447 research outputs found
Search for transient optical counterparts to high-energy IceCube neutrinos with Pan-STARRS1
In order to identify the sources of the observed diffuse high-energy neutrino
flux, it is crucial to discover their electromagnetic counterparts. IceCube
began releasing alerts for single high-energy ( TeV) neutrino
detections with sky localisation regions of order 1 deg radius in 2016. We used
Pan-STARRS1 to follow-up five of these alerts during 2016-2017 to search for
any optical transients that may be related to the neutrinos. Typically 10-20
faint ( mag) extragalactic transients are found within the
Pan-STARRS1 footprints and are generally consistent with being unrelated field
supernovae (SNe) and AGN. We looked for unusual properties of the detected
transients, such as temporal coincidence of explosion epoch with the IceCube
timestamp. We found only one transient that had properties worthy of a specific
follow-up. In the Pan-STARRS1 imaging for IceCube-160427A (probability to be of
astrophysical origin of 50 %), we found a SN PS16cgx, located at 10.0'
from the nominal IceCube direction. Spectroscopic observations of PS16cgx
showed that it was an H-poor SN at z = 0.2895. The spectra and light curve
resemble some high-energy Type Ic SNe, raising the possibility of a jet driven
SN with an explosion epoch temporally coincident with the neutrino detection.
However, distinguishing Type Ia and Type Ic SNe at this redshift is notoriously
difficult. Based on all available data we conclude that the transient is more
likely to be a Type Ia with relatively weak SiII absorption and a fairly normal
rest-frame r-band light curve. If, as predicted, there is no high-energy
neutrino emission from Type Ia SNe, then PS16cgx must be a random coincidence,
and unrelated to the IceCube-160427A. We find no other plausible optical
transient for any of the five IceCube events observed down to a 5
limiting magnitude of mag, between 1 day and 25 days after
detection.Comment: 20 pages, 6 figures, accepted to A&
All-sky search for time-integrated neutrino emission from astrophysical sources with 7 years of IceCube data
Since the recent detection of an astrophysical flux of high energy neutrinos,
the question of its origin has not yet fully been answered. Much of what is
known about this flux comes from a small event sample of high neutrino purity,
good energy resolution, but large angular uncertainties. In searches for
point-like sources, on the other hand, the best performance is given by using
large statistics and good angular reconstructions. Track-like muon events
produced in neutrino interactions satisfy these requirements. We present here
the results of searches for point-like sources with neutrinos using data
acquired by the IceCube detector over seven years from 2008--2015. The
discovery potential of the analysis in the northern sky is now significantly
below , on average
lower than the sensitivity of the previously published analysis of four
years exposure. No significant clustering of neutrinos above background
expectation was observed, and implications for prominent neutrino source
candidates are discussed.Comment: 19 pages, 17 figures, 3 tables; ; submitted to The Astrophysical
Journa
Search for non-relativistic Magnetic Monopoles with IceCube
The IceCube Neutrino Observatory is a large Cherenkov detector instrumenting
of Antarctic ice. The detector can be used to search for
signatures of particle physics beyond the Standard Model. Here, we describe the
search for non-relativistic, magnetic monopoles as remnants of the GUT (Grand
Unified Theory) era shortly after the Big Bang. These monopoles may catalyze
the decay of nucleons via the Rubakov-Callan effect with a cross section
suggested to be in the range of to
. In IceCube, the Cherenkov light from nucleon decays
along the monopole trajectory would produce a characteristic hit pattern. This
paper presents the results of an analysis of first data taken from May 2011
until May 2012 with a dedicated slow-particle trigger for DeepCore, a
subdetector of IceCube. A second analysis provides better sensitivity for the
brightest non-relativistic monopoles using data taken from May 2009 until May
2010. In both analyses no monopole signal was observed. For catalysis cross
sections of the flux of non-relativistic
GUT monopoles is constrained up to a level of at a 90% confidence level,
which is three orders of magnitude below the Parker bound. The limits assume a
dominant decay of the proton into a positron and a neutral pion. These results
improve the current best experimental limits by one to two orders of magnitude,
for a wide range of assumed speeds and catalysis cross sections.Comment: 20 pages, 20 figure
Searches for sterile neutrinos with the IceCube detector
The IceCube neutrino telescope at the South Pole has measured the atmospheric muon neutrino spectrum as a function of zenith angle and energy in the approximate 320 GeV to 20 TeV range, to search for the oscillation signatures of light sterile neutrinos. No evidence for anomalous nu(mu) or (nu) over bar (mu) disappearance is observed in either of two independently developed analyses, each using one year of atmospheric neutrino data. New exclusion limits are placed on the parameter space of the 3 + 1 model, in which muon antineutrinos experience a strong Mikheyev-Smirnov-Wolfenstein-resonant oscillation. The exclusion limits extend to sin(2)2 theta(24) <= 0.02 at Delta m(2) similar to 0.3 eV(2) at the 90% confidence level. The allowed region from global analysis of appearance experiments, including LSND and MiniBooNE, is excluded at approximately the 99% confidence level for the global best-fit value of vertical bar U-e4 vertical bar(2)
Observation and Characterization of a Cosmic Muon Neutrino Flux from the Northern Hemisphere using six years of IceCube data
The IceCube Collaboration has previously discovered a high-energy
astrophysical neutrino flux using neutrino events with interaction vertices
contained within the instrumented volume of the IceCube detector. We present a
complementary measurement using charged current muon neutrino events where the
interaction vertex can be outside this volume. As a consequence of the large
muon range the effective area is significantly larger but the field of view is
restricted to the Northern Hemisphere. IceCube data from 2009 through 2015 have
been analyzed using a likelihood approach based on the reconstructed muon
energy and zenith angle. At the highest neutrino energies between 191 TeV and
8.3 PeV a significant astrophysical contribution is observed, excluding a
purely atmospheric origin of these events at significance. The
data are well described by an isotropic, unbroken power law flux with a
normalization at 100 TeV neutrino energy of
and a hard spectral index of . The observed spectrum is
harder in comparison to previous IceCube analyses with lower energy thresholds
which may indicate a break in the astrophysical neutrino spectrum of unknown
origin. The highest energy event observed has a reconstructed muon energy of
which implies a probability of less than 0.005% for
this event to be of atmospheric origin. Analyzing the arrival directions of all
events with reconstructed muon energies above 200 TeV no correlation with known
-ray sources was found. Using the high statistics of atmospheric
neutrinos we report the currently best constraints on a prompt atmospheric muon
neutrino flux originating from charmed meson decays which is below in
units of the flux normalization of the model in Enberg et al. (2008).Comment: 20 pages, 21 figure
The IceCube Neutrino Observatory - Contributions to ICRC 2015 Part II: Atmospheric and Astrophysical Diffuse Neutrino Searches of All Flavors
Papers on atmospheric and astrophysical diffuse neutrino searches of all
flavors submitted to the 34th International Cosmic Ray Conference (ICRC 2015,
The Hague) by the IceCube Collaboration.Comment: 66 pages, 36 figures, Papers submitted to the 34th International
Cosmic Ray Conference, The Hague 2015, v2 has a corrected author lis
A combined maximum-likelihood analysis of the high-energy astrophysical neutrino flux measured with IceCube
Evidence for an extraterrestrial flux of high-energy neutrinos has now been
found in multiple searches with the IceCube detector. The first solid evidence
was provided by a search for neutrino events with deposited energies
TeV and interaction vertices inside the instrumented volume. Recent
analyses suggest that the extraterrestrial flux extends to lower energies and
is also visible with throughgoing, -induced tracks from the Northern
hemisphere. Here, we combine the results from six different IceCube searches
for astrophysical neutrinos in a maximum-likelihood analysis. The combined
event sample features high-statistics samples of shower-like and track-like
events. The data are fit in up to three observables: energy, zenith angle and
event topology. Assuming the astrophysical neutrino flux to be isotropic and to
consist of equal flavors at Earth, the all-flavor spectrum with neutrino
energies between 25 TeV and 2.8 PeV is well described by an unbroken power law
with best-fit spectral index and a flux at 100 TeV of
.
Under the same assumptions, an unbroken power law with index is disfavored
with a significance of 3.8 () with respect to the best
fit. This significance is reduced to 2.1 () if instead we
compare the best fit to a spectrum with index that has an exponential
cut-off at high energies. Allowing the electron neutrino flux to deviate from
the other two flavors, we find a fraction of at Earth.
The sole production of electron neutrinos, which would be characteristic of
neutron-decay dominated sources, is rejected with a significance of 3.6
().Comment: 16 pages, 10 figures; accepted for publication in The Astrophysical
Journal; updated one referenc
Lowering IceCube’s energy threshold for point source searches in the southern sky
Observation of a point source of astrophysical neutrinos would be a "smoking gun" signature of a cosmic-ray accelerator. While IceCube has recently discovered a diffuse flux of astrophysical neutrinos, no localized point source has been observed. Previous IceCube searches for point sources in the southern sky were restricted by either an energy threshold above a few hundred TeV or poor neutrino angular resolution. Here we present a search for southern sky point sources with greatly improved sensitivities to neutrinos with energies below 100 TeV. By selecting charged-current nu(mu) interacting inside the detector, we reduce the atmospheric background while retaining efficiency for astrophysical neutrino-induced events reconstructed with sub-degree angular resolution. The new event sample covers three years of detector data and leads to a factor of 10 improvement in sensitivity to point sources emitting below 100 TeV in the southern sky. No statistically significant evidence of point sources was found, and upper limits are set on neutrino emission from individual sources. A posteriori analysis of the highest-energy (similar to 100 TeV) starting event in the sample found that this event alone represents a 2.8 sigma deviation from the hypothesis that the data consists only of atmospheric background
Neutrinos and Cosmic Rays Observed by IceCube
The core mission of the IceCube Neutrino observatory is to study the origin
and propagation of cosmic rays. IceCube, with its surface component IceTop,
observes multiple signatures to accomplish this mission. Most important are the
astrophysical neutrinos that are produced in interactions of cosmic rays, close
to their sources and in interstellar space. IceCube is the first instrument
that measures the properties of this astrophysical neutrino flux, and
constrains its origin. In addition, the spectrum, composition and anisotropy of
the local cosmic-ray flux are obtained from measurements of atmospheric muons
and showers. Here we provide an overview of recent findings from the analysis
of IceCube data, and their implications on our understanding of cosmic rays.Comment: Review article, to appear in Advances in Space Research, special
issue "Origins of Cosmic Rays
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