•Antimicrobial agents are essential tools for treating and controlling bacterial infections in poultry.•Proper use of antimicrobials depends on knowledge of the interrelationships between bacteria, ...antimicrobial and host animal.•The pharmacotherapeutic characteristics of commonly used antimicrobial agents in broiler chickens are reviewed.•Anatomical–physiological features of poultry are reviewed with regard to drug disposition.
Antimicrobial agents are essential tools for treating and controlling bacterial infections in poultry production. Veterinarians have a huge responsibility when using antimicrobials in poultry producing meat and eggs for human consumption. The term ‘judicious use’ of antimicrobials implies the optimal selection of drug, dose and duration of antimicrobial treatment, along with a reduction in inappropriate and excessive use as a means of slowing the emergence of antimicrobial resistance.
The proper use of antimicrobials depends on the knowledge of interrelationships between bacteria, antimicrobial, host and consumer. This article reviews the anatomical–physiological features of poultry relating to drug disposition as well as the pharmacological and therapeutic characteristics of the most commonly used antimicrobials in broiler chickens. Doses frequently employed for flock treatment are presented as are accepted withdrawal times.
Aims.
We report on ESPRESSO high-resolution transmission spectroscopic observations of two primary transits of the highly irradiated, ultra-hot Jupiter-sized planet, WASP-76b. We investigated the ...presence of several key atomic and molecular features of interest that may reveal the atmospheric properties of the planet.
Methods.
We extracted two transmission spectra of WASP-76b with
R
≈ 140 000 using a procedure that allowed us to process the full ESPRESSO wavelength range (3800–7880 Å) simultaneously. We observed that at a high signal-to-noise ratio, the continuum of ESPRESSO spectra shows ‘wiggles’, which are likely caused by an interference pattern outside the spectrograph. To search for the planetary features, we visually analysed the extracted transmission spectra and cross-correlated the observations against theoretical spectra of different atomic and molecular species.
Results.
The following atomic features are detected: Li
I
, Na
I
, Mg
I
, Ca
II
, Mn
I
, K
I
, and Fe
I
. All are detected with a confidence level between 9.2
σ
(Na
I
) and 2.8
σ
(Mg
I
). We did not detect the following species: Ti
I
, Cr
I
, Ni
I
, TiO, VO, and ZrO. We impose the following 1
σ
upper limits on their detectability: 60, 77, 122, 6, 8, and 8 ppm, respectively.
Conclusions.
We report the detection of Li
I
on WASP-76b for the first time. In addition, we confirm the presence of Na
I
and Fe
I
as previously reported in the literature. We show that the procedure employed in this work can detect features down to the level of ~0.1% in the transmission spectrum and ~10 ppm by means of a cross-correlation method. We discuss the presence of neutral and singly ionised features in the atmosphere of WASP-76b.
The dissipation of energy flux in blazar jets plays a key role in the acceleration of relativistic particles. Two possibilities are commonly considered for the dissipation processes, magnetic ...reconnection – possibly triggered by instabilities in magnetically dominated jets – or shocks – for weakly magnetized flows. In this paper, we consider the polarimetric features expected for the two scenarios analyzing the results of state-of-the-art simulations. For the magnetic reconnection scenario we conclude, using results from global relativistic MHD simulations, that the emission likely occurs in turbulent regions with unstructured magnetic fields, although the simulations do not allow us to draw firm conclusions. On the other hand, with local particle-in-cell simulations we show that, for shocks with a magnetic field geometry suitable for particle acceleration, the self-generated magnetic field at the shock front is predominantly orthogonal to the shock normal and becomes quasi-parallel downstream. Based on this result we develop a simplified model to calculate the frequency-dependent degree of polarization, assuming that high-energy particles are injected at the shock and cool downstream. We apply our results to HBLs, blazars with the maximum of their synchrotron output at UV-soft X-ray energies. While in the optical band the predicted degree of polarization is low, in the X-ray emission it can ideally reach 50 per cent, especially during active/flaring states. The comparison between measurements in the optical and in the X-ray band made during active states (feasible with the planned IXPE satellite) is expected to provide valuable constraints on the dissipation and acceleration processes.
Context. Extreme TeV BL Lacs are a class of blazars with unique spectral and temporal features that are not easily reproducible using standard one-zone models based on single shock acceleration. To ...account for their peculiar properties, we elaborated a two-step acceleration model in which a recollimation shock and the subsequent downstream turbulence energize non-thermal electrons. Aims. We applied the model to a sample of extreme TeV BL Lacs with well-characterized spectral energy distributions. Since we used several sources, we automatized the exploration of the parameter space. This allowed us to derive the parameter distributions and study the correlations among them. Methods. We numerically solved a system of two coupled nonlinear differential equations to obtain the non-thermal particles and turbulence spectra. We calculated the spectral energy distribution via the synchrotron self-Compton emission model. The automatization of the parameter space exploration is possible through a Markov chain Monte Carlo (MCMC) ensemble sampler, in our case emcee. Results. We derived well-defined posterior distributions for the parameters, showing that the model is well constrained by available data and demonstrating the suitability of our method. The cross-correlations among some of the physical parameters are not trivial. Therefore, we conclude that MCMC sampling is a key instrument for characterizing the complexity of our multiparameter phenomenological model.
ABSTRACT
Polarimetric measurements, especially if extended at high energy, are expected to provide important insights into the mechanisms underlying the acceleration of relativistic particles in ...jets. In a previous work, we have shown that the polarization of the synchrotron X-ray emission produced by highly energetic electrons accelerated by a mildly relativistic shock carries essential imprints of the geometry and the structure of the magnetic fields in the downstream region. Here, we present the extension of our analysis to the non-stationary case, especially suitable to model the highly variable emission of high-energy emitting BL Lacs. We anticipate a large ($\Pi \approx 40{{\ \rm per\ cent}}$), almost time-independent degree of polarization in the hard/medium X-ray band, a prediction soon testable with the upcoming mission IXPE. The situation in other bands, in particular in the optical, is more complex. A monotonic decrease of the optical degree of polarization is observed during the development of a flare. At later stages, Π reaches zero and then it starts to increase, recovering large values at late times. The instant at which Π = 0 is marked by a rotation of the polarization angle by 90°. However, at optical frequencies, it is likely that more than one region contribute to the observed emission, potentially making it difficult to detect the predicted behaviour.
We report on 16 BL Lacertae objects that were proposed to be at z > 1. We present spectroscopic observations secured at the 10.4 m GTC that allowed us to assess the redshift of these sources. In ...particular, for five objects, we disprove the previous value of the redshift reported in the literature and found that they lie at z < 1. Moreover, two of them exhibit broad emission lines that are not characteristic of BL Lacertae objects. On the other hand, for eight targets, we improve the tentative value of z, previously based on only one feature, by detecting a number of emission lines. Finally, in three cases, we detect the onset of the Ly forest at z > 2.50. Based on the new high quality spectra, we found that only half of the observed objects can be classified as bona-fide BL Lacs.
Gamma-ray-emitting narrow-line Seyfert 1 (γ-NLS1) galaxies are thought to harbour relatively low-mass black holes (10^6–10^8 M_|$\odot$|) accreting close to the Eddington limit. They show ...characteristics similar to those of blazars, such as flux and spectral variability in the gamma-ray energy band and radio properties which point towards the presence of a relativistic jet. These characteristics make them an intriguing class of sources to be investigated with the Cherenkov Telescope Array (CTA), the next-generation ground-based gamma-ray observatory. We present our extensive set of simulations of all currently known γ-ray emitters identified as NLS1s (20 sources), investigating their detections and spectral properties, taking into account the effect of both the extragalactic background light in the propagation of gamma-rays and intrinsic absorption components. We find that the prospects for observations of γ-NLS1 with CTA are promising. In particular, the brightest sources of our sample, SBS 0846+513, PMN J0948+0022, and PKS 1502+036, can be detected during high/flaring states, the former two even in the case in which the emission occurs within the highly opaque central regions, which prevent gamma-rays above a few tens of GeV to escape. In this case, the low-energy threshold of CTA will play a key role. If, on the other hand, high-energy emission occurs outside the broad-line region, we can detect the sources up to several hundreds of GeV – depending on the intrinsic shape of the emitted spectrum. Therefore, CTA observations will provide valuable information on the physical conditions and emission properties of their jets.
Revisiting Proxima with ESPRESSO Suárez Mascareño, A.; Faria, J. P.; Figueira, P. ...
Astronomy & astrophysics,
07/2020, Letnik:
639
Journal Article
Recenzirano
Odprti dostop
Context.
The discovery of Proxima b marked one of the most important milestones in exoplanetary science in recent years. Yet the limited precision of the available radial velocity data and the ...difficulty in modelling the stellar activity calls for a confirmation of the Earth-mass planet.
Aims.
We aim to confirm the presence of Proxima b using independent measurements obtained with the new ESPRESSO spectrograph, and refine the planetary parameters taking advantage of its improved precision.
Methods.
We analysed 63 spectroscopic ESPRESSO observations of Proxima (Gl 551) taken during 2019. We obtained radial velocity measurements with a typical radial velocity photon noise of 26 cm s
−1
. We combined these data with archival spectroscopic observations and newly obtained photometric measurements to model the stellar activity signals and disentangle them from planetary signals in the radial velocity (RV) data. We ran a joint Markov chain Monte Carlo analysis on the time series of the RV and full width half maximum of the cross-correlation function to model the planetary and stellar signals present in the data, applying Gaussian process regression to deal with the stellar activity signals.
Results.
We confirm the presence of Proxima b independently in the ESPRESSO data and in the combined ESPRESSO+ HARPS+UVES dataset. The ESPRESSO data on its own shows Proxima b at a period of 11.218 ± 0.029 days, with a minimum mass of 1.29 ± 0.13
M
⊕
. In the combined dataset we measure a period of 11.18427 ± 0.00070 days with a minimum mass of 1.173 ± 0.086
M
⊕
. We get a clear measurement of the stellar rotation period (87 ± 12 d) and its induced RV signal, but no evidence of stellar activity as a potential cause for the 11.2 days signal. We find some evidence for the presence of a second short-period signal, at 5.15 days with a semi-amplitude of only 40 cm s
−1
. If caused by a planetary companion, it would correspond to a minimum mass of 0.29 ± 0.08
M
⊕
. We find that forthe case of Proxima, the full width half maximum of the cross-correlation function can be used as a proxy for the brightness changes and that its gradient with time can be used to successfully detrend the RV data from part of the influence of stellar activity. The activity-induced RV signal in the ESPRESSO data shows a trend in amplitude towards redder wavelengths. Velocities measured using the red end of the spectrograph are less affected by activity, suggesting that the stellar activity is spot dominated. This could be used to create differential RVs that are activity dominated and can be used to disentangle activity-induced and planetary-induced signals. The data collected excludes the presence of extra companions with masses above 0.6
M
⊕
at periods shorter than 50 days.
Aims. We aim to determine the redshift (or stringent lower limits) of a number of bright BL Lacs objects. Methods. We secured optical and near-infrared medium-resolution spectra of four bright BL Lac ...objects of unknown redshift using the spectrograph X-Shooter at the ESO-VLT. Results. In spite of the high quality of the spectra and the extended spectral range of the observations, we have not detected intrisic spectral features for these sources. However, we are able to provide strigent lower limits to their redshift. In particular, for the two TeV sources PG 1553+113 and H 1722+119, we infer z> 0.30 and z> 0.35 respectively. We also detect an intervening Ca II absorption doublet in the spectrum of MH 2136-428 that is ascribed to the halo of a nearby giant elliptical galaxy at a projected distance of ~100 kpc. Conclusions. Under the hypothesis that all BL Lacs are hosted by a luminous bulge-dominated galaxies, the spectroscopic observations of bright BL Lacs presently indicate that these objects are likely sources with extremely beamed nuclear emission. We present simulations to show under which circumstances it is possible to probe this hypothesis from the detection of very weak absorptions using the next generation of extremely large optical telescopes.
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