The Current Status of

concretecakeUrban and Civil

Nov 29, 2013 (3 years and 7 months ago)

60 views

October 22, 2004

KPS Fall meeting in Jeju

The Current Status of

Cosmic Ray Acceleration Theory


Hyesung Kang

Pusan National University

October 22, 2004

KPS Fall meeting in Jeju

-

CRs from Space provide high energy laboratories for


particle physics

(high energy interactions)

-

Astrophysical problems: the origin of CRs


Where are they from ?

Astrophysical sources


How are they accelerated ?

Acceleration mechanisms


How do they interact with matter, radiation, and B field ?


i.e. acceleration and energy loss at sources


and propagation along the ISM and/or the IGM

October 22, 2004

KPS Fall meeting in Jeju

12 orders of magnitude

32 orders of magnitude

Direct

Measurements

Air Shower

Measurements

E
-
2.7

E
-
3.1

CRs observed at Earth:

Particle energy spectrum

: power
-
law spectrum

-
N(E) ~ E
-
2.7
below the knee


knee energy: 10
15

eV


ankle energy: 10
18.5

eV

-

E: up to ~10
21

eV

-

“universal” acceleration


mechanism working on


a wide range of scales



shock acceleration


UHECRs: above the ankle

October 22, 2004

KPS Fall meeting in Jeju

Pointing to low energy CR sources: impossible due to Galactic
magnetic fields


identifying sources is difficult

slide from A. Olinto

October 22, 2004

KPS Fall meeting in Jeju

Influence of cosmic magnetic fields
:

confinement
, transportation

Source

Milky way

halo B?

Extra
-
galactic B

-
Clusters: 1
-
10
m
G

-
Filaments:~0.1

m
G

-
Voids: <~10
-
3

m
G




100

k
pc

weak deflection
: high E

strong deflection
: low E

Larmor radius:

thanks to Lemoine

1
18
)
1
)(
10
(
1


G
B
eV
E
Z
kpc
r
L
m
G
alactic B

-
disk: 5
-
8
m
G

-
halo: <1

m
G ?

October 22, 2004

KPS Fall meeting in Jeju


Cosmic Rays in the ISM of our Galaxy

radio synchrotron (408MHz)

CR electrons

+ magnetic field


Gamma ray above 100 MeV

CR protons

+ ISM collision
p
0

decay gamma ray

E
CR

~ E
gas

~ E
B
~ E
CMBR
~ 10
-
12

erg/cm
3

October 22, 2004

KPS Fall meeting in Jeju

Cas A

synchrotron

thermal

Radiation from CR particles
:

1) CR e + B field

Synchrotron (radio


X
-
ray)

2) CR e + CMBR


Inverse Compton scattering




up to TeV

-
ray

3) CR p + p


p
0

decay


GeV


-
ray



Photons do point sources !

October 22, 2004

KPS Fall meeting in Jeju

X
-
ray Synchrotron from CR electrons in SN1006

Clear Evidence for ~100 TeV = 10
14

eV electrons : CR protons as well ?

October 22, 2004

KPS Fall meeting in Jeju

Observational Evidences for CRs in Clusters of Galaxies


-

diffuse radio halos and relics: 30 clusters with


radio synchrotron (CR electrons + magnetic field)

-

EUV and hard X
-
ray emission
in excess of thermal radiation


due to
Inverse Compton scattering

of CBR

by CR electrons



presence of
CR electrons

of en
ergy


GeV

(


> 1000)



in
magnetic field

of intensity


m
G

Radio halos:

-

found in high Lx,
high Tx, high Mass
clusters (f~1/3)

-

with recent merger
events and significant
substructure

halo

relic

October 22, 2004

KPS Fall meeting in Jeju

-
Heliosphere (solar system): solar wind, interplanetary shocks

-
ISM of our Galaxy


-

E
CR

~ E
gas

~ E
B
~ E
CMBR
~ 10
-
12

erg/cm
3


dynamically important

in the ISM of galaxies


-

sources: SNRs, stellar wind (OB stars), pulsars

-
ICM inside Clusters of Galaxies (large scale structure of the U)







Why do we care about the CRs?


CRs are ubiquitous in astrophysical plasma.

-
E
CR,p


0.2

E
gas

,

E
B

~

(0.1
-
1)

E
gas


,

E
CR,e
~ 0.01 E
gas

-

sources: AGN, galactic wind, structure shocks, turbulence


October 22, 2004

KPS Fall meeting in Jeju

Standard Estimates for E
max

of an Accelerator


Containment: r
g

= (E)/(ZeB) < R


E
max

< ZeBR: large B, large R for high E



Diffusive shock acceleration (DSA) (nonrelativistic):


E
max

<
b
s
ZeBR



Relativistic shock DSA (analogous argument):


E
max

<
G
s
ZeBR



All lead roughly to (Hillas):
E
max

<
b
ZB
Gauss

R
pc

(ZeV)



Loss due to Coulomb, Synchrotron, IC for CR e’s


Photopair, Photopion for CR p’s



*adapted from T.W. Jones

October 22, 2004

KPS Fall meeting in Jeju

“Hillas Plot” for

some plausible accelerators


(after Hillas 1984)

E
max

= Z
b
a

B R

E
max
: highest possible energy (ZeV)

Z: charge of the CR particle = 1

V
a
/c =
b
a
: speed of accelerator=1

B: magnetic field strength (Gauss)

R: size of accelerator (pc)

B R = E
max

/(
Z
b
a

)=10
20

eV

R

B




the red line

slide from T.W. Jones

October 22, 2004

KPS Fall meeting in Jeju

Observational example:

particle spectra in the
Solar wind

(Mewaldt et al 2001)


-
Thermal+ CR populations

-
suprathermal particles


leak out of thermal pool


into CR population


CR

gas

-

Cosmic Rays = relativistic charged particles

-

Cosmic Rays =

nonthermal particles in astrophysics


:particles above Maxwellian distribution in p space

October 22, 2004

KPS Fall meeting in Jeju

-

collisionless shocks
form in low density astrophysical
plasamas via
EM viscosities


(collective interactions btw particles and underlying B)

B
o

shock transition zone

V
s

u
1

Shock formation needs

irregular B field

-

pre
-
existing turbulence

-

self
-
generated waves



thermalization &


scattering of CRs

-

CRs are byproducts of collisionless shock formation

-

Accelerated to higher E via
Fermi first order process

October 22, 2004

KPS Fall meeting in Jeju

u
1

u
2

Shock front

particle

upstream

downstream

shock rest frame

The key ideas behind DSA


(
D
iffusive

S
hock

A
cceleration
)



Alfven waves in a converging flow


act as converging mirrors




particles are scattered by waves




cross the shock many times




Fermi first order process”

u
u
p
p
|
|
~


energy gain

at each crossing

Converging mirrors

u

u

October 22, 2004

KPS Fall meeting in Jeju

-
When non
-
linear feedback due to CR pressure is insignificant

-
Test particle theory:
f(p) ~ p
-
q

or N(E) ~ E
-
q+2




“universal” power
-
law


q = 3r/(r
-
1) (r =
r
2
/
r
1
=u
1
/u
2
compression ratio across the shock)


determined solely by the shock Mach number

-

for strong gas shock (large M): r


4

(


= 5/3 gas adiabatic index)



q


4, f(p) dp= f
0

p
-
4

dp or N(E)dE = N
0

E
-
2

dE


Synchrotron j
n

 n

a

,


spectral index ~ similar to observed values of “q” and “
a


Simplest prediction of DSA theory

5
.
0
2
3



q
a
But DSA is very efficient, CR pressure is significant



Nonlinear feedback of diffusive CRs to the shock structure

October 22, 2004

KPS Fall meeting in Jeju

t=0

Kang, Jones & Gieseler 2002

-
1D Plane Shock simulations


DSA acceleration


CR modified shocks

-

presusor + subshock

-

reduced P
g

-

enhanced compression

precursor

No simple shock jump condition



Need numerical simulations
to calculate the CR
acceleration efficiency

Time evolution of

the
M
0

= 5

At t=0, pure gasdynamic shock


with P
c
=0.


October 22, 2004

KPS Fall meeting in Jeju

CR energy flux emerged from shock


F
CR
=
h
(M)

F
k


Thermal E

CR E

from DSA simulations

thermalization efficiency
:

d
(M)

CR acceleration efficiency:

h
(M)


r
1

V
s
= u
1

P
CR

kinetic energy flux thru shock


F
k

= (1/2)
r
1
V
s
3


net thermal energy flux


generated at shocks


F
th

= (3/2) [P
2
-
P
1
(r
2
/r
1
)

]
u
2



=
d
(M)

F
k

October 22, 2004

KPS Fall meeting in Jeju

SUMMARY 1: Diffusive Shock Acceleration Theory

1) Ubiquitous astrophysical shocks are efficient CR accelerators.

2) About 50 % of shock kinetic energy can be transferred to


CRs at strong shocks for
Ms

> 30.

3) Via thermal leakage process: a fraction of x= 10
-
4

-

10
-
3

of


the incoming particles become CRs (
at quasi
-
parallel shocks
).

4) direct measurements at heliospheric shocks : (up to GeV)


solar winds, interplanetary shocks, Earth

s bow shocks

5) CR e

s: observed at SNRs via photons (from radio to X
-
ray)


CR p

s: could be possible within a few years

6) Injection of electrons: needs a working model


quasi
-
perpendicular shocks: need detailed numerical studies


7) CRs are natural byproducts of

shock process


and CR


pressure can significantly modify the evolution and structure


of astrophysical shocks.

October 22, 2004

KPS Fall meeting in Jeju

SUMMARY 2: The Origin of CRs

1) Below the Knee (E<10
15
eV): SNR shocks


observations: E ~10
14
eV CR electrons in several remnants


but no concrete observations for CR protons yet


: need to detect pion
-
decay gamma rays

2) Between the Knee and the Ankle (E~10
18
eV): SNRs (core
-


collapse) expanding in stellar wind bubbles


heavy nuclei in strong magnetic fields

3) Above the Ankle (UHECRS) : uncertain


-
cluster shocks (Vs~ several 1000km/s, microgauss fields)


maybe up to 10
19
eV


-
hot spots in powerful radio jets : up to 10
21

eV


-
Gamma Ray Bursts internal shocks


-
Decay of primordial superheavy DM particles


or topological defects

October 22, 2004

KPS Fall meeting in Jeju

Abu
-
Zayyad etal, APh, 18, 237 (2002)

1 EeV

1 ZeV

Do we see the

GZK feature?

HiRes vs AGASA

Number of events:

E> 10
19

eV: ~ 10
3

E > 4x10
19

eV

: ~ 100

E > 10
20
eV: ~ 10


small statistics



More detections


are important

October 22, 2004

KPS Fall meeting in Jeju

Thank you !

October 22, 2004

KPS Fall meeting in Jeju

-
Particle Energy spectrum: power
-
law


over 12 orders of magnitude


universal mechanism?

-

Pointing is possible only for E>10
18
eV : source identification

-

E
CR

~ E
gas

~ E
B
~ E
CMBR
~ 10
-
12

erg/cm
3


dynamically important in the ISM of our Galaxy

-

could be important in Large Scale Structure of the Universe


e.g. clusters of galaxies, filaments and sheets of LSS


(Intern’l Conference on CRs and Magnetic Fields on LSS: 8/16
-
20,


2004, Busan, KOREA
)

-
Main CR
sources below the knee energy (10
15
eV): SNR shock


Galactic CR luminosity

: L
CRs
~ 10
41

erg/s

(CRs escaping from our Galaxy)


= 10% L
SNe

(10
51

erg x 1/(30years) x 10 % efficiency)



Key Observational Facts about the CR acceleration


in Astrophysical environments

q
E
E
N


)
(
October 22, 2004

KPS Fall meeting in Jeju


SNR

RX

J
1713
.
7
-
3946

interacting

with

molecular

clouds


Red
:


significance

contours

of

TeV

(IC

scattered

CMBR)

White
:

probability

contours

of

GeV

EGRET

source

(
p
0

decay
:

CR

p
)

Black
:

(non
-
thermal)

X
-
ray

contours

by

ROSAT

(synchrotron)

R
ai
nb
ow

co
lor
: CO from molecular clouds

Butt et al ‘01

CR protons

Not
confirmed
yet !

October 22, 2004

KPS Fall meeting in Jeju

Incomplete


thermalization

:anisotropic vel. distribution


in local fluid frame

:non
-
Maxwellian tail


= suprathermal particles



leak upstream of shock

B
0

uniform


field

self
-
generated


wave

leaking
particles

B
w


compressed

waves

hot thermalized
plasma

unshocked gas

CR streaming


:
induces MHD waves

:compressed and amplified


in downstream: B
w


diffusive scattering of


CRs

October 22, 2004

KPS Fall meeting in Jeju

CRs observed at Earth:

-
power
-
law spectrum below
the knee: f(p) ~ p
-
4.7


-
composition: ~“interstellar”


proton/electron ~ 50
-
100

J(E) ~ E
-
2.7
; f(p) ~ p
-
4.7

knee

ankle

0.01
0.1
1
10
10
11
10
12
10
13
10
14
10
15
10
16
10
17
10
18
10
19
10
20
10
21
E
(eV / nucleus)
HERA
RHIC
TEVATRON
LHC
fixed target
JACEE[11]
Akeno[12]
Tien Shan[13]
MSU[14]
Tibet[15]
CasaMia[16]
DICE[17]
HEGRA[18]
CASA-BLANCA[19]
KASCADE[20]
E
2.7
F

October 22, 2004

KPS Fall meeting in Jeju

or


Gamma Ray Burst Internal Shocks:


e.g., Waxman 1995, 2000; Vietri 1995
Ultrarelativistic shocks in fireballs:

~10
52
-
53

erg

G
>300, with internal shocks from variations


Waxman 1995, 1999: DSA at internal shocks;


R < 10
16

cm

If B in equipartition with radiation,

B~10
4
Gauss


E < ZeBR ~ 10
20

eV

(photopion losses not as restrictive,

But synchrotron/Compton losses should limit

E<10
19

eV)

Shock/Proton efficiency?

October 22, 2004

KPS Fall meeting in Jeju


UHECR Source Models Grouped in Two Categories


Top
-
Down (Many variants)



Decay of primordial superheavy DM particles


or topological defects (X=> UUHE
p
, baryons,
n
,

)


interaction of UUHE
n

(~10ZeV) with thermal 1.9 K CB
n

(“Z
-
bursts”)


Clustering of source superheavy DM in galactic halo should lead to


UHECR anisotropy.
n
,


backgrounds can also constrain.


Bottom
-
Up (“Astrophysical”) (Many variants)



Particles accelerated to 100’s EeV from low energy