549 research outputs found
Towards an informed quest for accretion disc winds in quasars: the intriguing case of Ton 28
We report on the detection of a blueshifted Fe K absorption feature in two consecutive XMM–Newton  observations of the luminous blue quasar Ton 28, at the 4σ cumulative significance. The rest energy of 9.2 keV implies the presence of an accretion disc wind with bulk outflow velocity of ∼0.28c, while the kinetic power is most likely a few per cent of the quasar luminosity. Remarkably, Ton 28 had been specifically selected as an optimal target to reveal an ultra-fast X-ray wind based on its total luminosity (Lbol > 1046 erg s−1) and [O III] λ5007 Å equivalent width (EW < 6 Å), suggestive of high accretion rate and low inclination, respectively. Other peculiar optical/UV emission-line properties include narrow Hβ, strong Fe II, and blueshifted C IV . These are key parameters in the Eigenvector 1 formalism, and are frequently found in active galaxies with ongoing accretion disc winds, hinting at a common physical explanation. Provided that the effectiveness of our selection method is confirmed with similar sources, this result could represent the first step towards the characterization of black hole winds through multiwavelength indicators in the absence of high-quality X-ray spectra
On the 2015 outburst of the EXor variable star V1118 Ori
After a long-lasting period of quiescence of about a decade, the source V1118
Ori, one of the most representative members of the EXor variables, is now
outbursting. Since the initial increase of the near-infrared flux of about 1
mag (JHK bands) registered on 2015 September 22, the source brightness has
remained fairly stable. We estimate DeltaV about 3 mag with respect to the
quiescence phase. An optical/near-IR low-resolution spectrum has been obtained
with the Large Binocular Telescope instruments MODS and LUCI2, and compared
with a spectrum of similar spectral resolution and sensitivity level taken
during quiescence. Together with the enhancement of the continuum, the outburst
spectrum presents a definitely higher number of emission lines, in particular
HI recombination lines of the Balmer, Paschen, and Brackett series, along with
bright permitted lines of several species, forbidden atomic lines, and CO
ro-vibrational lines. Both mass accretion and mass loss rates have
significantly increased (by to about an order of magnitude, mass accretion rate
= 1.2-4.8 10^-8 M_sun/yr, mass loss rate = 0.8-2 10^-9 M_sun/yr) with respect
to the quiescence phase. If compared with previous outbursts, the present one
appears less energetic. Alternatively, it could already be in the fading phase
(with the maximum brightness level reached when the source was not visible),
or, viceversa, still in the rising phase.Comment: Accepted ApJ Letter
Hole-depletion of ladders in SrCuO induced by correlation effects
The hole distribution in SrCuO is studied by low
temperature polarization dependent O K Near-Edge X-ray Absorption Fine
Structure measurements and state of the art electronic structure calculations
that include core-hole and correlation effects in a mean-field approach.
Contrary to all previous analysis, based on semi-empirical models, we show that
correlations and antiferromagnetic ordering favor the strong chain
hole-attraction. For the remaining small number of holes accommodated on
ladders, leg-sites are preferred to rung-sites. The small hole affinity of
rung-sites explains naturally the 1D - 2D cross-over in the phase diagram of
(La,Y,Sr,Ca)CuOComment: 6 pages, 8 figure
Large Binocular Telescope view of the atmosphere of GJ1214b
The atmospheric composition and vertical structure of the super-Earth GJ1214b
has been a subject of debate since its discovery in 2009. Recent studies have
indicated that high-altitude clouds might mask the lower layers. However, some
data points that were gathered at different times and facilities do not fit
this picture, probably because of a combination of stellar activity and
systematic errors. We observed two transits of GJ1214b with the Large Binocular
Camera, the dual-channel camera at the Large Binocular Telescope. For the first
time, we simultaneously measured the relative planetary radius
at blue and red optical wavelengths (), thus
constraining the Rayleigh scattering on GJ1214b after correcting for stellar
activity effects. To the same purpose, a long-term photometric follow-up of the
host star was carried out with WiFSIP at STELLA, revealing a rotational period
that is significantly longer than previously reported. Our new unbiased
estimates of yield a flat transmission spectrum extending to shorter
wavelengths, thus confirming the cloudy atmosphere scenario for GJ1214b.Comment: 11 pages, 5 figures, 3 tables. Published in A&A. Minor changes to
reflect the published versio
Quasars as standard candles II
A tight non-linear relation between the X-ray and the optical-ultraviolet (UV) emission has been observed in active galactic nuclei (AGN) over a wide range of redshift and several orders of magnitude in luminosity, suggesting the existence of an ubiquitous physical mechanism regulating the energy transfer between the accretion disc and the X-ray emitting corona. Recently, our group developed a method to use this relation in observational cosmology, turning quasars into standardizable candles. This work mainly seeks to investigate the potential evolution of this correction at high redshifts. We thus studied the LX − LUV relation for a sample of quasars in the redshift range 4 <  z <  7, adopting the selection criteria proposed in our previous work regarding their spectral properties. The resulting sample consists of 53 type 1 (unobscured) quasars, observed either with Chandra or XMM-Newton, for which we performed a full spectral analysis, determining the rest-frame 2 keV flux density, as well as more general X-ray properties such as the estimate of photon index, and the soft (0.5–2 keV) and hard (2–10 keV) unabsorbed luminosities. We find that the relation shows no evidence for evolution with redshift. The intrinsic dispersion of the LX–LUV for a sample free of systematics/contaminants is of the order of 0.22 dex, which is consistent with previous estimates from our group on quasars at lower redshift
Effect of NF-κB/Rel inhibition on spontaneous vs chemotherapy-induced apoptosis in AML and normal cord blood CD34+ cells
n/
Evidence of orbital reconstruction at interfaces in La0.67Sr0.33MnO3 films
Electronic properties of transition metal oxides at interfaces are influenced
by strain, electric polarization and oxygen diffusion. Linear dichroism (LD)
x-ray absorption, diffraction, transport and magnetization on thin
La0.7Sr0.3MnO3 films, allow identification of a peculiar universal interface
effect. We report the LD signature of preferential 3d-eg(3z2-r2) occupation at
the interface, suppressing the double exchange mechanism. This surface orbital
reconstruction is opposite of that favored by residual strain and independent
of dipolar fields, chemical nature of the substrate and capping.Comment: 13 pages, 5 figure
Bimagnon studies in cuprates with Resonant Inelastic X-ray Scattering at the O K edge. I - An assessment on La2CuO4 and a comparison with the excitation at Cu L3 and Cu K edges
We assess the capabilities of magnetic Resonant Inelastic X-ray Scattering
(RIXS) at the O edge in undoped cuprates by taking La_{2}CuO_{4} as a
benchmark case, based on a series of RIXS measurements that we present here. By
combining the experimental results with basic theory we point out the
fingerprints of bimagnon in the O edge RIXS spectra. These are a dominant
peak around 450 meV, the almost complete absence of dispersion both with
and polarization and the almost constant intensity vs. the transferred
momentum with polarization. This behavior is quite different from Cu
edge RIXS giving a strongly dispersing bimagnon tending to zero at the
center of the Brillouin zone. This is clearly shown by RIXS measurements at the
Cu edge that we present. The Cu bimagnon spectra and those at Cu
edge - both from the literature and from our data - however, have the same
shape. These similarities and differences are understood in terms of different
sampling of the bimagnon continuum. This panorama points out the unique
possibilities offered by O RIXS in the study of magnetic excitations in
cuprates near the center of the BZ
A powerful (and likely young) radio-loud quasar at z=5.3
We present the discovery of PSO J191.0569686.43172 (hereafter PSO
J19186), a new powerful radio-loud quasar (QSO) in the early Universe (z =
5.32). We discovered it by cross-matching the NRAO VLA Sky Survey (NVSS) radio
catalog at 1.4 GHz with the first data release of the Panoramic Survey
Telescope and Rapid Response System (Pan-STARRS PS1) in the optical. With a
NVSS flux density of 74.2 mJy, PSO J19186 is one of the brightest radio QSO
discovered at z5. The intensity of its radio emission is also confirmed
by the very high value of radio loudness (R>300). The observed radio spectrum
of PSO J19186 shows a possible turnover around 1 GHz (i.e., 6
GHz in the rest frame), making it a Gigahertz-Peaked Spectrum (GPS) source.
However, variability could affect the real shape of the radio spectrum, since
the data in hand have been taken 25 years apart. By assuming a peak of
the observed radio spectrum between 1 and 2 GHz (i.e. 6 and 13 GHz in
the rest-frame) we found a linear size of the source of 10-30 pc and a
corresponding kinetic age of 150-460 yr. This would make PSO J19186 a newly
born radio source. However, the large X-ray luminosity (5.310
erg s), the flat X-ray photon index (=1.32) and the
optical-X-ray spectral index (=1.329) are typical of
blazars. This could indicate that the non-thermal emission of PSO J19186 is
Doppler boosted. Further radio observations (both on arcsec and parsec scales)
are necessary to better investigate the nature of this powerful radio QSO.Comment: 10 pages, 9 figures, 5 tables, Accepted for publication in A&
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