34 research outputs found
The inner view of NGC 1052 using multiple X-ray observations
In this paper, we make a multi-epoch analysis of NGC 1052, one of the
prototypical LLAGN, using XMM-Newton, Suzaku and NuSTAR observations, taken
from 2001 to 2017. This is the first time that results from NuSTAR observations
are reported for NGC 1052. On the technical aspects, we found a
wavelength-dependent calibration issue between simultaneous XMM-Newton and
NuSTAR spectra. It is described by a change on the photon index of . We use ancillary Chandra
data to decontaminate the nuclear spectrum from circumnuclear contributors. We
find that two baseline models can fit the broad (0.5-50 keV) X-ray spectrum of
the source. One consists of a power-law like continuum which is absorbed by a
uniform absorber, reflection from neutral material, and a separate power-law
component in the soft band. The second model presents a clumpy absorber. The
reflection component is still present, but not the soft band power-law.
Instead, absorption by a warm absorber is necessary to fit the spectra. This is
the first time that a reflection component is established in this object,
thanks to high energy data from NuSTAR. This component is constant in flux and
shape, supporting the idea that is produced away from the central source
(probably the torus). We find flux, spectral slope and absorption variations on
timescales of months to years. We also find that a patchy-absober can explain
the behaviour of this source better as it is 200 times more likely than
the uniform absober while it yields to smaller intrinsic variations.Comment: 11 pages, 6 figures, 2 tables. Accepted for publication in MNRA
X-ray variability with WFXT: AGNs, transients and more
The Wide Field X-ray Telescope (WFXT) is a proposed mission with a high
survey speed, due to the combination of large field of view (FOV) and effective
area, i.e. grasp, and sharp PSF across the whole FOV. These characteristics
make it suitable to detect a large number of variable and transient X-ray
sources during its operating lifetime. Here we present estimates of the WFXT
capabilities in the time domain, allowing to study the variability of thousand
of AGNs with significant detail, as well as to constrain the rates and
properties of hundreds of distant, faint and/or rare objects such as X-ray
Flashes/faint GRBs, Tidal Disruption Events, ULXs, Type-I bursts etc. The
planned WFXT extragalactic surveys will thus allow to trace variable and
transient X-ray populations over large cosmological volumes.Comment: Proceedings of "The Wide Field X-ray Telescope Workshop", held in
Bologna, Italy, Nov. 25-26 2009 (arXiv:1010.5889). To appear in Memorie della
Societ\`a Astronomica Italiana 2010 - Minor corrections to text
Timescale-dependent X-ray to UV time lags of NGC 4593 using high-intensity XMM-Newton observations with Swift and AstroSat
We present a 140ks observation of NGC 4593 with XMM-Newton providing
simultaneous and continuous PN X-ray and OM UV (UVW1 2910\AA) lightcurves which
sample short-timescale variations better than previous observations. These
observations were simultaneous with 22d of Swift X-ray and UV/optical
monitoring, reported previously, and 4d of AstroSat X-ray (SXT), far (FUV
1541\AA), and near (NUV 2632\AA) UV allowing lag measurements between them and
the highly-sampled XMM. From the XMM we find that UVW1 lags behind the X-rays
by 29.51.3ks, half the lag previously determined from the Swift
monitoring. Re-examination of the \textit{Swift} data reveals a bimodal lag
distribution, with evidence for both the long and short lags. However if we
detrend the Swift lightcurves by LOWESS filtering with a 5d width, only the
shorter lag (23.821.2ks) remains. The NUV observations, compared to PN and
SXT, confirm the 30ks lag found by XMM and, after 4d filtering is applied
to remove the long-timescale component, the FUV shows a lag of 23ks. The
resultant new UVW1, FUV, and NUV lag spectrum extends to the X-ray band without
requiring additional X-ray to UV lag offset, which if the UV arises from
reprocessing of X-rays, implies direct illumination of the reprocessor. By
referencing previous Swift and HST lag measurements, we obtain an X-ray to
optical lag spectrum which agrees with a model using the KYNreverb
disc-reprocessing code, assuming the accepted mass of
and a spin approaching maximum. Previously noted
lag contribution from the BLR in the Balmer and Paschen continua are still
prominent.Comment: 13 pages, 23 figure
The relationship between X-ray variability amplitude and black hole mass in active galactic nuclei
We have investigated the relationship between the 2-10 keV X-ray variability
amplitude and black hole mass for a sample of 46 radio-quiet active galactic
nuclei observed by ASCA. Thirty-three of the objects in our sample exhibited
variability over a time-scale of ~40 ks, and we found a significant
anti-correlation between excess variance and mass. Unlike most previous
studies, we have quantified the variability using nearly the same time-scale
for all objects. Moreover, we provide a prescription for estimating the
uncertainties in excess variance which accounts both for measurement
uncertainties and for the stochastic nature of the variability. We also present
an analytical method to predict the excess variance from a model power spectrum
accounting for binning, sampling and windowing effects. Using this, we modelled
the variance-mass relation assuming all objects have a universal twice-broken
power spectrum, with the position of the breaks being dependent on mass. This
accounts for the general form of the relationship but there is considerable
scatter. We investigated this scatter as a function of the X-ray photon index,
luminosity and Eddington ratio. After accounting for the dependence of excess
variance on mass, we find no significant correlation with either luminosity or
X-ray spectral slope. We do find an anti-correlation between excess variance
and the Eddington ratio, although this relation might be an artifact owing to
the uncertainties in the mass measurements. It remains to be established that
enhanced X-ray variability is a property of objects with steep X-ray slopes or
large Eddington ratios.Comment: 13 pages, 5 figures, accepted for publication in MNRA
The Hot and Energetic Universe: The close environments of supermassive black holes
Most of the action in Active Galactic Nuclei (AGN) occurs within a few tens
of gravitational radii from the supermassive black hole, where matter in the
accretion disk may lose up to almost half of its energy with a copious
production of X-rays, emitted via Comptonization of the disk photons by hot
electrons in a corona and partly reflected by the accretion disk. Thanks to its
large effective area and excellent energy resolution, Athena+ contributions in
the understanding of the physics of accretion in AGN will be fundamental - and
unique - in many respects. It will allow us to map the disk-corona system -
which is crucial to understand the mechanism of energy extraction and the
relation of the corona with winds and jets - by studying the time lags between
reflected and primary photons. These lags have been recently discovered by
XMM-Newton, but only Athena+ will have the sensitivity required to fully
exploit this technique. Athena+ will also be able e.g. to determine robustly
the spin of the black hole in nearby sources (and to extend these measurements
beyond the local Universe), to establish the nature of the soft X-ray
components, and to map the circumnuclear matter within the AGN inner parsec
with unprecedented details.Comment: Supporting paper for the science theme "The Hot and Energetic
Universe" to be implemented by the Athena+ X-ray observatory
(http://www.the-athena-x-ray-observatory.eu). 9 pages, 8 figure