249 research outputs found
A search for x-ray counterparts of gamma-ray bursts with the ROSAT PSPC
We search for faint X-ray bursts with duration 10--300 seconds in the ROSAT
PSPC pointed observations with a total exposure of 1.6e7 seconds. We do not
detect any events shorter than ~100s, i.e. those that could be related to the
classic gamma-ray bursts. At the same time, we detect a number of long flares
with durations of several hundred seconds. Most, but not all, of the long
flares are associated with stars. If even a small number of those long flares,
that cannot identified with stars, are X-ray afterglows of GRB, the number of
X-ray afterglows greatly exceeds the number of BATSE GRB. This would imply that
the beaming factor of gamma-rays from the burst should be >100. The
non-detection of any short bursts in our data constrains the GRB counts at the
fluences 1--2.5 orders of magnitude below the BATSE limit. The constrained
burst counts are consistent with the extrapolation of the BATSE log N - log S
relation. Finally, our results do not confirm a reality of short X-ray flashes
found in the Einstein IPC data by Gotthelf, Hamilton and Helfand.Comment: Accepted to ApJ Letters. 4 pages with 3 figures, LaTeX2
The research of the maximum wind speed in Tomsk and calculations of dynamic load on antenna systems
The work is concerned with calculations and analysis of the maximum wind speed in Tomsk city. The data for analysis were taken from the TOR-station located in the north-eastern part of the city. The TOR-station sensors to measure a speed and a direction of wind are installed on the 10-meter meteorological mast. Wind is measured by M-63, which uses the standard approach and the program with one-minute averaging for wind gusts recording as well. According to the measured results in the research performed, the estimation of the dynamic and wind load on different types of antenna systems was performed. The work shows the calculations of wind load on ten types of antenna systems, distinguished by their different constructions and antenna areas. For implementation of calculations, we used methods developed in the Central Research and Development Institute of Building Constructions named after V.A. Kucherenko. The research results could be used for design engineering of the static antenna systems and mobile tracking systems for the distant objects
First hours of the GRB 030329 optical afterglow
We present the first results of the observations of the extremely bright
optical afterglow of gamma-ray burst (GRB) 030329 with the 1.5m Russian-Turkish
telescope RTT150 (TUBITAK National Observatory, Bakyrlytepe, Turkey). RTT150
was one of the first 1.5m-class telescopes pointed to the afterglow.
Observations were started approximately 6 hours after the burst. During the
first 5 hours of our observations the afterglow faded exactly as a power law
with index -1.19+-0.01 in each of the BVRI Bessel filters. After that, in all
BVRI filters simultaneously we observe a steepening of the power law light
curve. The power law decay index smoothly approaches the value ~= -1.9,
observed by other observatories later. This power law break occurs at t-t_0
=0.57 days and lasts for +-0.1 days. We observe no variability above the
gradual fading with the upper limits 10--1% on time scales 0.1--1000s. Spectral
flux distribution in four BVRI filters corresponds to the power law spectrum
with spectral index \alpha=0.66+-0.01. The change of the power law decay index
in the end of our observations can be interpreted as a signature of collimated
ultrarelativistic jet. The afterglow flux distribution in radio, optical and
x-rays is consistent with synchrotron spectrum. We continue our observations of
this unique object with RTT150.Comment: Astronomy Letters, Vol. 29, No. 9, p. 573; 6 pages, 5 figures;
pagination corrected; the original Russian version can be found at
http://hea.iki.rssi.ru/~br/030329/pfh030329.pd
Radiative corrections and parity nonconservation in heavy atoms
The self-energy and the vertex radiative corrections to the effect of parity
nonconservation in heavy atoms are calculated analytically in orders Z alpha^2
and Z^2 alpha^3 ln(lambda_C/r_0), where lambda_C and r_0 being the Compton
wavelength and the nuclear radius, respectively. The value of the radiative
correction is -0.85% for Cs and -1.41% for Tl. Using these results we have
performed analysis of the experimental data on atomic parity nonconservation.
The obtained values of the nuclear weak charge,
Q_W=-72.90(28)_{exp}(35)_{theor} for Cs, and Q_W=-116.7(1.2)_{exp}(3.4)_{theor}
for Tl, agree with predictions of the standard model. As an application of our
approach we have also calculated analytically dependence of the Lamb shift on
the finite nuclear size.Comment: 4 pages, 4 figure
Finite nuclear size and Lamb shift of p-wave atomic states
We consider corrections to the Lamb shift of p-wave atomic states due to the
finite nuclear size (FNS). In other words, these are radiative corrections to
the atomic isotop shift related to FNS. It is shown that the structure of the
corrections is qualitatively different from that for s-wave states. The
perturbation theory expansion for the relative correction for a -state
starts from -term, while for -states it starts
from term. Here is the fine structure constant and is
the nuclear charge. In the present work we calculate the -terms for
-states, the result for -state reads
. Even more interesting are
-states. In this case the ``correction'' is by several orders of
magnitude larger than the ``leading'' FNS shift.Comment: 4 pages, 2 figure
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