16 research outputs found
Using principal component analysis to understand the variability of PDS 456
We present a spectral-variability analysis of the low-redshift quasar PDS 456
using principal component analysis. In the XMM-Newton data, we find a strong
peak in the first principal component at the energy of the Fe absorption line
from the highly blueshifted outflow. This indicates that the absorption feature
is more variable than the continuum, and that it is responding to the
continuum. We find qualitatively different behaviour in the Suzaku data, which
is dominated by changes in the column density of neutral absorption. In this
case, we find no evidence of the absorption produced by the highly ionized gas
being correlated with this variability. Additionally, we perform simulations of
the source variability, and demonstrate that PCA can trivially distinguish
between outflow variability correlated, anti-correlated, and un-correlated with
the continuum flux. Here, the observed anti-correlation between the absorption
line equivalent width and the continuum flux may be due to the ionization of
the wind responding to the continuum. Finally, we compare our results with
those found in the narrow-line Seyfert 1 IRAS 13224-3809. We find that the Fe K
UFO feature is sharper and more prominent in PDS 456, but that it lacks the
lower energy features from lighter elements found in IRAS 13224-3809,
presumably due to differences in ionization
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
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Ultrafast outflows disappear in high-radiation fields
Ultrafast outflows (UFOs) are the most extreme winds launched by active
galactic nuclei (AGN) due to their mildly-relativistic speeds (~0.1-0.3c) and
are thought to significantly contribute to galactic evolution via AGN feedback.
Their nature and launching mechanism are however not well understood. Recently,
we have discovered the presence of a variable UFO in the narrow-line Seyfert 1
IRAS 13224-3809. The UFO varies in response to the brightness of the source. In
this work we perform flux-resolved X-ray spectroscopy to study the variability
of the UFO and found that the ionisation parameter is correlated with the
luminosity. In the brightest states the gas is almost completely ionised by the
powerful radiation field and the UFO is hardly detected. This agrees with our
recent results obtained with principal component analysis. We might have found
the tip of the iceberg: the high ionisation of the outflowing gas may explain
why it is commonly difficult to detect UFOs in AGN and possibly suggest that we
may underestimate their actual feedback. We have also found a tentative
correlation between the outflow velocity and the luminosity, which is expected
from theoretical predictions of radiation-pressure driven winds. This trend is
rather marginal due to the Fe XXV-XXVI degeneracy. Further work is needed to
break such degeneracy through time-resolved spectroscopy
NuSTAR observations of Mrk 766: Distinguishing reflection from absorption
We present two new NuSTAR observations of the narrow line Seyfert 1 (NLS1) galaxy Mrk 766 and give constraints on the two scenarios previously proposed to explain its spectrum and that of other NLS1s: relativistic reflection and partial covering. The NuSTAR spectra show a strong hard (> 15 keV) X-ray excess, while simultaneous soft X-ray coverage of one of the observations provided by XMM-Newton constrains the ionised absorption in the source. The pure reflection model requires a black hole of high spin (a > 0.92) viewed at a moderate inclination (i = 46 +1 −4 ). The pure partial covering model requires extreme parameters: the cut-off of the primary continuum is very low (22 +7 −5 keV) in one observation and the intrinsic X-ray emission must provide a large fraction (75%) of the bolometric luminosity. Allowing a hybrid model with both partial covering and reflection provides more reasonable absorption parameters and relaxes the constraints on reflection parameters. The fractional variability reduces around the iron K band and at high energies including the Compton hump, suggesting that the reflected emission is less variable than the continuum
Evidence for a dynamic corona in the short-term time lags of black hole X-ray binary MAXI J1820+070
\ua9 2023 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.In X-ray observations of hard state black hole X-ray binaries (BHXRBs), rapid variations in accretion disc and coronal power-law emission are correlated and show Fourier-frequency-dependent time lags. On short (0.1 s) time-scales, these lags are thought to be due to reverberation and therefore may depend strongly on the geometry of the corona. Low-frequency quasi-periodic oscillations (QPOs) are variations in X-ray flux that have been suggested to arise because of geometric changes in the corona, possibly due to general relativistic Lense-Thirring precession. Therefore, one might expect the short-term time lags to vary on the QPO time-scale. We performed novel spectral-timing analyses on Neutron Star Interior Composition ExploreR observations of the BHXRB MAXI J1820+070 during the hard state of its outburst in 2018 to investigate how the short-term time lags between a disc-dominated and a coronal power-law-dominated energy band vary on different time-scales. Our method can distinguish between variability due to the QPO and broad-band noise, and we find a linear correlation between the power-law flux and lag amplitude that is strongest at the QPO frequency. We also introduce a new method to resolve the QPO signal and determine the QPO phase dependence of the flux and lag variations, finding that both are very similar. Our results are consistent with a geometric origin of QPOs, but also provide evidence for a dynamic corona with a geometry varying in a similar way over a broad range of time-scales, not just the QPO time-scale
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
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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
MAXI J1820+070 with NuSTAR – II. Flaring during the hard to soft state transition with a long soft lag
ABSTRACT
We continue the analysis of NuSTAR data from the recent discovery outburst of MAXI J1820+070 (optical counterpart ASASSN-18ey), focussing on an observation including unusual flaring behaviour during the hard to soft state transition, which is a short phase of outbursts and so comparatively rarely observed. Two plateaus in flux are separated by a variable interval lasting ∼10 ks, which shows dipping then flaring stages. The variability is strongest (with fractional variability up to ) at high energies and reduces as the contribution from disc emission becomes stronger. Flux-resolved spectra show that the variability is primarily due to the power-law flux changing. We also find a long soft lag of the thermal behind the power-law emission, which is s during the flaring phase. The lag during the dipping stage has a different lag–energy spectrum, which may be due to a wave passing outwards through the disc. Time-resolved spectral fitting suggests that the lag during the flaring stage may be due to the disc re-filling after being disrupted to produce the power-law flare, perhaps related to the system settling after the jet ejection which occurred around 1 d before. The time-scales of these phenomena imply a low viscosity parameter, α ∼ 10−3, for the inner region of the disc.</jats:p
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Investigating the Ultracompact X-Ray Binary Candidate SLX 1735-269 with NICER and NuSTAR
Acknowledgements: This research has made use of MAXI data provided by RIKEN, JAXA, and the MAXI team (Matsuoka et al. 2009). This research has made use of data and/or software provided by the High Energy Astrophysics Science Archive Research Center (HEASARC), which is a service of the Astrophysics Science Division at NASA/GSFC. This research has made use of the NuSTAR Data Analysis Software (NuSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (USA).Abstract
We present two simultaneous NICER and NuSTAR observations of the ultracompact X-ray binary (UCXB) candidate SLX 1735−269 while the source was in two different spectral states. Using various reflection modeling techniques, we find that xillverCO, a model used for fitting X-ray spectra of UCXBs with high carbon and oxygen abundances is an improvement over relxill or relxillNS, which instead contains solar-like chemical abundances. This provides indirect evidence in support of the source being ultracompact. We also use this reflection model to get a preliminary measurement of the inclination of the system,
i
=
57
−
7
+
23
degrees. This is consistent with our timing analysis, where a lack of eclipses indicates an inclination of i < 80°. The timing analysis is otherwise inconclusive, and we cannot confidently measure the orbital period of the system.</jats:p