301 research outputs found
A close-pair binary in a distant triple supermassive black-hole system
Galaxies are believed to evolve through merging, which should lead to
multiple supermassive black holes in some. There are four known triple black
hole systems, with the closest pair being 2.4 kiloparsecs apart (the third
component is more distant at 3 kiloparsecs), which is far from the
gravitational sphere of influence of a black hole with mass 10
M (about 100 parsecs). Previous searches for compact black hole systems
concluded that they were rare, with the tightest binary system having a
separation of 7 parsecs. Here we report observations of a triple black hole
system at redshift z=0.39, with the closest pair separated by 140
parsecs. The presence of the tight pair is imprinted onto the properties of the
large-scale radio jets, as a rotationally-symmetric helical modulation, which
provides a useful way to search for other tight pairs without needing extremely
high resolution observations. As we found this tight pair after searching only
six galaxies, we conclude that tight pairs are more common than hitherto
believed, which is an important observational constraint for low-frequency
gravitational wave experiments.Comment: 21 pages, 6 figures. Published online by Nature on 25 June 2014.
Extremely minor differences with published version exis
Inclination and relativistic effects in the outburst evolution of black hole transients
We have systematically studied the effect of the orbital inclination in the
outburst evolution of black hole transients. We have included all the systems
observed by the Rossi X-ray timing explorer in which the thermal, accretion
disc component becomes strongly dominant at some point of the outburst.
Inclination is found to modify the shape of the tracks that these systems
display in the colour/luminosity diagrams traditionally used for their study.
Black hole transients seen at low inclination reach softer spectra and their
accretion discs look cooler than those observed closer to edge-on. This
difference can be naturally explained by considering inclination dependent
relativistic effects on accretion discs.Comment: 8 pages, 4 figures, accepted for publication in MNRA
Formation of the compact jets in the black hole GX 339-4
Galactic black hole binaries produce powerful outflows with emit over almost
the entire electromagnetic spectrum. Here, we report the first detection with
the Herschel observatory of a variable far-infrared source associated with the
compact jets of the black hole transient GX 339-4 during the decay of its
recent 2010-2011 outburst, after the transition to the hard state. We also
outline the results of very sensitive radio observations conducted with the
Australia Telescope Compact Array, along with a series of near-infrared,
optical (OIR) and X-ray observations, allowing for the first time the
re-ignition of the compact jets to be observed over a wide range of
wavelengths. The compact jets first turn on at radio frequencies with an
optically thin spectrum that later evolves to optically thick synchrotron
emission. An OIR reflare is observed about ten days after the onset of radio
and hard X-ray emission, likely reflecting the necessary time to build up
enough density, as well as to have acceleration (e.g. through shocks) along an
extended region in the jets. The Herschel measurements are consistent with an
extrapolation of the radio inverted power-law spectrum, but they highlight a
more complex radio to OIR spectral energy distribution for the jets.Comment: Accepted for publication in MNRAS Letter, 6 pages, 3 Figures + 1
online Tabl
Ubiquitous equatorial accretion disc winds in black hole soft states
High resolution spectra of Galactic Black Holes (GBH) reveal the presence of
highly ionised absorbers. In one GBH, accreting close to the Eddington limit
for more than a decade, a powerful accretion disc wind is observed to be
present in softer X-ray states and it has been suggested that it can carry away
enough mass and energy to quench the radio jet. Here we report that these
winds, which may have mass outflow rates of the order of the inner accretion
rate or higher, are an ubiquitous component of the jet-free soft states of all
GBH. We furthermore demonstrate that these winds have an equatorial geometry
with opening angles of few tens of degrees, and so are only observed in sources
in which the disc is inclined at a large angle to the line of sight. The
decrease in Fe XXV / Fe XXVI line ratio with Compton temperature, observed in
the soft state, suggests a link between higher wind ionisation and harder
spectral shapes. Although the physical interaction between the wind, accretion
flow and jet is still not fully understood, the mass flux and power of these
winds, and their presence ubiquitously during the soft X-ray states suggests
they are fundamental components of the accretion phenomenon.Comment: Accepted for publication in MNRAS Letter
Traces of past activity in the Galactic Centre
The Milky Way centre hosts a supermassive Black Hole (BH) with a mass of
~4*10^6 M_Sun. Sgr A*, its electromagnetic counterpart, currently appears as an
extremely weak source with a luminosity L~10^-9 L_Edd. The lowest known
Eddington ratio BH. However, it was not always so; traces of "glorious" active
periods can be found in the surrounding medium. We review here our current view
of the X-ray emission from the Galactic Center (GC) and its environment, and
the expected signatures (e.g. X-ray reflection) of a past flare. We discuss the
history of Sgr A*'s past activity and its impact on the surrounding medium. The
structure of the Central Molecular Zone (CMZ) has not changed significantly
since the last active phase of Sgr A*. This relic torus provides us with the
opportunity to image the structure of an AGN torus in exquisite detail.Comment: Invited refereed review. Chapter of the book: "Cosmic ray induced
phenomenology in star forming environments" (eds. Olaf Reimer and Diego F.
Torres
An overview of jets and outflows in stellar mass black holes
In this book chapter, we will briefly review the current empirical
understanding of the relation between accretion state and and outflows in
accreting stellar mass black holes. The focus will be on the empirical
connections between X-ray states and relativistic (`radio') jets, although we
are now also able to draw accretion disc winds into the picture in a systematic
way. We will furthermore consider the latest attempts to measure/order jet
power, and to compare it to other (potentially) measurable quantities, most
importantly black hole spin.Comment: Accepted for publication in Space Science Reviews. Also to appear in
the Space Sciences Series of ISSI - The Physics of Accretion on to Black
Holes (Springer Publisher
Evidence for a compact jet dominating the broadband spectrum of the black hole accretor XTE J1550-564
[abridged] The black hole X-ray binary XTE J1550-564 was monitored
extensively at X-ray, optical and infrared wavelengths throughout its outburst
in 2000. We show that it is possible to separate the optical/near-infrared
(OIR) jet emission from the OIR disc emission. Focussing on the jet component,
we find that as the source fades in the X-ray hard state, the OIR jet emission
has a spectral index consistent with optically thin synchrotron emission (alpha
~ -0.6 to -0.7, where F_nu \propto nu^alpha). This jet emission is tightly and
linearly correlated with the X-ray flux; L_OIR,jet \propto L_X^(0.98 +- 0.08)
suggesting a common origin. This is supported by the OIR, X-ray and OIR to
X-ray spectral indices being consistent with a single power law (alpha =
-0.73). Ostensibly the compact, synchrotron jet could therefore account for ~
100 % of the X-ray flux at low luminosities in the hard state. At the same
time, (i) an excess is seen over the power law decay of the X-ray flux at the
point in which the jet would start to dominate, (ii) the X-ray spectrum
slightly softens, which seems to be due to a high energy cut-off or break
shifting to a lower energy, and (iii) the X-ray rms variability increases. This
may be the strongest evidence to date of synchrotron emission from the compact,
steady jet dominating the X-ray flux of an X-ray binary. For XTE J1550-564,
this is likely to occur within the luminosity range ~ (2 e-4 - 2 e-3) L_Edd on
the hard state decline of this outburst. However, on the hard state rise of the
outburst and initially on the hard state decline, the synchrotron jet can only
provide a small fraction (~ a few per cent) of the X-ray flux. Both thermal
Comptonization and the synchrotron jet can therefore produce the hard X-ray
power law in accreting black holes.Comment: MNRAS accepted, 12 pages, 9 figure
The balance of power: accretion and feedback in stellar mass black holes
In this review we discuss the population of stellar-mass black holes in our
galaxy and beyond, which are the extreme endpoints of massive star evolution.
In particular we focus on how we can attempt to balance the available accretion
energy with feedback to the environment via radiation, jets and winds,
considering also possible contributions to the energy balance from black hole
spin and advection. We review quantitatively the methods which are used to
estimate these quantities, regardless of the details of the astrophysics close
to the black hole. Once these methods have been outlined, we work through an
outburst of a black hole X-ray binary system, estimating the flow of mass and
energy through the different accretion rates and states. While we focus on
feedback from stellar mass black holes in X-ray binary systems, we also
consider the applicability of what we have learned to supermassive black holes
in active galactic nuclei. As an important control sample we also review the
coupling between accretion and feedback in neutron stars, and show that it is
very similar to that observed in black holes, which strongly constrains how
much of the astrophysics of feedback can be unique to black holes.Comment: To be published in Haardt et al. Astrophysical Black Holes. Lecture
Notes in Physics. Springer 201
A tool to separate optical/infrared disc and jet emission in Xâray transient outbursts: the colourâmagnitude diagrams of XTE J1550â564
It is now established that thermal disc emission and nonâthermal jet emission can both play a role at optical/infrared (OIR) wavelengths in Xâray transients. The spectra of the jet and disc components differ, as do their dependence on mass accretion properties. Here we demonstrate that the OIR colourâmagnitude diagrams (CMDs) of the evolution of the Xâray transient XTE J1550â564 in outburst can be used to separate the disc from the jet. Monitoring in two wavebands is all that is required. This outburst in 2000 was well studied, and both disc and jet were known to contribute. During the outburst the data follow a wellâdefined path in the CMD, describing what would be expected from a heated singleâtemperature blackbody of approximately constant area, except when the data appear redder than this track. This is due to the nonâthermal jet component which dominates the OIR moreso during hard Xâray states at high luminosities, and which is quenched in the soft state. The CMD therefore shows stateâdependent hysteresis, in analogy with (but not identical to) the wellâestablished Xâray hardnessâintensity diagram of black hole transients. The blackbody originates in the Xâray illuminated, likely unwarped, outer accretion disc. We show that the CMD can be approximately reproduced by a model that assumes various correlations between Xâray, OIR disc and OIR jet fluxes. We find evidence for the OIR jet emission to be decoupled from the disc near the peak of the hard state.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/86884/1/j.1365-2966.2011.19204.x.pd
Quality Indicators for Colonoscopy Procedures: A Prospective Multicentre Method for Endoscopy Units
BACKGROUND AND AIMS: Healthcare professionals are required to conduct quality control of endoscopy procedures, and yet there is no standardised method for assessing quality. The topic of the present study was to validate the applicability of the procedure in daily practice, giving physicians the ability to define areas for continuous quality improvement. METHODS: In ten endoscopy units in France, 200 patients per centre undergoing colonoscopy were enrolled in the study. An evaluation was carried out based on a prospectively developed checklist of 10 quality-control indicators including five dependent upon and five independent of the colonoscopy procedure. RESULTS: Of the 2000 procedures, 30% were done at general hospitals, 20% at university hospitals, and 50% in private practices. The colonoscopies were carried out for a valid indication for 95.9% (range 92.5-100). Colon preparation was insufficient in 3.7% (range 1-10.5). Colonoscopies were successful in 95.3% (range 81-99). Adenoma detection rate was 0.31 (range 0.17-0.45) in successful colonoscopies. CONCLUSION: This tool for evaluating the quality of colonoscopy procedures in healthcare units is based on standard endoscopy and patient criteria. It is an easy and feasible procedure giving the ability to detect suboptimal practice and differences between endoscopy-units. It will enable individual units to assess the quality of their colonoscopy techniques
- âŠ