78 research outputs found
Nuclear absorption and emission in the AGN merger NGC 6240: the hard X-ray view
We present the analysis of four NuSTAR observations of the luminous infrared
galaxy merger NGC 6240, hosting a close pair of highly obscured active galactic
nuclei (AGN). Over a period of about two years, the source exhibits hard X-ray
variability of the order of 20 per cent, peaking around 20 keV. When the two
AGN are resolved with Chandra, column densities in the range cm are estimated for both of them. The exact values
are hard to determine, as they appear to depend on aspects that are sometimes
overlooked in Compton-thick objects, such as the covering factor of the
absorber, iron abundance, and the contamination in the Fe-K band from
foreground hot-gas emission. Nearly spherical covering and slightly subsolar
iron abundance are preferred in this case. While the southern nucleus is
suggested to be intrinsically more powerful, as also implied by the mid-IR and
2-10 keV brightness ratios, solutions involving a similar X-ray luminosity of
the two AGN cannot be ruled out. The observed variability is rather limited
compared to the one revealed by the Swift/BAT light curve, and it can be fully
explained by changes in the continuum flux from the two AGN, without requiring
significant column density variations. NGC 6240 is hereby confirmed to
represent a unique opportunity to investigate the X-ray (and broad-band)
properties of massive galaxy mergers, which were much more frequent in the
early Universe.Comment: 12 pages, 9 figures, 4 tables. Accepted for publication on MNRA
Does the X-ray outflow quasar PDS 456 have a UV outflow at 0.3c?
The quasar PDS 456 (at redshift ~0.184) has a prototype ultra-fast outflow
(UFO) measured in X-rays. This outflow is highly ionized with relativistic
speeds, large total column densities log N_H(cm^-2) > 23, and large kinetic
energies that could be important for feedback to the host galaxy. A UV spectrum
of PDS 456 obtained with the Hubble Space Telescope in 2000 contains one
well-measured broad absorption line (BAL) at ~1346A (observed) that might be
Ly-alpha at v ~ 0.06c or NV 1240 at v ~ 0.08c. However, we use photoionisation
models and comparisons to other outflow quasars to show that these BAL
identifications are problematic because other lines that should accompany them
are not detected. We argue that the UV BAL is probably CIV 1549 at v ~ 0.30c.
This would be the fastest UV outflow ever reported, but its speed is similar to
the X-ray outflow and its appearance overall is similar to relativistic UV BALs
observed in other quasars. The CIV BAL identification is also supported
indirectly by the tentative detection of another broad CIV line at v ~ 0.19c.
The high speeds suggest that the UV outflow originates with the X-ray UFO
crudely 20 to 30 r_g from the central black hole. We speculate that the CIV BAL
might form in dense clumps embedded in the X-ray UFO, requiring density
enhancements of only >0.4 dex compared clumpy structures already inferred for
the soft X-ray absorber in PDS 456. The CIV BAL might therefore be the first
detection of low-ionisation clumps proposed previously to boost the opacities
in UFOs for radiative driving.Comment: in press with MNRA
Multi-phase outflows as probes of AGN accretion history
Powerful outflows with a broad range of properties (such as velocity,
ionization, radial scale and mass loss rate) represent a key feature of active
galactic nuclei (AGN), even more so since they have been simultaneously
revealed also in individual objects. Here we revisit in a simple analytical
framework the recent remarkable cases of two ultraluminous infrared quasars,
IRAS F11119+3257 and Mrk 231, which allow us to investigate the physical
connection between multi-phase AGN outflows across the ladder of distance from
the central supermassive black hole (SMBH). We argue that any major deviations
from the standard outflow propagation models might encode unique information on
the past SMBH accretion history, and briefly discuss how this could help
address some controversial aspects of the current picture of AGN feedback.Comment: Accepted for publication on MNRA
Spatially resolved Fe K spectroscopy of NGC 4945
We present the imaging and spectroscopic analysis of the combined Chandra
ACIS-S observations of the Compton-thick Seyfert 2 galaxy NGC 4945. We
performed a spatially-resolved spectroscopy of the circumnuclear environment of
the source, picturing the innermost 200 parsecs around the highly absorbed
nucleus. The additional 200 ks ACIS-S data with respect to the previous
campaign allowed us to map with even greater detail the central structure of
this source and to discover an enhanced iron emission in the innermost nuclear
region, with respect to the associated Compton reflection continuum. We
revealed that the Equivalent Width of the iron K line is spatially
variable (ranging from 0.5 to 3 keV), on scales of tens of parsecs, likely due
to the ionization state and orientation effects of the reprocessing material,
with respect to the central X-ray illuminating source. A clump of highly
ionized Fe XXV He- is also detected, 40 parsecs east to the nucleus.
When observations taken years apart are considered, the central unresolved
reflected emission is found to remain constant.Comment: 10 pages, 6 figures, 4 tables, accepted for publication in MNRA
Discovery of Broad Soft X-ray Absorption Lines from the Quasar Wind in PDS 456
High resolution soft X-ray spectroscopy of the prototype accretion disk wind
quasar, PDS 456, is presented. Here, the XMM-Newton RGS spectra are analyzed
from the large 2013-2014 XMM-Newton campaign, consisting of 5 observations of
approximately 100 ks in length. During the last observation (hereafter OBS. E),
the quasar is at a minimum flux level and broad absorption line profiles are
revealed in the soft X-ray band, with typical velocity widths of km s. During a period of higher flux in the 3rd and 4th
observations (OBS. C and D, respectively), a very broad absorption trough is
also present above 1 keV. From fitting the absorption lines with models of
photoionized absorption spectra, the inferred outflow velocities lie in the
range . The absorption lines likely originate from He and H-like
neon and L-shell iron at these energies. Comparison with earlier archival data
of PDS 456 also reveals similar absorption structure near 1 keV in a 40 ks
observation in 2001, and generally the absorption lines appear most apparent
when the spectrum is more absorbed overall. The presence of the soft X-ray
broad absorption lines is also independently confirmed from an analysis of the
XMM-Newton EPIC spectra below 2 keV. We suggest that the soft X-ray absorption
profiles could be associated with a lower ionization and possibly clumpy phase
of the accretion disk wind, where the latter is known to be present in this
quasar from its well studied iron K absorption profile and where the wind
velocity reaches a typical value of 0.3.Comment: 44 pages, including 13 figures, accepted for publication in The
Astrophysical Journa
Short term X-ray spectral variability of the quasar PDS 456 observed in a low flux state
We present an analysis of the 2013 Suzaku campaign on the nearby luminous
quasar PDS 456, covering a total duration of ~1 Ms and a net exposure of 455
ks. During these observations, the X-ray flux was suppressed by a factor of >10
in the soft X-ray band when compared to other epochs. We investigated the
broadband continuum by constructing a spectral energy distribution, making use
of the optical/UV photometry and hard X-ray spectra from the later
XMM-Newton/NuSTAR campaign in 2014. The high energy part of this low flux state
cannot be accounted for by self-consistent accretion disc and corona models
without attenuation by absorbing gas, which partially covers a substantial
fraction of the line of sight towards the X-ray source. Two absorption layers
are required, of column density and ,
with average covering factors of ~80% (with typical 5% variations) and 60%
(10-15%), respectively. In these observations PDS 456 displays significant
short term X-ray spectral variability, on timescales of ~100 ks, which can be
accounted for by variable covering of the absorbing gas. The partial covering
absorber prefers an outflow velocity of at
the >99.9% confidence level over the case where . This is
consistent with the velocity of the highly ionised outflow responsible for the
blueshifted iron K absorption profile. We therefore suggest that the partial
covering clouds could be the denser, or clumpy part of an inhomogeneous
accretion disc wind. Finally we estimate the size-scale of the X-ray source
from its variability. The radial extent of the X-ray emitter is found to be of
the order ~15-20 , although the hard X-ray (>2 keV) emission may
originate from a more compact or patchy corona of hot electrons, which is ~6-8
in size.Comment: 38 pages, 13 figures, accepted for publication in MNRA
Relationship between Latitude and Melanoma in Italy
Objective. Evaluate the ecological relationship between skin melanoma epidemiology and latitude in Italy. Methods. We used data from the Italian network of cancer registries (Airtum). In a Poisson model, we evaluated the effect on incidence, mortality, and survival of latitude, adjusting for some demographic, social, phenotypic, and behavioural variables. Results. Incidence increased in Italy by 17% for each degree of increase in latitude. The effect of latitude was statistically significantly present also adjusting for other variables (incidence rate ratio = 1.08). The effect of latitude on increasing mortality (mortality rate ratio = 1.27) and improving survival (relative excess risk of death = 0.93) was no longer present in the multivariate model. Conclusion. Melanoma incidence, mortality, and survival vary in Italy according to latitude. After adjustment for several confounders, incidence still grows with growing latitude. Presumably, latitude expresses other variables that might be related to individual susceptibility and/or local care
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