397 research outputs found
A return to strong radio flaring by Circinus X-1 observed with the Karoo Array Telescope test array KAT-7
Circinus X-1 is a bright and highly variable X-ray binary which displays
strong and rapid evolution in all wavebands. Radio flaring, associated with the
production of a relativistic jet, occurs periodically on a ~17-day timescale. A
longer-term envelope modulates the peak radio fluxes in flares, ranging from
peaks in excess of a Jansky in the 1970s to an historic low of milliJanskys
during the years 1994 to 2007. Here we report first observations of this source
with the MeerKAT test array, KAT-7, part of the pathfinder development for the
African dish component of the Square Kilometre Array (SKA), demonstrating
successful scientific operation for variable and transient sources with the
test array. The KAT-7 observations at 1.9 GHz during the period 13 December
2011 to 16 January 2012 reveal in temporal detail the return to the
Jansky-level events observed in the 1970s. We compare these data to
contemporaneous single-dish measurements at 4.8 and 8.5 GHz with the HartRAO
26-m telescope and X-ray monitoring from MAXI. We discuss whether the overall
modulation and recent dramatic brightening is likely to be due to an increase
in the power of the jet due to changes in accretion rate or changing Doppler
boosting associated with a varying angle to the line of sight.Comment: 7 pages, 5 figures, accepted for publication in MNRAS 14 May 201
Simultaneous mm/X-ray intraday variability in the radio-quiet AGN MCG+08-11-11
Most of the Active Galactic Nuclei (AGN) are radio-quiet (RQ) and,
differently from radio-loud (RL) AGN, do not show signature of large-scale and
powerful jets. The physical origin of their radio emission remains then broadly
unclear. The observation of flat/inverted radio spectra at GHz frequencies
seems to support however the presence of an unresolved synchrotron
self-absorbed region in the close environment of the supermassive black hole.
Its size could be as small as that of the X-ray corona. Since synchrotron self
absorption decreases strongly with frequency, these sources need to be observed
in the millimetric (mm) domain. We report here a 12h simultaneous mm-X-ray
observation of the RQ AGN MCG+08-11-11 by NOEMA and NuSTAR. The mm flux shows a
weak but clear increase along the pointing with a fractional variability of
\%. The 3-10 keV flux of NuSTAR also increases and shows a
fractional variability of \%. A structure function analysis shows a
local maximum in the mm light curve corresponding to 2-3\% of variability on
timescale of seconds (100-300 light crossing time).
Assuming an optically thick mm emitting medium, this translates into an upper
limit of its size of 1300 . The observation of fast variability in
radio-mm and X-ray wavelengths, as well as a similar variability trend, well
support the mm emission to be emitted by a region close, and potentially
related to, the X-ray corona like an outflow/weak jet.Comment: Accepted in A&A Letters. 5 pages main text, 3 pages of appendices, 12
figure
A weak compact jet in a soft state of Cygnus X-1
We present evidence for the presence of a weak compact jet during a soft
X-ray state of Cygnus X-1. Very-high-resolution radio observations were taken
with the VLBA, EVN and MERLIN during a hard-to-soft spectral state change,
showing the hard state jet to be suppressed by a factor of about 3-5 in radio
flux and unresolved to direct imaging observations (i.e. < 1 mas at 4 cm). High
time-resolution X-ray observations with the RXTE-PCA were also taken during the
radio monitoring period, showing the source to make the transition from the
hard state to a softer state (via an intermediate state), although the source
may never have reached the canonical soft state. Using astrometric VLBI
analysis and removing proper motion, parallax and orbital motion signatures,
the residual positions show a scatter of ~0.2 mas (at 4 cm) and ~3 mas (at 13
cm) along the position angle of the known jet axis; these residuals suggest
there is a weak unresolved outflow, with varying size or opacity, during
intermediate and soft X-ray states. Furthermore, no evidence was found for
extended knots or shocks forming within the jet during the state transition,
suggesting the change in outflow rate may not be sufficiently high to produce
superluminal knots.Comment: Accepted in MNRAS; 4 figures and 1 tabl
Radio observations of NGC 6388: an upper limit on the mass of its central black hole
We present the results of deep radio observations with the Australia
Telescope Compact Array (ATCA) of the globular cluster NGC 6388. We show that
there is no radio source detected (with a r.m.s. noise level of 27 uJy) at the
cluster centre of gravity or at the locations of the any of the Chandra X-ray
sources in the cluster. Based on the fundamental plane of accreting black holes
which is a relationship between X-ray luminosity, radio luminosity and black
hole mass, we place an upper limit of 1500 M_sun on the mass of the putative
intermediate-mass black hole located at the centre of NGC 6388. We discuss the
uncertainties of this upper limit and the previously suggested black hole mass
of 5700 M_sun based on surface density profile analysis.Comment: 6 pages, 2 figures, accepted for publication in MNRA
The infrared/X-ray correlation of GX 339-4: Probing hard X-ray emission in accreting black holes
GX 339-4 has been one of the key sources for unravelling the accretion
ejection coupling in accreting stellar mass black holes. After a long period of
quiescence between 1999 and 2002, GX 339-4 underwent a series of 4 outbursts
that have been intensively observed by many ground based observatories [radio,
infrared(IR), optical] and satellites (X-rays). Here, we present results of
these broad-band observational campaigns, focusing on the optical-IR
(OIR)/X-ray flux correlations over the four outbursts. We found tight OIR/X-ray
correlations over four decades with the presence of a break in the IR/X-ray
correlation in the hard state. This correlation is the same for all four
outbursts. This can be interpreted in a consistent way by considering a
synchrotron self-Compton origin of the X-rays in which the break frequency
varies between the optically thick and thin regime of the jet spectrum. We also
highlight the similarities and differences between optical/X-ray and IR/X-ray
correlations which suggest a jet origin of the near-IR emission in the hard
state while the optical is more likely dominated by the blackbody emission of
the accretion disc in both hard and soft state. However we find a non
negligible contribution of 40 per cent of the jet emission in the V-band during
the hard state.
We finally concentrate on a soft-to-hard state transition during the decay of
the 2004 outburst by comparing the radio, IR, optical and hard X-rays light
curves. It appears that unusual delays between the peak of emission in the
different energy domains may provide some important constraints on jet
formation scenario.Comment: Accepted for publication in MNRAS, 12 pages, 8 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
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
The XMM-Newton serendipitous survey. VII. The third XMM-Newton serendipitous source catalogue
Thanks to the large collecting area (3 x ~1500 cm at 1.5 keV) and wide
field of view (30' across in full field mode) of the X-ray cameras on board the
European Space Agency X-ray observatory XMM-Newton, each individual pointing
can result in the detection of hundreds of X-ray sources, most of which are
newly discovered. Recently, many improvements in the XMM-Newton data reduction
algorithms have been made. These include enhanced source characterisation and
reduced spurious source detections, refined astrometric precision, greater net
sensitivity and the extraction of spectra and time series for fainter sources,
with better signal-to-noise. Further, almost 50\% more observations are in the
public domain compared to 2XMMi-DR3, allowing the XMM-Newton Survey Science
Centre (XMM-SSC) to produce a much larger and better quality X-ray source
catalogue. The XMM-SSC has developed a pipeline to reduce the XMM-Newton data
automatically and using improved calibration a new catalogue version has been
produced from XMM-Newton data made public by 2013 Dec. 31 (13 years of data).
Manual screening ensures the highest data quality. This catalogue is known as
3XMM. In the latest release, 3XMM-DR5, there are 565962 X-ray detections
comprising 396910 unique X-ray sources. For the 133000 brightest sources,
spectra and lightcurves are provided. For all detections, the positions on the
sky, a measure of the quality of the detection, and an evaluation of the X-ray
variability is provided, along with the fluxes and count rates in 7 X-ray
energy bands, the total 0.2-12 keV band counts, and four hardness ratios. To
identify the detections, a cross correlation with 228 catalogues is also
provided for each X-ray detection. 3XMM-DR5 is the largest X-ray source
catalogue ever produced. Thanks to the large array of data products, it is an
excellent resource in which to find new and extreme objects.Comment: 23 pages, version accepted for publication in A&
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