92 research outputs found
Environmental distribution and seasonal dynamics of Marteilia refringens and Bonamia ostreae, two protozoan parasites of the European flat oyster, Ostrea edulis
IntroductionMarteilia refringens and Bonamia ostreae are protozoan parasites responsible for mortalities of farmed and wild flat oysters Ostrea edulis in Europe since 1968 and 1979, respectively. Despite almost 40 years of research, the life-cycle of these parasites is still poorly known, especially regarding their environmental distribution.MethodsWe carried out an integrated field study to investigate the dynamics of M. refringens and B. ostreae in Rade of Brest, where both parasites are known to be present. We used real-time PCR to monitor seasonally over four years the presence of both parasites in flat oysters. In addition, we used previously developed eDNA based-approaches to detect parasites in planktonic and benthic compartments for the last two years of the survey.ResultsM. refringens was detected in flat oysters over the whole sampling period, sometimes with a prevalence exceeding 90%. It was also detected in all the sampled environmental compartments, suggesting their involvement in parasite transmission and overwintering. In contrast, B. ostreae prevalence in flat oysters was low and the parasite was almost never detected in planktonic and benthic compartments. Finally, the analysis of environmental data allowed describing the seasonal dynamics of both parasites in Rade of Brest: M. refringens was more detected in summer and fall than in winter and spring, contrary to B. ostreae which showed higher prevalence in winter and spring.DiscussionThe present study emphasizes the difference between M. refringens and B. ostreae ecology, the former presenting a wider environmental distribution than the latter, which seems closely associated to flat oysters. Our findings highlight the key role of planktonic and benthic compartments in M. refringens transmission and storage or potential overwintering, respectively. More generally, we provide here a method that could be useful not only to further investigate non cultivable pathogens life-cycle, but also to support the design of more integrated surveillance programs
Εισοδηματικές ανισότητες και φιλανθρωπία
<p>All variables were kriged on different variogram models depending on the data (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0044155#pone-0044155-t001" target="_blank">Table 1</a>). Geometrical scales were used to maximize the visualization of both gradients and the patchiness of the different variables. Mollusk maps are at different scales to account for the discrepancy in the data between the 2 samplings. <b>A, B</b>: Chl <i>a</i> concentration (µg.L<sup>−1</sup>); <b>C, D</b>: SPiM amount (mg.L<sup>−1</sup>). <b>E, F</b>: Bottom mean current velocities and direction at the 2 sampling periods, calculated by the MARS-3D hydrodynamic model.</p
Multi-messenger astronomy with INTEGRAL
At the time of defining the science objectives of the INTernational Gamma-Ray
Astrophysics Laboratory (INTEGRAL), such a rapid and spectacular development of
multi-messenger astronomy could not have been predicted, with new impulsive
phenomena becoming accessible through different channels.
Neutrino telescopes have routinely detected energetic neutrino events coming
from unknown cosmic sources since 2013. Gravitational wave detectors opened a
novel window on the sky in 2015 with the detection of the merging of two black
holes and in 2017 with the merging of two neutron stars, followed by signals in
the full electromagnetic range. Finally, since 2007, radio telescopes detected
extremely intense and short burst of radio waves, known as Fast Radio Bursts
(FRBs) whose origin is for most cases extragalactic, but enigmatic.
The exceptionally robust and versatile design of the INTEGRAL mission has
allowed researchers to exploit data collected not only with the pointed
instruments, but also with the active cosmic-ray shields of the main
instruments to detect impulses of gamma-rays in coincidence with unpredictable
phenomena. The full-sky coverage, mostly unocculted by the Earth, the large
effective area, the stable background, and the high duty cycle (85%) put
INTEGRAL in a privileged position to give a major contribution to
multi-messenger astronomy.
In this review, we describe how INTEGRAL has provided upper limits on the
gamma-ray emission from black-hole binary mergers, detected a short gamma-ray
burst in coincidence with a binary neutron star merger, contributed to define
the spectral energy distribution of a blazar associated with a neutrino event,
set upper limits on impulsive and steady gamma-ray emission from cosmological
FRBs, and detected a magnetar flare associated with fast radio bursting
emission.Comment: Accepted for publication on New Astronomy Reviews as invited
contributio
The characterization of the distant blazar GB6 J1239+0443 from flaring and low activity periods
In 2008 AGILE and Fermi detected gamma-ray flaring activity from the
unidentified EGRET source 3EG J1236+0457, recently associated with a flat
spectrum radio quasar GB6 J1239+0443 at z=1.762. The optical counterpart of the
gamma-ray source underwent a flux enhancement of a factor 15-30 in 6 years, and
of ~10 in six months. We interpret this flare-up in terms of a transition from
an accretion-disk dominated emission to a synchrotron-jet dominated one. We
analysed a Sloan Digital Sky Survey (SDSS) archival optical spectrum taken
during a period of low radio and optical activity of the source. We estimated
the mass of the central black hole using the width of the CIV emission line. In
our work, we have also investigated SDSS archival optical photometric data and
UV GALEX observations to estimate the thermal-disk emission contribution of GB6
J1239+0443. Our analysis of the gamma-ray data taken during the flaring
episodes indicates a flat gamma-ray spectrum, with an extension of up to 15
GeV, with no statistically-relevant sign of absorption from the broad line
region, suggesting that the blazar-zone is located beyond the broad line
region. This result is confirmed by the modeling of the broad-band spectral
energy distribution (well constrained by the available multiwavelength data) of
the flaring activity periods and by the accretion disk luminosity and black
hole mass estimated by us using archival data.Comment: 30 pages, 7 figures, 4 tables MNRAS Accepted on 2012 June 1
A magnetar giant flare in the nearby starburst galaxy M82
Giant flares, short explosive events releasing up to 10 erg of energy
in the gamma-ray band in less than one second, are the most spectacular
manifestation of magnetars, young neutron stars powered by a very strong
magnetic field, 10 G in the magnetosphere and possibly higher in the
star interior. The rate of occurrence of these rare flares is poorly
constrained, as only three have been seen from three different magnetars in the
Milky Way and in the Large Magellanic Cloud in about 50 years since the
beginning of gamma-ray astronomy. This sample can be enlarged by the discovery
of extragalactic events, since for a fraction of a second giant flares reach
peak luminosities above 10 erg/s, which makes them visible by current
instruments up to a few tens of Mpc. However, at these distances they appear
similar to, and difficult to distinguish from, regular short gamma-ray bursts
(GRBs). The latter are much more energetic events, 10 erg, produced
by compact binary mergers and originating at much larger distances. Indeed,
only a few short GRBs have been proposed, with different levels of confidence,
as magnetar giant flare candidates in nearby galaxies. Here we report the
discovery of a short GRB positionally coincident with the central region of the
starburst galaxy M82. Its spectral and timing properties, together with the
limits on its X-ray and optical counterparts obtained a few hours after the
event and the lack of an associated gravitational wave signal, qualify with
high confidence this event as a giant flare from a magnetar in M82.Comment: Submitted version. New figures. Accepted for publication in Nature
with minor modification
GRB 070707: the first short gamma-ray burst observed by INTEGRAL
INTEGRAL has observed 47 long-duration GRBs (T_90 > 2s) and 1 short-duration
GRB (T_90 < 2s) in five years of observation since October 2002. This work
presents the properties of the prompt emission of GRB 070707, which is the
first short hard GRB observed by INTEGRAL. The spectral and temporal properties
of GRB 070707 were determined using the two sensitive coded-mask gamma-ray
instruments on board INTEGRAL, IBIS and SPI. The T_90 duration was 0.8s, and
the spectrum of the prompt emission was obtained by joint deconvolution of IBIS
and SPI data to yield a best fit power-law with photon index alpha = -1.19
+0.14 -0.13, which is consistent with the characteristics of short-hard
gamma-ray bursts. The peak flux over 1 second was 1.79 photons/cm^2/s and the
fluence over the same interval was 2.07 x 10^-7 erg/cm^2 in the energy range
20-200keV. The spectral lag measured between 25-50keV and 100-300keV is 20 +/-
5ms, consistent with the small or negligible lags measured for short bursts.
The spectral and temporal properties of GRB 070707 are comparable to those of
the short hard bursts detected by other gamma-ray satellites, including BATSE
and Swift. We estimate a lower limit on the Lorentz factor Gamma >~ 25 for GRB
070707, assuming the typical redshift for short GRBs of z=0.35. This limit is
consistent with previous estimates for short GRBs and is smaller than the lower
limits of Gamma >~ 100 calculated for long GRBs. If GRB 070707 is a member of
the recently postulated class of short GRBs at z ~ 1, the lower limit on Gamma
increases to Gamma >~ 35.Comment: 7 pages, 3 figures, accepted for publication in A&
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