258 research outputs found
Chandra X-ray Observations of the Two Brightest Unidentified High Galactic Latitude Fermi-LAT gamma-ray Sources
We present Chandra ACIS-I X-ray observations of 0FGL J1311.9-3419 and 0FGL
J1653.4-0200, the two brightest high Galactic latitude (|b|>10 deg) gamma-ray
sources from the 3 month Fermi-LAT bright source list that are still
unidentified. Both were also detected previously by EGRET, and despite
dedicated multi-wavelength follow-up, they are still not associated with
established classes of gamma-ray emitters like pulsars or radio-loud active
galactic nuclei. X-ray sources found in the ACIS-I fields of view are
catalogued, and their basic properties are determined. These are discussed as
candidate counterparts to 0FGL J1311.9-3419 and 0FGL J1653.4-0200, with
particular emphasis on the brightest of the 9 and 13 Chandra sources detected
within their respective Fermi-LAT 95% confidence regions. Further follow-up
studies, including optical photometric and spectroscopic observations are
necessary to identify these X-ray candidate counterparts in order to ultimately
reveal the nature of these enigmatic gamma-ray objects.Comment: ApJ, accepted. 18 pages, 5 figure
Influence of the enterosorbent on quality of eggs
In this article research the influence of natural montmorillonite containing sorbent used as a mineral supplement in animal feed in an amount of 30 g per 1 kg of sorbent feed on commercial quality table eggs at his dacha hens-layers. Found that feeding hens’ mineral feed additive reduces the toxic chemical elements in a chicken egg. It was found that the weight of the eggs in the experimental group compared to the control group, was significantly increased by 3,5% (p <0,05) after the completion of feeding the mineral sorbent. Despite the fact that in the control group, egg weight did not change and remained virtually unchange
Identification of new cataclysmic variables in the 1RXS and USNO-B1.0 catalogs
As a result of applying the original optical variability search method on
publicly available data, we have found eight new cataclysmic variables and two
possible Optically Violent Variable quasars among the previously unidentified
X-ray sources in the ROSAT catalog. We describe the search method and present
the characteristics of the newly identified variable stars. The obtained
results demonstrate the large potential of the concept of Virtual Observatory
for identifying new objects of astrophysical interest.Comment: 16 pages, 11 figures, 2 tables; submitted to Astronomy Letter
The core shift effect in the blazar 3C 454.3
Opacity-driven shifts of the apparent VLBI core position with frequency (the
"core shift" effect) probe physical conditions in the innermost parts of jets
in active galactic nuclei. We present the first detailed investigation of this
effect in the brightest gamma-ray blazar 3C454.3 using direct measurements from
simultaneous 4.6-43 GHz VLBA observations, and a time lag analysis of 4.8-37
GHz lightcurves from the UMRAO, CrAO, and Metsahovi observations in 2007-2009.
The results support the standard Konigl model of jet physics in the VLBI core
region. The distance of the core from the jet origin r_c(nu), the core size
W(nu), and the lightcurve time lag DT(nu) all depend on the observing frequency
nu as r_c(nu)~W(nu)~ DT(nu)~nu^-1/k. The obtained range of k=0.6-0.8 is
consistent with the synchrotron self-absorption being the dominating opacity
mechanism in the jet. The similar frequency dependence of r_c(nu) and W(nu)
suggests that the external pressure gradient does not dictate the jet geometry
in the cm-band core region. Assuming equipartition, the magnetic field strength
scales with distance r as B = 0.4(r/1pc)^-0.8 G. The total kinetic power of
electron/positron jet is about 10^44 ergs/s.Comment: Accepted for publication in MNRAS; 10 pages, 6 figure
Effect of high pressure on the thermoelectrical properties of single-walled and double-walled carbon nanotubes
The effect of high pressure on the Seebeck coefficient and temperature dependences of the electrical resistance of single-wall and double-walled carbon nanotubes was studied in order to detect phase transformations occurring in carbon nanotubes in the pressure range 4-46 GPa. Diamond anvil cells with conductive synthetic diamonds were used to create high pressures. We observed a number of features associated with the structure changes of nanotubes. Temperature dependences of the electrical resistance of single and double-walled carbon nanotubes have the form characteristic of nondegenerate semiconductors. Analysis of results indicates the destruction of the structure of carbon nanotubes at high pressure. © Published under licence by IOP Publishing Ltd
Comparative performance of selected variability detection techniques in photometric time series
Photometric measurements are prone to systematic errors presenting a
challenge to low-amplitude variability detection. In search for a
general-purpose variability detection technique able to recover a broad range
of variability types including currently unknown ones, we test 18 statistical
characteristics quantifying scatter and/or correlation between brightness
measurements. We compare their performance in identifying variable objects in
seven time series data sets obtained with telescopes ranging in size from a
telephoto lens to 1m-class and probing variability on time-scales from minutes
to decades. The test data sets together include lightcurves of 127539 objects,
among them 1251 variable stars of various types and represent a range of
observing conditions often found in ground-based variability surveys. The real
data are complemented by simulations. We propose a combination of two indices
that together recover a broad range of variability types from photometric data
characterized by a wide variety of sampling patterns, photometric accuracies,
and percentages of outlier measurements. The first index is the interquartile
range (IQR) of magnitude measurements, sensitive to variability irrespective of
a time-scale and resistant to outliers. It can be complemented by the ratio of
the lightcurve variance to the mean square successive difference, 1/h, which is
efficient in detecting variability on time-scales longer than the typical time
interval between observations. Variable objects have larger 1/h and/or IQR
values than non-variable objects of similar brightness. Another approach to
variability detection is to combine many variability indices using principal
component analysis. We present 124 previously unknown variable stars found in
the test data.Comment: 29 pages, 8 figures, 7 tables; accepted to MNRAS; for additional
plots, see http://scan.sai.msu.ru/~kirx/var_idx_paper
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