Is current management of the Antarctic krill fishery in the Atlantic sector of the Southern Ocean precautionary?

This paper explains the management of the Antarctic krill (Euphausia superba) fishery in the Atlantic sector of the Southern Ocean, and current knowledge about the state of the regional krill stock. In this region, krill fishing is permitted in an area of approximately 3.5 million km2 which is divided into four subareas (labelled Subareas 48.1 to 48.4) for management and reporting purposes. The effective regional catch limit (or ‘trigger level’), established in 1991, is 0.62 million tonnes year–1, equivalent to ~1% of the regional biomass estimated in 2000. Each subarea has also had its own catch limit, between 0.093 and 0.279 million tonnes year–1, since 2009. There is some evidence for a decline in the abundance of krill in the 1980s, but no evidence of a further decline in recent decades. Local-scale monitoring programs have been established in three of the subareas to monitor krill biomass in survey grids covering between 10 000 and 125 000 km2. Cautious extrapolation from these local monitoring programs provides conservative estimates of the regional biomass in recent years. This suggests that fishing at the trigger level would be equivalent to a long-term exploitation rate (annual catch divided by biomass) of <7%, which is below the 9.3% level considered appropriate to maintain the krill stock and support krill predators. Subarea catch limits exceed 9.3% of conservatively estimated subarea biomass in up to 20% of years due to high variability in krill biomass indices. The actual exploitation rate in each subarea has remained <3% because annual catches have been <50% of the trigger level since 1991. Comparison with the 9.3% reference exploitation rate suggests that current management is precautionary at the regional scale. The subarea catch limits help prevent excessive concentration of catch at the subarea scale. Finer-scale management might be necessary to manage the risk of adverse impacts which might occur as a result of concentrated fishing in sensitive areas or climate change. Frequent assessment of the krill stock will enhance CCAMLR’s ability to manage these risks. Continuing the local monitoring programs will provide valuable information on krill variability, but more information is required on how the monitored biomass relates to biomass at the subarea and regional scales

Towards a Proof Theory of G\"odel Modal Logics

Analytic proof calculi are introduced for box and diamond fragments of basic modal fuzzy logics that combine the Kripke semantics of modal logic K with the many-valued semantics of G\"odel logic. The calculi are used to establish completeness and complexity results for these fragments

Constraints on dark matter models from a Fermi LAT search for high-energy cosmic-ray electrons from the Sun

During its first year of data taking, the Large Area Telescope (LAT) onboard the Fermi Gamma-Ray Space Telescope has collected a large sample of high-energy cosmic-ray electrons and positrons (CREs). We present the results of a directional analysis of the CRE events, in which we searched for a flux excess correlated with the direction of the Sun. Two different and complementary analysis approaches were implemented, and neither yielded evidence of a significant CRE flux excess from the Sun. We derive upper limits on the CRE flux from the Sun's direction, and use these bounds to constrain two classes of dark matter models which predict a solar CRE flux: (1) models in which dark matter annihilates to CREs via a light intermediate state, and (2) inelastic dark matter models in which dark matter annihilates to CREs.Comment: 18 pages, 8 figures, accepted for publication in Physical Review D - contact authors: Francesco Loparco ([email protected]), M. Nicola Mazziotta ([email protected]) and Jennifer Siegal-Gaskins ([email protected]

Fermi-LAT Study of Gamma-ray Emission in the Direction of Supernova Remnant W49B

We present an analysis of the gamma-ray data obtained with the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope in the direction of SNR W49B (G43.3-0.2). A bright unresolved gamma-ray source detected at a significance of 38 sigma is found to coincide with SNR W49B. The energy spectrum in the 0.2-200 GeV range gradually steepens toward high energies. The luminosity is estimated to be 1.5x10^{36} (D/8 kpc)^2 erg s^-1 in this energy range. There is no indication that the gamma-ray emission comes from a pulsar. Assuming that the SNR shell is the site of gamma-ray production, the observed spectrum can be explained either by the decay of neutral pi mesons produced through the proton-proton collisions or by electron bremsstrahlung. The calculated energy density of relativistic particles responsible for the LAT flux is estimated to be remarkably large, U_{e,p}>10^4 eV cm^-3, for either gamma-ray production mechanism.Comment: 9 pages, 10 figure

Gamma-ray flares from the Crab Nebula

A young and energetic pulsar powers the well-known Crab Nebula. Here we describe two separate gamma-ray (photon energy >100 MeV) flares from this source detected by the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. The first flare occurred in February 2009 and lasted approximately 16 days. The second flare was detected in September 2010 and lasted approximately 4 days. During these outbursts the gamma-ray flux from the nebula increased by factors of four and six, respectively. The brevity of the flares implies that the gamma rays were emitted via synchrotron radiation from PeV (10^15 eV) electrons in a region smaller than 1.4 10^-2 pc. These are the highest energy particles that can be associated with a discrete astronomical source, and they pose challenges to particle acceleration theory.Comment: Contact authors: Rolf Buehler,[email protected]; Stefan Funk,[email protected]; Roger Blandford,rdb3@stanford ; 16 pages,2 figure

Fermi observations of high-energy gamma-ray emission from GRB 090217A

The Fermi observatory is advancing our knowledge of Gamma-Ray Bursts (GRBs) through pioneering observations at high energies, covering more than 7 decades in energy with the two on-board detectors, the Large Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM). Here we report on the observation of the long GRB 090217A which triggered the GBM and has been detected by the LAT with a significance greater than 9 sigma. We present the GBM and LAT observations and on-ground analyses, including the time-resolved spectra and the study of the temporal profile from 8 keV up to 1 GeV. All spectra are well reproduced by a Band model. We compare these observations to the first two LAT-detected, long bursts GRB 080825C and GRB 080916C. These bursts were found to have time-dependent spectra and exhibited a delayed onset of the high-energy emission, which are not observed in the case of GRB 090217A. We discuss some theoretical implications for the high-energy emission of GRBs.Comment: 17 pages, 4 figures. Contact Authors: Fred, Piron; Sara, Cutini; Andreas, von Kienli

Constraints on the Cosmic-Ray Density Gradient beyond the Solar Circle from Fermi gamma-ray Observations of the Third Galactic Quadrant

We report an analysis of the interstellar $\gamma$-ray emission in the third Galactic quadrant measured by the {Fermi} Large Area Telescope. The window encompassing the Galactic plane from longitude 210\arcdeg to 250\arcdeg has kinematically well-defined segments of the Local and the Perseus arms, suitable to study the cosmic-ray densities across the outer Galaxy. We measure no large gradient with Galactocentric distance of the $\gamma$-ray emissivities per interstellar H atom over the regions sampled in this study. The gradient depends, however, on the optical depth correction applied to derive the \HI\ column densities. No significant variations are found in the interstellar spectra in the outer Galaxy, indicating similar shapes of the cosmic-ray spectrum up to the Perseus arm for particles with GeV to tens of GeV energies. The emissivity as a function of Galactocentric radius does not show a large enhancement in the spiral arms with respect to the interarm region. The measured emissivity gradient is flatter than expectations based on a cosmic-ray propagation model using the radial distribution of supernova remnants and uniform diffusion properties. In this context, observations require a larger halo size and/or a flatter CR source distribution than usually assumed. The molecular mass calibrating ratio, $X_{\rm CO} = N({\rm H_{2}})/W_{\rm CO}$, is found to be $(2.08 \pm 0.11) \times 10^{20} {\rm cm^{-2} (K km s^{-1})^{-1}}$ in the Local-arm clouds and is not significantly sensitive to the choice of \HI\ spin temperature. No significant variations are found for clouds in the interarm region.Comment: Corresponding authors: I. A. Grenier ([email protected]); T. Mizuno ([email protected]); L. Tibaldo ([email protected]) accepted for publication in Ap

Fermi Gamma-ray Space Telescope Observations of the Gamma-ray Outburst from 3C 454.3 in November 2010

The flat-spectrum radio quasar 3C 454.3 underwent an extraordinary 5-day gamma-ray outburst in November 2010 where the daily flux measured with the Fermi Large Area Telescope (LAT) at photon energies E>100 MeV reached (66+/-2) x 10^-6 ph cm^-2 s^-1. This is a factor of 3 higher than its previous maximum flux recorded in December 2009 and ~5 times brighter than the Vela pulsar, which is normally the brightest source in the gamma-ray sky. The 3-hr peak flux was (85+/-5) x 10^-6 ph cm^-2 s^-1, corresponding to an apparent isotropic luminosity of 2.1+/-0.2 10^50 erg s^-1, the highest ever recorded for a blazar. In this paper, we investigate the features of this exceptional event in the gamma-ray band of the Fermi-LAT. In contrast to previous flares of the same source observed with the Fermi-LAT, clear spectral changes are observed during the flare.Comment: Contact authors: Lise Escande, Charles Dermer and Benoit Lott. One new figure. Accepted for publication by ApJ

Fermi Gamma-ray Space Telescope Observations of Recent Gamma-ray Outbursts from 3C 454.3

The flat spectrum radio quasar 3C~454.3 underwent an extraordinary outburst in December 2009 when it became the brightest gamma-ray source in the sky for over one week. Its daily flux measured with the Fermi Large Area Telescope at photon energies E>100 MeV reached F = 22+/-1 x 10^-6 ph cm^-2 s^-1, representing the highest daily flux of any blazar ever recorded in high-energy gamma-rays. It again became the brightest source in the sky in 2010 April, triggering a pointed-mode observation by Fermi. The correlated gamma-ray temporal and spectral properties during these exceptional events are presented and discussed. The main results show flux variability over time scales less than 3 h and very mild spectral variability with an indication of gradual hardening preceding major flares. No consistent loop pattern emerged in the gamma-ray spectral index vs flux plane. A minimum Doppler factor of ~ 15 is derived, and the maximum energy of a photon from 3C 454.3 is ~ 20 GeV. The spectral break at a few GeV is inconsistent with Klein-Nishina softening from power-law electrons scattering Ly_alpha line radiation, and a break in the underlying electron spectrum in blazar leptonic models is implied.Comment: submitted to the Astrophysical Journa

Gamma-Ray Emission Concurrent with the Nova in the Symbiotic Binary V407 Cygni

Novae are thermonuclear explosions on a white dwarf surface fueled by mass accreted from a companion star. Current physical models posit that shocked expanding gas from the nova shell can produce X-ray emission but emission at higher energies has not been widely expected. Here, we report the Fermi Large Area Telescope detection of variable gamma-ray (0.1-10 GeV) emission from the recently-detected optical nova of the symbiotic star V407 Cygni. We propose that the material of the nova shell interacts with the dense ambient medium of the red giant primary, and that particles can be accelerated effectively to produce pi0 decay gamma-rays from proton-proton interactions. Emission involving inverse Compton scattering of the red giant radiation is also considered and is not ruled out.Comment: 38 pages, includes Supplementary Online Material; corresponding authors: C.C. Cheung, A.B. Hill, P. Jean, S. Razzaque, K.S. Woo