100 research outputs found
Interpreting the long-term variability of the changing-look AGN Mrk 1018
We present a thorough study of the Changing-Look Active Galactic Nucleus
(CL-AGN) Mrk 1018, utilizing an extensive dataset spanning optical, UV, and
X-ray spectro-photometric data from 2005 to 2019. We analysed X-ray spectra and
broad-band photometry, and performed optical-to-X-ray spectral energy
distribution (SED) fitting to comprehend the observed changing-look behaviour.
We found that over the 14 years in analysis, significant changes in X-ray
spectra occurred, as the hardness ratio increases by a factor of ~2. We
validated also the broad-band dimming, with optical, UV, and X-ray luminosities
decreasing by factors of >7, >24 and ~9, respectively. These dims are
attributed to the declining UV emission. We described the X-ray spectra with a
two-Comptonization model, revealing a consistent hot comptonizing medium but a
cooling warm component. This cooling, linked to the weakening of the magnetic
fields in the accretion disk, explains the UV dimming. We propose that the
weakening is caused by the formation of a jet, in turn originated from the
change of state of the inner accretion flow. Our optical-to-X-ray SED fitting
supports this conclusion, as the normalised accretion rate is super-critical
(0.06>0.02) in the bright state and sub-critical (0.01<0.02) in the
faint state. Instabilities arising at the interface of the state-transition are
able to reduce the viscous timescale to the observed ~10 years of Mrk 1018
variability. We explored a possible triggering mechanism for this state
transition, involving gaseous clouds pushed onto the AGN sub-pc regions by a
recent merging event or by cold chaotic accretion. This scenario, if validated
by future simulations, could enhance our understanding of CL-AGN and raises
questions about an accretion rate of ~0.02, coupled with minor disturbances in
the accretion disk, being the primary factor in the changing-look phenomenon.Comment: 18 pages, 8 figure
Evidence for a clumpy disc-wind in the star forming Seyfert\,2 galaxy MCG--03--58--007
We report the results of a detailed analysis of a deep simultaneous \textit{XMM-Newton & NuSTAR} observation of the nearby () and
bright () starburst-AGN
Seyfert\,2 system: MCG--03--58--007. From the broadband fitting we show that
most of the obscuration needs to be modeled with a toroidal type reprocessor
such as \texttt{MYTorus} \citep{MurphyYaqoob09}. Nonetheless the signature of a
powerful disc-wind is still apparent at higher energies and the observed rapid
short-term X-ray spectral variability is more likely caused by a variable zone
of highly ionized fast wind rather than by a neutral clumpy medium. We also
detect X-ray emission from larger scale gas as seen from the presence of
several soft narrow emission lines in the RGS, originating from a contribution
of a weak star forming activity together with a dominant photoionized component
from the AGN.Comment: 16 pages, 9 figures, accepted for publication in MNRA
AGN X-ray spectroscopy with neural networks
We explore the possibility of using machine learning to estimate physical parameters directly from active galactic nucleus (AGN) X-ray spectra without needing computationally expensive spectral fitting. Specifically, we consider survey quality data, rather than long pointed observations, to ensure that this approach works in the regime where it is most likely to be applied. We simulate Athena Wide Field Imager spectra of AGN with warm absorbers, and train simple neural networks to estimate the ionization and column density of the absorbers. We find that this approach can give comparable accuracy to spectral fitting, without the risk of outliers caused by the fit sticking in a false minimum, and with an improvement of around three orders of magnitude in speed. We also demonstrate that using principal component analysis to reduce the dimensionality of the data prior to inputting it into the neural net can significantly increase the accuracy of the parameter estimation for negligible computational cost, while also allowing a simpler network architecture to be used
The properties of the X-ray corona in the distant (z = 3.91) quasar APM 08279+5255
We present new joint XMM-Newton and NuSTAR observations of APM08279+5255, a gravitationally-lensed, broad-absorption line quasar (z = 3:91). After showing a fairly stable flux ( f210 ' 45:5 1013 erg s1) from 2000 to 2008, APM08279+5255 was found in a fainter state in the latest X-ray exposures ( f210 ' 2:7 1013 erg s1), which can likely be ascribed to a lower X-ray activity. Moreover, the 2019 data present a prominent FeK emission line and do not show any significant absorption line. This fainter state, coupled to the first hard X-ray sampling of APM08279+5255, allowed us to measure X-ray reflection and the high-energy cuto in this source for the first time. From the analysis of previous XMM-Newton and Chandra observations, X-ray reflection is demonstrated to be a long-lasting feature of this source, but less prominent prior to 2008, possibly due to a stronger primary emission. The estimated high-energy cuto (Ecut = 99+91 35 keV) sets a new redshift record for the farthest ever measured and places APM08279+5255 in the allowed region of the compactness-temperature diagram of X-ray coronae, in agreement with previous results on high-z quasars
Detection of a possible multiphase ultra-fast outflow in IRAS 13349+2438 with NuSTAR and XMM-Newton
We present joint NuSTAR and XMM-Newton observations of the bright, variable
quasar IRAS 13349+2438. This combined dataset shows two clear iron absorption
lines at 8 and 9 keV, which are most likely associated with two layers of
mildly relativistic blueshifted absorption, with velocities of 0.14c and 0.27c.
We also find strong evidence for a series of Ly absorption lines at
intermediate energies in a stacked XMM-Newton EPIC-pn spectrum, at the same
blueshift as the lower velocity iron feature. This is consistent with a
scenario where an outflowing wind is radially stratified, so faster, higher
ionization material is observed closer to the black hole, and cooler, slower
material is seen from streamlines at larger radii.Comment: 5 pages, 2 figures, accepted for publication in MNRAS letter
A new powerful and highly variable disk wind in an AGN-star forming galaxy, the case of MCG-03-58-007
We present the discovery of a new candidate for a fast disk wind, in the
nearby Seyfert 2 galaxy MCG-03-58-007. This wind is discovered in a deep Suzaku
observation that was performed in 2010. Overall the X-ray spectrum of
MCG-03-58-007 is highly absorbed by a neutral column density of NH~10^23 cm^-2,
in agreement with the optical classification as a type 2 AGN. In addition, this
observation unveiled the presence of two deep absorption troughs at E = 7.4 +-
0.1 keV and E = 8.5 +- 0.2 keV. If associated with blue-shifted FeXXVI, these
features can be explained with the presence of two highly ionised (log \xi/(erg
cm/s)~ 5.5) and high column density (NH~5-8 x 10^23cm^-2) outflowing absorbers
with v_out1~ -0.1c and v_out2~ -0.2c. The disk wind detected during this
observation is most likely launched from within a few hundreds gravitational
radii from the central black and has a kinetic output that matches the
prescription for significant feedback. The presence of the lower velocity
component of the disk wind is independently confirmed by the analysis of a
follow-up XMM-Newton & NuSTAR observation. A faster (v_out~ -0.35 c) component
of the wind is also seen in this second observation. During this observation we
also witnessed an occultation event lasting \Delta t ~ 120 ksec, which we
ascribe to an increase of the opacity of the disk wind (\Delta NH~1.4x10^24
cm^-2). Our interpretation is that the slow zone (v_out~ -0.1c) of the wind is
the most stable but inhomogeneous component, while the faster zones could be
associated with two different inner streamlines of the wind.Comment: 12 pages, 10 figures, 3 tables. Accepted for publication in MNRA
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