382 research outputs found
Suzaku View of the Swift/BAT Active Galactic Nuclei. V. Torus Structure of Two Luminous Radio-Loud Active Galactic Nuclei (3C 206 and PKS 0707-35)
We present the results from broadband X-ray spectral analysis of 3C 206 and PKS 070735 with Suzaku and Swift/BAT, two of the most luminous unobscured and obscured radio-loud active galactic nuclei (AGNs) with hard X-ray luminosities of 10(sup 45.5) erg per second and 10(sup 44.9) erg per second (14-195 keV), respectively. Based on the radio core luminosity, we estimate that the X-ray spectrum of 3C 206 contains a significant (60% in the 14-195 keV band) contribution from the jet, while it is negligible in PKS 070735.We can successfully model the spectra with the jet component (for 3C 206), the transmitted emission, and two reflection components from the torus and the accretion disk. The reflection strengths from the torus are found to be R(sub torus)(Omega/2pi) = 0.29 +/- 0.18 and 0.41 +/- 0.18 for 3C 206 and PKS 070735, respectively, which are smaller than those in typical Seyfert galaxies. Utilizing the torus model by Ikeda et al., we quantify the relation between the half-opening angle of a torus (theta(sub oa)) and the equivalent width of an iron-K line. The observed equivalent width of 3C 206, less than 71 eV, constrains the column density in the equatorial plane to N(sup eq)(sub H) lesst han 10(sup 23) per square centimeter, or the half-opening angle to theta(sub oa) greater than 80 deg. if N(sup eq)(sub H) = 10(sup 24) per square centimeter is assumed. That of PKS 070735, 72 +/- 36 eV, is consistent with N(sup eq)(sub H) 10(sup 23) per square centimeter. Our results suggest that the tori in luminous radio-loud AGNs are only poorly developed. The trend is similar to that seen in radio-quiet AGNs, implying that the torus structure is not different between AGNs with jets and without jets
ALMA polarimetric studies of rotating jet/disk systems
We have recently obtained polarimetric data at mm wavelengths with ALMA for
the young systems DG Tau and CW Tau, for which the rotation properties of jet
and disk have been investigated in previous high angular resolution studies.
The motivation was to test the models of magneto-centrifugal launch of jets via
the determination of the magnetic configuration at the disk surface. The
analysis of these data, however, reveals that self-scattering of dust thermal
radiation dominates the polarization pattern. It is shown that even if no
information on the magnetic field can be derived in this case, the polarization
data are a powerful tool for the diagnostics of the properties and the
evolution of dust in protoplanetary disks.Comment: 9 pages, 3 figures, to appear in "Jet Simulations, Experiments and
Theory. Ten years after JETSET, what is next ?", C. Sauty ed., Springer
Natur
Suzaku Observation of the Brightest Broad-Line Radio Galaxy 4C 50.55 (IGR J 21247+5058)
We report the results from a deep Suzaku observation of 4C 50.55 (IGR J
21247+5058), the brightest broad-line radio galaxy in the hard X-ray (> 10 keV)
sky. The simultaneous broad band spectra over 1-60 keV can be represented by a
cut-off power law with two layers of absorption and a significant reflection
component from cold matter with a solid angle of \Omega/2\pi \approx 0.2. A
rapid flux rise by ~ 20% over 2 \times 10^4 sec is detected in the 2-10 keV
band. The spectral energy distribution suggests that there is little
contribution to the total X-ray emission from jets. Applying a thermal
Comptonization model, we find that corona is optically thick (\tau_e \approx 3)
and has a relatively low temperature (kT_e \approx 30 keV). The narrow iron-K
emission line is consistent with a picture where the standard disk is truncated
and/or its inner part is covered by optically thick Comptonizing corona
smearing out relativistic broad line features. The inferred disk structure may
be a common feature of accretion flows onto black holes that produce powerful
jets.Comment: 8 pages, 7 figure
JWST imaging of edge-on protoplanetary disks. I. Fully vertically mixed 10m grains in the outer regions of a 1000 au disk
Scattered light imaging of protoplanetary disks provides key insights on the
geometry and dust properties in the disk surface. Here we present JWST
2--21\,m images of a 1000\,au-radius edge-on protoplanetary disk
surrounding an 0.4\, young star in Taurus, 2MASS\,J04202144+2813491.
These observations represent the longest wavelengths at which a protoplanetary
disk is spatially resolved in scattered light. We combine these observations
with HST optical images and ALMA continuum and CO mapping. We find that the
changes in the scattered light disk morphology are remarkably small across a
factor of 30 in wavelength, indicating that dust in the disk surface layers is
characterized by an almost gray opacity law. Using radiative transfer models,
we conclude that grains up to m in size are fully coupled to
the gas in this system, whereas grains m are strongly settled
towards the midplane. Further analyses of these observations, and similar ones
of other edge-on disks, will provide strong empirical constraints on disk
dynamics and evolution and grain growth models. In addition, the 7.7 and
12.\,m JWST images reveal an X-shaped feature located above the warm
molecular layer traced by CO line emission. The highest elevations at which
this feature is detectable roughly match the maximal extent of the disk in
visible wavelength scattered light as well as of an unusual kinematic signature
in CO. We propose that these phenomena could be related to a disk wind
entraining small dust grains.Comment: Accepted for publication in the Astronomical Journa
JWST imaging of edge-on protoplanetary disks II. Appearance of edge-on disks with a tilted inner region: case study of IRAS04302+2247
We present JWST imaging from 2m to 21m of the edge-on
protoplanetary disk around the embedded young star IRAS04302+2247. The
structure of the source shows two reflection nebulae separated by a dark lane.
The source extent is dominated by the extended filamentary envelope at
4.4m and shorter wavelengths, transitioning at 7m and longer
wavelengths to more compact lobes of scattered light from the disk itself. The
dark lane thickness does not vary significantly with wavelength, which we
interpret as an indication for intermediate-sized (m) grains in the
upper layers of the disk. Intriguingly, we find that the brightest nebula of
IRAS40302 switches side between 12.8m and 21m. We explore the effect
of a tilted inner region on the general appearance of edge-on disks. We find
that radiative transfer models of a disk including a tilted inner region can
reproduce an inversion in the brightest nebula. In addition, for specific
orientations, the model also predicts strong lateral asymmetries, which can
occur for more than half possible viewing azimuths. A large number of edge-on
protoplanetary disks observed in scattered light show such lateral asymmetries
(15/20), which suggests that a large fraction of protoplanetary disks might
host a tilted inner region. Stellar spots may also induce lateral asymmetries,
which are expected to vary over a significantly shorter timescale. Variability
studies of edge-on disks would allow to test the dominant scenario for the
origin of these asymmetries.Comment: Accepted for publication in Ap
Barium in twilight zone suspended matter as a potential proxy for particulate organic carbon remineralization : results for the North Pacific
Author Posting. © Elsevier B.V., 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 55 (2008): 1673-1683, doi:10.1016/j.dsr2.2008.04.020.This study focuses on the fate of exported organic carbon in the twilight zone at two
contrasting environments in the North Pacific: the oligotrophic ALOHA site (22°45'
N 158°W; Hawaii; studied during JuneâJuly 2004) and the mesotrophic Subarctic
Pacific K2 site (47°N, 161°W; studied during July-August 2005). Earlier work has
shown that non-lithogenic, excess particulate Ba (Baxs) in the mesopelagic water
column is a potential proxy of organic carbon remineralization. In general Baxs
contents were significantly larger at K2 than at ALOHA. At ALOHA the Baxs profiles
from repeated sampling (5 casts) showed remarkable consistency over a period of
three weeks, suggesting that the system was close to being at steady state. In contrast,
more variability was observed at K2 (6 casts sampled) reflecting the more dynamic
physical and biological conditions prevailing in this environment. While for both sites
Baxs concentrations increased with depth, at K2 a clear maximum was present
between the base of the mixed layer at around 50m and 500m, reflecting production
and release of Baxs. Larger mesopelagic Baxs contents and larger bacterial production
in the twilight zone at the K2 site indicate that more material was exported from the
upper mixed layer for bacterial degradation deeper, compared to the ALOHA site.
Furthermore, application of a published transfer function (Dehairs et al., 1997)
relating oxygen consumption to the observed Baxs data indicated that the latter were in
good agreement with bacterial respiration, calculated from bacterial production. These
results corroborate earlier findings highlighting the potential of Baxs as a proxy for
organic carbon remineralization.
The range of POC remineralization rates calculated from twilight zone excess
particulate Ba contents did also compare well with the depth dependent POC flux
decrease as recorded by neutrally buoyant sediment traps, except in 1 case (out of 4).
This discrepancy could indicate that differences in sinking velocities cause an
3
uncoupling of the processes occurring in the fine suspended particle pool from those
affecting the larger particle pool which sustains the vertical flux, thus rendering
comparison between both approaches risky.This research was supported by Federal Science Policy
Office, Brussels through contracts EV/03/7A, SD/CA/03A, the Research Foundation
Flanders through grant G.0021.04 and Vrije Universiteit Brussel via grant GOA 22, as
well as the US National Science Foundation programs in Chemical and Biological
Oceanography
Broad Line Radio Galaxies Observed with Fermi-LAT: The Origin of the GeV Gamma-Ray Emission
We report on a detailed investigation of the gamma-ray emission from 18 broad
line radio galaxies (BLRGs) based on two years of Fermi Large Area Telescope
(LAT) data. We confirm the previously reported detections of 3C 120 and 3C 111
in the GeV photon energy range; a detailed look at the temporal characteristics
of the observed gamma-ray emission reveals in addition possible flux
variability in both sources. No statistically significant gamma-ray detection
of the other BLRGs was however found in the considered dataset. Though the
sample size studied is small, what appears to differentiate 3C 111 and 3C 120
from the BLRGs not yet detected in gamma-rays is the particularly strong
nuclear radio flux. This finding, together with the indications of the
gamma-ray flux variability and a number of other arguments presented, indicate
that the GeV emission of BLRGs is most likely dominated by the beamed radiation
of relativistic jets observed at intermediate viewing angles. In this paper we
also analyzed a comparison sample of high accretion-rate Seyfert 1 galaxies,
which can be considered radio-quiet counterparts of BLRGs, and found none were
detected in gamma-rays. A simple phenomenological hybrid model applied for the
broad-band emission of the discussed radio-loud and radio-quiet type 1 active
galaxies suggests that the relative contribution of the nuclear jets to the
accreting matter is > 1 percent on average for BLRGs, whilst <0.1 percent for
Seyfert 1 galaxies.Comment: 18 pages, 9 figures, accepted for publication in the Ap
Swelling-Activated Ca2+ Channels Trigger Ca2+ Signals in Merkel Cells
Merkel cell-neurite complexes are highly sensitive touch receptors comprising epidermal Merkel cells and sensory afferents. Based on morphological and molecular studies, Merkel cells are proposed to be mechanosensory cells that signal afferents via neurotransmission; however, functional studies testing this hypothesis in intact skin have produced conflicting results. To test this model in a simplified system, we asked whether purified Merkel cells are directly activated by mechanical stimulation. Cell shape was manipulated with anisotonic solution changes and responses were monitored by Ca2+ imaging with fura-2. We found that hypotonic-induced cell swelling, but not hypertonic solutions, triggered cytoplasmic Ca2+ transients. Several lines of evidence indicate that these signals arise from swelling-activated Ca2+-permeable ion channels. First, transients were reversibly abolished by chelating extracellular Ca2+, demonstrating a requirement for Ca2+ influx across the plasma membrane. Second, Ca2+ transients were initially observed near the plasma membrane in cytoplasmic processes. Third, voltage-activated Ca2+ channel (VACC) antagonists reduced transients by half, suggesting that swelling-activated channels depolarize plasma membranes to activate VACCs. Finally, emptying internal Ca2+ stores attenuated transients by 80%, suggesting Ca2+ release from stores augments swelling-activated Ca2+ signals. To identify candidate mechanotransduction channels, we used RT-PCR to amplify ion-channel transcripts whose pharmacological profiles matched those of hypotonic-evoked Ca2+ signals in Merkel cells. We found 11 amplicons, including PKD1, PKD2, and TRPC1, channels previously implicated in mechanotransduction in other cells. Collectively, these results directly demonstrate that Merkel cells are activated by hypotonic-evoked swelling, identify cellular signaling mechanisms that mediate these responses, and support the hypothesis that Merkel cells contribute to touch reception in the Merkel cell-neurite complex
- âŠ