Radio Detection of Ultra-High Energy Cosmic Rays
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Transcript of Radio Detection of Ultra-High Energy Cosmic Rays
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Here: Theory of Radio Air Shower
Detection
For rest see subsequent talks by
Dallier & Buitink
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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
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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.
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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
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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
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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)
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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
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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
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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.
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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
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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.
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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
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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
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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
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Extraction of Energy & NmaxH
ueg
e e
t al. (in
pre
para
tion
)Shower-to-Shower fluctuation is only 5%.
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Pulse shape
Raw radio pulse of a 1019 eV proton
shower as seen north of the shower core
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Contributions in terms of energy
Hueg
e e
t al. (2
00
7)
|E|
(µV
/m)
t (ns)
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Contributions in terms of depth
Hueg
e e
t al. (2
00
7)
|E|
(µV
/m)
t (ns)
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Curvature
Lafebre et al. (2008), in prep.
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Extraction of Xmax
Lafebre et al. (2008), in prep.
Huege et al. (2008)
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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
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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
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Cross Calibration of LOPES10 and KASCADE
B-field
Distance
UHECR Particle Energy
Horneffer-Formula 2006/2007
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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!
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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.
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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
+
-
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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
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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)!
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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
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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
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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
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Cosmic Rays in the Radio
νMoon
S. Lafebre
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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 ...