1,313 research outputs found
Inclination-dependent spectral and timing properties in transient black hole X-ray binaries
We use a simple one-dimensional parameterisation of timing properties to show
that hard and hard-intermediate state transient black hole X-ray binaries with
the same power-spectral shape have systematically harder X-ray power-law
emission in higher-inclination systems. We also show that the power-spectral
shape and amplitude of the broadband noise (with low-frequency quasi-periodic
oscillations, QPOs, removed) is independent of inclination, confirming that it
is well-correlated with the intrinsic structure of the emitting regions and
that the "type C" QPO, which is inclination-dependent, has a different origin
to the noise, probably geometric. Our findings suggest that the power-law
emission originates in a corona which is flattened in the plane of the disc,
and not in a jet-like structure which would lead to softer spectra at higher
inclinations. However, there is tentative evidence that the
inclination-dependence of spectral shape breaks down deeper into the hard
state. This suggests either a change in the coronal geometry and possible
evidence for contribution from jet emission, or alternatively an even more
optically thin flow in these states.Comment: 6 Pages, 4 Figures, accepted as a Letter by MNRA
Power-Colours: Simple X-ray Binary Variability Comparison
We demonstrate a new method of variability classification using observations
of black hole X-ray binaries. Using `power colours' -- ratios of integrated
power in different Fourier frequency bands -- we can clearly differentiate
different canonical black hole states as the objects evolve during outburst. We
analyse (~ 2400) Rossi X-ray Timing Explorer observations of 12 transient low
mass black hole X-ray binaries and find that the path taken around the power
colour-colour diagram as the sources evolve is highly consistent from object to
object. We discuss how the consistency observed in the power colour-colour
diagram between different objects allows for easy state classification based on
only a few observations, and show how the power-spectral shapes can be simply
classified using a single parameter, the power-spectral `hue'. To illustrate
the benefits of our simple model-independent approach, we show that the
persistent high mass X-ray binary Cyg X-1 shows very similar power-spectral
evolution to the transient black hole sources, with the main difference being
caused by a combination of a lack of quasi-periodic oscillations and an excess
of low-frequency power-law noise in the Cyg X-1 power spectra during the
transitional state. We also compare the transient objects to the neutron star
atoll source Aquila X-1, demonstrating that it traces a different path in the
power colour-colour plot. Thus, power-colours could be an effective method to
classify newly discovered X-ray binaries.Comment: 13 pages, 9 figures, accepted by MNRA
The nature of X-ray spectral variability in Seyfert Galaxies
We use a model-independent technique to investigate the nature of the 2-15
keV X-ray spectral variability in four Seyfert galaxies and distinguish between
spectral pivoting and the two-component model for spectral variability. Our
analysis reveals conclusively that the softening of the X-ray continuum with
increasing flux in MCG -6-30-15 and NGC 3516 is a result of summing two
spectral components: a soft varying component (SVC) with spectral shape
independent of flux and a constant hard component (HCC). In contrast, the
spectral variability in NGC 4051 can be well described by simple pivoting of
one component, together with an additional hard constant component. The
spectral variability model for NGC 5506 is ambiguous, due to the smaller range
of fluxes sampled by the data. We investigate the shape of the hard spectral
component in MCG -6-30-15 and find that it appears similar to a pure reflection
spectrum, but requires a large reflected fraction (R>3). We briefly discuss
physical interpretations of the different modes of spectral variability.Comment: Accepted for publication in MNRAS letter
The Ubiquity of the rms-flux relation in Black Hole X-ray Binaries
We have investigated the short term linear relation between the rms
variability and the flux in 1,961 observations of 9 black hole X-ray binaries.
The rms-flux relation for the 1-10 Hz range is ubiquitously observed in any
observation with good variability signal to noise (> 3 % 1-10 Hz fractional
rms). This concurs with results from a previous study of Cygnus X-1 (Gleissner
et. al. 2004), and extends detection of the rms-flux relation to a wider range
of states. We find a strong dependence of the flux intercept of the rms-flux
relation on source state; as the source transitions from the hard state into
the hard intermediate state the intercept becomes strongly positive. We find
little evidence for flux dependence of the broad-band noise within the PSD
shape, excepting a small subset of observations from one object in an anomalous
soft-state. We speculate that the ubiquitous linear rms-flux relation in the
broad band noise of this sample, representing a range of different states and
objects, indicates that its formation mechanism is an essential property of the
luminous accretion flow around black holes.Comment: 12 pages, 6 figures, accepted for publication in MNRA
The curious time lags of PG 1244+026: Discovery of the iron K reverberation lag
High-frequency iron K reverberation lags, where the red wing of the line
responds before the line centroid, are a robust signature of relativistic
reflection off the inner accretion disc. In this letter, we report the
discovery of the Fe K lag in PG 1244+026 from ~120 ks of data (1 orbit of the
XMM-Newton telescope). The amplitude of the lag with respect to the continuum
is 1000 s at a frequency of ~1e-4 Hz. We also find a possible
frequency-dependence of the line: as we probe higher frequencies (i.e. shorter
timescales from a smaller emitting region) the Fe K lag peaks at the red wing
of the line, while at lower frequencies (from a larger emitting region) we see
the dominant reflection lag from the rest frame line centroid. The mean energy
spectrum shows a strong soft excess, though interestingly, there is no
indication of a soft lag. Given that this source has radio emission and it has
little reported correlated variability between the soft excess and the hard
band, we explore one possible explanation in which the soft excess in this
source is dominated by the steep power-law like emission from a jet, and that a
corona (or base of the jet) irradiates the inner accretion disc, creating the
blurred reflection features evident in the spectrum and the lag. General
Relativistic ray-tracing models fit the Fe K lag well, with the best-fit giving
a compact X-ray source at a height of 5 gravitational radii and a black hole
mass of 1.3e7 Msun.Comment: 6 pages, 6 figures, resubmitted to MNRAS after moderate revisions.
This paper focuses on the discovery of the Fe K reverberation lag in PG
1244+026. We point the interested reader to Alston, Done & Vaughan (See
today: arXiv:submit/0851673), which focuses on the soft lags in this sourc
Revealing the X-ray source in IRAS 13224-3809 through flux-dependent reverberation lags
IRAS 13224-3809 was observed in 2011 for 500 ks with the XMM-Newton
observatory. We detect highly significant X-ray lags between soft (0.3 - 1 keV)
and hard (1.2 - 5 keV) energies. The hard band lags the soft at low frequencies
(i.e. hard lag), while the opposite (i.e. soft lag) is observed at high
frequencies. In this paper, we study the lag during flaring and quiescent
periods. We find that the frequency and absolute amplitude of the soft lag is
different during high-flux and low-flux periods. During the low flux intervals,
the soft lag is detected at higher frequencies and with smaller amplitude.
Assuming that the soft lag is associated with the light travel time between
primary and reprocessed emission, this behaviour suggests that the X-ray source
is more compact during low-flux intervals, and irradiates smaller radii of the
accretion disc (likely because of light bending effects). We continue with an
investigation of the lag dependence on energy, and find that isolating the
low-flux periods reveals a strong lag signature at the Fe K line energy,
similar to results found using 1.3 Ms of data on another well known Narrow-Line
Seyfert I galaxy, 1H0707-495.Comment: 6 pages, 8 figures, accepted for publication in MNRA
Short term X-ray rms variability of Cyg X-1
A linear dependence of the amplitude of broadband noise variability on flux
for GBHC and AGN has been recently shown by Uttley & McHardy (2001). We present
the long term evolution of this rms-flux-relation for Cyg X-1 as monitored from
1998-2002 with RXTE. We confirm the linear relationship in the hard state and
analyze the evolution of the correlation for the period of 1996-2002. In the
intermediate and the soft state, we find considerable deviations from the
otherwise linear relationship. A possible explanation for the rms-flux-relation
is a superposition of local mass accretion rate variations.Comment: 3 pages, 3 figures, Proceedings of the 4th Microquasar Workshop, eds.
Ph Durouchoux, Y. Fuchs and J. Rodriguez, published by the Center for Space
Physics: Kolkat
X-ray reverberation around accreting black holes
Luminous accreting stellar mass and supermassive black holes produce
power-law continuum X-ray emission from a compact central corona. Reverberation
time lags occur due to light travel time-delays between changes in the direct
coronal emission and corresponding variations in its reflection from the
accretion flow. Reverberation is detectable using light curves made in
different X-ray energy bands, since the direct and reflected components have
different spectral shapes. Larger, lower frequency, lags are also seen and are
identified with propagation of fluctuations through the accretion flow and
associated corona. We review the evidence for X-ray reverberation in active
galactic nuclei and black hole X-ray binaries, showing how it can be best
measured and how it may be modelled. The timescales and energy-dependence of
the high frequency reverberation lags show that much of the signal is
originating from very close to the black hole in some objects, within a few
gravitational radii of the event horizon. We consider how these signals can be
studied in the future to carry out X-ray reverberation mapping of the regions
closest to black holes.Comment: 72 pages, 32 figures. Accepted for publication in The Astronomy and
Astrophysics Review. Corrected for mostly minor typos, but in particular
errors are corrected in the denominators of the covariance and rms spectrum
error equations (Eqn. 14 and 15
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