637 research outputs found
Properties of AGN coronae in the NuSTAR era
The focussing optics of NuSTAR have enabled high signal-to-noise spectra to
be obtained from many X-ray bright Active Galactic Nuclei (AGN) and Galactic
Black Hole Binaries (BHB). Spectral modelling then allows robust
characterization of the spectral index and upper energy cutoff of the coronal
power-law continuum, after accounting for reflection and absorption effects.
Spectral-timing studies, such as reverberation and broad iron line fitting, of
these sources yield coronal sizes, often showing them to be small and in the
range of 3 to 10 gravitational radii in size. Our results indicate that coronae
are hot and radiatively compact, lying close to the boundary of the region in
the compactness - temperature diagram which is forbidden due to runaway pair
production. The coincidence suggests that pair production and annihilation are
essential ingredients in the coronae of AGN and BHB and that they control the
shape of the observed spectra.Comment: 11 pages, 8 figures, accepted for publication in MNRA
Radio continuum and X-ray emission from the most extreme FIR-excess galaxy NGC 1377: An extremely obscured AGN revealed
Galaxies which strongly deviate from the radio-far IR correlation are of
great importance for studies of galaxy evolution as they may be tracing early,
short-lived stages of starbursts and active galactic nuclei (AGNs). The most
extreme FIR-excess galaxy NGC1377 has long been interpreted as a young dusty
starburst, but millimeter observations of CO lines revealed a powerful
collimated molecular outflow which cannot be explained by star formation alone.
We present new radio observations at 1.5 and 10 GHz obtained with the Jansky
Very Large Array (JVLA) and Chandra X-ray observations towards NGC1377. The
observations are compared to synthetic starburst models to constrain the
properties of the central energy source. We obtained the first detection of the
cm radio continuum and X-ray emission in NGC1377. We find that the radio
emission is distributed in two components, one on the nucleus and another
offset by 4.5 to the South-West. We confirm the extreme FIR-excess of the
galaxy, with a 4.2, which deviates by more than
7- from the radio-FIR correlation. Soft X-ray emission is detected on
the off-nucleus component. From the radio emission we estimate for a young
( Myr) starburst a star formation rate SFR0.1 M yr. Such
a SFR is not sufficient to power the observed IR luminosity and to drive the CO
outflow. We find that a young starburst cannot reproduce all the observed
properties of the nucleus of NGC1377. We suggest that the galaxy may be
harboring a radio-quiet, obscured AGN of 10M, accreting at
near-Eddington rates. We speculate that the off-nucleus component may be
tracing an hot-spot in the AGN jet.Comment: 14 pages, accepted for publication on Astronomy and Astrophysics on
08/07/201
Coronal Properties of Swift/BAT-selected Seyfert 1 AGNs Observed with NuSTAR
The NuSTAR observatory, with its high sensitivity in hard X-rays, has enabled detailed broadband modeling of the X-ray spectra of active galactic nuclei (AGNs), thereby allowing constraints to be placed on the high-energy cutoff of the X-ray coronal continuum. We investigate the spectral properties of a sample of 46 NuSTAR-observed Seyfert 1 AGNs selected from the Swift/Burst Alert Telescope 70 month hard X-ray survey. Our measurements of the high-energy cutoff of the continuum from modeling the NuSTAR X-ray spectra are used to map out the temperature–compactness (θ–l) plane for AGN coronae. We find that most of the coronae lie clustered near the boundary for runaway pair production, suggesting that annihilation and pair production act to regulate the temperature of the corona. We discuss the implications of coronae whose high-energy cutoff may indicate a low coronal temperature on the heating and thermalization mechanisms in the corona
Relativistic spectroscopy of the extreme NLS1 IRAS13224-3809
The narrow line Seyfert 1 (NLS1) IRAS 13224-3809 is the most X-ray variable
active galactic nucleus (AGN), exhibiting 0.3-10 keV flux changes of over an
order of magnitude within an hour. We report on the results of the 1.5 Ms 2016
XMM-Newton/NuSTAR observing campaign, which revealed the presence of a 0.24c
ultra-fast outflow in addition to the well-known strong relativistic
reflection. We also summarise other key results of the campaign, such as the
first detection of a non-linear RMS-flux relation in an accreting source,
correlations between outflow absorption strength/velocity and source flux, and
a disconnect between the X-ray and UV emission. Our results are consistent with
a scenario where a disk wind is launched close to the black hole, imprinting
absorption features into the spectrum and variability.Comment: 6 pages, 7 figures, contributed talk at "Revisiting narrow-line
Seyfert 1 galaxies and their place in the Universe" (Padova, April 2018).
Accepted for publication in Proceedings of Science, PoS(NLS1-2018)03
The hard X-ray perspective on the soft X-ray excess
The X-ray spectra of many active galactic nuclei (AGN) exhibit a `soft
excess' below 1keV, whose physical origin remains unclear. Diverse models have
been suggested to account for it, including ionised reflection of X-rays from
the inner part of the accretion disc, ionised winds/absorbers, and
Comptonisation. The ionised reflection model suggests a natural link between
the prominence of the soft excess and the Compton reflection hump strength
above 10keV, but it has not been clear what hard X-ray signatures, if any, are
expected from the other soft X-ray candidate models. Additionally, it has not
been possible up until recently to obtain high-quality simultaneous
measurements of both soft and hard X-ray emission necessary to distinguish
these models, but upcoming joint XMM-NuSTAR programmes provide precisely this
opportunity. In this paper, we present an extensive analysis of simulations of
XMM+NuSTAR observations, using two candidate soft excess models as inputs, to
determine whether such campaigns can disambiguate between them by using hard
and soft X-ray observations in tandem. The simulated spectra are fit with the
simplest "observer's model" of a black body and neutral reflection to
characterise the strength of the soft and hard excesses. A plot of the strength
of the hard excess against the soft excess strength provides a diagnostic plot
which allows the soft excess production mechanism to be determined in
individual sources and samples using current state-of-the-art and next
generation hard X-ray enabled observatories. This approach can be
straightforwardly extended to other candidate models for the soft excess.Comment: 12 pages, 11 figures, accepted for publication in ApJ. Added
reference
Disentangling the Complex Broadband X-ray Spectrum of IRAS 13197-1627 with NuSTAR, XMM-Newton and Suzaku
We present results from a coordinated -+ observation of
the type 1.8 Seyfert galaxy IRAS 13197-1627. This is a highly complex source,
with strong contributions from relativistic reflection from the inner accretion
disk, neutral absorption and further reprocessing by more distant material, and
ionised absorption from an outflow. We undertake a detailed spectral analysis
combining the broadband coverage provided by -+ with a
multi-epoch approach incorporating archival observations performed by
- and . Our focus is on characterising the reflection from
the inner accretion disk, which previous works have suggested may dominate the
AGN emission, and constraining the black hole spin. Using lamppost disk
reflection models, we find that the results for the inner disk are largely
insensitive to assumptions regarding the geometry of the distant reprocessor
and the precise form of the illuminating X-ray continuum. However, these
results do depend on the treatment of the iron abundance of the distant
absorber/reprocessor. The multi-epoch data favour a scenario in which the AGN
is chemically homogeneous, and we find that a rapidly rotating black hole is
preferred, with , but a slowly-rotating black hole is not
strongly excluded. In addition to the results for the inner disk, we also find
that both the neutral and ionised absorbers vary from epoch to epoch, implying
that both have some degree of inhomogeneity in their structure.Comment: 15 pages, 7 figures, accepted for publication in MNRA
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