112 research outputs found
Investigating Galactic supernova remnant candidates with LOFAR
We investigate six supernova remnant (SNR) candidates --- G51.21+0.11,
G52.37-0.70, G53.07+0.49, G53.41+0.03, G53.84-0.75, and the possible shell
around G54.1-0.3 --- in the Galactic Plane using newly acquired LOw-Frequency
ARray (LOFAR) High-Band Antenna (HBA) observations, as well as archival
Westerbork Synthesis Radio Telescope (WSRT) and Very Large Array Galactic Plane
Survey (VGPS) mosaics. We find that G52.37-0.70, G53.84-0.75, and the possible
shell around pulsar wind nebula G54.1+0.3 are unlikely to be SNRs, while
G53.07+0.49 remains a candidate SNR. G51.21+0.11 has a spectral index of
, but lacks X-ray observations and as such requires further
investigation to confirm its nature. We confirm one candidate, G53.41+0.03, as
a new SNR because it has a shell-like morphology, a radio spectral index of
and it has the X-ray spectral characteristics of a
1000-8000 year old SNR. The X-ray analysis was performed using archival
XMM-Newton observations, which show that G53.41+0.03 has strong emission lines
and is best characterized by a non-equilibrium ionization model, consistent
with an SNR interpretation. Deep Arecibo radio telescope searches for a pulsar
associated with G53.41+0.03 resulted in no detection, but place stringent upper
limits on the flux density of such a source if it is beamed towards Earth.Comment: 9 pages, 4 figures, 1 tabl
Scattering features and variability of the Crab pulsar
We report on Westerbork Synthesis Radio Telescope observations of the Crab
pulsar at 350 MHz from 2012 November 24 until 2015 June 21. During this period
we consistently observe variations in the pulse profile of the Crab. Both
variations in the scattering width of the pulse profile as well as delayed
copies, also known as echoes, are seen regularly. These observations support
the classification of two types of echoes: those that follow the truncated
exponential shape expected for the thin-screen scattering approximation, and
echoes that show a smoother, more Gaussian shape. During a sequence of
high-cadence observations in 2015, we find that these non-exponential echoes
evolve in time by approaching the main pulse and interpulse in phase,
overlapping the main pulse and interpulse, and later receding. We find a pulse
scatter-broadening time scale, , scaling with frequency as
, with , which is consistent with expected
values for thin-screen scattering modelsComment: 10 pages, 7 figure
Learning in Collaborative Moments
In this article, we describe experiences with dialogue evenings within a research collaboration on long-term care and dementia in the Netherlands. What started as a conventional process of ‘reporting back’ to interlocutors transformed over the course of two years into learning and knowing together. We argue that learning took place in three different articulations. First, participants learnt to expand their notion of knowledge. Second, they learnt to relate differently to each other and, therewith, to dementia. And third, participants learnt how to generate knowledge with each other. We further argue that these processes did not happen continuously, but in moments. We suggest that a framework of collaborative moments can be helpful for research projects that are not set up collaboratively from the start. Furthermore, we point to the work required to facilitate these moments.</jats:p
Antibiotics Shaping Bacterial Genome: Deletion of an IS91 Flanked Virulence Determinant upon Exposure to Subinhibitory Antibiotic Concentrations
The nucleoid-associated proteins Hha and YdgT repress the expression of the toxin α-hemolysin. An Escherichia coli mutant lacking these proteins overexpresses the toxin α-hemolysin encoded in the multicopy recombinant plasmid pANN202-312R. Unexpectedly, we could observe that this mutant generated clones that no further produced hemolysin (Hly-). Generation of Hly- clones was dependent upon the presence in the culture medium of the antibiotic kanamycin (km), a marker of the hha allele (hha::Tn5). Detailed analysis of different Hly- clones evidenced that recombination between partial IS91 sequences that flank the hly operon had occurred. A fluctuation test evidenced that the presence of km in the culture medium was underlying the generation of these clones. A decrease of the km concentration from 25 mg/l to 12.5 mg/l abolished the appearance of Hly- derivatives. We considered as a working hypothesis that, when producing high levels of the toxin (combination of the hha ydgT mutations with the presence of the multicopy hemolytic plasmid pANN202-312R), the concentration of km of 25 mg/l resulted subinhibitory and stimulated the recombination between adjacent IS91 flanking sequences. To further test this hypothesis, we analyzed the effect of subinhibitory km concentrations in the wild type E. coli strain MG1655 harboring the parental low copy number plasmid pHly152. At a km concentration of 5 mg/l, subinhibitory for strain MG1655 (pHly152), generation of Hly- clones could be readily detected. Similar results were also obtained when, instead of km, ampicillin was used. IS91 is flanking several virulence determinants in different enteric bacterial pathogenic strains from E. coli and Shigella. The results presented here evidence that stress generated by exposure to subinhibitory antibiotic concentrations may result in rearrangements of the bacterial genome. Whereas some of these rearrangements may be deleterious, others may generate genotypes with increased virulence, which may resume infection
Detection of radio emission from stars via proper-motion searches
We present a method for identifying radio stellar sources using their
proper-motion. We demonstrate this method using the FIRST, VLASS, RACS-low and
RACS-mid radio surveys, and astrometric information from Gaia Data Release 3.
We find eight stellar radio sources using this method, two of which have not
previously been identified in the literature as radio stars. We determine that
this method probes distances of ~90pc when we use FIRST and RACS-mid, and
~250pc when we use FIRST and VLASS. We investigate the time baselines required
by current and future radio sky surveys to detect the eight sources we found,
with the SKA (6.7 GHz) requiring <3 years between observations to find all
eight sources. We also identify nine previously known and 43 candidate variable
radio stellar sources that are detected in FIRST (1.4 GHz) but are not detected
in RACS-mid (1.37 GHz). This shows that many stellar radio sources are
variable, and that surveys with multiple epochs can detect a more complete
sample of stellar radio sources.Comment: 20 pages, 6 figures, 6 tables, accepted for publication in PAS
Periodic Radio Emission from the T8 Dwarf WISE J062309.94-045624.6
We present the detection of rotationally modulated, circularly polarized
radio emission from the T8 brown dwarf WISE J062309.94-045624.6 between 0.9 and
2.0 GHz. We detected this high proper motion ultracool dwarf with the
Australian SKA Pathfinder in GHz imaging data from the Rapid ASKAP
Continuum Survey. We observed WISE J062309.94-045624.6 to have a time and
frequency averaged Stokes I flux density of mJy beam, with
an absolute circular polarization fraction of , and calculated a
specific radio luminosity of erg s Hz. In
follow-up observations with the Australian Telescope Compact Array and MeerKAT
we identified a multi-peaked pulse structure, used dynamic spectra to place a
lower limit of kG on the dwarf's magnetic field, and measured a
h periodicity which we concluded to be due to rotational
modulation. The luminosity and period we measured are comparable to those of
other ultracool dwarfs observed at radio wavelengths. This implies that future
megahertz to gigahertz surveys, with increased cadence and improved
sensitivity, are likely to detect similar or later-type dwarfs. Our detection
of WISE J062309.94-045624.6 makes this dwarf the coolest and latest-type star
observed to produce radio emission.Comment: Accepted for publication in ApJ Letters; 11 pages, 3 figures and 2
table
MeerTRAP: Twelve Galactic fast transients detected in a real-time, commensal MeerKAT survey
MeerTRAP is a real-time untargeted search project using the MeerKAT telescope
to find single pulses from fast radio transients and pulsars. It is performed
commensally with the MeerKAT large survey projects (LSPs), using data from up
to 64 of MeerKAT's 13.96~m dishes to form hundreds of coherent beams on sky,
each of which is processed in real time to search for millisecond-duration
pulses. We present the first twelve Galactic sources discovered by MeerTRAP,
with DMs in the range of 33--381~pc~cm. One source may be Galactic or
extragalactic depending on the Galactic electron density model assumed.
Follow-up observations performed with the MeerKAT, Lovell, and Parkes radio
telescopes have detected repeat pulses from seven of the twelve sources. Pulse
periods have been determined for four sources. Another four sources could be
localised to the arcsecond-level using a novel implementation of the tied-array
beam localisation method.Comment: 16 pages, 14 figure
Spawning aggregation of bigeye trevally, Caranx sexfasciatus, highlights the ecological importance of oil and gas platforms
Open Access via the Elsevier Agreement Acknowledgements We gratefully acknowledge the field and logistical support provided by the Crew of the Resolution. This research project was funded by Chevron through its Anchor Partnership with the UK National Decommissioning Centre. We also acknowledge in-kind support from Net Zero Technology Centre and the University of Aberdeen through their partnership in the UK National Decommissioning Centre.Peer reviewedPublisher PD
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