26 research outputs found
Discovery of an ~2-h high-frequency X-ray QPO and iron Kα reverberation in the active galaxy MS 2254.9-3712
We report the discovery of a Hz ( hr) X-ray
quasi-periodic oscillation (QPO) in the active galaxy MS 2254.9-3712, using a
ks XMM-Newton observation. The QPO is significantly detected () in the keV band only, connecting its origin with the
primary X-ray power-law continuum. We detect a highly coherent soft lag between
the keV and keV energy bands at the QPO frequency and
at a frequency band in a 3:2 ratio, strongly suggesting the presence of a QPO
harmonic. An iron K reverberation lag is found at the harmonic
frequency, indicating the reflecting material subtends some angle to the
primary continuum, which is modulated by the QPO mechanism. Frequency resolved
spectroscopy reveals the QPO and harmonic to have a hard energy dependence.
These properties of the QPO variability, together with the current black hole
mass estimate, , are consistent
with the QPO originating from the same process as the high frequency QPO
phenomenon observed in black hole X-ray binaries. Principle component analysis
reveals the spectral variability in MS 2254.9-3712 is similar to that of the
active galaxy RE J1034+396, a source which also displays an X-ray QPO. This
suggests a distinct spectral variability pattern for accreting black holes when
in a state where QPOs are present
Revealing the ultrafast outflow in IRAS 13224-3809 through spectral variability
We present an analysis of the long-term X-ray variability of the extreme
narrow-line Seyfert 1 (NLS1) galaxy IRAS 13224-3809 using principal component
analysis (PCA) and fractional excess variability (Fvar) spectra to identify
model-independent spectral components. We identify a series of variability
peaks in both the first PCA component and Fvar spectrum which correspond to the
strongest predicted absorption lines from the ultra-fast outflow (UFO)
discovered by Parker et al. (2017). We also find higher order PCA components,
which correspond to variability of the soft excess and reflection features. The
subtle differences between RMS and PCA results argue that the observed
flux-dependence of the absorption is due to increased ionization of the gas,
rather than changes in column density or covering fraction. This result
demonstrates that we can detect outflows from variability alone, and that
variability studies of UFOs are an extremely promising avenue for future
research
A global look at X-ray time lags in Seyfert galaxies
X-ray reverberation, where light-travel time delays map out the compact geometry around the inner accretion flow in supermassive black holes, has been discovered in several of the brightest, most variable and well-known Seyfert galaxies. In this work, we expand the study of X-ray reverberation to all Seyfert galaxies in the archive above a nominal rms variability and exposure level (a total of 43 sources). Approximately 50 per cent of sources exhibit iron K reverberation, in that the broad iron K emission line responds to rapid variability in the continuum. We also find that on long time-scales, the hard band emission lags behind the soft band emission in 85 per cent of sources. This ‘low-frequency hard lag’ is likely associated with the coronal emission, and so this result suggests that most sources with X-ray variability show intrinsic variability from the nuclear region. We update the known iron K lag amplitude versus black hole mass relation, and find evidence that the height or extent of the coronal source (as inferred by the reverberation time delay) increases with mass accretion rate.EK thanks Ari Laor for interesting discussions on this work and acknowledges support from the International Space Science Institute. This work is based on observations obtained with XMM–Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. EK thanks the Gates Cambridge Scholarship and the Hubble Fellowship Program. Support for Program number HSTHF2-51360.001-A was provided by NASA through a Hubble Fellowship grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. EK, WNA, and ACF acknowledge support from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 312789, StrongGravity. CSR acknowledges support from NASA under grant NNX14AF86G. EMC gratefully acknowledges support from the National Science Foundation through CAREER award number 1351222
XMM–Newton campaign on ultraluminous X-ray source NGC 1313 X-1: wind versus state variability
Most ultraluminous X-ray sources (ULXs) are thought to be powered by neutron stars and black holes accreting beyond the Eddington limit. If the compact object is a black hole or a neutron star with a magnetic field ≲1012 G, the accretion disc is expected to thicken and launch powerful winds driven by radiation pressure. Evidence of such winds has been found in ULXs through the high-resolution spectrometers onboardXMM–Newton, but several unknowns remain, such as the geometry and launching mechanism of these winds. In order to better understand ULX winds and their link to the accretion regime, we have undertaken a major campaign with XMM–Newton to study the ULX NGC 1313 X-1, which is known to exhibit strong emission and absorption features from a mildly relativistic wind. The new observations show clear changes in the wind with a significantly weakened fast component (0.2c) and the rise of a new wind phase which is cooler and slower (0.06–0.08c). We also detect for the first time variability in the emission lines which indicates an origin within the accretion disc or in the wind. We describe the variability of the wind in the framework of variable super-Eddington accretion rate and discuss a possible geometry for the accretion disc
The remarkable X-ray variability of IRAS 13224-3809 - I. The variability process
We present a detailed X-ray timing analysis of the highly variable NLS1
galaxy, IRAS 13224-3809. The source was recently monitored for 1.5 Ms with
XMM-Newton which, combined with 500 ks archival data, makes this the best
studied NLS1 galaxy in X-rays to date. We apply standard time- and
Fourier-domain in order to understand the underlying variability process. The
source flux is not distributed lognormally, as would be expected for accreting
sources. The first non-linear rms-flux relation for any accreting source in any
waveband is found, with . The light
curves exhibit significant strong non-stationarity, in addition to that caused
by the rms-flux relation, and are fractionally more variable at lower source
flux. The power spectrum is estimated down to Hz and consists of
multiple peaked components: a low-frequency break at Hz, with
slope down to low frequencies; an additional component breaking at
Hz. Using the high-frequency break we estimate the black hole
mass , and mass accretion rate
in Eddington units, . The non-stationarity is
manifest in the PSD with the normalisation of the peaked components increasing
with decreasing source flux, as well as the low-frequency peak moving to higher
frequencies. We also detect a narrow coherent feature in the soft band PSD at
mHz, modelled with a Lorentzian the feature has and an
%. We discuss the implication of these results for
accretion of matter onto black holes
Is there a UV/X-ray connection in IRAS 13224-3809?
We present results from the optical, ultraviolet and X-ray monitoring of the NLS1 galaxy IRAS 13224-3809 taken with Swift and XMM-Newton during 2016. IRAS 13224-3809 is the most variable bright AGN in the X-ray sky and shows strong X-ray reflection, implying that the X-rays strongly illuminate the inner disc. Therefore, it is a good candidate to study the relationship between coronal X-ray and disc UV emission. However, we find no correlation between the X-ray and UV flux over the available ~40 day monitoring, despite the presence of strong X-ray variability and the variable part of the UV spectrum being consistent with irradiation of a standard thin disc. This means either that the X-ray flux which irradiates the UV emitting outer disc does not correlate with the X-ray flux in our line of sight and/or that another process drives the majority of the UV variability. The former case may be due to changes in coronal geometry, absorption or scattering between the corona and the disc
Black hole spin: theory and observation
In the standard paradigm, astrophysical black holes can be described solely
by their mass and angular momentum - commonly referred to as `spin' - resulting
from the process of their birth and subsequent growth via accretion. Whilst the
mass has a standard Newtonian interpretation, the spin does not, with the
effect of non-zero spin leaving an indelible imprint on the space-time closest
to the black hole. As a consequence of relativistic frame-dragging, particle
orbits are affected both in terms of stability and precession, which impacts on
the emission characteristics of accreting black holes both stellar mass in
black hole binaries (BHBs) and supermassive in active galactic nuclei (AGN).
Over the last 30 years, techniques have been developed that take into account
these changes to estimate the spin which can then be used to understand the
birth and growth of black holes and potentially the powering of powerful jets.
In this chapter we provide a broad overview of both the theoretical effects of
spin, the means by which it can be estimated and the results of ongoing
campaigns.Comment: 55 pages, 5 figures. Published in: "Astrophysics of Black Holes -
From fundamental aspects to latest developments", Ed. Cosimo Bambi, Springer:
Astrophysics and Space Science Library. Additional corrections mad
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Ultraviolet and X-ray variability of active galactic nuclei with Swift
We analyse a sample of 21 active galactic nuclei (AGN) using data from the
Swift satellite to study the variability properties of the population in the
X-ray, UV and optical band. We find that the variable part of the UV-optical
emission has a spectrum consistent with a powerlaw, with an average index of
, as would be expected from central illumination of a thin disc
(index of -7/3). We also calculate the slope of a powerlaw from UV to X-ray
variable emission, ; the average for this sample is
. The anticorrelation of with the UV luminosity, , previously found in the average
emission is also present in the variable part: .
Correlated variability between the emission in X-rays and UV is detected
significantly for 9 of the 21 sources. All these cases are consistent with the
UV lagging the X-rays, as would be seen if the correlated UV variations were
produced by the reprocessing of X-ray emission. The observed UV lags are
tentatively longer than expected for a standard thin disc.ACF, AML and DJKB acknowledge support from the ERC Advanced Grant FEEDBACK 340442. WNA acknowledges support from the European Union Seventh Framework Programme (FP7/2013-2017) under grant agreement n.312789, StrongGravity. DB acknowledges an STFC studentship. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester.This is the final version of the article. It first appeared from Oxford University Press via https://doi.org/10.1093/mnras/stw248
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Detection of a QPO in five XMM-Newton observations of RE J1034+396
The X-ray quasi-periodic oscillation (QPO) at Hz in
RE J1034+396 has been robustly observed in the 0.2-10 keV band of one
ks XMM-Newton observation, but was not detected in subsequent observations.
Here, we investigate the power spectral density (PSD) of 8 archival XMM-Newton
observations of RE J1034+396, and search for the presence of QPOs in three
energy bands: soft (0.3-0.8 keV); hard (1.0-4.0 keV) and total (0.2-10.0 keV).
We find a significant detection of a QPO feature in the hard-band PSD of 5 low
flux/spectrally-harder observations. The QPO frequency has remained persistent
at Hz over years of observations, though it
is no longer detected in the soft band, except in the original observation.
This result increases the duration where the QPO is present by a factor of
three (now ks), allowing for a better understanding of the QPO
phenomenon observed in both Active Galactic Nuclei (AGN) and black hole X-ray
binaries (BHBs)