8,537 research outputs found
A radio and infrared exploration of the Cygnus X-3 environments
To confirm, or rule out, the possible hot spot nature of two previously
detected radio sources in the vicinity of the Cygnus X-3 microquasar.
We present the results of a radio and near infrared exploration of the
several arc-minute field around the well known galactic relativistic jet source
Cygnus X-3 using the Very Large Array and the Calar Alto 3.5~m telescope.
The data this paper is based on do not presently support the hot spot
hypothesis. Instead, our new observations suggest that these sources are most
likely background or foreground objects. Actually, none of them appears to be
even barely extended as would be expected if they were part of a bow shock
structure. Our near infrared observations also include a search for extended
emission in the Bracket (2.166 m) and (2.122 m)
lines as possible tracers of shocked gas in the Cygnus X-3 surroundings. The
results were similarly negative and the corresponding upper limits are
reported.Comment: Accepted for publication in A&A; 5 pages, 4 figure
ESR study of the single-ion anisotropy in the pyrochlore antiferromagnet Gd2Sn2O7
Single-ion anisotropy is of importance for the magnetic ordering of the
frustrated pyrochlore antiferromagnets Gd2Ti2O7 and Gd2Sn2O7. The anisotropy
parameters for the Gd2Sn2O7 were measured using the electron spin resonance
(ESR) technique. The anisotropy was found to be of the easy plane type, with
the main constant D=140mK. This value is 35% smaller than the value of the
corresponding anisotropy constant in the related compound Gd2Ti2O7.Comment: 8 pages, 3 figure
Chandra X-ray counterpart of KS 1741-293
We aim to investigate the nature of the high energy source KS 1741-293 by
revisiting the radio and infrared associations proposed in the early 1990s. Our
work is mostly based on the analysis of modern survey and archive data,
including the NRAO, MSX, 2MASS and Chandra archives, and catalogues. We also
have obtained deep CCD optical observations by ourselves. The coincidence of KS
1741-293 with an extended radio and far-infrared source, tentatively suggested
in 1994, is no longer supported by modern observational data. Instead, a
Chandra source is the only peculiar object found to be consistent with all
high-energy error circles of KS 1741-293 and we propose it to be its most
likely X-ray counterpart. We also report the existence of a non-thermal radio
nebula in the vicinity of the KS 1741-293 position with the appearance of a
supernova remnant. The possibility of being associated to this X-ray binary is
discussed.Comment: 5 pages, 4 figures, 2 tables. Accepted for publication in Astronomy &
Astrophysic
Voltage dip generator for testing wind turbines connected to electrical networks
This paper describes a new voltage dip generator that allows the shape of the time profile of the voltage generated to be configured. The use of this device as a tool to test the fault ride-through capability of wind turbines connected to the electricity grid can provide some remarkable benefits: First, this system offers the possibility of adapting the main features of the time–voltage profile generated (dip depth, dip duration, the ramp slope during the recovery process after clearing fault, etc.) to the specific requirements set forth by the grid operation codes, in accordance with different network electrical systems standards. Second, another remarkable ability of this system is to provide sinusoidal voltage and current wave forms during the overall testing process without the presence of harmonic components. This is made possible by the absence of electronic converters. Finally, the paper includes results and a discussion on the experimental data obtained with the use of a reduced size laboratory prototype that was constructed to validate the operating features of this new device
On the Effect of Correlation on the Capacity of Backscatter Communication Systems
We analyse the effect of correlation between the forward and backward links
on the capacity of backscatter communication systems. To that aim, we obtain an
analytical expression for the average capacity under a correlated Rayleigh
product fading channel, as well as closed-form asymptotic expressions for the
high and low signal-to-noise ratio (SNR) regimes. Our results show that
correlation is indeed detrimental for a fixed target SNR; contrarily to the
common belief, we also see that correlation can be actually beneficial in some
instances when a fixed power budget is considered.Comment: This work has been submitted for publication. Copyright may be
transferred without notice, after which this version may no longer be
accessibl
Early Science with the Large Millimetre Telescope: Molecules in the Extreme Outflow of a proto-Planetary Nebula
Extremely high velocity emission likely related to jets is known to occur in
some proto-Planetary Nebulae. However, the molecular complexity of this
kinematic component is largely unknown. We observed the known extreme outflow
from the proto-Planetary Nebula IRAS 16342-3814, a prototype water fountain, in
the full frequency range from 73 to 111 GHz with the RSR receiver on the Large
Millimetre Telescope. We detected the molecules SiO, HCN, SO, and CO.
All molecular transitions, with the exception of the latter are detected for
the first time in this source, and all present emission with velocities up to a
few hundred km s. IRAS 16342-3814 is therefore the only source of this
kind presenting extreme outflow activity simultaneously in all these molecules,
with SO and SiO emission showing the highest velocities found of these species
in proto-Planetary Nebulae. To be confirmed is a tentative weak SO component
with a FWHM 700 km s. The extreme outflow gas consists of dense
gas (n 10--10 cm), with a mass larger than
0.02--0.15 M. The relatively high abundances of SiO and SO may
be an indication of an oxygen-rich extreme high velocity gas.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical
Society Letter
The high-redshift gamma-ray burst GRB140515A
High-redshift gamma-ray bursts have several advantages for the study of the
distant universe, providing unique information about the structure and
properties of the galaxies in which they exploded. Spectroscopic identification
with large ground-based telescopes has improved our knowledge of the class of
such distant events. We present the multi-wavelength analysis of the high-
Swift gamma-ray burst GRB140515A (). The best estimate of the
neutral hydrogen fraction of the intergalactic medium (IGM) towards the burst
is . The spectral absorption lines detected for this event
are the weakest lines ever observed in gamma-ray burst afterglows, suggesting
that GRB140515A exploded in a very low density environment. Its circum-burst
medium is characterised by an average extinction (A) that
seems to be typical of events. The observed multi-band light curves
are explained either with a very flat injected spectrum () or with a
multi-component emission (). In the second case a long-lasting central
engine activity is needed in order to explain the late time X-ray emission. The
possible origin of GRB140515A from a Pop III (or from a Pop II stars with local
environment enriched by Pop III) massive star is unlikely.Comment: 10 pages, 8 figures, 5 tables, submitted to Astronomy & Astrophysic
Quasiparticle Density of States of Clean and Dirty s-Wave Superconductors in the Vortex State
The quasiparticle density of states (DOS) in the vortex state has been probed
by specific heat measurements under magnetic fields (H) for clean and dirty
s-wave superconductors, Y(Ni1-xPtx)2B2C and Nb1-xTaxSe2. We find that the
quasiparticle DOS per vortex is appreciably H-dependent in the clean-limit
superconductors, while it is H-independent in the dirty superconductors as
expected from a conventional rigid normal electron core picture. We discuss
possible origins for our observations in terms of the shrinking of the vortex
core radius with increasing H.Comment: 5 pages, 4 figures, to appear in J. Phys. Soc. Jpn. Vol. 68 No.
- …