Solar Energetic Particle Spectrum on 13 December 2006 Determined by IceTop Page: 3 of 7
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The IceTop air shower array now under con-
struction at the South Pole as the surface compo-
nent of the IceCube neutrino telescope (Achterberg et al.
2006) detected an unusual near-solar-minimum
Ground Level Enhancement (GLE) after a solar
flare on 13 December 2006. Beginning at 0220
1jjj Physikalisches I., RWTH Aachen U., D-52056
2Physics & Astronomy, U. Alaska Anchorage, AK 99508
3CTSPS, Clark-Atlanta U., Atlanta, GA 30314
4Physics, Southern U., Baton Rouge, LA 70813
5Physics, U. California, Berkeley, CA 94720
6Lawrence Berkeley National Laboratory, Berkeley, CA
7I. fur Physik, Humboldt-Universitt zu Berlin, D-12489
8Science Faculty CP230, U. Libre de Bruxelles, B-1050
9Vrije U. Brussel, Dienst ELEM, B-1050 Brussels
1oPhysics, Chiba U., Chiba Japan 263-8522
11Physics & Astronomy, U. Canterbury, Christchurch NZ
12Physics, U. Maryland, College Park, MD 20742
13Physics, Universitat Dortmund, D-44221 Dortmund
14Subatomic and Radiation Physics, U. Gent, B-9000
15MPI fur Kernphysik, D-69177 Heidelberg
16Physics and Astronomy, U. California, Irvine, CA
17High Energy Physics, Ecole Poly F6d6rale, CH-1015
18Physics and Astronomy, U. Kansas, Lawrence, KS
19Astronomy, U. Wisconsin, Madison, WI 53706
20Physics, U. Wisconsin, Madison, WI 53706
21Institute of Physics, U. Mainz, D-55099 Mainz
22U. Mons-Hainaut, B-7000 Mons
23Physics & Astronomy & BRI, U. Delaware, Newark,
24Physics, U. Oxford, Oxford OXi 3NP
25Physics, U. Wisconsin, River Falls, WI 54022
26Physics, Stockholm U., SE-10691 Stockholm
27Astronomy & Astrophysics, PA State, Univ. Park, PA
28Physics, PA State, Univ. Park, PA 16802
29High Energy Physics, Uppsala U., S-75121 Uppsala
30Physics & Astronomy, Utrecht U./SRON, NL-3584
31Physics, U. Wuppertal, D-42119 Wuppertal
32DESY, D-15735 Zeuthen
33Phys. Inst., U. Erlangen-Nurnberg, D-91058 Erlangen
34Fisica, U. Bari, I-70126 Bari
35 Pure & Applied Sciences, Kalmar U., S-39182 Kalmar
UT, the 4B class flare occurred at solar coordi-
nates S06 W24, accompanied by strong (X3.4)
X-ray emission and type II and IV radio bursts.
The LASCO coronagraph on the SOHO spacecraft
observed a halo CME launch from the Sun at ~
0225 UT with speed estimated to be ~ 1770 km/s.
We have begun (Bieber et al. 2007) a comprehen-
sive analysis of the propagation of solar energetic
particles in this event. However the focus of this
Letter is the new and unique ability of IceTop to
derive the energy spectrum of these particles in
the multi-GeV regime from a single detector with
a well defined viewing direction.
When completed, IceTop will have approxi-
mately 500 square meters of ice Cherenkov col-
lecting area arranged in an array of 80 stations on
a 125 m triangular grid to detect air showers from
one PeV to one EeV. Each station consists of two,
two meter diameter tanks filled with ice to a depth
of 90 cm. Tanks are instrumented with two Dig-
ital Optical Modules (DOM) operated at differ-
ent gain settings to provide appropriate dynamic
range to cover both large and small air showers.
Each DOM contains a 10 inch photomultiplier and
an advanced readout system capable of digitiz-
ing the full waveform. For historical reasons, the
two discriminator counting rates recorded in each
DOM are termed SPE (Single Photo Electron),
and MPE (Multi Photo Electron). In the present
analysis the SPE threshold corresponds approxi-
mately to 20 photoelectrons (PE), and the MPE
threshold to 100 PE.
Due to the high altitude (2835m) and the nearly
zero geomagnetic cutoff at the South Pole, sec-
ondary particle spectra at the detector retain a
significant amount of information on the spectra
of the primary particles. In a thin, ionization de-
tector these secondary particles either would not
interact, or would produce virtually indistinguish-
able signals. This is not the case in the thick Ice-
Top detector, where a traversing muon produces
130 PE and the typical electron only 15 PE. Signal
amplitude therefore carries information about the
composition and spectra of the incident particles,
albeit integrated over broad regions of the spec-
trum. In particular, differences in counting rates
of discriminators at different thresholds allow us
to infer the particle spectrum incident at the top
of the atmosphere.
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Collaboration, IceCube & Klein, Spencer. Solar Energetic Particle Spectrum on 13 December 2006 Determined by IceTop, article, October 11, 2008; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc929668/m1/3/: accessed November 12, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.