7,143 research outputs found
Broad-band X-ray spectral evolution of GX 339-4 during a state transition
We report on X-ray and soft gamma-ray observations of the black-hole
candidate GX 339-4 during its 2007 outburst, performed with the RXTE and
INTEGRAL satellites. The hardness-intensity diagram of all RXTE/PCA data
combined shows a q-shaped track similar to that observed in previous
outbursts.The evolution in the diagram suggested that a transition from
hard-intermediate state to soft-intermediate state occurred, simultaneously
with INTEGRAL observations performed in March. The transition is confirmed by
the timing analysis presented in this work, which reveals that a weak type-A
quasi-periodic oscillation (QPO) replaces a strong type-C QPO. At the same
time, spectral analysis shows that the flux of the high-energy component shows
a significant decrease in its flux. However, we observe a delay (roughly one
day) between variations of the spectral parameters of the high-energy component
and changes in the flux and timing properties. The changes in the high-energy
component can be explained either in terms the high-energy cut-off or in terms
of a variations in the reflection component. We compare our results with those
from a similar transition during the 2004 outburst of GX 339-4.Comment: 8 pages, 6 figures, accepted for publication in MNRAS Main Journa
Radio and X-ray observations during the outburst decay of the Black Hole Candidate XTE J1908+094
Obtaining simultaneous radio and X-ray data during the outburst decay of soft
X-ray transients is a potentially important tool to study the disc - jet
connection. Here we report results of the analysis of (nearly) simultaneous
radio (VLA or WSRT) and Chandra X-ray observations of XTE J1908+094 during the
last part of the decay of the source after an outburst. The limit on the index
of a radio - X-ray correlation we find is consistent with the value of 0.7
which was found for other black hole candidates in the low/hard state.
Interestingly, the limit we find seems more consistent with a value of 1.4
which was recently shown to be typical for radiatively efficient accretion flow
models. We further show that when the correlation-index is the same for two
sources one can use the differences in normalisation in the radio - X-ray flux
correlation to estimate the distance towards the sources if the distance of one
of them is accurately known (assuming black hole spin and mass and jet Lorentz
factor differences are unimportant or minimal). Finally, we observed a strong
increase in the rate of decay of the X-ray flux. Between March 23, 2003 and
April 19, 2003 the X-ray flux decayed with a factor ~5 whereas between April
19, 2003 and May 13, 2003, the X-ray flux decreased by a factor ~750. The
source (0.5-10 keV) luminosity at the last Chandra observation was L~3x10^32
(d/8.5 kpc)^2 erg s^-1.Comment: 7 pages, 3 figures, accepted for publication by MNRA
Correlated X-ray and Optical Variability in V404 Cyg in Quiescence
We report simultaneous X-ray and optical observations of V404 Cyg in
quiescence. The X-ray flux varied dramatically by a factor of >20 during a 60ks
observation. X-ray variations were well correlated with those in Halpha,
although the latter include an approximately constant component as well.
Correlations can also be seen with the optical continuum, although these are
less clear. We see no large lag between X-ray and optical line variations; this
implies they are causally connected on short timescales. As in previous
observations, Halpha flares exhibit a double-peaked profile suggesting emission
distributed across the accretion disk. The peak separation is consistent with
material extending outwards to at least the circularization radius. The prompt
response in the entire Halpha line confirms that the variability is powered by
X-ray (and/or EUV) irradiation.Comment: 5 pages; Accepted for publication in the Astrophysical Journal
Letter
Radio emission and jets from microquasars
To some extent, all Galactic binary systems hosting a compact object are
potential `microquasars', so much as all galactic nuclei may have been quasars,
once upon a time. The necessary ingredients for a compact object of stellar
mass to qualify as a microquasar seem to be: accretion, rotation and magnetic
field. The presence of a black hole may help, but is not strictly required,
since neutron star X-ray binaries and dwarf novae can be powerful jet sources
as well. The above issues are broadly discussed throughout this Chapter, with a
a rather trivial question in mind: why do we care? In other words: are jets a
negligible phenomenon in terms of accretion power, or do they contribute
significantly to dissipating gravitational potential energy? How do they
influence their surroundings? The latter point is especially relevant in a
broader context, as there is mounting evidence that outflows powered by
super-massive black holes in external galaxies may play a crucial role in
regulating the evolution of cosmic structures. Microquasars can also be thought
of as a form of quasars for the impatient: what makes them appealing, despite
their low number statistics with respect to quasars, are the fast variability
time-scales. In the first approximation, the physics of the jet-accretion
coupling in the innermost regions should be set by the mass/size of the
accretor: stellar mass objects vary on 10^5-10^8 times shorter time-scales,
making it possible to study variable accretion modes and related ejection
phenomena over average Ph.D. time-scales. [Abridged]Comment: 28 pages, 13 figures, To appear in Belloni, T. (ed.): The Jet
Paradigm - From Microquasars to Quasars, Lect. Notes Phys. 794 (2009
The first accurate parallax distance to a black hole
Using astrometric VLBI observations, we have determined the parallax of the
black hole X-ray binary V404 Cyg to be 0.418 +/- 0.024 milliarcseconds,
corresponding to a distance of 2.39 +/- 0.14 kpc, significantly lower than the
previously accepted value. This model-independent estimate is the most accurate
distance to a Galactic stellar-mass black hole measured to date. With this new
distance, we confirm that the source was not super-Eddington during its 1989
outburst. The fitted distance and proper motion imply that the black hole in
this system likely formed in a supernova, with the peculiar velocity being
consistent with a recoil (Blaauw) kick. The size of the quiescent jets inferred
to exist in this system is less than 1.4 AU at 22 GHz. Astrometric observations
of a larger sample of such systems would provide useful insights into the
formation and properties of accreting stellar-mass black holes.Comment: Accepted for publication in ApJ Letters. 6 pages, 2 figure
A Low-Flux State in IRAS 00521-7054 seen with NuSTAR and XMM-Newton: Relativistic Reflection and an Ultrafast Outflow
We present results from a deep, coordinated -+
observation of the Seyfert 2 galaxy IRAS 00521-7054. The data provide
the first detection of this source in high-energy X-rays ( keV), and
the broadband data show this to be a highly complex source which exhibits
relativistic reflection from the inner accretion disc, further reprocessing by
more distant material, neutral absorption, and evidence for ionised absorption
in an extreme, ultrafast outflow (). Based on lamppost
disc reflection models, we find evidence that the central supermassive black
hole is rapidly rotating (), consistent with previous estimates from
the profile of the relativistic iron line, and that the accretion disc is
viewed at a fairly high inclination (). Based on extensive
simulations, we find the ultrafast outflow is detected at 4
significance (or greater). We also estimate that the extreme outflow should be
sufficient to power galaxy-scale feedback, and may even dominate the energetics
of the total output from the system.Comment: 12 pages, 8 figures; accepted for publication in MNRA
The radio spectrum of a quiescent stellar mass black hole
Observations of V404 Cyg performed with the Westerbork Synthesis Radio
Telescope at four frequencies, over the interval 1.4-8.4 GHz, have provided us
with the first broadband radio spectrum of a `quiescent' stellar mass black
hole. The measured mean flux density is of 0.35 mJy, with a spectral index
alpha=+ 0.09\pm0.19$ (such that S_nu \propto nu^{alpha}). Synchrotron emission
from an inhomogeneous partially self-absorbed outflow of plasma accounts for
the flat/inverted radio spectrum, in analogy with hard state black hole X-ray
binaries, indicating that a steady jet is being produced between a few 10^{-6}
and a few per cent of the Eddington X-ray luminosity.Comment: accepted for publication in MNRA
A Full Characterisation of the Supermassive Black Hole in IRAS 09149-6206
We present new broadband X-ray observations of the type-I Seyfert galaxy IRAS
09149-6206, taken in 2018 with -, and . The source
is highly complex, showing a classic 'warm' X-ray absorber, additional
absorption from highly ionised iron, strong relativistic reflection from the
innermost accretion disc and further reprocessing by more distant material. By
combining X-ray timing and spectroscopy, we have been able to fully
characterise the supermassive black hole in this system, constraining both its
mass and - for the first time - its spin. The mass is primarily determined by
X-ray timing constraints on the break frequency seen in the power spectrum, and
is found to be (1
uncertainties). This is in good agreement with previous estimates based on the
H and H line widths, and implies that IRAS 09149-6206 is
radiating at close to (but still below) its Eddington luminosity. The spin is
constrained via detailed modelling of the relativistic reflection, and is found
to be (90% confidence), adding IRAS 09149-6206 to
the growing list of radio-quiet AGN that host rapidly rotating black holes. The
outflow velocities of the various absorption components are all relatively
modest (), implying these are unlikely to drive
significant galaxy-scale AGN feedback.Comment: 19 pages, 15 figures, accepted for publication in MNRA
The black hole candidate MAXIJ1659-152 in and towards quiescence in X-ray and radio
In this paper we report on Expanded Very Large Array radio and Chandra and
Swift X-ray observations of the outburst decay of the transient black hole
candidate MAXI J1659-152 in 2011. We discuss the distance to the source taking
the high inclination into account and we conclude that the source distance is
probably 6+-2 kpc. The lowest observed flux corresponds to a luminosity of
2x10^31 (d/6 kpc)^2 erg/s This, together with the orbital period of 2.4 hr
reported in the literature, suggests that the quiescent X-ray luminosity is
higher than predicted on the basis of the orbital period -- quiescent X-ray
luminosity relationship. The relation between the accretion and ejection
mechanisms can be studied using the observed correlation between the radio and
X-ray luminosities as these evolve over an outburst. We determine the behaviour
of MAXI J1659-152 in the radio -- X-ray diagram at low X-ray luminosities using
the observations reported in this paper and at high X-ray luminosities using
values reported in the literature. At high X-ray luminosities the source lies
closer to the sources that follow a correlation index steeper than 0.6-0.7.
However, when compared to other sources that follow a steeper correlation
index, the X-ray luminosity in MAXI J1659-152 is also lower. The latter can
potentially be explained by the high inclination of MAXI J1659-152 if the X-ray
emission comes from close to the source and the radio emission is originating
in a more extended region. However, it is probable that the source was not in
the canonical low-hard state during these radio observations and this may
affect the behaviour of the source as well. At intermediate X-ray luminosities
the source makes the transition from the radio underluminous sources in the
direction of the relation traced by the 'standard' correlation similar to what
has been reported for H1743-322. (abridged)Comment: Accepted for publication by MNRAS, 9 pages, 4 figure
- âŠ