ABSTRACT In this paper searches for flaring astrophysical neutrino sources and sources with periodic emission with the IceCube neutrino telescope are presented. In contrast to time-integrated ...searches, where steady emission is assumed, the analyses presented here look for a time-dependent signal of neutrinos using the information from the neutrino arrival times to enhance the discovery potential. A search was performed for correlations between neutrino arrival times and directions, as well as neutrino emission following time-dependent light curves, sporadic emission, or periodicities of candidate sources. These include active galactic nuclei, soft γ-ray repeaters, supernova remnants hosting pulsars, microquasars, and X-ray binaries. The work presented here updates and extends previously published results to a longer period that covers 4 years of data from 2008 April 5 to 2012 May 16, including the first year of operation of the completed 86 string detector. The analyses did not find any significant time-dependent point sources of neutrinos, and the results were used to set upper limits on the neutrino flux from source candidates.
Saturn's moons Titan and Enceladus appear to satisfy three key criteria for life: presence of liquid water, nutrient availability, and metabolic energy sources. Consequently, these ocean worlds are ...the focus of astrobiology research investigations that aim to assess the potential for life beyond Earth. One plausible source of metabolic energy on these moons is acetylene (C2H2), a simple organic compound that is the second most abundant photochemical product in Titan's atmosphere and has been identified as a likely constituent of Enceladus' ocean. Acetylenotrophy, or the microbial fermentation of acetylene, is utilized by microbes on Earth in a number of environments. Here, we have calculated the energy yield of acetylenotrophy to be 69–78 kJ/mol C within the oceans of Titan and Enceladus, greater than the widely considered, hydrogenotrophic methanogenesis, at 25–65 kJ/mol C. Therefore, we propose acetylenotrophy as a potential metabolism on these moons that should be considered in future astrobiology studies on worlds with abundant acetylene.
•Fermentation of acetylene (acetylenotrophy) is a ubiquitous and under-studied metabolism on Earth.•Acetylene may be abundant on ocean worlds such as Titan and Enceladus.•On ocean worlds, acetylenotrophy is more energy-yielding than hydrogenotrophic methanogenesis.•Acetylenotrophy may be a critical catabolic strategy in establishing microbial communities in alien oceans.
Abstract
Ultraluminous infrared galaxies (ULIRGs) have infrared luminosities
L
IR
≥ 10
12
L
⊙
, making them the most luminous objects in the infrared sky. These dusty objects are generally powered by ...starbursts with star formation rates that exceed 100
M
⊙
yr
−1
, possibly combined with a contribution from an active galactic nucleus. Such environments make ULIRGs plausible sources of astrophysical high-energy neutrinos, which can be observed by the IceCube Neutrino Observatory at the South Pole. We present a stacking search for high-energy neutrinos from a representative sample of 75 ULIRGs with redshift
z
≤ 0.13 using 7.5 yr of IceCube data. The results are consistent with a background-only observation, yielding upper limits on the neutrino flux from these 75 ULIRGs. For an unbroken
E
−2.5
power-law spectrum, we report an upper limit on the stacked flux
Φ
ν
μ
+
ν
¯
μ
90
%
=
3.24
×
10
−
14
TeV
−
1
cm
−
2
s
−
1
(
E
/
10
TeV
)
−
2.5
at 90% confidence level. In addition, we constrain the contribution of the ULIRG source population to the observed diffuse astrophysical neutrino flux as well as model predictions.
Eleginops maclovinus is an endemic fish to Chile that lives in proximity to salmonid culture centers, feeding off of uneaten pellet and salmonid feces. Occurring in the natural environment, this ...interaction between native and farmed fish could result in the horizontal transmission of pathogens affecting the aquaculture industry. The aim of this study was to evaluate the innate and adaptive immune responses of E. maclovinus challenged with P. salmonis. Treatment injections (in duplicate) were as follows: control (100 μL of culture medium), wild type LF-89 strain (100 μL, 1 × 108 live bacteria), and antibiotic resistant strain Austral-005 (100 μL, 1 × 108 live bacteria). The fish were sampled at various time-points during the 35-day experimental period. The gene expression of TLRs (1, 5, and 8), NLRCs (3 and 5), C3, IL-1β, MHCII, and IgMs were significantly modulated during the experimental period in both the spleen and gut (excepting TLR1 and TLR8 spleen expressions), with tissue-specific expression profiles and punctual differences between the injected strains. Anti-P. salmonis antibodies increased in E. maclovinus serum from day 14–28 for the LF-89 strain and from day 14–35 for the Austral-005 strain. These results suggest temporal activation of the innate and adaptive immune responses in E. maclovinus tissues when injected by distinct P. salmonis strains. The Austral-005 strain did not always cause the greatest increases/decreases in the number of transcripts, so the magnitude of the observed immune response (mRNA) may not be related to antibiotic resistance. This is the first immunological study to relate a pathogen widely studied in salmonids with a native fish.
•Eleginops maclovinus is living in proximity to salmonid culture centers feeding off of uneaten pellet and salmonid feces.•The aim of this study was to evaluate the innate and adaptive immune responses of E. maclovinus challenged with P. salmonis.•The results suggest activation of the immune response in E. maclovinus injected by distinct P. salmonis strains.•This is the first immunological study to relate a pathogen widely studied in salmonids with a native fish.
We report on the observation of anisotropy in the arrival direction distribution of cosmic rays at PeV energies. The analysis is based on data taken between 2009 and 2012 with the IceTop air shower ...array at the south pole. IceTop, an integral part of the IceCube detector, is sensitive to cosmic rays between 100 TeV and 1 EeV. With the current size of the IceTop data set, searches for anisotropy at the 10 super(-3) level can, for the first time, be extended to PeV energies. We divide the data set into two parts with median energies of 400 TeV and 2 PeV, respectively. In the low energy band, we observe a strong deficit with an angular size of about 30degrees and an amplitude of (-1.58 + or - 0.46 sub(stat) + or - 0.52 sub(sys)) x 10 super(-3) at a location consistent with previous observations of cosmic rays with the IceCube neutrino detector. The study of the high energy band shows that the anisotropy persists to PeV energies and increases in amplitude to (-3.11 + or - 0.38 sub(stat) + or - 0.96 sub(sys)) x 10 super(-3).
We present the results of a search for neutrino point sources using the IceCube data collected between 2008 April and 2011 May with three partially completed configurations of the detector: the 40-, ...59-, and 79-string configurations. The live-time of this data set is 1040 days. An unbinned maximum likelihood ratio test was used to search for an excess of neutrinos above the atmospheric background at any given direction in the sky. By adding two more years of data with improved event selection and reconstruction techniques, the sensitivity was improved by a factor of 3.5 or more with respect to the previously published results obtained with the 40-string configuration of IceCube. We performed an all-sky survey and a dedicated search using a catalog of a priori selected objects observed by other telescopes. In both searches, the data are compatible with the background-only hypothesis. In the absence of evidence for a signal, we set upper limits on the flux of muon neutrinos. For an E super(-2) neutrino spectrum, the observed limits are (0.9-5) x 10 super(-12) TeV super(-1) cm super(-2) s super(-1) for energies between 1 TeV and 1 PeV in the northern sky and (0.9-23.2) x 10 super(-12) TeV super(-1) cm super(-2) s super(-1) for energies between 10 super(2) TeV and 10 super(2) PeV in the southern sky. We also report upper limits for neutrino emission from groups of sources that were selected according to theoretical models or observational parameters and analyzed with a stacking approach. Some of the limits presented already reach the level necessary to quantitatively test current models of neutrino emission.
The presence of a population of point sources in a data set modifies the underlying neutrino-count statistics from the Poisson distribution. This deviation can be exactly quantified using the ...non-Poissonian template fitting technique, and in this work we present the first application of this approach to the IceCube high-energy neutrino data set. Using this method, we search in 7 yr of IceCube data for point-source populations correlated with the disk of the Milky Way, the Fermi bubbles, the Schlegel, Finkbeiner, and Davis dust map, or with the isotropic extragalactic sky. No evidence for such a population is found in the data using this technique, and in the absence of a signal, we establish constraints on population models with source-count distribution functions that can be described by a power law with a single break. The derived limits can be interpreted in the context of many possible source classes. In order to enhance the flexibility of the results, we publish the full posterior from our analysis, which can be used to establish limits on specific population models that would contribute to the observed IceCube neutrino flux.
IceCube is a neutrino observatory deployed in the glacial ice at the geographic South Pole. The
ν
μ
energy unfolding described in this paper is based on data taken with IceCube in its 79-string ...configuration. A sample of muon neutrino charged-current interactions with a purity of 99.5% was selected by means of a multivariate classification process based on machine learning. The subsequent unfolding was performed using the software
Truee
. The resulting spectrum covers an E
ν
-range of more than four orders of magnitude from 125 GeV to 3.2 PeV. Compared to the Honda atmospheric neutrino flux model, the energy spectrum shows an excess of more than
1.9
σ
in four adjacent bins for neutrino energies
E
ν
≥
177.8
TeV
. The obtained spectrum is fully compatible with previous measurements of the atmospheric neutrino flux and recent IceCube measurements of a flux of high-energy astrophysical neutrinos.
We present the results of the first IceCube search for dark matter annihilation in the center of the Earth. Weakly interacting massive particles (WIMPs), candidates for dark matter, can scatter off ...nuclei inside the Earth and fall below its escape velocity. Over time the captured WIMPs will be accumulated and may eventually self-annihilate. Among the annihilation products only neutrinos can escape from the center of the Earth. Large-scale neutrino telescopes, such as the cubic kilometer IceCube Neutrino Observatory located at the South Pole, can be used to search for such neutrino fluxes. Data from 327 days of detector livetime during 2011/2012 were analyzed. No excess beyond the expected background from atmospheric neutrinos was detected. The derived upper limits on the annihilation rate of WIMPs in the Earth and the resulting muon flux are an order of magnitude stronger than the limits of the last analysis performed with data from IceCube's predecessor AMANDA. The limits can be translated in terms of a spin-independent WIMP-nucleon cross section. For a WIMP mass of 50 GeV this analysis results in the most restrictive limits achieved with IceCube data.
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