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LOFAR CKP: Main Motivation Exploring the sub-second transient radio sky: Extensive Air showers as...
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Transcript of LOFAR CKP: Main Motivation Exploring the sub-second transient radio sky: Extensive Air showers as...
LOFAR CKP: Main Motivation
Exploring the sub-second transient radio sky:Extensive Air showers as guaranteed signalRadio flashes from the moon (UHECR and
other?)Identify and understand other sporadic signals
(“RFI”, lightning, SETI, astrophysical sub-ms pulses with TKP)
Develop the techniques to work on raw time series data (transient buffer board & tied-array beam) in near field and far-field.
Astroparticle Physics:Radio Detection of Particles
Cosmic Rays in atmosphere: Geosynchrotron emission (10-
100 MHz) Radio fluorescence and
Bremsstrahlung (~GHz) Radar reflection signals (any?) VLF emission, process
unclear (<1 MHz) Neutrinos and cosmic rays in
solids: Cherenkov emission (100 MHz - 2 GHz) polar ice cap (balloon or
satellite) inclined neutrinos through
earth crust (radio array) CRs and Neutrinos hitting the
moon (telescope)
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 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)
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
What are UHECRs made of? Current 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
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
Radio CR Simulation Results:Extraction of Energy & Nmax
Hu
eg
e e
t al. (in
pre
para
tion
)Shower-to-Shower fluctuation is only 5%!
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)!
Transient Buffering
COMPENSATECABLE LENGTHDIFFERENCES
DETECT
TRANSIENTS
FREEZE ONTRIGGER
(from RCU)antenna
dataSEPARATESUBBANDS
select
Detection control
(to CEP)Transient
buffer data
Store/Read-outcontrol
Subbanddata
Receiver banddata
Local Control Unit
Trigger
External triggerG. trigger
Phased Array Beam Steering
LOFAR low-band element receives radiation from all directions.
Phased Arrays have a virtual steerable “focal surface” which can be adapted “at will”.
Buffering raw-data in each antenna allows offline beam steering.
Normal far-field imaging is just inclining a plane.
Phased Array Beam Steering
Curving the virtual “focal surface”
allows near-field imaging.
Offline processing allows one to
scan an entire volume at all
frequencies and time ranges.
Search for fast and unpredictable
bursts.
Distinguish cosmic from terrestrial
effects.
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
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!
Observing Time
UHEP/Moon: Initially 1 month of accumulated observing time under good ionospheric
conditions sensitivity that is orders of magnitude better than the sensitivity of existing
experiments Extend to three months to reach UHECR-extrapolation and show GZK cut-off
VHECR mode A: About 1 month of accumulated observing time 1000 good events.
VHECR mode B: Continuous observations, and at least 1/3 of the time with the low-band
antennas. HECR:
based on availability of resources TS-mode: triggered by dynamic spectrum – indicating unusual radio
conditions (e.g. lightning) One-Second All Sky Survey (OSASS) – Take several full-buffer dumps and
image entire sky (Flux calibration and transient search) Map tied array data (Calibration for Moon and transient search)
Summary
Technical goal of CKP: Tempo-spatial properties of sub-second radio flares
UHECRs:Understand the radio emission properties of extensive
airshowers in great detail Precise composition analysis of CRs (“What are they?”) Precise localization of UHECRs (“Where do they come from”?) Closely interact with AUGER observatory (Radio@Auger, MAXIMA).
Improve limits on super-GZK CRs to meaningful values.Explore other methods (passive radar, isotropic emission?)
Be open for other and new fast radio phenomena:Lightning investigation (with KNMI – Dutch Meteorological Inst.)Lunar radio flares from meteorite impactsSearch for astrophysical sub-second radio bursts:
One-Second All-Sky Survey (OSASS)Transient SETI (here rely on open-source/open-data model)
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 ...