307 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&
Neutrinos below 100 TeV from the southern sky employing refined veto techniques to IceCube data
Many Galactic sources of gamma rays, such as supernova remnants, are expected
to produce neutrinos with a typical energy cutoff well below 100 TeV. For the
IceCube Neutrino Observatory located at the South Pole, the southern sky,
containing the inner part of the Galactic plane and the Galactic Center, is a
particularly challenging region at these energies, because of the large
background of atmospheric muons. In this paper, we present recent advancements
in data selection strategies for track-like muon neutrino events with energies
below 100 TeV from the southern sky. The strategies utilize the outer detector
regions as veto and features of the signal pattern to reduce the background of
atmospheric muons to a level which, for the first time, allows IceCube
searching for point-like sources of neutrinos in the southern sky at energies
between 100 GeV and several TeV in the muon neutrino charged current channel.
No significant clustering of neutrinos above background expectation was
observed in four years of data recorded with the completed IceCube detector.
Upper limits on the neutrino flux for a number of spectral hypotheses are
reported for a list of astrophysical objects in the southern hemisphere.Comment: 19 pages, 17 figures, 2 table
Impact of chronic stress protocols in learning and memory in rodents: systematic review and meta-analysis
The idea that maladaptive stress impairs cognitive function has been a cornerstone of decades in basic and clinical research. However, disparate findings have reinforced the need to aggregate results from multiple sources in order to confirm the validity of such statement. In this work, a systematic review and meta-analyses were performed to aggregate results from rodent studies investigating the impact of chronic stress on learning and memory. Results obtained from the included studies revealed a significant effect of stress on global cognitive performance. In addition, stressed rodents presented worse consolidation of learned memories, although no significantly differences between groups at the acquisition phase were found. Despite the methodological heterogeneity across studies, these effects were independent of the type of stress, animals' strains or age. However, our findings suggest that stress yields a more detrimental effect on spatial navigation tests' performance. Surprisingly, the vast majority of the selected studies in this field did not report appropriate statistics and were excluded from the quantitative analysis. We have therefore purposed a set of guidelines termed PROBE (Preferred Reporting Orientations for Behavioral Experiments) to promote an adequate reporting of behavioral experiments.This work was funded by the European Commission (FP7) "SwitchBox" (Contract HEALTH-F2-2010-259772) project and co-financed by the Portuguese North Regional Operational Program (ON.2 - O Novo Norte) under the National Strategic Reference Framework (QREN), through the European Regional Development Fund (FEDER), and by Fundacao Calouste Gulbenkian (Portugal) (Contract grant number: P-139977; project "Better mental health during ageing based on temporal prediction of individual brain ageing trajectories (TEMPO)"). PSM is supported by an FCT fellowship grant, from the PhD-iHES program, with the reference PDE/BDE/113601/2015.info:eu-repo/semantics/publishedVersio
The IceCube Neutrino Observatory - Contributions to ICRC 2017 Part VI: IceCube-Gen2, the Next Generation Neutrino Observatory
Papers on research & development towards IceCube-Gen2, the next generation neutrino observatory at South Pole, submitted to the 35th International Cosmic Ray Conference (ICRC 2017, Busan, South Korea) by the IceCube-Gen2 Collaboration
Brownian motors: noisy transport far from equilibrium
Transport phenomena in spatially periodic systems far from thermal
equilibrium are considered. The main emphasize is put on directed transport in
so-called Brownian motors (ratchets), i.e. a dissipative dynamics in the
presence of thermal noise and some prototypical perturbation that drives the
system out of equilibrium without introducing a priori an obvious bias into one
or the other direction of motion. Symmetry conditions for the appearance (or
not) of directed current, its inversion upon variation of certain parameters,
and quantitative theoretical predictions for specific models are reviewed as
well as a wide variety of experimental realizations and biological
applications, especially the modeling of molecular motors. Extensions include
quantum mechanical and collective effects, Hamiltonian ratchets, the influence
of spatial disorder, and diffusive transport.Comment: Revised version (Aug. 2001), accepted for publication in Physics
Report
Investigation of two Fermi-LAT gamma-ray blazars coincident with high-energy neutrinos detected by IceCube
After the identification of the gamma-ray blazar TXS 0506+056 as the first
compelling IceCube neutrino source candidate, we perform a systematic analysis
of all high-energy neutrino events satisfying the IceCube realtime trigger
criteria. We find one additional known gamma-ray source, the blazar GB6
J1040+0617, in spatial coincidence with a neutrino in this sample. The chance
probability of this coincidence is 30% after trial correction. For the first
time, we present a systematic study of the gamma-ray flux, spectral and optical
variability, and multi-wavelength behavior of GB6 J1040+0617 and compare it to
TXS 0506+056. We find that TXS 0506+056 shows strong flux variability in the
Fermi-LAT gamma-ray band, being in an active state around the arrival of
IceCube-170922A, but in a low state during the archival IceCube neutrino flare
in 2014/15. In both cases the spectral shape is statistically compatible () with the average spectrum showing no indication of a significant
relative increase of a high-energy component. While the association of GB6
J1040+0617 with the neutrino is consistent with background expectations, the
source appears to be a plausible neutrino source candidate based on its
energetics and multi-wavelength features, namely a bright optical flare and
modestly increased gamma-ray activity. Finding one or two neutrinos originating
from gamma-ray blazars in the given sample of high-energy neutrinos is
consistent with previously derived limits of neutrino emission from gamma-ray
blazars, indicating the sources of the majority of cosmic high-energy neutrinos
remain unknown.Comment: 22 pages, 11 figures, 2 Table
LeptonInjector and LeptonWeighter: A neutrino event generator and weighter for neutrino observatories
We present a high-energy neutrino event generator, called LeptonInjector,
alongside an event weighter, called LeptonWeighter. Both are designed for
large-volume Cherenkov neutrino telescopes such as IceCube. The neutrino event
generator allows for quick and flexible simulation of neutrino events within
and around the detector volume, and implements the leading Standard Model
neutrino interaction processes relevant for neutrino observatories:
neutrino-nucleon deep-inelastic scattering and neutrino-electron annihilation.
In this paper, we discuss the event generation algorithm, the weighting
algorithm, and the main functions of the publicly available code, with
examples.Comment: 28 pages, 10 figures, 3 table
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