68 research outputs found
Gaia DR2 Distances and Peculiar Velocities for Galactic Black Hole Transients
We report on a first census of Galactic black hole X-ray binary (BHXRB)
properties with the second data release (DR2) of {\em Gaia}, focusing on
dynamically confirmed and strong candidate black hole transients. DR2 provides
five-parameter astrometric solutions including position, parallax and proper
motion for 11 of a sample of 24 systems. Distance estimates are tested with
parallax inversion as well as Bayesian inference. We derive an empirically
motivated characteristic scale length of =2.170.12 kpc for this BHXRB
population to infer distances based upon an exponentially decreasing space
density prior. Geometric DR2 parallaxes provide new, independent distance
estimates, but the faintness of this population in quiescence results in
relatively large fractional distance uncertainties. Despite this, DR2 estimates
generally agree with literature distances. The most discrepant case is BW Cir,
for which detailed studies of the donor star have suggested a distant location
at >~25 kpc. A large DR2 measured parallax and relatively high proper motion
instead prefer significantly smaller distances, suggesting that the source may
instead be amongst the nearest of XRBs. However, both distances create problems
for interpretation of the source, and follow-up data are required to resolve
its true nature. DR2 also provides a first distance estimate to one source,
MAXI J1820+070, and novel proper motion estimates for 7 sources. Peculiar
velocities relative to Galactic rotation exceed 50 km s for the
bulk of the sample, with a median system kinetic energy of peculiar motion of
5 10 erg. BW Cir could be a new high-velocity BHXRB if
its astrometry is confirmed. A putative anti-correlation between peculiar
velocity and black hole mass is found, as expected in mass-dependent BH kick
formation channels, but this trend remains weak in the DR2 data.Comment: MNRAS in pres
Classifying Optical (Out)bursts in Cataclysmic Variables: The Distinct Observational Characteristics of Dwarf Novae, Micronovae, Stellar Flares, and Magnetic Gating
Cataclysmic variables can experience short optical brightenings, which are commonly attributed to phenomena such as dwarf novae outbursts, micronovae, donor flares, or magnetic gating bursts. Since these events exhibit similar observational characteristics, their identification has often been ambiguous. In particular, magnetic gating bursts and micronovae have been suggested as alternative interpretations of the same phenomena. Here we show that the timescales and energies separate the optical brightenings into separate clusters consistent with their different classifications. This suggests that micronovae and magnetic gating bursts are in fact separate phenomena. Based on our findings, we develop diagnostic diagrams that can distinguish between these bursts/flares based on their properties. We demonstrate the effectiveness of this approach on observations of a newly identified intermediate polar, CTCV J0333-4451, which we classify as a magnetic gating system. CTCV J0333-4451 is the third highest spin-to-orbital period ratio intermediate polar with magnetic gating, suggesting that these bursts are common among these rare systems
Millihertz X-ray variability during the 2019 outburst of black hole candidate Swift~J1357.20933
Swift J1357.20933 is a black-hole candidate X-ray transient, which
underwent its third outburst in 2019, during which several multi-wavelength
observations were carried out.~Here, we report results from the \emph{Neil
Gehrels Swift} and \emph{NICER} observatories and radio data from
\emph{AMI}.~For the first time,~millihertz quasi-periodic X-ray oscillations
with frequencies varying between ~1--5~ were found in
\emph{NICER} observations and a similar feature was also detected in one
\emph{Swift}--\textsc{XRT} dataset.~Our spectral analysis indicate that the
maximum value of the measured X-ray flux is much lower compared to the peak
values observed during the 2011 and 2017 outbursts.~This value is ~100
times lower than found with \emph{MAXI} on MJD~58558 much (~68 days)
earlier in the outburst, suggesting that the \emph{Swift} and \emph{NICER}
fluxes belong to the declining phase of the 2019 outburst.~An additional soft
component was detected in the \textsc{XRT} observation with the highest flux
level, but at a relatively low ~~, and which we fitted with a disc component at a
temperature of ~keV.~The optical/UV magnitudes obtained from
\emph{Swift}--\textsc{UVOT} showed a correlation with X-ray observations,
indicating X-ray reprocessing to be the plausible origin of the optical and UV
emission.~However, the source was not significantly detected in the radio
band.~There are currently a number of models that could explain this
millihertz-frequency X-ray variability; not least of which involves an X-ray
component to the curious dips that, so far, have only been observed in the
optical.Comment: 14 pages, Accepted for publication in MNRA
Adherence Barriers to Antimicrobial Treatment Guidelines in Teaching Hospital, the Netherlands
To optimize appropriate antimicrobial use in a university hospital and identify barriers hampering implementation strategies, physicians were interviewed regarding their opinions on antimicrobial policies. Results indicated that effective strategies should include regular updates of guidelines that incorporate the views of relevant departments and focus on addressing senior staff and residents because residents do not make independent decisions in a teaching-hospital setting
The black hole X-ray transient Swift J1357.2-0933 as seen with Swift and NuSTAR during its 2017 outburst
We report on observations of black hole Swift J1357.2–0933, a member of the modest population of very faint X-ray transients. This source has previously shown intense dips in the optical light curve, a phenomena that has been linked to the existence of a ‘unique toroidal structure’ in the inner region of the disc, seen at a high inclination. Our observations, carried out by the Neil Gehrels Swift and NuSTAR X-ray observatories, do not show the presence of intense dips in the optical light curves. We find that the X-ray light curves do not show any features that would straightforwardly support an edge-on configuration or high inclination configuration of the orbit. This is similar to what was seen in the X-ray observations of the source during its 2011 outburst. Moreover, the broad-band spectra were well described with an absorbed power-law model without any signatures of cut-off at energies above 10 keV, or any reflection from the disc or the putative torus. Thus, the X-ray data do not support the unique ‘obscuring torus’ scenario proposed for J1357. We also performed a multiwavelength study using the data of X-ray telescope and Ultraviolet/Optical Telescope aboard Swift, taken during the ∼4.5 months duration of the 2017 outburst. This is consistent with what was previously inferred for this source. We found a correlation between the simultaneous X-ray and ultraviolet/optical data and our study suggests that most of the reprocessed flux must be coming out in the ultraviolet.Publisher PDFPeer reviewe
A qualitative study of the perceptions and experiences of Pre-Registration House Officers on teamwork and support
BACKGROUND: Following the implementation of a new final Year 5 curriculum in one medical school we carried out a study to explore the experience of the transition from final student year to Pre-Registration House Officer (PRHO). This study looks at the experiences of two successive cohorts of PRHOs in relation to team work, support and shared responsibility in their transition from final year students to qualified doctors. The involvement of PRHOs in teams is likely to change in the development of Foundation programmes. METHODS: A qualitative study with semi-structured interviews with 33 PRHOs, stratified by gender, ethnicity and maturity, from two study cohorts, qualifying in 2001 and 2002, from one medical school in the UK, in their first three months following medical graduation. RESULTS: Most PRHOs reported positive experiences for their inclusion as a full member of their first ward teams. This contributed to their increasing confidence and competence in this early period of career transition. However, a number of organisational barriers were identified, e.g. incomplete teams, shift work, which produced problems in their integration for one third of newly qualified doctors. CONCLUSION: Recently introduced policies, intended to improve the working lives of newly qualified doctors have produced both benefits and unintended adverse impacts on PRHOs. The changes of the new PRHO Foundation programme will have further impact. Foundation doctors may need to relate to wider teams with more interaction and less protection. Such changes will need to be managed carefully to protect the PRHO at a vulnerable time
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