6 research outputs found
Observation of anisotropy in the galactic cosmic-ray arrival directions at 400 TeV with IceCube
In this paper we report the first observation in the Southern hemisphere of an energy dependence in the Galactic cosmic-ray anisotropy up to a few hundred TeV. This measurement was performed using cosmic-ray-induced muons recorded by the partially deployed IceCube observatory between 2009 May and 2010 May. The data include a total of 33 Ă 10âč muon events with a median angular resolution of âŒ3âŠ. A sky map of the relative intensity in arrival direction over the Southern celestial sky is presented for cosmic-ray median energies of 20 and 400 TeV. The same large-scale anisotropy observed at median energies around 20 TeV is not present at 400 TeV. Instead, the high-energy sky map shows a different anisotropy structure including a deficit with a post-trial significance of â6.3Ï. This anisotropy reveals a new feature of the Galactic cosmic-ray distribution, which must be incorporated into theories of the origin and propagation of cosmic rays.R. Abbasi ... G.C. Hill, et al., IceCube Collaboratio
Time-dependent searches for point sources of neutrinos with the 40-string and 22-string configurations of IceCube
This paper presents searches for flaring sources of neutrinos using the
IceCube neutrino telescope. For the first time, a search is performed over the
entire parameter space of energy, direction and time looking for neutrino
flares of 20 microseconds to a year duration from astrophysical sources among
the atmospheric neutrino and muon backgrounds. Searches which integrate over
time are less sensitive to flares because they are affected by a larger
background of atmospheric neutrinos and muons that can be reduced by the time
constraint. Flaring sources considered here, such as active galactic nuclei,
soft gamma-ray repeaters and gamma-ray bursts, are promising candidate neutrino
emitters. We used mainly data taken between April 5, 2008 and May 20, 2009 by a
partially completed configuration of IceCube with 40 strings. For the presented
searches an unbinned maximum likelihood method is used with a time-dependent
prior to test several different source hypotheses. An "untriggered" search
covers any possible time-dependent emission from sources not correlated to any
other observation using other astrophysical messengers such as photons.
Moreover, a similar time scan is performed for a predefined catalogue of
sources that exhibit intense photon flares. Searches triggered by
multi-wavelength information on flares from blazars and soft gamma-ray
repeaters are performed using the 40 string data and also the data taken by the
previous configuration of 22 strings in operation between May 31, 2007 and
April 5, 2008. Flares for which extensive and continuous monitoring is
available from Fermi-LAT and SWIFT and flares detected by imaging Cherenkov
telescopes with shorter time-scale monitoring are considered. The results from
all searches are compatible with a fluctuation of the background.Comment: 37 pages, 14 figures. Accepted to the Astrophysical Journa