Here: Theory of
Radio Air Shower
Detection
For rest see
subsequent talks by
Dallier & Buitink
Radio Images of Cosmic Accelerators
Cygnus A
Cas A
NRAO/AUI
Fornax A
1.4 , 5, & 8.4 GHz
... is there anything else that radio astronomy can offer?
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 produced
how they are produced
what they are made off
exact shape of the energy spectrum
Auger: UHECR Spectrum
Auger 2007, ICRC
divided by E-3
 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 cutoff”)?
 UHECRs are extragalactic
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 Methods
Can 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
Longitudinal Shower Profile
 Fluorescence
Depth in Atmosphere
+ Sees entire shower
evolution
+ Oversees large volume
- Only works during clear,
moonless nights (10% duty
cycle)
- Light absorption by
aerosols
 Cherenkov particle
detectors
Particle Number
+ Works 100% of time
+ Well studied
- Only sees particles
reaching ground
- Local detection only
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
Earth
B-Field  UHECRs produce particle
showers in atmosphere
~0.3 G
 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
coherent
E-Field
 Etotal=Ne*Ee
 Power  Ee2  Ne2
 GJy flares on 20 ns scales
Falcke & Gorham (2003), Huege & Falcke (2004,2005)
Tim Huege, PhD Thesis 2005 (MPIfR+Univ Bonn
Different Approaches
Buitink 2008, PhD Nijmegen, in prep.
Radiation Formulae
for transversal acceleration or current
Particle-based:
Current-based:
Geosynchrotron:
Falcke & Gorham,
Huege & Falcke
Kahn & Lerche,
Werner & Scholten
The difference lies in the approximation of the current:
Here no emission
from shower
maximum
dN/dt=0!
Falcke & Gorham,
Huege & Falcke
Kahn & Lerche,
Werner & Scholten
Simulation design
T. Huege: REAS2 radio code
 Monte Carlo simulation
 Calculate electric field from a single particle
at different positions on the ground
 Add pulses from many electrons and positrons
 Separation of particle and radiation codes
 Intermediate step saves calculation time
 Different sources of particle distributions:
Parameterizations,
Corsika, Seneca, …
Frequency spectrum
|E| (µV/m/MHz)
Huege et al. (2005)
v (MHz)
Corsika histograms
S. Lafebre: LOFAR air shower library on BlueGene Supercomputer
Corsika simulations with
50 slices
at equidistant shower
depths
Record e+/e–
characteristics:
Energy
Lateral distance
± 20 g/cm2
Arrival time
Momentum angles
Extraction of Energy & Nmax
Huege et al. (in preparation)
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
|E| (µV/m)
Huege et al. (2007)
t (ns)
Contributions in terms of
depth
|E| (µV/m)
Huege et al. (2007)
t (ns)
Curvature
Lafebre et al. (2008), in prep.
Extraction of Xmax
Huege et al. (2008)
Lafebre et al. (2008), in prep.
LOPES:
LOFAR Prototype Station
250 particle detector
huts
30 Radio Antennas
40-80 MHz
raw RF data buffer
LOPES Collaboration: MPIfR Bonn, ASTRON, FZ
Karlsruhe, RU Nijmegen, KASCADE Grande
Imaging of CR radio pulses with
LOPES
A. Nigl 2007, PhD
Horneffer, LOPES30 event
See also Falcke et al. (LOPES collaboration) 2005, Nature, 435, 313
Cross Calibration of
LOPES10 and KASCADE
UHECR Particle Energy
B-field
Distance
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:
Actual 3D radio mapping of a CR burst
No simulation!
 3D: space
 2D: 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)
Positional Accuracy
Particle Detectors vs. Radio Antennas
Interferometry
gives excellent
position
information!
Air showers are
amplified and
modified in
thunderstorm
electric field!
~ average
beamsize
The radio
emission from
normal
showers is
directly
associated
with the
particle
shower within
our beamsize.
Nigl 2007, PhD, RU Nijmegen
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?
Vertical
+ E-Field
-
CORSIKA air
shower simulation
with thunderstorm
electric fields
Positron “Rain”
Buitink et al. (LOPES coll.) 2007, (ICRC)
Thunderstorm Events
 CORSIKA simulations
with thunderstorm electric
fields
 Electrons and positrons
are accelerated and
deflected (“Electron rain”)
 This can lead to
increased radio emission
CORSIKA air shower simulation with
thunderstorm electric fields
 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)
CRs
with
LOFAR
(100xLOPES):
Every dipole has a 1s “Transient Buffer” storing the full
electro-magnetic wave information (all-sky, all-frequency)!
2 x 2 km2 core area
Antenna fields
LOFAR:
~900 dipoles will
see one shower
LOFAR advantages
 ~900 dual-polarized dipoles within 2x2 km
 ~900 dual-polarized dipoles out to 50 km
 Antennas are grouped in station fields and
are synchronized and triggered centrally
 Antennas 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 resolution
Limited 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 HighPrecision UHECR Astrophysics
Ultra-High Energy (SuperGZK) 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:




radio from
neutrinos hitting the moon
ANITA
GLUE
FORTE
RICE
from Gorham et al. (2000)
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 ...