460 research outputs found
Potential Sea Level Rise Inundation in the Mediterranean: From Susceptibility Assessment to Risk Scenarios for Policy Action
Coastal ecosystems and anthropic activities are prone to be affected by the negative impact of marine-related processes induced by climate change, such as erosion, flooding and permanent inundation. Studies aiming at defining potential risk scenarios represent a valuable tool for the identification of the most suitable coastal adaptation measures. After outlining sea level rise implications at the Mediterranean scale, this paper deals with inundation risk scenarios for the years 2050 and 2100 for the north-eastern sector of the Island of Gozo (Malta), central Mediterranean Sea. The analysis, carried out by applying an index-based procedure, firstly required the evaluation of the susceptibility to inundation of the investigated coastal stretch under different sea level projections. Then, the spatial combination of inundation susceptibility with the exposure and vulnerability of the area allowed identification of the most critical sectors in terms of coastal risk. The results of the analysis showed that, under the worst-case climate scenarios, 5.5% and 8.1% of the investigated coastal sector are prone to very high inundation risk (Class R4) in 2050 and 2100, respectively. In particular, the bays of Ramla and Marsalforn, which are characterized by significant economic and touristic activities, were found to be the sites where the expected impacts of future sea level rise will be higher if no management strategy and adaptation action are taken in the near future
Search for astrophysical sources of neutrinos using cascade events in IceCube
The IceCube neutrino observatory has established the existence of a flux of
high-energy astrophysical neutrinos inconsistent with the expectation from
atmospheric backgrounds at a significance greater than . This flux has
been observed in analyses of both track events from muon neutrino interactions
and cascade events from interactions of all neutrino flavors. Searches for
astrophysical neutrino sources have focused on track events due to the
significantly better angular resolution of track reconstructions. To date, no
such sources have been confirmed. Here we present the first search for
astrophysical neutrino sources using cascades interacting in IceCube with
deposited energies as small as 1 TeV. No significant clustering was observed in
a selection of 263 cascades collected from May 2010 to May 2012. We show that
compared to the classic approach using tracks, this statistically-independent
search offers improved sensitivity to sources in the southern sky, especially
if the emission is spatially extended or follows a soft energy spectrum. This
enhancement is due to the low background from atmospheric neutrinos forming
cascade events and the additional veto of atmospheric neutrinos at declinations
.Comment: 14 pages, 9 figures, 1 tabl
Measurement of the multi-TeV neutrino cross section with IceCube using Earth absorption
Neutrinos interact only very weakly, so they are extremely penetrating.
However, the theoretical neutrino-nucleon interaction cross section rises with
energy such that, at energies above 40 TeV, neutrinos are expected to be
absorbed as they pass through the Earth. Experimentally, the cross section has
been measured only at the relatively low energies (below 400 GeV) available at
neutrino beams from accelerators \cite{Agashe:2014kda, Formaggio:2013kya}. Here
we report the first measurement of neutrino absorption in the Earth, using a
sample of 10,784 energetic upward-going neutrino-induced muons observed with
the IceCube Neutrino Observatory. The flux of high-energy neutrinos transiting
long paths through the Earth is attenuated compared to a reference sample that
follows shorter trajectories through the Earth. Using a fit to the
two-dimensional distribution of muon energy and zenith angle, we determine the
cross section for neutrino energies between 6.3 TeV and 980 TeV, more than an
order of magnitude higher in energy than previous measurements. The measured
cross section is (stat.) (syst.)
times the prediction of the Standard Model \cite{CooperSarkar:2011pa},
consistent with the expectation for charged and neutral current interactions.
We do not observe a dramatic increase in the cross section, expected in some
speculative models, including those invoking new compact dimensions
\cite{AlvarezMuniz:2002ga} or the production of leptoquarks
\cite{Romero:2009vu}.Comment: Preprint version of Nature paper 10.1038/nature2445
Search for astrophysical sources of neutrinos using cascade events in IceCube
The IceCube neutrino observatory has established the existence of a flux of
high-energy astrophysical neutrinos inconsistent with the expectation from
atmospheric backgrounds at a significance greater than . This flux has
been observed in analyses of both track events from muon neutrino interactions
and cascade events from interactions of all neutrino flavors. Searches for
astrophysical neutrino sources have focused on track events due to the
significantly better angular resolution of track reconstructions. To date, no
such sources have been confirmed. Here we present the first search for
astrophysical neutrino sources using cascades interacting in IceCube with
deposited energies as small as 1 TeV. No significant clustering was observed in
a selection of 263 cascades collected from May 2010 to May 2012. We show that
compared to the classic approach using tracks, this statistically-independent
search offers improved sensitivity to sources in the southern sky, especially
if the emission is spatially extended or follows a soft energy spectrum. This
enhancement is due to the low background from atmospheric neutrinos forming
cascade events and the additional veto of atmospheric neutrinos at declinations
.Comment: 14 pages, 9 figures, 1 tabl
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&
Book Reviews
With the observation of high-energy astrophysical neutrinos by the IceCube Neutrino Observatory, interest has risen in models of PeV-mass decaying dark matter particles to explain the observed flux. We present two dedicated experimental analyses to test this hypothesis. One analysis uses 6 years of IceCube data focusing on muon neutrino âtrackâ events from the Northern Hemisphere, while the second analysis uses 2 years of âcascadeâ events from the full sky. Known background components and the hypothetical flux from unstable dark matter are fitted to the experimental data. Since no significant excess is observed in either analysis, lower limits on the lifetime of dark matter particles are derived: we obtain the strongest constraint to date, excluding lifetimes shorter than s at 90% CL for dark matter masses above 10 TeV
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