~ 1 per 30 yrs in our galaxy
Supernova explosion energy ~ 1051 ergs Supernova can supply energy to
galactic cosmic rays ???
Summer Lectures, DESY, August 26th Berlin
Origin of cosmic rays ?
,
apparent sourcedirection
charged particle
0 -> ± -> +
nucleus + X -> + X‘
-> e +
Summer Lectures, DESY, August 26th Berlin
Multiwavelength Astronomy
December 5th Kolkata
optical view of our Galaxy
Thermal radiation of T=3.000 - 10.000 K
Classical Astronomy “The passive Universe”
optical (eV)
December 5th Kolkata
underlying structure fully revealed in infrared image
Infrared (10-2eV)
Thermal radiation of T=3.000 - 10.000 K
Classical Astronomy “The passive Universe”
(Spitzer)
December 5th Kolkata
Non-thermal Astronomy“The revolutionary Universe”
SN1987A
• 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 Astronomy: “First window to violent universe”
Radio waves emitted by synchrotron radiation of relativistic electrons gyrating in magnetic fields Rotation axis
Magnetic axis
jets inradio galaxies
Cyg-A Crab
Pulsed radio emission from pulsars
Radio (10-6eV)
December 5th Kolkata
(Chandra)
X-ray Astronomy: Direct probe of high energy universe
CrabCyg-A
X-ray emission is bremsstrahlung of hot gas (T=107-108K)
hot intergalactic gas
Sources:pulsarsX-ray binaries AGNs…..
X-ray (103eV)
Non-thermal synchrotron radiation
December 5th Kolkata
TeV Gamma-rays(1012eV)
• Youngest astronomic discipline • First significant measurement of
TeV -ray emission from Crab Nebula by Whipple telescope in 1989
Very High Energy -ray Astronomy
• Flux Too Low• Numerous background from
charged particles
Next Lectures :
December 4th Berlin
We studied Cosmic rays and its propagation
Next lecture : Acceleration of Cosmic rays
What type of sources can accelerate cosmic rays ???
Backup Slides
December 4th Berlin
Post MSc Lectures, December, SINP
Post MSc Lectures, December, SINP
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
Central Question in HE Astrophysics
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
• 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