188 research outputs found
Short Timescale Evolution of the Polarized Radio Jet during V404 Cygni's 2015 Outburst
We present a high time resolution, multi-frequency linear polarization
analysis of Very Large Array (VLA) radio observations during some of the
brightest radio flaring (~1 Jy) activity of the 2015 outburst of V404 Cygni.
The VLA simultaneously captured the radio evolution in two bands (each with two
1 GHz base-bands), recorded at 5/7 GHz and 21/26 GHz, allowing for a broadband
polarimetric analysis. Given the source's high flux densities, we were able to
measure polarization on timescales of ~13 minutes, constituting one of the
highest temporal resolution radio polarimetric studies of a black hole X-ray
binary (BHXB) outburst to date. Across all base-bands, we detect variable,
weakly linearly polarized emission (<1%) with a single, bright peak in the
time-resolved polarization fraction, consistent with an origin in an evolving,
dynamic jet component. We applied two independent polarimetric methods to
extract the intrinsic electric vector position angles and rotation measures
from the 5 and 7 GHz base-band data and detected a variable intrinsic
polarization angle, indicative of a rapidly evolving local environment or a
complex magnetic field geometry. Comparisons to the simultaneous,
spatially-resolved observations taken with the Very Long Baseline Array at 15.6
GHz, do not show a significant connection between the jet ejections and the
polarization state.Comment: 24 pages, 9 figures, accepted by MNRA
Sturdier DNA nanotubes via ligation
DNA nanotubes are crystalline self-assemblies of DNA tiles ~10 nm in diameter that readily grow tens of micrometers in length. Easy assembly,
programmability, and stiffness make them interesting for many applications, but DNA nanotubes begin to melt at temperatures below 40 °C,
break open when deposited on mica or scanned by AFM, and disintegrate in deionized water. These weaknesses can be traced to the presence
of discontinuities in the phosphate backbone, called nicks. The nanotubes studied here have five nicks, one in the core of a tile and one at
each corner. We report the successful ligation of all four corner nicks by T4 DNA ligase. Although ligation does not change the nanotubes’
stiffness, ligated nanotubes withstand temperatures over 70 °C, resist breaking during AFM, and are stable in pure water for over a month.
Ligated DNA nanotubes are thus physically and chemically sturdy enough to withstand the manipulations necessary for many technological
applications
European ALMA operations: the interaction with and support to the users
The Atacama Large Millimetre/submillimetre Array (ALMA) is one of the largest
and most complicated observatories ever built. Constructing and operating an
observatory at high altitude (5000m) in a cost effective and safe manner, with
minimal effect on the environment creates interesting challenges. Since the
array will have to adapt quickly to prevailing weather conditions, ALMA will be
operated exclusively in service mode. By the time of full science operations,
the fundamental ALMA data product shall be calibrated, deconvolved data cubes
and images, but raw data and data reduction software will be made available to
users as well. User support is provided by the ALMA Regional Centres (ARCs)
located in Europe, North America and Japan. These ARCs constitute the interface
between the user community and the ALMA observatory in Chile. For European
users the European ARC is being set up as a cluster of nodes located throughout
Europe, with the main centre at the ESO Headquarters in Garching. The main
centre serves as the access portal and in synergy with the distributed network
of ARC nodes, the main aim of the ARC is to optimize the ALMA science output
and to fully exploit this unique and powerful facility. The aim of this article
is to introduce the process of proposing for observing time, subsequent
execution of the observations, obtaining and processing of the data in the ALMA
epoch. The complete end-to-end process of the ALMA data flow from the proposal
submission to the data delivery is described.Comment: 7 pages, three figure
Ethyl cyanide on Titan: Spectroscopic detection and mapping using ALMA
We report the first spectroscopic detection of ethyl cyanide (CHCN)
in Titan's atmosphere, obtained using spectrally and spatially resolved
observations of multiple emission lines with the Atacama Large
Millimeter/submillimeter array (ALMA). The presence of CHCN in Titan's
ionosphere was previously inferred from Cassini ion mass spectrometry
measurements of CHCNH. Here we report the detection of 27
rotational lines from CHCN (in 19 separate emission features detected
at confidence), in the frequency range 222-241 GHz. Simultaneous
detections of multiple emission lines from HCN, CHCN and CHCCH were
also obtained. In contrast to HCN, CHCN and CHCCH, which peak in
Titan's northern (spring) hemisphere, the emission from CHCN is found
to be concentrated in the southern (autumn) hemisphere, suggesting a distinctly
different chemistry for this species, consistent with a relatively short
chemical lifetime for CHCN. Radiative transfer models show that most of
the CHCN is concentrated at altitudes 300-600 km, suggesting production
predominantly in the mesosphere and above. Vertical column densities are found
to be in the range (2-5) cm.Comment: Published in 2015, ApJL, 800, L1
The radio continuum spectrum of Mira A and Mira B up to submillimeter wavelengths
We present new measurements of the flux densities at submillimeter
wavelengths based on ALMA band 7 (338 GHz) and band 9 (679 GHz) observations to
better constrain the origin of the continuum emission of the Mira AB binary
system and to check its orbit. We have measured the Mira A and Mira B continuum
in ALMA band 7, with a resolution of ~0"31, and for the first time in ALMA band
9, with a resolution of ~0"18. We resolved the binary system at both bands, and
derived the continuum spectral index of the stars and their relative position.
We also analyzed ALMA SciVer data obtained in bands 6 and 3. Measurements at
centimeter wavelengths obtained by other authors have been included in our
study of the spectral energy distribution of the Mira components. The Mira A
continuum emission has a spectral index of 1.98+-0.04 extending from
submillimeter down to centimeter wavelengths. The spectral index of the Mira B
continuum emission is 1.93+-0.06 at wavelengths ranging from submillimeter to
~3.1 mm, and a shallower spectral index of 1.22+-0.09 at longer wavelengths.
The Mira A continuum emission up to submillimeter wavelengths is consistent
with that of a radio photosphere surrounding the evolved star for which models
predict a spectral index close to 2. The Mira B continuum emission cannot be
described with a single ionized component. An extremely compact and dense
region around the star can produce the nearly thermal continuum measured in the
0.4-3.1 mm wavelength range, and an inhomogeneous, less dense, and slightly
larger ionized envelope could be responsible for the emission at longer
wavelengths. Our results illustrate the potential of ALMA for high precision
astrometry of binary systems. We have found a significant discrepancy of ~14
milliarcsec between the ALMA measurements and the predicted orbit positions.Comment: 6 pages, 3 figures, 2 tables, accepted for publication in Astronomy
and Astrophysic
CO(1-0) line imaging of massive star-forming disc galaxies at z=1.5-2.2
We present detections of the CO(J= 1-0) emission line in a sample of four massive star-forming galaxies at z~1.5-2.2 obtained with the Karl G. Jansky Very Large Array (VLA). Combining these observations with previous CO(2-1) and CO(3-2) detections of these galaxies, we study the excitation properties of the molecular gas in our sample sources. We find an average line brightness temperature ratios of R_{21}=0.70+\-0.16 and R_{31}=0.50+\-0.29, based on measurements for three and two galaxies, respectively. These results provide additional support to previous indications of sub-thermal gas excitation for the CO(3-2) line with a typically assumed line ratio R_{31}~0.5. For one of our targets, BzK-21000, we present spatially resolved CO line maps. At the resolution of 0.18'' (1.5 kpc), most of the emission is resolved out except for some clumpy structure. From this, we attempt to identify molecular gas clumps in the data cube, finding 4 possible candidates. We estimate that <40 % of the molecular gas is confined to giant clumps (~1.5 kpc in size), and thus most of the gas could be distributed in small fainter clouds or in fairly diffuse extended regions of lower brightness temperatures than our sensitivity limit
The MRO-accompanied modes of Re-implantation into SiO2-host matrix: XPS and DFT based scenarios
The following scenarios of Re-embedding into SiO2-host by pulsed
Re-implantation were derived and discussed after XPS-and-DFT electronic
structure qualification: (i) low Re-impurity concentration mode -> the
formation of combined substitutional and interstitial impurities with
Re2O7-like atomic and electronic structures in the vicinity of oxygen
vacancies; (ii) high Re-impurity concentration mode -> the fabrication of
interstitial Re-metal clusters with the accompanied formation of ReO2-like
atomic structures and (iii) an intermediate transient mode with Re-impurity
concentration increase, when the precursors of interstitial defect clusters are
appeared and growing in the host-matrix structure occur. An amplification
regime of Re-metal contribution majority to the final Valence Band structure
was found as one of the sequences of intermediate transient mode. It was shown
that most of the qualified and discussed modes were accompanied by the MRO
(middle range ordering) distortions in the initial oxygen subnetwork of the
a-SiO2 host-matrix because of the appeared mixed defect configurations.Comment: 19 pages, 7 figures, accepted to J. Alloys and Compound
ALMA Maps of Dust and Warm Dense Gas Emission in the Starburst Galaxy IC 5179
We present our high-resolution
(, 34 pc) observations of
the CO(6-5) line emission, which probes the warm and dense molecular gas, and
the 434 m dust continuum emission in the nuclear region of the starburst
galaxy IC 5179, conducted with the Atacama Large Millimeter Array (ALMA). The
CO(6-5) emission is spatially distributed in filamentary structures with many
dense cores and shows a velocity field that is characteristic of a
circum-nuclear rotating gas disk, with 90% of the rotation speed arising within
a radius of pc. At the scale of our spatial resolution, the
CO(6-5) and dust emission peaks do not always coincide, with their surface
brightness ratio varying by a factor of 10. This result suggests that
their excitation mechanisms are likely different, as further evidenced by the
Southwest to Northeast spatial gradient of both CO-to-dust continuum ratio and
Pa- equivalent width. Within the nuclear region (radius300 pc)
and with a resolution of 34 pc, the CO line flux (dust flux density)
detected in our ALMA observations is Jy km/s ( mJy), which
account for 22% (2.4%) of the total value measured by Herschel.Comment: Accepted for publication in Ap
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