Here: Theory of Radio Air Shower

Detection

For rest see subsequent talks by

Dallier & Buitink

Radio Images of Cosmic Accelerators

Cas ACygnus A

Fornax ANRAO/AUI

... is there anything else that radio astronomy can offer?

1.4 , 5, & 8.4 GHz

Cosmic Ray Energy Spectrum

Cosmic rays are very energetic particles (v~c) accelerated in the cosmos

The differential Cosmic Ray spectrum is described by an almost universal power law with a E-2.75 decline.

Low-energy cosmic rays can be directly measured.

High-energy cosmic rays are measured through their air showers.

What we (don’t) know about UHECRs

We know:their energies (up to 1020 eV).their overall energy spectrum

We don’t know:where they are producedhow they are producedwhat they are made offexact shape of the energy spectrum

Auger: UHECR Spectrum

Reliable energy spectrum up to >1020 eV from surface detectors (SD)

Evidence for a suppresion above 1019.6 eV

Interaction of UHECRs with cosmic microwave background (“GZK cut-off”)?

UHECRs are extragalactic

Auger 2007, ICRCdivided by E-3

30 expected for E-2.6, 2 seen

Auger: Clustering of UHECRs

New data confirms correlation with AGN clustering. Chance probability: 2× 10-3

The beginning of “charged particle astronomy”!

AUGER Collaboration (2007), Science 9. Nov. (2007)

Current Detection MethodsCan we do even better?

Fluorescence+ Sees entire shower

evolution+ Oversees large volume- Only works during clear,

moonless nights (10% duty cycle)

- Light absorption by aerosols

Cherenkov particle detectors+ Works 100% of time+ Well studied- Only sees particles

reaching ground- Expensive & cumbersome

Current Detection Methods

Fluorescence+ Sees entire shower

evolution+ Oversees large volume- Only works during clear,

moonless nights (10% duty cycle)

- Light absorption by aerosols

Cherenkov particle detectors+ Works 100% of time+ Well studied- Only sees particles

reaching ground- Local detection only

Longitudinal Shower Profile

Depth

in

Atm

osp

here

Particle Number

Advantages of Radio Emission from Air Showers Cheap detectors High duty cycle (24 hours/day) Low attenuation, good calibratability

(also distant and inclined showers) Bolometric, i.e. good energy

measurement (integral over shower evolution)

Interferometry gives precise directions

Complementarity with SD gives composition

But, does it work? Problems before 2001:

No theoretical understanding No experimental understanding since

1974.

Coherent Geosynchrotron Radio Pulses in Earth Atmosphere

UHECRs produce particle showers in atmosphere

Shower front is ~2-3 m thick ~ wavelength at 100 MHz

e± emit synchrotron in geomagnetic field

Emission from all e± (Ne) add up coherently

Radio power grows quadratically with Ne

Etotal=Ne*Ee

Power Ee2 Ne

2

GJy flares on 20 ns scales

coherentE-Field

show

er front

e± ~

50 M

eV

Geo-synchrotron

Falcke & Gorham (2003), Huege & Falcke (2004,2005) Tim Huege, PhD Thesis 2005 (MPIfR+Univ Bonn

EarthB-Field~0.3 G

Different Approaches

Particle-based:

Current-based:

Geosynchrotron:Falcke & Gorham,

Huege & Falcke

Kahn & Lerche, Werner & Scholten

The difference lies in the approximation of the current:

Falcke & Gorham, Huege & Falcke

Kahn & Lerche, Werner & Scholten

Here no emission from shower maximum dN/dt=0!

Radiation Formulae for transversal acceleration or current

Buitink 2008, PhD Nijmegen, in prep.

Simulation design

Monte Carlo simulationCalculate electric field from a single particle

at different positions on the groundAdd pulses from many electrons and positrons

Separation of particle and radiation codesIntermediate step saves calculation timeDifferent sources of particle distributions:

Parameterizations,Corsika, Seneca, …

T. Huege: REAS2 radio code

Frequency spectrum|E

| (µ

V/m

/MH

z)

v (MHz)

Hueg

e e

t al. (2

00

5)

20 m

140 m

260 m

380 m

500 m

Corsika histograms

Corsika simulations with 50 slicesat equidistant shower depths

Record e+/e– characteristics:

EnergyLateral distanceArrival timeMomentum angles

± 20 g/cm2

S. Lafebre: LOFAR air shower library on BlueGene Supercomputer

Extraction of Energy & NmaxH

ueg

e e

t al. (in

pre

para

tion

)Shower-to-Shower fluctuation is only 5%.

Pulse shape

Raw radio pulse of a 1019 eV proton

shower as seen north of the shower core

Contributions in terms of energy

Hueg

e e

t al. (2

00

7)

|E|

(µV

/m)

t (ns)

Contributions in terms of depth

Hueg

e e

t al. (2

00

7)

|E|

(µV

/m)

t (ns)

Curvature

Lafebre et al. (2008), in prep.

Extraction of Xmax

Lafebre et al. (2008), in prep.

Huege et al. (2008)

LOPES:LOFAR Prototype Station

LOPES Collaboration: MPIfR Bonn, ASTRON, FZ LOPES Collaboration: MPIfR Bonn, ASTRON, FZ Karlsruhe, RU Nijmegen, KASCADE GrandeKarlsruhe, RU Nijmegen, KASCADE Grande

250 particle detector 250 particle detector hutshuts

30 Radio Antennas30 Radio Antennas40-80 MHz40-80 MHz

raw RF data bufferraw RF data buffer

Imaging of CR radio pulses with LOPES

See also Falcke et al. (LOPES collaboration) 2005, Nature, 435, 313

Horneffer, LOPES30 event

A. Nigl 2007, PhD

Cross Calibration of LOPES10 and KASCADE

B-field

Distance

UHECR Particle Energy

Horneffer-Formula 2006/2007

Nanosecond Radio Imaging in 3D

Off-line correlation of radio waves captured in buffer memory

We can map out a 5D image cube:3D: space2D: frequency & time

Image shows brightest part of a radio airshower in a 3D volume at t=tmax and all freq.

Bähren, Horneffer, Falcke et al. (RU Nijmegen)

Actual 3D radio mapping of a CR burst No simulation!

Positional Accuracy

linear improvement with SNR

Air showers are amplified and modified in

thunderstorm electric field!

Nigl 2007, PhD, RU Nijmegen

Particle Detectors vs. Radio Antennas

~ averagebeamsize

Interferometry gives excellent

position information!

The radio emission from

normal showers is

directly associated with the particle

shower within our beamsize.

Thunderstorm Events

CORSIKA simulations with thunderstorm electric fields

Electrons and positrons are accelerated and deflected (“Electron rain”)

This can lead to increased radio emission

The shower is modified in thunderstorms not the radio emission …

Does this have relevance for CR lightning initiation?

Buitink et al. (LOPES coll.) 2007, (ICRC)

Positron “Rain”

Vertical E-Field

CORSIKA air shower simulation with thunderstorm electric fields

+

-

Thunderstorm Events

CORSIKA simulations with thunderstorm electric fields

Electrons and positrons are accelerated and deflected (“Electron rain”)

This can lead to increased radio emission

The shower is modified in thunderstorms not the radio emission …

Does this have relevance for CR lightning initiation?

Buitink et al. (LOPES coll.) 2007, (ICRC)

CORSIKA air shower simulation with thunderstorm electric fields

CRs with LOFAR (100xLOPES):

LOFAR:

~900 dipoles will see one shower2

x 2

km

2 c

ore

are

a

Antenna fields

Every dipole has a 1s “Transient Buffer” storing the full electro-magnetic wave information (all-sky, all-frequency)!

LOFAR advantages

~900 dual-polarized dipoles within 2x2 km~900 dual-polarized dipoles out to 50 kmAntennas are grouped in station fields and

are synchronized and triggered centrallyAntennas can be combined later to see radio

out to large distances (SNR increase by ~factor 100 over LOPES antenna)!

Precise shower front and hence accurate composition & direction

Excellent energy resolutionLimited to energies around a few 1015-18 eV

Auger Expansion (MAXIMA) advantages

20 km2 dual polarized test array (~100 antennas) Gives high duty cycle for hybrid events (+SD) Combination with surface detectors and

fluorescence telescopes will allow triple coincidences (“tri”-brid events)

Cross-calibration between methods Eventually will need complete Auger with radio

antennas Accurate determination of all UHECR

parameters with ~100% hybrid events LOFAR + Radio@Auger: Beginning of High-

Precision UHECR Astrophysics

Ultra-High Energy (Super-GZK) Neutrino Detections

Ultra-high energy particle showers hitting the moon produce radio Cherenkov emission (Zas, Gorham, …).

This provides the largest and cleanest particle detector available for direct detections at the very highest energies.

In the forward direction (Cherenkov cone) the maximum of the emission is in the GHz range.

Current Experiments: ANITA GLUE FORTE RICE

from Gorham et al. (2000)from Gorham et al. (2000)

radio from neutrinos hitting the moon

Cosmic Rays in the Radio

νMoon

S. Lafebre

Conclusions

Challenges for UHECRs in the future: getting better composition and energy analysis (to reduce uncertainty in

GZK cut-off determination estimate) Get even better directional information to improve clustering analysis &

identify sources Get to the super-GZK particles Become bigger, better, cheaper, & smarter

Radio emission of UHECR should give: excellent energy resolution (5%?) precise 3D localization and imaging (~0.1°) Composition from shower front and pulse shape high duty cycle

With Auger “charged particle astronomy” has begun: GZK cutoff, AGN correlation, …

With Radio high-precision particle astronomy will begin But this requires still a significant experimental effort ...