Control of site selectivity is an exciting direction for synthetic organic chemistry owing to the possibility of selective modification of multifunctionalized molecules, ultimately including ...biomacromolecules. In this review, our recent research related to site selectivity in two types of transformation, namely, the acylation of hydroxy groups and C–H amination, is summarized. Regarding the acylation of hydroxy groups, catalyst-controlled site selectivity enables unconventional retrosynthetic analysis, leading to efficient syntheses of sugar-related natural and unnatural products. Regarding C–H amination, the discovery of unprecedented reaction sites in intermolecular amination mediated by dirhodium nitrenes is described. The findings of this research demonstrate the power of site-selective transformation in the synthesis of a particular class of compounds.
We present the results from the X-ray spectral analysis of high-redshift active galactic nuclei (AGN) in the Chandra Deep Field South (CDFS), making use of the new 4 Ms data set and new X-ray ...spectral models from Brightman & Nandra, which account for Compton scattering and the geometry of the circumnuclear material. Our goals are to ascertain to what extent the torus paradigm of local AGN is applicable at earlier epochs and to evaluate the evolution of the Compton thick fraction with redshift, important for X-ray background synthesis models and understanding the accretion history of the Universe. In addition to the torus models, we measure the fraction of scattered nuclear light, f
scatt, known to be dependent on the covering factor of the circumnuclear material, and use this to aid in our understanding of its geometry. We find that the covering factor of the circumnuclear material is correlated with the line-of-sight column density N
H, and as such the most heavily obscured AGN are in fact also the most geometrically buried. We come to these conclusions from the result that f
scatt decreases as N
H increases and from the prevalence of the torus model with the smallest opening angle as the best-fitting model in the fits to the most obscured AGN. We find that a significant fraction of sources (∼20 per cent) in the CDFS are likely to be buried in material with close to 4π coverage having been best fitted by the torus model with a 0° opening angle. Furthermore, we find 41 Compton thick sources in the CDFS using the new torus models, 29 of which we report here for the first time. We bin our sample by redshift in order to investigate the evolution of the Compton thick fraction by epoch. We take into account the incompleteness and contamination rates in the spectral identification of Compton thick AGN using data from simulations. We also account for the bias against the X-ray selection of heavily obscured sources due to flux suppression in the Chandra band, by restricting to intrinsic luminosities at which the CDFS is sensitive to Compton thick AGN (L
X∼ 1044 at z= 2.5). We find a significant increase in the intrinsic Compton thick fraction, normalized to L
X= 1043.5 erg s−1, from ≈20 per cent in the local Universe to ≈40 per cent at z=1 - 4.
We construct an X-ray spectral model from the clumpy torus in an active galactic nucleus, designated as "XCLUMPY," utilizing the Monte Carlo simulation for Astrophysics and Cosmology framework. The ...adopted geometry of the torus is the same as that in Nenkova et al. who assume a power-law distribution of clumps in the radial direction and a normal distribution in the elevation direction. We investigate the dependence of the X-ray continuum and Fe K fluorescence line profile on the torus parameters. Our model is compared with other torus models: MYTorus model, Ikeda model, and CTorus model. As an example, we also present the results applied to the broadband X-ray spectra of the Circinus galaxy observed with XMM-Newton, Suzaku, and NuSTAR. Our model can well reproduce the data, yielding a hydrogen column density along the equatorial plane cm−2, a torus angular width degree, and a 2-10 keV luminosity . These results are discussed in comparison with the observations in other wavelengths.
We present the most up to date X-ray luminosity function (XLF) and absorption function of active galactic nuclei (AGNs) over the redshift range from 0 to 5, utilizing the largest, highly complete ...sample ever available obtained from surveys performed with Swift/BAT, MAXI, ASCA, XMM-Newton, Chandra, and ROSAT. The combined sample, including that of the Subaru/XMM-Newton Deep Survey, consists of 4039 detections in the soft (0.5-2 keV) and/or hard (>2 keV) band. We utilize a maximum likelihood method to reproduce the count rate versus redshift distribution for each survey, by taking into account the evolution of the absorbed fraction, the contribution from Compton-thick (CTK) AGNs, and broadband spectra of AGNs, including reflection components from tori based on the luminosity- and redshift-dependent unified scheme. We find that the shape of the XLF at z ~ 1-3 is significantly different from that in the local universe, for which the luminosity-dependent density evolution model gives much better description than the luminosity and density evolution model. These results establish the standard population synthesis model of the X-ray background (XRB), which well reproduces the source counts, the observed fractions of CTK AGNs, and the spectrum of the hard XRB. The number ratio of CTK AGNs to the absorbed Compton-thin (CTN) AGNs is constrained to be approximately 0.5-1.6 to produce the 20-50 keV XRB intensity within present uncertainties, by assuming that they follow the same evolution as CTN AGNs. The growth history of supermassive black holes is discussed based on the new AGN bolometric luminosity function.
The black hole mass and accretion rate in ultraluminous X-ray sources (ULXs) in external galaxies, whose X-ray luminosities exceed those of the brightest black holes in our Galaxy by hundreds and ...thousands of times, is an unsolved problem. Here we report that all ULXs ever spectroscopically observed have almost the same optical spectra, apparently of WNL type (late nitrogen Wolf-Rayet stars) or LBV (luminous blue variables) in their hot state, which are very scarce stellar objects. We show that the spectra do not originate from WNL/LBV-type donors but from very hot winds from the accretion disks with nearly normal hydrogen content, which have similar physical conditions to the stellar winds from these stars. The optical spectra are similar to that of SS 433, the only known supercritical accretor in our Galaxy, although the ULX spectra indicate a higher wind temperature. Our results suggest that ULXs with X-ray luminosities of ∼1040 erg s-1 must constitute a homogeneous class of objects, which most likely have supercritical accretion disks.
ABSTRACT We report the results obtained by a systematic, broadband (0.5-150 keV) X-ray spectral analysis of moderately obscured (Compton-thin, 22 ≤ log N H < 24 ) active galactic nuclei (AGNs) ...observed with Suzaku and Swift/Burst Alert Telescope (BAT). Our sample consists of 45 local AGNs at z < 0.1 with log L 14 − 195 keV > 42 detected in the Swift/BAT 70-month survey, whose Suzaku archival data are available as of 2015 December. All spectra are uniformly fit with a baseline model composed of an absorbed cutoff power-law component, reflected emission accompanied by a narrow fluorescent iron-K line from cold matter (torus), and scattered emission. The main results based on the above analysis are as follows. (1) The photon index is correlated with Eddington ratio, but not with luminosity or black hole mass. (2) The ratio of the luminosity of the iron-K line to the X-ray luminosity an indicator of the covering fraction of the torus, shows significant anticorrelation with luminosity. (3) The averaged reflection strength derived from stacked spectra above 14 keV is larger in less luminous ( log L 10 − 50 keV ≤ 43.3 , R = 1.04 − 0.19 + 0.17 ) or highly obscured ( log N H > 23 , R = 1.03 − 0.17 + 0.15 ) AGNs than in more luminous ( log L 10 − 50 keV > 43.3 , R = 0.46 − 0.09 + 0.08 ) or lightly obscured ( log N H ≤ 23 , R = 0.59 − 0.10 + 0.09 ) objects. (4) The ratio of the luminosity of the O IV 25.89 m line to the X-ray luminosity is significantly smaller in AGNs with lower soft X-ray scattering fractions, suggesting that the former luminosity underestimates the intrinsic power of an AGN buried in a torus of small opening angle.
Abstract
We investigate the relation of black hole mass versus host stellar mass and that of mass accretion rate versus star formation rate (SFR) in moderately luminous (
), X-ray selected broad-line ...active galactic nuclei (AGNs) at
z
= 1.18–1.68 in the Subaru/XMM-Newton Deep Field. The far-infrared to far-ultraviolet spectral energy distributions of 85 AGNs are reproduced with the latest version of Code Investigating GALaxy Emission (
CIGALE
), where the AGN clumpy torus model
SKIRTOR
is implemented. Most of their hosts are confirmed to be main-sequence star-forming galaxies. We find that the mean ratio of the black hole mass (
M
BH
) to the total stellar mass (
M
stellar
) is
, which is similar to the local black hole–to–bulge mass ratio. This suggests that if the host galaxies of these moderately luminous AGNs at
z
∼ 1.4 are dominated by bulges, they already established the local black hole mass–bulge mass relation; if they are disk dominant, their black holes are overmassive relative to the bulges. The AGN bolometric luminosities and SFR show a good correlation with ratios higher than that expected from the local black hole-to-bulge mass relation, suggesting that these AGNs are in a SMBH-growth dominant phase.
We consider the Cauchy problem in Rn for quasilinear thermoelastic Kirchhoff-type plate equations where the heat conduction is modeled by either the Cattaneo law or by the Fourier law. Additionally, ...we take into account possible inertial effects. Considering nonlinearities which are of fourth-order in the space variable, we deal with a quasilinear system which triggers difficulties typical for nonlinear Schrödinger equations. The different models considered are systems of mixed type comparable to Schrödinger–parabolic or Schrödinger–hyperbolic systems. The main task consists in proving sophisticated a priori estimates leading to obtaining the global existence of solutions for small data, neither known nor expected for the Cauchy problem in pure plate theory nor available before for the coupled system under investigation, where only special cases (bounded domains within with analytic semigroup setting, or the Cauchy problem with semilinear nonlinearities) had been treated before.
We report results from the X-ray and optical monitoring of the black hole candidate MAXI J1820+070 (=ASSASN-18ey) over the entire period of its outburst from 2018 March to October. In this outburst, ...the source exhibited two sets of "fast rise and slow decay"-type long-term flux variations. We found that the 1-100 keV luminosities at two peaks were almost the same, although a significant spectral softening was only seen in the second flux rise. This confirms that the state transition from the low/hard state to the high/soft state is not determined by the mass accretion rate alone. The X-ray spectrum was reproduced with the disk blackbody emission and its Comptonization, and the long-term spectral variations seen in this outburst were consistent with a disk truncation model. The Comptonization component, with a photon index of 1.5-1.9 and electron temperature of 40 keV, was dominant during the low/hard state periods, and its contribution rapidly decreased (increased) during the spectral softening (hardening). During the high/soft-state period, in which the X-ray spectrum became dominated by the disk blackbody component, the inner disk radius was almost constant, suggesting that the standard disk was present down to the innermost stable circular orbit. The long-term evolution of optical and X-ray luminosities and their correlation suggest that the jets substantially contributed to the optical emission in the low/hard state, while they are quenched and the outer disk emission dominated the optical flux in the intermediate state and the high/soft state.
Abstract
We present systematic broadband X-ray spectral analysis of 52 Compton-thick (
24
≤
log
N
H
LOS
/
cm
−
2
) active galactic nucleus (CTAGN) candidates selected by the Swift/Burst Alert ...Telescope all-sky hard X-ray survey observed with Chandra, X-ray Multi-Mirror Mission-Newton (XMM-Newton), Swift/X-Ray Telescope, Suzaku, and NuSTAR. The XMM-Newton data of 10 objects and the NuSTAR data of 15 objects are published for the first time. We use an X-ray spectral model from a clumpy torus (XClumpy) to determine the torus properties. As a result, the hydrogen column density along the line of sight
N
H
LOS
obtained from the XClumpy model indicates that 24 objects are Compton-thin AGNs and 28 objects are CTAGNs in a 90% confidence interval. The main reason is the difference in the torus model applied. The hydrogen column density along the equatorial direction
N
H
Equ
of CTAGNs inferred from the XClumpy model is larger than that of less obscured AGNs. The Compton-thin torus covering factor
C
22
obtained from the XClumpy model is consistent with that of Ricci et al. in the low Eddington ratio (
log
R
Edd
≤
−
1.0
), whereas
C
22
inferred from the XClumpy model is larger than that of Ricci et al. in the high Eddington ratio (
−
1.0
≤
log
R
Edd
). The average value of the Compton-thick torus covering factor
C
24
obtained from the XClumpy model is
36
−
4
+
4
%. This value is larger than that of Ricci et al. (
C
24
≃
27
−
4
+
4
%) based on the assumption that all AGNs have intrinsically the same torus structure. These results suggest that the structure of CTAGNs may be intrinsically different from that of less obscured AGNs.
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