Paul Evenson June 2009 1 Uppsala University June 9, 2009 Solar Physics with the IceTop Air Shower...
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![Page 1: Paul Evenson June 2009 1 Uppsala University June 9, 2009 Solar Physics with the IceTop Air Shower Array Paul Evenson University of Delaware (aka New Sweden)](https://reader035.fdocuments.us/reader035/viewer/2022062309/56649f275503460f94c3fdc5/html5/thumbnails/1.jpg)
Paul Evenson June 2009 1
Uppsala UniversityJune 9, 2009
Solar Physics with the
IceTop Air Shower Array
Paul Evenson
University of Delaware (aka New Sweden)
Department of Physics and Astronomy
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Paul Evenson June 2009 2
The First Extraterrestrial Event Detected by IceCube
Dec 14, 2006 photograph of auroras near Madison, WI
Dec 13, 2006 X3-Class Solar Flare (SOHO)
IceTop and Spaceship Earth Observations of the Solar Flare
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Paul Evenson June 2009 3
Solar Flares
• Somewhere in this picture, particles are being accelerated to GeV energy.
• Can you tell where?• I certainly can’t!• Possibly different
mechanisms are even operating at the same time.
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Paul Evenson June 2009 4
Energy Transport – Conduction and Convection Zones
• It takes approximately one million years for the energy to be conducted (by radiation to the outer part of the sun.
• Near the surface, convective motion sets in
• Approximately 100,000 years of sunlight is stored in the convection zone
• Magnetic phenomena partially control release of this energy
• “Little Ice Ages”
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Paul Evenson June 2009 5
Magnetic Dynamo
• The churning of the convection cells, and differential rotation of the sun generate the solar magnetic field
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Paul Evenson June 2009 6
Magnetic Energy Also Powers Flares
• Exact mechanism is unknown
• Production of GeV particles is common, but the mechanism is also unknown
• Shocks produced by the release are a popular candidate
• We want to study the spectrum and relative timing of the energetic particles
• Understanding may also shed light on astrophysical particle accelerators
• IceTop was designed to measure the spectrum of high energy cosmic rays
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Paul Evenson June 2009 8
IceTop Detectors
• Blocks of clear ice produced in tanks at the Pole
• Cherenkov radiation measured by standard IceCube photon detectors
• Sweden is one production site for these “Digital Optical Modules” or DOM
• Two tanks separated by 10 meters form a station
2 m
0.9 m
Diffusely reflecting liner
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Paul Evenson June 2009 9
PY03:4
PY04:12PY05:16
PY06:18
PY07:18
PY08:12
IIceCube Layout
100 m
Grid north
South Pole
Large showers with E ~ 100-1000 PeV will clarify transition from galactic to
extra-galactic cosmic rays.
Showers triggering 4 stations give ~300 TeV threshold for EAS array
Small showers (2-10 TeV) associated with the dominant muon background in the deep detector are detected as 2-tank coincidences at a station.
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Paul Evenson June 2009 10
Low Energy (1 GeV) “Showers”
• Particles with energy as low as 1 GeV produce secondaries that survive to the surface
• Rarely does a single detector see more than one secondary from a primary
• Large detectors can have high enough counting rates to make statistically significant measurements of the primary flux
• Conventional detectors count muons or neutrons
• Energy spectra are determined from detectors located at different geomagnetic cutoffs
• Flux anisotropy is a source of error in the spectral measurement
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Paul Evenson June 2009 11
Why IceTop Works as a GeV Particle Spectrometer
• The IceTop detectors are thick (90 g/cm2) so the Cherenkov light output is a function of both the species and energy of incoming particles
• Individual waveform recording, and extensive onboard processing, allow the return of pulse height spectra with 10 second time resolution even at the kilohertz counting rate inherent to the detector
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Paul Evenson June 2009 12
Secondary Particle Spectra
• At the South Pole, spectra of secondary particles “remember” a lot of information about the primary spectrum.
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Paul Evenson June 2009 13
Particle Response Functions (Arbitrary Normalization)
• IceTop tank particle response functions change with selection of the threshold
• We are now working with FLUKA calculated response functions
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Paul Evenson June 2009 14
IceTop Event Overview
• A lot of this structure is due to pressure variations
• Much is due to cosmic ray variability
• The flare event and the “Forbush Decrease” at the end of day 347 are clear
• The blast of plasma that produces the decrease is what triggers the anomalous auroral activity
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Solar Particle Spectrum Determination (I)
• Excess count rate (averaged over approximately one hour near the peak of the event) as a function of pre-event counting rate.
• Each point represents one discriminator in one DOM.
• By using the response function for each DOM we fit a power law (in momentum) to the data
• The lines show this fit and the one sigma (systematic) errors
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Paul Evenson June 2009 16
Solar Particle Spectrum Determination (II)
• IceTop proton spectrum (heavy blue line with one sigma error band).
• Black line is the assumed background cosmic-ray proton spectrum
• Points are maximum proton fluxes from GOES spacecraft data.
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Paul Evenson June 2009 17
Putting the IceTop Observation in Context
Spaceship EarthNeutron Monitor Array
Spaceship Earth is a network of neutron monitors strategically deployed to provide precise, real-time, 3-dimensional measurements of the angular distribution of solar cosmic rays:
• 12 Neutron Monitors on 4 continents• Multi-national participation:
– Bartol Research Institute, University of Delaware (U.S.A.)
– IZMIRAN (Russia)– Polar Geophysical Inst. (Russia)– Inst. Solar-Terrestrial Physics (Russia)– Inst. Cosmophysical Research and
Aeronomy (Russia)– Inst. Cosmophysical Research and Radio
Wave Propagation (Russia)– Australian Antarctic Division– Aurora College (Canada)
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Cosmic Ray Detectors at High Latitude
Trajectories are shown for vertically incident primaries corresponding to the 10-, 20-, … 90-percentile rigidities of a typical solar spectrum
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Station Location is Carefully Chosen
• Circles denote station geographical locations. • Average asymptotic direction (squares) and
range (lines) are separated from station geographical locations.
STATION CODES
IN: Inuvik, Canada FS: Fort Smith, Canada PE: Peawanuck, Canada NA: Nain, Canada BA: Barentsburg, NorwayMA: Mawson, Antarctica AP: Apatity, Russia NO: Norilsk, Russia TB: Tixie Bay, Russia CS: Cape Schmidt, Russia TH: Thule, Greenland MC: McMurdo, Antarctica
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Paul Evenson June 2009 20
Determination of the Pitch Angle Distribution
• Individual station data fitted to an angular distribution of the form
f(μ) = c0 + c1 exp(b μ), with μ cosine of pitch angle, and c0, c1, and b free
parameters. The symmetry axis from which pitch angles are measured was also a free parameter.
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13 December 2006 Event Animation
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Neutron Monitor Response Calculated from IceTop Spectrum
• Good agreement (with understanding of viewing direction)
• Continuous determination of precise spectrum
• All information on anisotropy comes from the monitor network
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Towards Precision Spectral Information
• We are reconfiguring IceTop to provide uniform coverage from 500 to 10,000 Hz
• Up to 2000 Hz each DOM will generate a rate histogram
• Above 2000 Hz the SPE discriminators will be used, set to a range of thresholds
• For larger events this will enable us to go far beyond the simple power spectrum analysis
• Exact spectral shape is diagnostic of particle acceleration mechanisms.
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Standard CalibrationTechnique: Latitude Survey
• By observing the change in counting rate as a function of geomagnetic cutoff, response functions can be directly measured
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Our Plan
• Assemble an IceTop tank in a portable freezer in Stockholm / Uppsala / Landskrona (TBD)
• Fill with water and freeze• Load on Oden• Take data on 2009-10 voyage to McMurdo
and back• If this works, do it again another year but
bring it back on a C-17 to do the survey at high altitude
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Container Used For Latitude Surveys On
Polar Star And Polar Sea
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Example of a Latitude Survey
• Left: Course plot with geomagnetic cutoff contours in units of GV
• Right: Counting rate of two detectors and geomagnetic cutoff as a function of time
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Determining a Response Function
• Counting rate of a 3NM64 is plotted against cutoff.
• To deal with the scatter of the points we fit a “Dorman Function” as indicated.
• This function has an analytic derivative as shown. This derivative is exactly the response function for this particular detector.
• In the collaboration involving Uppsala we will derive a whole sequence of response functions for different thresholds, but each will be determined by a method similar to this
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Summary
• IceTop, the surface component of the IceCube Neutrino Observatory at the South Pole, is an air shower detector aimed primarily at studying PeV and above cosmic rays.
• In this mode the 160 (planned) detectors are operated in coincidence.
• Individual detectors are sensitive to the secondary products of particles with energy as low as one GeV, typical of energetic solar particle events.
• Information on the spectrum of particles at a few GeV can be extracted from IceTop,
• We are working to get a better calibration of these detectors as part of a collaboration including Uppsala University.