Azospirillum brasilense Az39, a model rhizobacterium with AHL quorum quenching capacity

AimsThe aim of this research was to analyze the Quorum sensing (QS) and Quorum quenching (QQ) mechanisms based on N‐acyl‐L‐homoserine lactones (AHLs) in A. brasilense Az39, a strain with remarkable capacity to benefit a wide range of crops under agronomic conditions. Methods and ResultsWe performed an in silico and in vitro analysis of the quorum mechanisms in A. brasilense Az39. The results obtained in vitro using the reporter strains C. violaceum and A. tumefaciens and Liquid Chromatography coupled to Mass‐Mass Spectrometry (LC‐MS/MS) analysis showed that although Az39 does not produce AHL molecules, it is capable of degrading them by at least two hypothetical enzymes identified by bioinformatics approach, associated to the bacterial cell. In Az39 cultures supplemented with 500 nmol l−1 of the C3 unsubstituted AHLs (C4, C6, C8, C10, C12, C14), AHL levels were lower than in non‐inoculated LB media controls. Similar results were observed upon addition of AHLs with hydroxy (OH‐) and keto (oxo‐) substitutions in carbon 3. These results not only demonstrate the ability of Az39 to degrade AHLs. They also show the wide spectrum of molecules that can be degraded by this bacterium. ConclusionsAlthough A.brasilense Az39 is a silent bacterium unable to produce AHL signals, it is able to interrupt the communications between other bacteria and/or plants by a quorum quenching activity

Constraints on redshifts of blazars from extragalactic background light attenuation using Fermi-LAT data

The extragalactic high-energy $\gamma$-ray sky is dominated by blazars, which are active galactic nuclei with their jets pointing towards us. Distance measurements are of fundamental importance yet for some of these sources are challenging because any spectral signature from the host galaxy may be outshone by the non-thermal emission from the jet. In this paper, we present a method to constrain redshifts for these sources that relies only on data from the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. This method takes advantage of the signatures that the pair-production interaction between photons with energies larger than approximately 10 GeV and the extragalactic background light leaves on $\gamma$-ray spectra. We find upper limits for the distances of 303 $\gamma$-ray blazars, classified as 157 BL Lacertae objects, 145 of uncertain class, and 1 flat-spectrum-radio quasar, whose redshifts are otherwise unknown. These derivations can be useful for planning observations with imaging atmospheric Cherenkov telescopes and also for testing theories of supermassive black hole evolution. Our results are applied to estimate the detectability of these blazars with the future Cherenkov Telescope Array, finding that at least 21 of them could be studied in a reasonable exposure of 20 h.Comment: 13 pages, 7 figures, 1 table; Accepted by MNRA

Evidence for proton acceleration up to TeV energies based on VERITAS and Fermi-LAT observations of the Cas A SNR

We present a study of $\gamma$-ray emission from the core-collapse supernova remnant Cas~A in the energy range from 0.1GeV to 10TeV. We used 65 hours of VERITAS data to cover 200 GeV - 10 TeV, and 10.8 years of \textit{Fermi}-LAT data to cover 0.1-500 GeV. The spectral analysis of \textit{Fermi}-LAT data shows a significant spectral curvature around $1.3 \pm 0.4_{stat}$ GeV that is consistent with the expected spectrum from pion decay. Above this energy, the joint spectrum from \textit{Fermi}-LAT and VERITAS deviates significantly from a simple power-law, and is best described by a power-law with spectral index of $2.17\pm 0.02_{stat}$ with a cut-off energy of $2.3 \pm 0.5_{stat}$ TeV. These results, along with radio, X-ray and $\gamma$-ray data, are interpreted in the context of leptonic and hadronic models. Assuming a one-zone model, we exclude a purely leptonic scenario and conclude that proton acceleration up to at least 6 TeV is required to explain the observed $\gamma$-ray spectrum. From modeling of the entire multi-wavelength spectrum, a minimum magnetic field inside the remnant of $B_{\mathrm{min}}\approx150\,\mathrm{\mu G}$ is deduced.Comment: 33 pages, 9 Figures, 6 Table

Direct measurement of stellar angular diameters by the VERITAS Cherenkov Telescopes

The angular size of a star is a critical factor in determining its basic properties. Direct measurement of stellar angular diameters is difficult: at interstellar distances stars are generally too small to resolve by any individual imaging telescope. This fundamental limitation can be overcome by studying the diffraction pattern in the shadow cast when an asteroid occults a star, but only when the photometric uncertainty is smaller than the noise added by atmospheric scintillation. Atmospheric Cherenkov telescopes used for particle astrophysics observations have not generally been exploited for optical astronomy due to the modest optical quality of the mirror surface. However, their large mirror area makes them well suited for such high-time-resolution precision photometry measurements. Here we report two occultations of stars observed by the VERITAS Cherenkov telescopes with millisecond sampling, from which we are able to provide a direct measurement of the occulted stars' angular diameter at the $\leq0.1$ milliarcsecond scale. This is a resolution never achieved before with optical measurements and represents an order of magnitude improvement over the equivalent lunar occultation method. We compare the resulting stellar radius with empirically derived estimates from temperature and brightness measurements, confirming the latter can be biased for stars with ambiguous stellar classifications.Comment: Accepted for publication in Nature Astronom

Very high-energy gamma-ray follow-up program using neutrino triggers from IceCube

We describe and report the status of a neutrino-triggered program in IceCube that generates real-time alerts for gamma-ray follow-up observations by atmospheric-Cherenkov telescopes (MAGIC and VERITAS). While IceCube is capable of monitoring the whole sky continuously, high-energy gamma-ray telescopes have restricted fields of view and in general are unlikely to be observing a potential neutrino-flaring source at the time such neutrinos are recorded. The use of neutrino-triggered alerts thus aims at increasing the availability of simultaneous multi-messenger data during potential neutrino flaring activity, which can increase the discovery potential and constrain the phenomenological interpretation of the high-energy emission of selected source classes (e. g. blazars). The requirements of a fast and stable online analysis of potential neutrino signals and its operation are presented, along with first results of the program operating between 14 March 2012 and 31 December 2015

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" 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 the X-ray and optical/ultraviolet bands) and VERITAS (covering the TeV gamma-ray band), along with contemporaneous observations from other gamma-ray facilities (MAGIC and Fermi-Large Area Telescope) 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 greater than or similar to 4 x 10(-4) 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

Participación comunitaria por medio de la arborización barrial

Forestación de los Barrios Napal y Plan Federal de la ciudad de Bahía Blanca, provincia de Buenos Aires, partiendo desde la participación comunitaria de ambos barrios y la interacción con la comunidad educativa en todos sus niveles (Jardín de Infantes N° 912, Escuela Primaria Básica N° 37y N°65, Escuela Secundaria Básica N°348, Universidad Nacional del Sur Departamento de Biología, Bioquímica y Farmacia, Departamento de Ciencias de la salud), Municipalidad de Bahía Blanca (a través de la Delegación Villa Rosas y la Unidad Sanitaria Barrio Colon ), INTA y el Centro de Orientación Familiar de Dirección de Psicología Comunitaria y Pedagogía Social (COF) a fin de lograr la unión e identidad barrial. Además de la forestación, el proyecto incluye charlas mensuales en el SUM del barrio sobre temáticas de interés (huertas, nutrición, violencia de género, medio ambiente, etc.), y el acondicionamiento de dicho SUM (instalación de gas, estufa y horno). La idea surge de las necesidades de los vecinos y de las inquietudes de los trabajadores de las distintas instituciones. Las problemáticas barriales incluyen la falta de identidad barrial, la falta de participación comunitaria, la rivalidad barrial y la falta de árboles. Se constituyó el espacio de reuniones en red institucionales con la participación de vecinos para tratar los distintos temas relacionados con el proyecto, y se formaron comisiones de trabajo constituidas tanto por vecinos como personas que trabajan en el barrio. La importancia de la solución de las problemáticas reside en que la participación lograda va a poder ser usada por los vecinos como medio para conseguir solucionar otras problemáticas barriales, y en que por medio de la plantación de los árboles se va a impactar positivamente en la salud y el medio ambiente de la comunidad. Desde la participación popular lograda pueden gestarse condiciones para modificar los límites simbólicos de la propia comunidad, comenzando a vivirse como genuinos aportadores de lecturas para la construcción de políticas sociales, desde el barrio y trascendiéndolo

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&