255 research outputs found
METHICILLIN - RESISTANT STAPHYLOCOCCUS AUREUS IN PIG PRODUCTION CHAIN
The aims of this study were (i) to estimate the prevalence of Staphylococcus aureus (S.a) in pig farm environments; (ii) to evaluate the presence of S.a in pork processing environments (iii) to detect the presence of methicillin-resistant (MRSA) among isolated strains. Samples of pig stool, farm environment and pork processing environment were collected. These samples were submitted to detection of S.a following the international method: UNI EN ISO 6888-2 and the Minimum Inhibitory Concentrations (MIC) tests were performed by using the automated VITEK 2 system. In addition, a PCR for the detection of the mecA gene was applied. Overall, S. aureus were more frequently detected from pig farms than from pork processing environments. Among the n.51 isolated strains, n. 49 (96%) were methicillin resistant (MRSA) and only n.2 strains were methicillin sensitive (MSSA). The results of the present study highlighted that further studies are needed to elucidate transmission routes of MRSA in pig production chain
Studio preliminare sulla diffusione di Staphylococcus aureus meticillino-resistente nella filiera suina
Unprecedented study of the broadband emission of Mrk 421 during flaring activity in March 2010
Context. Because of its proximity, Mrk 421 is one of the best sources on which to study the nature of BL Lac objects. Its proximity allows us to characterize its broadband spectral energy distribution (SED).
Aims. The goal is to better understand the mechanisms responsible for the broadband emission and the temporal evolution of Mrk 421. These mechanisms may also apply to more distant blazars that cannot be studied with the same level of detail.
Methods. A flare occurring in March 2010 was observed for 13 consecutive days (from MJD 55 265 to MJD 55 277) with unprecedented wavelength coverage from radio to very high energy (VHE; E> 100 GeV) γ-rays with MAGIC, VERITAS, Whipple, Fermi-LAT, MAXI, RXTE, Swift, GASP-WEBT, and several optical and radio telescopes. We modeled the day-scale SEDs with one-zone and two-zone synchrotron self-Compton (SSC) models, investigated the physical parameters, and evaluated whether the observed broadband SED variability can be associated with variations in the relativistic particle population.
Results. The activity of Mrk 421 initially was high and then slowly decreased during the 13-day period. The flux variability was remarkable at the X-ray and VHE bands, but it was minor or not significant at the other bands. The variability in optical polarization was also minor. These observations revealed an almost linear correlation between the X-ray flux at the 2–10 keV band and the VHE γ-ray flux above 200 GeV, consistent with the γ-rays being produced by inverse-Compton scattering in the Klein-Nishina regime in the framework of SSC models. The one-zone SSC model can describe the SED of each day for the 13 consecutive days reasonably well, which once more shows the success of this standard theoretical scenario to describe the SEDs of VHE BL Lacs such as Mrk 421. This flaring activity is also very well described by a two-zone SSC model, where one zone is responsible for the quiescent emission, while the other smaller zone, which is spatially separated from the first, contributes to the daily variable emission occurring at X-rays and VHE γ-rays. The second blob is assumed to have a smaller volume and a narrow electron energy distribution with 3 × 104<γ< 6 × 105, where γ is the Lorentz factor of the electrons. Such a two-zone scenario would naturally lead to the correlated variability at the X-ray and VHE bands without variability at the optical/UV band, as well as to shorter timescales for the variability at the X-ray and VHE bands with respect to the variability at the other bands.
Conclusions. Both the one-zone and the two-zone SSC models can describe the daily SEDs via the variation of only four or five model parameters, under the hypothesis that the variability is associated mostly with the underlying particle population. This shows that the particle acceleration and cooling mechanism that produces the radiating particles might be the main mechanism responsible for the broadband SED variations during the flaring episodes in blazars. The two-zone SSC model provides a better agreement with the observed SED at the narrow peaks of the low- and high-energy bumps during the highest activity, although the reported one-zone SSC model could be further improved by varying the parameters related to the emitting region itself (δ, B and R), in addition to the parameters related to the particle population.Fil: Aleksic, J.. IFAE; EspañaFil: Ansoldi, S.. Università di Udine; ItaliaFil: Antonelli, L. A.. INAF National Institute for Astrophysics; ItaliaFil: Antoranz, P.. Università di Siena; ItaliaFil: Babic, A.. University of Rijeka; CroaciaFil: Bangale, P.. Max-Planck-Institut für Physik; AlemaniaFil: Barres de Almeida, U.. Max-Planck-Institut für Physik; AlemaniaFil: Barrio, J. A.. Universidad Complutense de Madrid; EspañaFil: Becerra Gonzalez, J.. Inst. de Astrofísica de Canarias; EspañaFil: Bednarek, W.. University of Łódź,; PoloniaFil: Bernardini, E.. Deutsches Elektronen-Synchrotron (DESY); AlemaniaFil: Biasuzzi, B.. Università di Udine; ItaliaFil: Biland, A.. ETH Zurich; SuizaFil: Blanch, O.. IFAE; EspañaFil: Boller, A.. ETH Zurich; SuizaFil: Bonnefoy, S.. Universidad Complutense de Madrid; EspañaFil: Bonnoli, G.. INAF National Institute for Astrophysics ; ItaliaFil: Borracci, F.. Max-Planck-Institut für Physik; AlemaniaFil: Bretz, T.. Universität Würzburg ; AlemaniaFil: Carmona, E.. Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas ; EspañaFil: Carosi, A.. INAF National Institute for Astrophysics; ItaliaFil: Colin, P.. Max-Planck-Institut für Physik; AlemaniaFil: Colombo, E.. Inst. de Astrofísica de Canarias; EspañaFil: Contreras, J. L.. Universidad Complutense; EspañaFil: Cortina, J.. IFAE; EspañaFil: Covino, S.. INAF National Institute for Astrophysics; ItaliaFil: Da Vela, P.. Università di Siena; ItaliaFil: Dazzi, F.. Max-Planck-Institut für Physik; AlemaniaFil: Pichel, Ana Carolina. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Rovero, Adrian Carlos. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: The Veritas Collaboration.Fil: The MAGIC Collaboration
Detection of very high energy gamma-ray emission from the gravitationally-lensed blazar QSO B0218+357 with the MAGIC telescopes
Context. QSO B0218+357 is a gravitationally lensed blazar located at a
redshift of 0.944. The gravitational lensing splits the emitted radiation into
two components, spatially indistinguishable by gamma-ray instruments, but
separated by a 10-12 day delay. In July 2014, QSO B0218+357 experienced a
violent flare observed by the Fermi-LAT and followed by the MAGIC telescopes.
Aims. The spectral energy distribution of QSO B0218+357 can give information on
the energetics of z ~ 1 very high energy gamma- ray sources. Moreover the
gamma-ray emission can also be used as a probe of the extragalactic background
light at z ~ 1. Methods. MAGIC performed observations of QSO B0218+357 during
the expected arrival time of the delayed component of the emission. The MAGIC
and Fermi-LAT observations were accompanied by quasi-simultaneous optical data
from the KVA telescope and X-ray observations by Swift-XRT. We construct a
multiwavelength spectral energy distribution of QSO B0218+357 and use it to
model the source. The GeV and sub-TeV data, obtained by Fermi-LAT and MAGIC,
are used to set constraints on the extragalactic background light. Results.
Very high energy gamma-ray emission was detected from the direction of QSO
B0218+357 by the MAGIC telescopes during the expected time of arrival of the
trailing component of the flare, making it the farthest very high energy
gamma-ray sources detected to date. The observed emission spans the energy
range from 65 to 175 GeV. The combined MAGIC and Fermi-LAT spectral energy
distribution of QSO B0218+357 is consistent with current extragalactic
background light models. The broad band emission can be modeled in the
framework of a two zone external Compton scenario, where the GeV emission comes
from an emission region in the jet, located outside the broad line region.Comment: 11 pages, 6 figures, accepted for publication in A&
Multiwavelength observations of Mrk 501 in 2008
Context. Blazars are variable sources on various timescales over a broad energy range spanning from radio to very high energy (>100 GeV, hereafter VHE). Mrk 501 is one of the brightest blazars at TeV energies and has been extensively studied since its first VHE detection in 1996. However, most of the γ-ray studies performed on Mrk 501 during the past years relate to flaring activity, when the source detection and characterization with the available γ-ray instrumentation was easier toperform. Aims: Our goal is to characterize the source γ-ray emission in detail, together with the radio-to-X-ray emission, during the non-flaring (low) activity, which is less often studied than the occasional flaring (high) activity. Methods: We organized a multiwavelength (MW) campaign on Mrk 501 between March and May 2008. This multi-instrument effort included the most sensitive VHE γ-ray instruments in the northern hemisphere, namely the imaging atmospheric Cherenkov telescopes MAGIC and VERITAS, as well as Swift, RXTE, the F-GAMMA, GASP-WEBT, and other collaborations and instruments. This provided extensive energy and temporal coverage of Mrk 501 throughout the entire campaign. Results: Mrk 501 was found to be in a low state of activity during the campaign, with a VHE flux in the range of 10%-20% of the Crab nebula flux. Nevertheless, significant flux variations were detected with various instruments, with a trend of increasing variability with energy and a tentative correlation between the X-ray and VHE fluxes. The broadband spectral energy distribution during the two different emission states of the campaign can be adequately described within the homogeneous one-zone synchrotron self-Compton model, with the (slightly) higher state described by an increase in the electron number density. Conclusions: The one-zone SSC model can adequately describe the broadband spectral energy distribution of the source during the two months covered by the MW campaign. This agrees with previous studies of the broadband emission of this source during flaring and non-flaring states. We report for the first time a tentative X-ray-to-VHE correlation during such a low VHE activity. Although marginally significant, this positive correlation between X-ray and VHE, which has been reported many times during flaring activity, suggests that the mechanisms that dominate the X-ray/VHE emission during non-flaring-activity are not substantially different from those that are responsible for the emission during flaring activity.Fil: Aleksic, J.. IFAE; EspañaFil: Ansoldi, S.. Università di Udine; ItaliaFil: Antonelli, L. A.. INAF National Institute for Astrophysics; ItaliaFil: Antoranz, P.. Università di Siena; ItaliaFil: Babic, A.. University of Rijeka ; Croacia. University of Split; CroaciaFil: Bangale, P.. Max-Planck-Institut für Physik; AlemaniaFil: Barres de Almeida, U.. Max-Planck-Institut für Physik; AlemaniaFil: Barrio, J. A.. Universidad Complutense de Madrid; EspañaFil: Becerra Gonzalez, J.. Inst. de Astrofísica de Canarias; EspañaFil: Bednarek, W.. University of Lodz; PoloniaFil: Berger, K.. Inst. de Astrofísica de Canarias; EspañaFil: Bernardini, E.. Deutsches Elektronen-Synchrotron (DESY); AlemaniaFil: Biland, A.. ETH Zurich; SuizaFil: Blanch, O.. IFAE; EspañaFil: Bock, R. K.. Max-Planck-Institut für Physik; AlemaniaFil: Bonnefoy, S.. Universidad Complutense de Madrid; EspañaFil: Bonnoli, G.. INAF National Institute for Astrophysics; ItaliaFil: Borracci, F.. Max-Planck-Institut für Physik; AlemaniaFil: Bretz, T.. Universität Würzburg; Alemania. Now at École polytechnique fédérale de Lausanne (EPFL); SuizaFil: Carmona, E.. Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas; EspañaFil: Carosi, A.. INAF National Institute for Astrophysics; ItaliaFil: Carreto Fidalgo, D.. Universität Würzburg; AlemaniaFil: Colin, P.. Max-Planck-Institut für Physik; AlemaniaFil: Colombo, E.. Inst. de Astrofísica de Canarias; EspañaFil: Contreras, J. L.. Universidad Complutense de Madrid; EspañaFil: Cortina, J.. IFAE; EspañaFil: Covino, S.. INAF National Institute for Astrophysics; ItaliaFil: Da Vela, P.. Università di Siena; ItaliaFil: Dazzi, F.. Università di Udine; ItaliaFil: Pichel, Ana Carolina. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: The MAGIC collaboration.Fil: The VERITAS collaboration
A search for spectral hysteresis and energy-dependent time lags from X-ray and TeV gamma-ray observations of Mrk 421
Blazars are variable emitters across all wavelengths over a wide range of
timescales, from months down to minutes. It is therefore essential to observe
blazars simultaneously at different wavelengths, especially in the X-ray and
gamma-ray bands, where the broadband spectral energy distributions usually
peak.
In this work, we report on three "target-of-opportunity" (ToO) observations
of Mrk 421, one of the brightest TeV blazars, triggered by a strong flaring
event at TeV energies in 2014. These observations feature long, continuous, and
simultaneous exposures with XMM-Newton (covering X-ray and optical/ultraviolet
bands) and VERITAS (covering TeV gamma-ray band), along with contemporaneous
observations from other gamma-ray facilities (MAGIC and Fermi-LAT) and a number
of radio and optical facilities. Although neither rapid flares nor significant
X-ray/TeV correlation are detected, these observations reveal subtle changes in
the X-ray spectrum of the source over the course of a few days. We search the
simultaneous X-ray and TeV data for spectral hysteresis patterns and time
delays, which could provide insight into the emission mechanisms and the source
properties (e.g. the radius of the emitting region, the strength of the
magnetic field, and related timescales). The observed broadband spectra are
consistent with a one-zone synchrotron self-Compton model. We find that the
power spectral density distribution at Hz from the
X-ray data can be described by a power-law model with an index value between
1.2 and 1.8, and do not find evidence for a steepening of the power spectral
index (often associated with a characteristic length scale) compared to the
previously reported values at lower frequencies.Comment: 45 pages, 15 figure
Measurement of the Crab Nebula spectrum over three decades in energy with the MAGIC telescopes
The MAGIC stereoscopic system collected 69 hours of Crab Nebula data between
October 2009 and April 2011. Analysis of this data sample using the latest
improvements in the MAGIC stereoscopic software provided an unprecedented
precision of spectral and night-by-night light curve determination at gamma
rays. We derived a differential spectrum with a single instrument from 50 GeV
up to almost 30 TeV with 5 bins per energy decade. At low energies, MAGIC
results, combined with Fermi-LAT data, show a flat and broad Inverse Compton
peak. The overall fit to the data between 1 GeV and 30 TeV is not well
described by a log-parabola function. We find that a modified log-parabola
function with an exponent of 2.5 instead of 2 provides a good description of
the data (). Using systematic uncertainties of red the MAGIC and
Fermi-LAT measurements we determine the position of the Inverse Compton peak to
be at (53 3stat + 31syst -13syst) GeV, which is the most precise
estimation up to date and is dominated by the systematic effects. There is no
hint of the integral flux variability on daily scales at energies above 300 GeV
when systematic uncertainties are included in the flux measurement. We consider
three state- of-the-art theoretical models to describe the overall spectral
energy distribution of the Crab Nebula. The constant B-field model cannot
satisfactorily reproduce the VHE spectral measurements presented in this work,
having particular difficulty reproducing the broadness of the observed IC peak.
Most probably this implies that the assumption of the homogeneity of the
magnetic field inside the nebula is incorrect. On the other hand, the
time-dependent 1D spectral model provides a good fit of the new VHE results
when considering a 80 {\mu}G magnetic field. However, it fails to match the
data when including the morphology of the nebula at lower wavelengths.Comment: accepted by JHEAp, 9 pages, 6 figure
Limits to dark matter annihilation cross-section from a combined analysis of MAGIC and Fermi-LAT observations of dwarf satellite galaxies
We present the first joint analysis of gamma-ray data from the MAGIC
Cherenkov telescopes and the Fermi Large Area Telescope (LAT) to search for
gamma-ray signals from dark matter annihilation in dwarf satellite galaxies. We
combine 158 hours of Segue 1 observations with MAGIC with 6-year observations
of 15 dwarf satellite galaxies by the Fermi-LAT. We obtain limits on the
annihilation cross-section for dark matter particle masses between 10 GeV and
100 TeV - the widest mass range ever explored by a single gamma-ray analysis.
These limits improve on previously published Fermi-LAT and MAGIC results by up
to a factor of two at certain masses. Our new inclusive analysis approach is
completely generic and can be used to perform a global, sensitivity-optimized
dark matter search by combining data from present and future gamma-ray and
neutrino detectors.Comment: 19 pages, 3 figures. V2: Few typos corrected and references added.
Matches published version JCAP 02 (2016) 03
Detection of bridge emission above 50 GeV from the Crab pulsar with the MAGIC telescopes
The Crab pulsar is the only astronomical pulsed source detected at very high
energy (VHE, E>100GeV) gamma-rays. The emission mechanism of VHE pulsation is
not yet fully understood, although several theoretical models have been
proposed. In order to test the new models, we measured the light curve and the
spectra of the Crab pulsar with high precision by means of deep observations.
We analyzed 135 hours of selected MAGIC data taken between 2009 and 2013 in
stereoscopic mode. In order to discuss the spectral shape in connection with
lower energies, 4.6 years of {\it Fermi}-LAT data were also analyzed. The known
two pulses per period were detected with a significance of and
. In addition, significant emission was found between the two
pulses with . We discovered the bridge emission above 50 GeV
between the two main pulses. This emission can not be explained with the
existing theories. These data can be used for testing new theoretical models.Comment: 5 pages, 4 figure
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