We present a new sample of compact steep spectrum (CSS) sources with radio luminosity below 1026 W Hz−1 at 1.4 GHz; these are called low-luminosity compact (LLC) objects. The sources have been ...selected from the Faint Images of the Radio Sky at Twenty-cm (FIRST) survey and observed with the multi-element radio linked interferometer network (MERLIN) at the L and C bands. The main criterion used for selection was the luminosity of the objects, and approximately one-third of the CSS sources from the new sample have a value of radio luminosity comparable to Fanaroff–Riley type 1 sources (FR Is). About 80 per cent of the sources have been resolved and about 30 per cent have weak extended emission and disturbed structures when compared with the observations of higher-luminosity CSS sources. We have studied the correlation between radio power and linear size, and the redshift with a larger sample that also included published samples of compact objects and large-scale FR IIs and FR Is. In the radio power versus linear size diagram, the LLC objects occupy the space below the main evolutionary path of radio objects. We suggest that many of these might be short-lived objects, and their radio emission may be disrupted several times before they become FR IIs. We conclude that there exists a large population of short-lived LLC objects unexplored so far, and some of these could be precursors to large-scale FR Is.
Methanol and water vapour masers are signposts of early stages of high-mass star formation but it is generally thought that due to different excitation processes they probe distinct parts of stellar ...environments. Here we present observations of the intermediate-mass young stellar object G107.298+5.639, revealing for the first time that 34.4 d flares of the 6.7 GHz methanol maser emission alternate with flares of individual features of the 22 GHz water maser. High angular resolution data reveal that a few components of both maser species showing periodic behaviour coincide in position and velocity and all the periodic water maser components appear in the methanol maser region of size of 360 au. The maser flares could be caused by variations in the infrared radiation field induced by cyclic accretion instabilities in a circumstellar or protobinary disc. The observations do not support either the stellar pulsations or the seed photon flux variations as the underlying mechanisms of the periodicity in the source.
Abstract
The high brightness temperatures, Tb ≳ 1013 K, detected in several active galactic nuclei by RadioAstron space VLBI observations challenge theoretical limits. Refractive scattering by the ...interstellar medium may affect such measurements. We quantify the scattering properties and the sub-mas scale source parameters for the quasar B0529+483. Using RadioAstron correlated flux density measurements at 1.7, 4.8, and 22 GHz on projected baselines up to 240 000 km we find two characteristic angular scales in the quasar core, about 100 and 10 μas. Some indications of scattering substructure are found. Very high brightness temperatures, Tb ≥ 1013 K, are estimated at 4.8 and 22 GHz even taking into account the refractive scattering. Our findings suggest a clear dominance of the particle energy density over the magnetic field energy density in the core of this quasar.
In 2016 September, the microquasar Cygnus X-3 underwent a giant radio flare, which was monitored for 6 d with the Medicina Radio Astronomical Station and the Sardinia Radio Telescope. Long ...observations were performed in order to follow the evolution of the flare on an hourly scale, covering six frequency ranges from 1.5 to 25.6 GHz. The radio emission reached a maximum of 13.2 +/- 0.7 Jy at 7.2 GHz and 10 +/- 1 Jy at 18.6 GHz. Rapid flux variations were observed at high radio frequencies at the peak of the flare, together with rapid evolution of the spectral index: α steepened from 0.3 to 0.6 (with Sν ∝ ν −α) within 5 h. This is the first time that such fast variations are observed, giving support to the evolution from optically thick to optically thin plasmons in expansion moving outward from the core. Based on the Italian network (Noto, Medicina and SRT) and extended to the European antennas (Torun, Yebes, Onsala), very long baseline interferometry (VLBI) observations were triggered at 22 GHz on five different occasions, four times prior to the giant flare, and once during its decay phase. Flux variations of 2 h duration were recorded during the first session. They correspond to a mini-flare that occurred close to the core 10 d before the onset of the giant flare. From the latest VLBI observation we infer that 4 d after the flare peak the jet emission was extended over 30 mas.
Aims. The FR I/FR II dichotomy is a much debated issue in the astrophysics of extragalactic radio sources. Study of the properties of HYbrid MOrphology Radio Sources (HYMORS) may bring crucial ...information and lead to a step forward in understanding the origin of FR I/FR II dichotomy. HYMORS are a rare class of double-lobed radio sources where each of the two lobes clearly exhibits a different FR morphology. This article describes follow-up high resolution VLBA observations of the five discovered by us HYMORS. The main aim of the observations was to answer the questions of whether the unusual radio morphology is connected to the orientation of objects towards the observer. Methods. The milliarcsecond-scale structures are good probes of the galactic medium, the possible asymmetries, and orientation of the central engines of the sources. We obtained the high resolution radio maps of five hybrid radio morphology objects with the VLBA at C-band and L-band. Results. The cores of all five sources have been detected at both radio bands. Two of them revealed milliarcsecond core-jet structures, the next two objects showed hints of parsec-scale jets, and the last one remained point-like at both frequencies. Conclusions. We compared properties of observed milliarcsecond structures of hybrid sources with the larger scale ones previously detected with the VLA. We find that on both scales the fluxes of their central components are similar, which may indicate the lack of additional emission in the proximity of the nucleus. This suggests that jets present on the ~1−10 kpc scale in those objects are FR II-like. When possible, the detected core-jet structures were used for estimating the core’s spatial orientation. The result is that neither the FR I-like nor the FR II-like side is preferred, which may suggest that no specific spatial orientation of HYMORS is required to explain their radio morphology. Their estimated viewing angles indicate they are unbeamed objects. The 178/151 MHz luminosity of observed HYMORS exceed the traditional FR I/FR II break luminosity, indicating they have radio powers similar to FR IIs.
We report Multi-Element Radio-Linked Interferometer Network, Very Large Array, One-Centimetre Radio Array, Very Long Baseline Array (VLBA), Effelsberg and Giant Metrewave Radio Telescope observations ...beginning 4.5 days after the discovery of RS Ophiuchi undergoing its 2006 recurrent nova outburst. Observations over the first 9 weeks are included, enabling us to follow spectral development throughout the three phases of the remnant development. We see dramatic brightening on days 4 to 7 at 6 GHz and an accompanying increase in other bands, particularly 1.46 GHz, consistent with transition from the initial ‘free expansion’ phase to the adiabatic expansion phase. This is complete by day 13 when the flux density at 5 GHz is apparently declining from an unexpectedly early maximum (compared with expectations from observations of the 1985 outburst). The flux density recovered to a second peak by approximately day 40, consistent with behaviour observed in 1985. At all times the spectral index is consistent with mixed non-thermal and thermal emission. The spectral indices are consistent with a non-thermal component at lower frequencies on all dates, and the spectral index changes show that the two components are clearly variable. The estimated extent of the emission at 22 GHz on day 59 is consistent with the extended east and west features seen at 1.7 GHz with the VLBA on day 63 being entirely non-thermal. We suggest a two-component model, consisting of a decelerating shell seen in mixed thermal and non-thermal emission plus faster bipolar ejecta generating the non-thermal emission, as seen in contemporaneous VLBA observations. Our estimated ejecta mass of 4 ± 2 × 10−7 M⊙ is consistent with a white dwarf (WD) mass of 1.4 M⊙. It may be that this ejecta mass estimate is a lower limit, in which case a lower WD mass would be consistent with the data.
Abstract Background Current guidelines for the treatment of methicillin-resistant Staphylococcus aureus (MRSA) bacteremia recommend targeting a vancomycin AUC24 /MIC ≥400. Data on the association ...between AUC24 /MIC and microbiological clearance in patients with concomitant MRSA bacteremia and MRSA osteomyelitis are limited. Objective The objective of this study is to evaluate the association between the vancomycin AUC24 /MIC and time to microbiological clearance in patients with concomitant MRSA bacteremia and MRSA osteomyelitis. Methods Adult inpatients with concomitant MRSA bacteremia and MRSA osteomyelitis treated with vancomycin from January 1, 2007, through December 31, 2011, were evaluated. Classification and regression tree analysis was used to identify the AUC24 /MIC associated with time to microbiological clearance. Results Fifty-nine patients had complete data available for review and were included in the analysis. Classification and regression tree analysis identified an AUC/MIC of 293 as the breakpoint that provides the greatest difference in time to microbiological clearance. On univariate analysis, mean (SD) time to clearance was 2 days shorter when the AUC/MIC was >293 (4 2 days vs 6 3 days, P = 0.01). Mean (SD) infection-related length of stay was 13 (6) versus 18 (14) days in patients with an AUC24 /MIC ratio >293 or ≤293, respectively ( P = 0.25). In patients with an AUC24 /MIC ≤293, 39% versus 17% ( P = 0.09) had recurrent bacteremia and were readmitted compared with patients with an AUC/MIC >293. Only 9% were able to achieve an AUC24 /MIC >293 when the vancomycin MIC was >1 μg/mL. Conclusions We observed a >2.5-fold increase in time to microbiological clearance in patients with concomitant MRSA bacteremia and MRSA osteomyelitis unable to achieve a vancomycin AUC24 /MIC >293. A 5-day increase in hospital and infection-related length of stay was observed when this target was not achieved. Recurrence of bacteremia and hospital readmissions were higher in the cohort who did not achieve an AUC24 /MIC >293. Only 9% of patients were able to achieve an AUC24 /MIC >293 if the isolate MIC was >1 μg/mL. Trough concentration did not correlate with AUC24 /MIC. In patients with concomitant MRSA bacteremia and MRSA osteomyelitis treated with vancomycin, stewardship programs should optimize pharmacodynamic parameters, specifically AUC24 /MIC, or alternative therapies should be considered.
The so-called HYbrid MOrphology Radio Sources (HYMORS) are a class of objects that appear to have a mixed Fanaroff-Riley (FR) morphology in a single object; i.e. a HYMORS has an FR I-type lobe on one ...side of its nucleus and an FR II-type lobe on the other side. Because of this unique feature and given that the origin of the FR morphological dichotomy is still unclear, HYMORS may possibly play a crucial role in our understanding of the FR-dichotomy. As the number of known HYMORS is quite small, we aimed to increase that number by inspecting a few areas of the sky covered by the VLA FIRST survey and by selecting 21 HYMORS candidates based on the morphology shown in the FIRST images. They were observed with the VLA in B-conf. at 4.9 GHz. Three objects from the initial sample turned out to be actual HYMORS and two others very likely to fulfill the criteria. These five were subsequently re-observed with the VLA in A-conf. at 1.4 GHz. Our results provide strong support to the findings of Gopal-Krishna & Wiita (2000, A&A, 363, 507), namely that there are two different kinds of jets in HYMORS; consequently, the existence of FR-dichotomy as a whole is difficult to reconcile with the class of explanations that posit fundamental differences in the central engine.
Objective: To review the evidence on vitamin A supplementation (VAS) and bronchopulmonary dysplasia (BPD) in extremely-low-birth-weight infants. We also discuss the impact of a vitamin A shortage on ...BPD rates. Data Sources: A PubMed search inclusive of dates 1946 to March 2016 was performed using the search terms bronchopulmonary dysplasia, chronic lung disease (CLD), and vitamin A. Study Selection and Data Extraction: All English-language studies were evaluated. Only those investigating VAS by intramuscular administration were included. Data Synthesis: A total of 6 studies were evaluated. Additionally, a report on the incidence of BPD during a national shortage was reviewed. Investigators found mixed results with VAS and incidence of CLD or death in a varying number of neonates. In the largest evaluation, investigators found a statistically significant decrease in the rate of death or BPD: 55% in the VAS group versus 62% in the placebo group. The number needed to treat to prevent 1 case of BPD was 15 infants. Few studies found an increased incidence of adverse events following VAS. A report over a 2-year shortage period found that whereas the rate of VAS declined dramatically, BPD rates remained stable. This large observational evaluation calls into question the place of vitamin A in BPD prevention. Conclusions: VAS has been identified as a strategy to decrease the incidence of BPD. Initial large-scale prospective evaluations have shown clear benefit of VAS in reducing the incidence of CLD or death. However, changing definitions of BPD and implementation of noninvasive ventilation strategies limit the application of early studies. During a drug shortage, VAS declined dramatically, but BPD rates remained stable. With concerns of sepsis and necrotizing enterocolitis in small-scale studies, and in light of the recent shortage evidence, further evaluations are necessary before VAS can be recommended as a cornerstone of BPD prevention.
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