149 research outputs found
Individual optical variability of Active Galactic Nuclei from the MEXSAS2 sample
Most of the variability studies of active galactic nuclei (AGNs) are based on
ensemble analyses. Nevertheless, it is interesting to provide estimates of the
individual variability properties of each AGN, in order to relate them with
intrinsic physical quantities. A useful dataset is provided by the Catalina
Surveys Data Release 2 (CSDR2), which encompasses almost a decade of
photometric measurements of million objects repeatedly observed
hundreds of times. We aim to investigate the individual optical variability
properties of 795 AGNs originally included in the Multi-Epoch XMM Serendipitous
AGN Sample 2 (MEXSAS2). Our goals consist in: (i) searching for correlations
between variability and AGN physical quantities; (ii) extending our knowledge
of the variability features of MEXSAS2 from the X-ray to the optical. We use
the structure function (SF) to analyse AGN flux variations. We model the SF as
a power-law, , and we compute its
variability parameters. We introduce the V-correction as a simple tool to
correctly quantify the amount of variability in the rest frame of each source.
We find a significant decrease of variability amplitude with increasing
bolometric, optical and X-ray luminosity. We obtain the indication of an
intrinsically weak positive correlation between variability amplitude and
redshift, . Variability amplitude is also positively correlated with
. The slope of the SF, , is weakly correlated with
the bolometric luminosity and/or with the black hole mass
. When comparing optical to X-ray variability properties, we find
that X-ray variability amplitude is approximately the same for those AGNs with
larger or smaller variability amplitude in the optical. On the contrary, AGNs
with steeper SF in the optical do present steeper SF in the X-ray, and vice
versa.Comment: 13 pages, 14 figures, 3 tables, accepted for publication in MNRA
X-HESS: a large sample of highly accreting serendipitous AGN under the XMM-Newton microscope
The bulk of X-ray spectroscopic studies of active galactic nuclei (AGN) are
focused on local () sources with low-to-moderate () Eddington
ratio (). It is then mandatory to overcome this
limitation and improve our understanding of highly accreting AGN. In this work
we present the preliminary results from the analysis of a sample of
high- radio-quiet AGN at , based on
the 10th release of the XMM-Newton serendipitous source catalogue, that we
named as XMM-Newton High-Eddington Serendipitous AGN Sample (X-HESS). Almost
of the X-HESS AGN have multi-epoch archival observations and
of the sources can rely on simultaneous OM optical data. First
results reveal sources showing signatures of ultra-fast outflows and remarkable
long- and short-term X-ray flux variations. Indeed in J095847.88+690532.7 (), one of the most densely monitored objects hosting a
supermassive black hole, we discovered a variation of the
soft X-ray flux by a factor of > 2 over approximately one week (rest-frame).
Large variations in the power-law continuum photon index are also
observed, questioning expectations from previously reported relations, for which would be a
ubiquitous hallmark of AGN with .Comment: 7 pages, 5 figures, proceedings of the XMM-Newton Workshop 2022
"Black hole accretion under the X-ray microscope". Accepted for publication
in Astronomische Nachrichte
The lively accretion disk in NGC 2992. I. Transient iron K emission lines in the high flux state
We report on one of the brightest flux levels of the Seyfert 2 galaxy NGC
2992 ever observed in X-rays, on May 2019. The source has been monitored every
few days from March 26, 2019 to December 14, 2019 by Swift-XRT, and
simultaneous XMM-Newton (250 ks) and NuSTAR (120 ks) observations were
triggered on May 6, 2019. The high count rate of the source (its 2-10 keV flux
ranged between 0.7 and erg cm s) allows us to
perform a time-resolved spectroscopy, probing spatial scales of tens of
gravitational radii from the central black hole. By constructing a map of the
excess emission over the primary continuum, we find several emission structures
in the 5.0-7.2 keV energy band. From fitting the 50 EPIC pn spectral slices of
5 ks duration, we interpret them as a constant narrow iron K line
and three variable components in the iron K complex. When a self-consistent
model accounting for the accretion disk emission is considered (KYNrline), two
of these features (in the 5.0-5.8 keV and 6.8-7.2 keV bands) can be ascribed to
a flaring region of the accretion disk located at -40
r from the black hole. The third one (6.5-6.8 keV) is likely produced
at much larger radii ( r). The inner radius and the
azimuthal extension retrieved from the coadded spectra of the flaring states
are r and ,
suggesting that the emitting region responsible for the broad iron K component
is a relatively compact annular sector within the disk. Our findings support a
physical scenario in which the accretion disk in NGC 2992 becomes more active
at high accretion rates ().Comment: 12 pages, 12 figures, 1 table. Accepted for publication in MNRA
X-ray spectroscopic survey of highly accreting AGN
Improving our understanding of the nuclear properties of high-Eddington-ratio (λEdd) active galactic nuclei (AGN) is necessary since at this regime the radiation pressure is expected to affect the structure and efficiency of the accretion disc-corona system. This may cause departures from the typical nuclear properties of low-λEdd AGN, which have been largely studied so far. We present here the X-ray spectral analysis of 14 radio-quiet, λEdd ≥ 1 AGN at 0.4 ≤ z ≤ 0.75, observed with XMM-Newton. Optical/UV data from simultaneous Optical Monitor observations have also been considered. These quasars were selected to have relatively high values of black hole mass (MBH ~ 108-8.5 M⊙) and bolometric luminosity (Lbol ~ 1046 erg s-1) in order to complement previous studies of high- λEdd AGN at lower MBH and Lbol. We studied the relation between λEdd and other key X-ray spectral parameters, such as the photon index (Γ) of the power-law continuum, the X-ray bolometric correction (kbol,X), and the optical/UV-to-X-ray spectral index (αox). Our analysis reveals that, despite the homogeneous optical and supermassive black hole accretion properties, the X-ray properties of these high-λEdd AGN are quite heterogeneous. We indeed measured values of Γ between 1.3 and 2.5, at odds with the expectations based on previously reported Γ-λEdd relations, for which Γ ≥ 2 would be a ubiquitous hallmark of AGN with λEdd ~ 1. Interestingly, we found that ~30% of the sources are X-ray weak, with an X-ray emission about a factor of ~10-80 fainter than that of typical AGN at similar UV luminosities. The X-ray weakness seems to be intrinsic and not due to the presence of absorption along the line of sight to the nucleus. This result may indicate that high-λEdd AGN commonly undergo periods of intrinsic X-ray weakness. Furthermore, results from follow-up monitoring with Swift of one of these X-ray weak sources suggest that these periods can last for several years
The first broad-band X-ray view of the narrow-line Seyfert 1 Ton S180
We present joint \textit{XMM-Newton} and \textit{NuSTAR} observations of the
`bare' narrow line Seyfert 1 Ton S180 (), carried out in 2016 and
providing the first hard X-ray view of this luminous galaxy. We find that the
0.4--30 keV band cannot be self-consistently reproduced by relativistic
reflection models, which fail to account simultaneously for the soft and hard
X-ray emission. The smooth soft excess prefers extreme blurring parameters,
confirmed by the nearly featureless nature of the RGS spectrum, while the
moderately broad Fe K line and the modest hard excess above 10 keV appear to
arise in a milder gravity regime. By allowing a different origin of the soft
excess, the broadband X-ray spectrum and overall spectral energy distribution
(SED) are well explained by a combination of: (a) direct thermal emission from
the accretion disc, dominating from the optical to the far/extreme UV; (b)
Comptonization of seed disc photons by a warm ( keV) and
optically thick () corona, mostly contributing to the soft X-rays;
(c) Comptonization by a standard hot ( keV) and
optically thin () corona, responsible for the primary X-ray
continuum; and (d) reflection from the mid/outer part of the disc. The two
coronae are suggested to be rather compact, with R. Our SED analysis implies that Ton S180 accretes
at super-Eddington rates. This is a key condition for the launch of a wind,
marginal (i.e., 3.1 significance) evidence of which is indeed found in
the RGS spectrum.Comment: 20 pages, 12 figures. Accepted for publication MNRA
A new emulated Monte Carlo radiative transfer disc-wind model: X-Ray Accretion Disc-wind Emulator - XRADE
We present a new X-Ray Accretion Disc-wind Emulator (xrade) based on the 2.5D Monte Carlo radiative transfer code that provides a physically motivated, self-consistent treatment of both absorption and emission from a disc wind by computing the local ionization state and velocity field within the flow. xrade is then implemented through a process that combines X-ray tracing with supervised machine learning. We develop a novel emulation method consisting in training, validating, and testing the simulated disc-wind spectra into a purposely built artificial neural network. The trained emulator can generate a single synthetic spectrum for a particular parameter set in a fraction of a second, in contrast to the few hours required by a standard Monte Carlo radiative transfer pipeline. The emulator does not suffer from interpolation issues with multidimensional spaces that are typically faced by traditional X-ray fitting packages such as xspec. xrade will be suitable to a wide number of sources across the black hole mass, ionizing luminosity, and accretion rate scales. As an example, we demonstrate the applicability of xrade to the physical interpretation of the X-ray spectra of the bright quasar PDS 456, which hosts the best-established accretion disc wind observed to date. We anticipate that our emulation method will be an indispensable tool for the development of high-resolution theoretical models, with the necessary flexibility to be optimized for the next generation microcalorimeters onboard future missions, like X-Ray Imaging and Spectroscopy Mission (XRISM)/Resolve and Athena/X-ray Integral Field Unit (X-IFU). This tool can also be implemented across a wide variety of X-ray spectral models and beyond
HYPerluminous quasars at the Epoch of ReionizatION (HYPERION). A new regime for the X-ray nuclear properties of the first quasars
The existence of luminous quasars (QSO) at the Epoch of Reionization (EoR;
i.e. z>6) powered by supermassive black holes (SMBH) with masses
challenges models of early SMBH formation. To shed light
on the nature of these sources we started a multiwavelength programme based on
a sample of 18 HYPerluminous quasars at the Epoch of ReionizatION (HYPERION).
These are the luminous QSOs whose SMBH must have had the fastest mass growth
during the Universe first Gyr. In this paper we present the HYPERION sample and
report on the first of the 3 years planned observations of the 2.4 Ms
XMM-Newton Multi-Year Heritage program on which HYPERION is based. The goal of
this program is to accurately characterize the X-ray nuclear properties of QSOs
at the EoR. Through a joint X-ray spectral analysis of 10 sources, in the
rest-frame keV range, we report a steep average photon index
(). Absorption is not required. The average is
inconsistent at level with the canonical 1.8-2 value measured in
QSO at z<6. This spectral slope is also much steeper than that reported in
lower-z QSOs with similar luminosity or accretion rate, thus suggesting a
genuine redshift evolution. Alternatively, we can interpret this result as the
presence of an unusually low-energy cutoff keV on a standard
power-law. We also report on mild indications that HYPERION QSOs
show higher soft X-ray emission at 2 keV compared to the UV one at 2500A than
expected by lower-z luminous AGN. We speculate that a redshift-dependent
coupling between the corona and accretion disc or intrinsically different
coronal properties may account for the steep spectral slopes, especially in the
presence of powerful winds. The reported slopes, if confirmed at lower
luminosities, may have an important impact on future X-ray AGN studies in the
early Universe.Comment: 21 pages (including appendix), 12 figures, 4 tables. Accepted for
pubblication in A&
The Open Universe survey of Swift-XRT GRB fields: a complete sample of HBL blazars
We have analysed all the X-ray images centred on Gamma Ray Bursts generated
by Swift over the last 15 years using automatic tools that do not require any
expertise in X-ray astronomy, producing results in excellent agreement with
previous findings. This work, besides presenting the largest medium-deep survey
of the X-ray sky and a complete sample of blazars, wishes to be a step in the
direction of achieving the ultimate goal of the Open Universe Initiative, that
is to enable non expert people to fully benefit of space science data, possibly
extending the potential for scientific discovery, currently confined within a
small number of highly specialised teams, to a much larger population. We have
used the Swift_deepsky Docker container encapsulated pipeline to build the
largest existing flux-limited and unbiased sample of serendipitous X-ray
sources. Swift_deepsky runs on any laptop or desktop computer with a modern
operating system. The tool automatically downloads the data and the calibration
files from the archives, runs the official Swift analysis software and produces
a number of results including images, the list of detected sources, X-ray
fluxes, SED data, and spectral slope estimations. We used our source list to
build the LogN-LogS of extra-galactic sources, which perfectly matches that
estimated by other satellites. Combining our survey with multi-frequency data
we selected a complete radio flux-density limited sample of High Energy Peaked
(HBL) blazars.Comment: Accepted for publication in A&A. 8 pages, 7 figure
A new emulated Monte Carlo radiative transfer disc-wind model: X-Ray Accretion Disc-wind Emulator – XRADE
Abstract We present a new X-Ray Accretion Disk-wind Emulator (xrade) based on the 2.5D Monte Carlo radiative transfer code which provides a physically-motivated, self-consistent treatment of both absorption and emission from a disk-wind by computing the local ionization state and velocity field within the flow. xrade is then implemented through a process that combines X-ray tracing with supervised machine learning. We develop a novel emulation method consisting in training, validating, and testing the simulated disk-wind spectra into a purposely built artificial neural network. The trained emulator can generate a single synthetic spectrum for a particular parameter set in a fraction of a second, in contrast to the few hours required by a standard Monte Carlo radiative transfer pipeline. The emulator does not suffer from interpolation issues with multi-dimensional spaces that are typically faced by traditional X-ray fitting packages such as xspec. xrade will be suitable to a wide number of sources across the black-hole mass, ionizing luminosity, and accretion rate scales. As an example, we demonstrate the applicability of xrade to the physical interpretation of the X-ray spectra of the bright quasar PDS 456, which hosts the best-established accretion-disk wind observed to date. We anticipate that our emulation method will be an indispensable tool for the development of high-resolution theoretical models, with the necessary flexibility to be optimized for the next generation micro-calorimeters on board future missions, like XRISM/Resolve and Athena/X-IFU. This tool can also be implemented across a wide variety of X-ray spectral models and beyond
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