141 research outputs found
THERMAL VARIATIONS IN OCTOBER 2013 IN NORTH-WESTERN ROMANIA
The present analysis refers two weather situations in October 2013 in north-western Romania, represented by a period of cold weather in the first part of the month, and, respectively, a warm period in the last decade of the month. The cold wave produced minimum daily temperatures ranging between -6.4 and -1.9°C, in the lower areas, while in the mountainous region they were between -9.4 and -7.2°C. These values are by 0.2 to 5.6°C lower than the absolute daily minimum temperatures registered between 1961-2012 period. Positive deviations from the maximum daily absolute temperatures up to 4.0°C were recorded in the warm period at the end of the month. The data base used in the study was made up of minimum and maximum daily temperatures for the periods 3-8 and 22-30 October 2013, registered at 14 meteorological stations situated in north-western Romania. Other data used were the air temperature at standard isobaric levels of 850, 700 and 500 hPa, in the period 1973-2013. Synoptic reanalysis maps for the period 1961-2013 were also used
A multiple-beam CLEAN for imaging intra-day variable radio sources
The CLEAN algorithm, widely used in radio interferometry for the
deconvolution of radio images, performs well only if the raw radio image (dirty
image) is, to good approximation, a simple convolution between the instrumental
point-spread function (dirty beam) and the true distribution of emission across
the sky. An important case in which this approximation breaks down is during
frequency synthesis if the observing bandwidth is wide enough for variations in
the spectrum of the sky to become significant. The convolution assumption also
breaks down, in any situation but snapshot observations, if sources in the
field vary significantly in flux density over the duration of the observation.
Such time-variation can even be instrumental in nature, for example due to
jitter or rotation of the primary beam pattern on the sky during an
observation. An algorithm already exists for dealing with the spectral
variation encountered in wide-band frequency synthesis interferometry. This
algorithm is an extension of CLEAN in which, at each iteration, a set of N
`dirty beams' are fitted and subtracted in parallel, instead of just a single
dirty beam as in standard CLEAN. In the wide-band algorithm the beams are
obtained by expanding a nominal source spectrum in a Taylor series, each term
of the series generating one of the beams. In the present paper this algorithm
is extended to images which contain sources which vary over both frequency and
time. Different expansion schemes (or bases) on the time and frequency axes are
compared, and issues such as Gibbs ringing and non-orthogonality are discussed.
It is shown that practical considerations make it often desirable to
orthogonalize the set of beams before commencing the cleaning. This is easily
accomplished via a Gram-Schmidt technique.Comment: 9 pages, 7 figures. Accepted for publication in A&
Discovery of a large and bright bow shock nebula associated with low mass X-ray binary SAX J1712.6-3739
In a multiwavelength program dedicated to identifying optical counterparts of
faint persistent X-ray sources in the Galactic Bulge, we find an accurate X-ray
position of SAX J1712.6-3739 through Chandra observations, and discover its
faint optical counterpart using our data from EFOSC2 on the ESO 3.6m telescope.
We find this source to be a highly extincted neutron star LMXB with blue
optical colours. We serendipitously discover a relatively bright and large bow
shock shaped nebula in our deep narrowband H alpha imaging, most likely
associated with the X-ray binary. A nebula like this has never been observed
before in association with a LMXB, and as such provides a unique laboratory to
study the energetics of accretion and jets. We put forward different models to
explain the possible ways the LMXB may form this nebulosity, and outline how
they can be confirmed observationally.Comment: Accepted for publication in MNRAS-Letters; 5 pages, 4 figures, 2
tables. Quality of figure 2 downgraded because of arXiv file size limit
Electrocardiographic and echocardiographic changes in patients with thyreotoxic cardiopathy
Thyreotoxic cardiopathy represents a cardiac pathology, caused by the toxic influence of the thyroid hormones on the myocardium. The aim of this
study is to determine the frequency of cardiovascular changes in patients with thyreotoxic cardiopathy according to the ECG and EchoCG results. The
study included 72 patients with Graves’ disease and thyreotoxic cardiopathy, whose medical records have been analyzed. Such criteria, as heart rate,
heart rhythm disorders, left ventricle hypertrophy, repolarization abnormalities (in ECG), ejection fraction, valve disorders, heart cavities dilation, left
ventricle hypertrophy, impaired cardiac relaxation and pulmonary hypertension (in EchoCG) have been taken into consideration. The results showed
a high percentage of patients with ECG disturbances (75%) and a high percentage of patients with EchoCG disturbances (100%). According to the
ECG results, the disturbances included heart rhythm disorders (51.4%), left ventricle hypertrophy (36.1%) and repolarization abnormalities (53.3%).
The most frequent heart rhythm disorders determined by ECG have been atrial fibrillation (19.5%), sinus tachycardia (13.9%), Guis’ fascicular blocks
(13.9%) and extrasystoles (9.7%). The EchoCG examination of the patients identified valve disorders (94.4%), the left ventricle hypertrophy (52.8%),
the left ventricle impaired relaxation (11.1%), the simultaneous dilatation of three cavities of heart (left atrium, right ventricle and right atrium) (26.4%)
and pulmonary hypertension (52.8%). However, the influence of concomitant cardiovascular diseases (25%) on the obtained results cannot be excluded,
since the moment of their appearance is unknown
A weak compact jet in a soft state of Cygnus X-1
We present evidence for the presence of a weak compact jet during a soft
X-ray state of Cygnus X-1. Very-high-resolution radio observations were taken
with the VLBA, EVN and MERLIN during a hard-to-soft spectral state change,
showing the hard state jet to be suppressed by a factor of about 3-5 in radio
flux and unresolved to direct imaging observations (i.e. < 1 mas at 4 cm). High
time-resolution X-ray observations with the RXTE-PCA were also taken during the
radio monitoring period, showing the source to make the transition from the
hard state to a softer state (via an intermediate state), although the source
may never have reached the canonical soft state. Using astrometric VLBI
analysis and removing proper motion, parallax and orbital motion signatures,
the residual positions show a scatter of ~0.2 mas (at 4 cm) and ~3 mas (at 13
cm) along the position angle of the known jet axis; these residuals suggest
there is a weak unresolved outflow, with varying size or opacity, during
intermediate and soft X-ray states. Furthermore, no evidence was found for
extended knots or shocks forming within the jet during the state transition,
suggesting the change in outflow rate may not be sufficiently high to produce
superluminal knots.Comment: Accepted in MNRAS; 4 figures and 1 tabl
A doublet of cosmic-ray events with primary energies >10^20 eV
The Telescope Array Collaboration has observed a cosmic-ray event with
estimated primary energy of 1.38*10^20 eV whose arrival direction coincides
(see arxiv:1205.5984), given the angular resolution of 1.5 deg, with that of an
event with estimated primary energy of 1.23*10^20 eV observed by the Pierre
Auger Observatory. The total number of events with energies >10^20 eV published
by both experiments is six. I estimate the statistical significance of the
doublet, which is rather weak, and point out that the arrival directions of
events in the doublet coincide with the Galactic X-ray source Aql X-1.Comment: 4 pages, 3 figures, submitted to JETP Letters; v.2: a misprint
correcte
Black hole candidate XTE J1752-223: Swift observations of canonical states during outburst
We present Swift broadband observations of the recently discovered black hole
candidate, X-ray transient, XTE J1752-223, obtained over the period of outburst
from October 2009 to June 2010. From Swift-UVOT data we confirm the presence of
an optical counterpart which displays variability correlated, in the soft
state, to the X-ray emission observed by Swift-XRT. The optical counterpart
also displays hysteretical behaviour between the states not normally observed
in the optical bands, suggesting a possible contribution from a synchrotron
emitting jet to the optical emission in the rising hard state. We offer a
purely phenomenological treatment of the spectra as an indication of the
canonical spectral state of the source during different periods of the
outburst. We find that the high energy hardness-intensity diagrams over two
separate bands follows the canonical behavior, confirming the spectral states.
Our XRT timing analysis shows that in the hard state there is significant
variability below 10Hz which is more pronounced at low energies, while during
the soft state the level of variability is consistent with being minimal. These
properties of XTE J1752-223 support its candidacy as a black hole in the
Galactic centre region.Comment: 8 pages, 8 figures; MNRAS in pres
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