1,547 research outputs found
From Multiwavelength to Mass Scaling: Accretion and Ejection in Microquasars and AGN
A solid theoretical understanding of how inflowing, accreting plasma around
black holes and other compact objects gives rise to outflowing winds and jets
is still lacking, despite decades of observations. The fact that similar
processes and morphologies are observed in both X-ray binaries as well as
active galactic nuclei has led to suggestions that the underlying physics could
scale with black hole mass, which could provide a new handle on the problem. In
the last decade, simultaneous broadband campaigns of the fast-varying X-ray
binaries particularly in their microquasar state have driven the development
of, and in some cases altered, our ideas about the inflow/outflow connection in
accreting black holes. Specifically the discovery of correlations between the
radio, infrared and X-ray bands has revealed a remarkable connectivity between
the various emission regions, and argued for a more holistic approach to
tackling questions about accretion. This article reviews the recent major
observational and theoretical advances that focus specifically on the relation
between the two "sides" of the accretion process in black holes, with an
emphasis on how new tools can be derived for comparisons across the mass scale.Comment: 31 pages, 6 figures, To appear in Belloni, T. (ed.): The Jet Paradigm
- From Microquasars to Quasars, Lect. Notes Phys. 794 (2009
X-ray and Radio Monitoring of GX 339-4 and Cyg X-1
Previous work by Motch et al. (1985) suggested that in the low/hard state of
GX339-4, the soft X-ray power-law extrapolated backward in energy agrees with
the IR flux level. Corbel and Fender (2002) later showed that the typical hard
state radio power-law extrapolated forward in energy meets the backward
extrapolated X-ray power-law at an IR spectral break, which was explicitly
observed twice in GX339-4. This has been cited as further evidence that jet
synchrotron radiation might make a significant contribution to the observed
X-rays in the hard state. We explore this hypothesis with a series of
simultaneous radio/X-ray hard state observations of GX339-4. We fit these
spectra with a simple, but remarkably successful, doubly broken power-law model
that indeed requires a spectral break in the IR. For most of these
observations, the break position as a function of X-ray flux agrees with the
jet model predictions. We then examine the radio flux/X-ray flux correlation in
Cyg X-1 through the use of 15 GHz radio data, obtained with the Ryle radio
telescope, and Rossi X-ray Timing Explorer data, from the All Sky Monitor and
pointed observations. We find evidence of `parallel tracks' in the radio/X-ray
correlation which are associated with `failed transitions' to, or the beginning
of a transition to, the soft state. We also find that for Cyg X-1 the radio
flux is more fundamentally correlated with the hard, rather than the soft,
X-ray flux.Comment: To Appear in the Proceedings of "From X-ray Binaries to Quasars:
Black Hole Accretion on All Mass Scales" (Amsterdam, July 2004). Eds. T
Maccarone, R. Fender, L. H
Modeling the X-ray Contribution of X-ray Binary Jets
Astrophysical jets exist in both XRBs and AGN, and seem to share common
features, particularly in the radio. While AGN jets are known to emit X-rays,
the situation for XRB jets is not so clear. Radio jets have been resolved in
several XRBs in the low/hard state, establishing that some form of outflow is
routinely present in this state. Interestingly, the flat-to-inverted radio
synchrotron emission associated with these outflows strongly correlates with
the X-ray emission in several sources, suggesting that the jet plasma plays a
role at higher frequencies. In this same state, there is increasing evidence
for a turnover in the IR/optical where the flat-to-inverted spectrum seems to
connect to an optically thin component extending into the X-rays. We discuss
how jet synchrotron emission is likely to contribute to the X-rays, in addition
to inverse Compton up-scattering, providing a natural explanation for these
correlations and the turnover in the IR/optical band. We present model
parameters for fits to several sources, and address some common misconceptions
about the jet model.Comment: 4 pages, 1 Table, conference proceedings for "The Physics of
Relativistic Jets in the Chandra and XMM Era, Bologna, 2002", Eds. G.
Brunetti, D. E. Harris, R. M. Sambruna & G. Sett
Breaking degeneracy in jet dynamics: multi-epoch joint modelling of the BL Lac PKS 2155-304
Supermassive black holes can launch powerful jets which can be some of the
most luminous multi-wavelength sources; decades after their discovery their
physics and energetics are still poorly understood. The past decade has seen a
dramatic improvement in the quality of available data, but despite this
improvement the semi-analytical modelling of jets has advanced slowly: simple
one-zone models are still the most commonly employed method of interpreting
data, in particular for AGN jets. These models can roughly constrain the
properties of jets but they cannot unambiguously couple their emission to the
launching regions and internal dynamics, which can be probed with simulations.
However, simulations are not easily comparable to observations because they
cannot yet self-consistently predict spectra. We present an advanced
semi-analytical model which accounts for the dynamics of the whole jet,
starting from a simplified parametrization of Relativistic Magnetohydrodynamics
in which the magnetic flux is converted into bulk kinetic energy. To benchmark
the model we fit six quasisimultaneous, multi-wavelength spectral energy
distributions of the BL Lac PKS 2155-304 obtained by the TANAMI program, and we
address the degeneracies inherent to such a complex model by employing a
state-of-the-art exploration of parameter space, which so far has been mostly
neglected in the study of AGN jets. We find that this new approach is much more
effective than a single-epoch fit in providing meaningful constraints on model
parameters.Comment: Accepted for publication on MNRA
Radio / X-ray correlation in the low/hard state of GX 339--4
We present the results of a long-term study of the black hole candidate GX
339-4 using simultaneous radio (from the Australia Telescope Compact Array) and
X-ray (from the Rossi X-ray Timing Explorer and BeppoSAX) observations
performed between 1997 and 2000. We find strong evidence for a correlation
between these two emission regimes that extends over more than three decades in
X-ray flux, down to the quiescence level of GX 339-4. This is the strongest
evidence to date for such strong coupling between radio and X-ray emission. We
discuss these results in light of a jet model that can explain the radio/X-ray
correlation. This could indicate that a significant fraction of the X-ray flux
that is observed in the low-hard state of black hole candidates may be due to
optically thin synchrotron emission from the compact jet.Comment: 8 pages. Accepted for publication in Astronomy & Astrophysics, 200
Exploring Accretion and Disk-Jet Connections in the LLAGN M81*
We report on a year-long effort to monitor the central supermassive black
hole in M81 in the X-ray and radio bands. Using Chandra and the VLA, we
obtained quasi-simultaneous observations of M81* on seven occasions during
2006. The X-ray and radio luminosity of M81* are not strongly correlated on the
approximately 20-day sampling timescale of our observations, which is
commensurate with viscous timescales in the inner flow and orbital timecales in
a radially-truncated disk. This suggests that short-term variations in black
hole activity may not be rigidly governed by the "fundamental plane", but
rather adhere to the plane in a time-averaged sense. Fits to the X-ray spectra
of M81* with bremsstrahlung models give temperatures that are inconsistent with
the outer regions of very simple advection-dominated inflows. However, our
results are consistent with the X-ray emission originating in a transition
region where a truncated disk and advective flow may overlap. We discuss our
results in the context of models for black holes accreting at small fractions
of their Eddington limit, and the fundamental plane of black hole accretion.Comment: Accepted for publication in Ap
A Phase Lag between Disk and Corona in GRMHD Simulations of Precessing Tilted Accretion Disks
In the course of its evolution, a black hole (BH) accretes gas from a wide
range of directions. Given a random accretion event, the typical angular
momentum of an accretion disc would be tilted by 60 relative to
the BH spin. Misalignment causes the disc to precess at a rate that increases
with BH spin and tilt angle. We present the first general-relativistic
magnetohydrodynamic (GRMHD) simulations spanning a full precession period of
highly tilted (60), moderately thin () accretion discs around
a rapidly spinning () BH. While the disc and jets precess in phase,
we find that the corona, sandwiched between the two, lags behind by . For spectral models of BH accretion, the implication is that hard
non-thermal (corona) emission lags behind the softer (disc) emission, thus
potentially explaining some properties of the hard energy lags seen in Type-C
low frequency quasi-periodic oscillations in X-Ray binaries. While strong jets
are unaffected by this disc-corona lag, weak jets stall when encountering the
lagging corona at distances black hole radii. This interaction may
quench large-scale jet formation.Comment: 5 pages, 4 figures, submitted to MNRAS, see YouTube playlist for 3D
renderings:
https://www.youtube.com/playlist?list=PLDO1oeU33GwmwOV_Hp9s7572JdU8JPSS
The millimetre variability of M81* -- Multi-epoch dual frequency mm-observations of the nucleus of M81
There are still many open questions as to the physical mechanisms at work in
Low Luminosity AGN that accrete in the extreme sub-Eddington regime.
Simultaneous multi-wavelength studies have been very successful in constraining
the properties of SgrA*, the extremely sub-Eddington black hole at the centre
of our Milky Way. M81*, the nucleus of the nearby spiral galaxy M81, is an
ideal source to extend the insights obtained on SgrA* toward higher luminosity
AGN. Here we present observations at 3 and 1 mm that were obtained within the
framework of a coordinated,multi-wavelength campaign on M81*. The continuum
emission from M81* was observed during three epochs with the IRAM Plateau de
Bure Interferometer simultaneously at wavelengths of 3 and 1 mm. We present the
first flux measurements of M81* at wavelengths around 1 mm. We find that M81*
is a continuously variable source with the higher variability observed at the
shorter wavelength. Also, the variability at 3 and 1 mm appears to be
correlated. Like SgrA*, M81* appears to display the strongest flux density and
variability in the mm-to-submm regime. There remains still some ambiguity
concerning the exact location of the turnover frequency from optically thick to
optically thin emission. The observed variability time scales point to an upper
size limit of the emitting region of the order 25 Schwarzschild radii. The data
show that M81* is indeed a system with very similar physical properties to
SgrA* and an ideal bridge toward high luminosity AGN. The data obtained clearly
demonstrate the usefulness and, above all, the necessity of simultaneous
multi-wavelength observations of LLAGN.Comment: accepted for publication in A&
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