Context.
The AGN bolometric correction is a key element for understanding black hole (BH) demographics and computing accurate BH accretion histories from AGN luminosities. However, current estimates ...still differ from each other by up to a factor of two to three, and rely on extrapolations at the lowest and highest luminosities.
Aims.
Here we revisit this fundamental question by presenting general hard X-ray (
K
X
) and optical (
K
O
) bolometric corrections, computed by combining several AGN samples spanning the widest (about 7 dex) luminosity range ever used for this type of studies.
Methods.
We analysed a total of ∼1000 type 1 and type 2 AGN for which we performed a dedicated SED-fitting.
Results.
We provide a bolometric correction separately for type 1 and type 2 AGN; the two bolometric corrections agree in the overlapping luminosity range. Based on this we computed for the first time a universal bolometric correction for the whole AGN sample (both type 1 and type 2). We found that
K
X
is fairly constant at log(
L
BOL
/
L
⊙
) < 11, while it increases up to about one order of magnitude at log(
L
BOL
/
L
⊙
) ∼ 14.5. A similar increasing trend has been observed when its dependence on either the Eddington ratio or the BH mass is considered, while no dependence on redshift up to
z
∼ 3.5 has been found. In contrast, the optical bolometric correction appears to be fairly constant (i.e.
K
O
∼ 5) regardless of the independent variable. We also verified that our bolometric corrections correctly predict the AGN bolometric luminosity functions. According to this analysis, our bolometric corrections can be applied to the whole AGN population in a wide range of luminosity and redshift.
Abstract
We study the relation between obscuration and supermassive black hole (SMBH) accretion using a large sample of hard X-ray selected active galactic nuclei (AGNs). We find a strong decrease in ...the fraction of obscured sources above the Eddington limit for dusty gas (
log
λ
Edd
≳
−
2
) confirming earlier results, and consistent with the radiation-regulated unification model. This also explains the difference in the Eddington ratio distribution functions (ERDFs) of type 1 and type 2 AGNs obtained by a recent study. The break in the ERDF of nearby AGNs is at
log
λ
Edd
*
=
−
1.34
±
0.07
. This corresponds to the
λ
Edd
where AGNs transition from having most of their sky covered by obscuring material to being mostly devoid of absorbing material. A similar trend is observed for the luminosity function, which implies that most of the SMBH growth in the local universe happens when the AGN is covered by a large reservoir of gas and dust. These results could be explained with a radiation-regulated growth model, in which AGNs move in the
N
H
–
λ
Edd
plane during their life cycle. The growth episode starts with the AGN mostly unobscured and accreting at low
λ
Edd
. As the SMBH is further fueled,
λ
Edd
,
N
H
and the covering factor increase, leading the AGN to be preferentially observed as obscured. Once
λ
Edd
reaches the Eddington limit for dusty gas, the covering factor and
N
H
rapidly decrease, leading the AGN to be typically observed as unobscured. As the remaining fuel is depleted, the SMBH goes back into a quiescent phase.
ABSTRACT
Accreting supermassive black holes (SMBHs), also known as active galactic nuclei (AGN), are generally surrounded by large amounts of gas and dust. This surrounding material reprocesses the ...primary X-ray emission produced close to the SMBH and gives rise to several components in the broadband X-ray spectra of AGN, including a power-law possibly associated with Thomson-scattered radiation. In this work, we study the properties of this scattered component for a sample of 386 hard-X-ray-selected, nearby ($z\sim0.03$) obscured AGN from the 70-month Swift/BAT catalogue. We investigate how the fraction of Thomson-scattered radiation correlates with different physical properties of AGN, such as line-of-sight column density, X-ray luminosity, black hole mass, and Eddington ratio. We find a significant negative correlation between the scattering fraction and the column density. Based on a large number of spectral simulations, we exclude the possibility that this anticorrelation is due to degeneracies between the parameters. The negative correlation also persists when considering different ranges of luminosity, black hole mass, and Eddington ratio. We discuss how this correlation might be either due to the angle dependence of the Thomson cross-section or to more obscured sources having a higher covering factor of the torus. We also find a positive correlation between the scattering fraction and the ratio of O iii λ5007 to X-ray luminosity. This result is consistent with previous studies and suggests that the Thomson-scattered component is associated with the narrow-line region.
ABSTRACT
We present a detailed study of ionized outflows in a large sample of ∼650 hard X-ray-detected active galactic neuclei (AGNs). Using optical spectroscopy from the BAT AGN Spectroscopic Survey ...(BASS), we are able to reveal the faint wings of the O iii emission lines associated with outflows covering, for the first time, an unexplored range of low AGN bolometric luminosity at low redshift (z ∼0.05). We test if and how the incidence and velocity of ionized outflow is related to AGN physical parameters: black hole mass ($\rm \mathit{ M}_{BH}$), gas column density ($\rm \mathit{ N}_{H}$), Eddington ratio ($\rm \lambda _{Edd}$), O iii, X-ray, and bolometric luminosities. We find a higher occurrence of ionized outflows in type 1.9 (55 per cent) and type 1 AGNs (46 per cent) with respect to type 2 AGNs (24 per cent). While outflows in type 2 AGNs are evenly balanced between blue and red velocity offsets with respect to the O iii narrow component, they are almost exclusively blueshifted in type 1 and type 1.9 AGNs. We observe a significant dependence between the outflow occurrence and accretion rate, which becomes relevant at high Eddington ratios log($\rm \lambda _{Edd}$) ≳ −1.7. We interpret such behaviour in the framework of covering factor-Eddington ratio dependence. We do not find strong trends of the outflow maximum velocity with AGN physical parameters, as an increase with bolometric luminosity can be only identified when including samples of AGNs at high luminosity and high redshift taken from literature.
Being one of the most commonly used electrochemical mediators for analytical applications, Prussian Blue has found a wide use in the biosensor field during the last years. Its particular ...characteristic of catalysing hydrogen peroxide reduction has been applied in the construction of a large number of oxidase enzyme-based biosensors for clinical, environmental and food analysis.
By modifying an electrode surface with Prussian Blue, it is in fact possible to easily detect hydrogen peroxide at an applied potential around 0.0
V versus Ag/AgCl, thus making possible coupling with oxidase enzymes while also avoiding or reducing electrochemical interferences.
Papers dealing with glucose, lactate, cholesterol and galactose biosensors that are based on the use of Prussian Blue have recently appeared in the most important analytical chemistry journals.
Another recent trend is the use of a choline probe based on choline oxidase for pesticide determination to exploit the inhibition of acetylcholinesterase by these compounds.
In addition, the use of Prussian Blue in the development of biosensors for food analysis has captured the interest of many research groups and led to improved methods for the detection of glutamate, galactose, alcohol, fructosyl amine, formate, lysine and oxalate.
This review will focus on the biosensing aspects of Prussian Blue-based sensors giving a general overview of the advantages provided by such mediator as well as its drawbacks. A comprehensive bibliographic reference list is presented together with the most up to date research findings in this field and possible future applications. The commercial potential of sensors based on this mediator will also be discussed.
Nano-mechanical resonators have gained an increasing importance in nanotechnology owing to their contributions to both fundamental and applied science. Yet, their small dimensions and mass raises ...some challenges as their dynamics gets dominated by nonlinearities that degrade their performance, for instance in sensing applications. Here, we report on the precise control of the nonlinear and stochastic bistable dynamics of a levitated nanoparticle in high vacuum. We demonstrate how it can lead to efficient signal amplification schemes, including stochastic resonance. This work contributes to showing the use of levitated nanoparticles as a model system for stochastic bistable dynamics, with applications to a wide variety of fields.
Nanomechanical resonators are widely operated as force and mass sensors with sensitivities in the zepto-Newton (10–21) and yocto-gram (10–24) regime, respectively. Their accuracy, however, is usually ...undermined by high uncertainties in the effective mass of the system, whose estimation is a nontrivial task. This critical issue can be addressed in levitodynamics, where the nanoresonator typically consists of a single silica nanoparticle of well-defined mass. Yet, current methods assess the mass of the levitated nanoparticles with uncertainties up to a few tens of percent, therefore preventing to achieve unprecedented sensing performances. Here, we present a novel measurement protocol that uses the electric field from a surrounding plate capacitor to directly drive a charged optically levitated particle in moderate vacuum. The developed technique estimates the mass within a statistical error below 1% and a systematic error of ∼2%, and paves the way toward more reliable sensing and metrology applications of levitodynamics systems.
Impact induced damages in stiffened composite structures are usually settled with constrained design criteria and recurring maintenance tasks, that affect weight savings potentialities of composite ...materials as well as operative costs. To overcome those penalties due to hidden damages, this paper deals with detection, localization and size assessment of stringers disbondings with monitoring techniques by permanently attached piezoelectric transducers (PZT) capable to excite and sense guided ultrasonic waves. A composite stiffened plate typically designed for wingbox structures is investigated to test a novel detection technique capable to predict arrival time of guided waves scattered from stringers detecting, as a consequence, any possible change in a specific scattering area. Theoretical aspects are investigated to correctly exploit the technique leading to a geometrical reduction which returns the optimal configuration of sensors. Several measurements are carried out to validate the hypothesis and the approach effectiveness. A promising result in agreement with state-of-the-art ultrasonic nondestructive testing is thus obtained and discussed. Furthermore it is shown that processing Lamb wave reflections signals is possible to improve the localization accuracy respect to a general purpose reconstruction algorithm while making use of fewer number of sensors possible.
Abstract
We report the virial measurements of the black hole (BH) mass of a sample of 17 type 2 active galactic nuclei (AGN), drawn from the Swift/BAT 70-month 14–195 keV hard X-ray catalogue, where ...a faint BLR component has been measured via deep NIR (0.8–2.5 μm) spectroscopy. We compared the type 2 AGN with a control sample of 33 type 1 AGN. We find that the type 2 AGN BH masses span the 5 < log(M
BH/M⊙) < 7.5 range, with an average log(M
BH/M⊙) = 6.7, which is ∼0.8 dex smaller than found for type 1 AGN. If type 1 and type 2 AGN of the same X-ray luminosity log(
$L_{\rm 14{\rm -}195}$
/erg s−1) ∼ 43.5 are compared, type 2 AGN have 0.5 dex smaller BH masses than type 1 AGN. Although based on few tens of objects, this result disagrees with the standard AGN unification scenarios in which type 1 and type 2 AGN are the same objects observed along different viewing angles with respect to a toroidal absorbing material.
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