Post MSc Lectures, December, SINP Pratik Majumdar SINP, Kolkata Outline: Cosmic rays History and Discovery Composition and propagation Non thermal

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


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


Astroparticle Physics

Cosmic rays

Gamma ray astronomy

Gravitational waves

Neutrino astronomy

Dark matter

Solar neutrinos

Neutrino masses

Cosmology

Beyond Standard Model


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 )


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:


Particle Physics Cosmic Rays

Tracks in Spark Chambers

Electrons and positrons in cloud chambers


Discovering Elementary particles

Anderson and Neddermeyer discovered muons (1936)

Nuclear emulsion plates

Blackett and others went to high altitudes, Pic du Midi

obs.


Cosmic rays (1930-1945)First detection of Air showers

Cosmic rays, gamma rays and neutrinos are all linked


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


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?


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


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



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


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.


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 :


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


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


Number Density of Cosmic Rays



Energy Density of Cosmic Rays

Number density is then :

Calculate energy density :



Energetics to CR sources


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)


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)


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


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)


(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


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



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


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

Documents

Post MSc Lectures, December, SINP Pratik Majumdar SINP, Kolkata Outline: Cosmic rays History and Discovery Composition and propagation Non thermal