999 research outputs found
Gamma photometric redshifts for long gamma-ray bursts
It is known that the soft tail of the gamma-ray bursts' spectra show excesses
from the exact power-law dependence. In this article we show that this
departure can be detected in the peak flux ratios of different BATSE DISCSC
energy channels. This effect allows to estimate the redshift of the bright long
gamma-ray bursts in the BATSE Catalog. A verification of these redshifts is
obtained for the 8 GRB which have both BATSE DISCSC data and measured optical
spectroscopic redshifts. There is good correlation between the measured and
esti redshifts, and the average error is . The method is
similar to the photometric redshift estimation of galaxies in the optical
range, hence it can be called as "gamma photometric redshift estimation". The
estimated redshifts for the long bright gamma-ray bursts are up to . For the the faint long bursts - which should be up to - the
redshifts cannot be determined unambiguously with this method.Comment: accepted in A&A, 7 pages incl. 7 figure
'On the difference between the short and long gamma-ray bursts'
We argue that the distributions of both the intrinsic fluence and the
intrinsic duration of the gamma-ray emission in gamma-ray bursts from the BATSE
sample are well represented by log-normal distributions, in which the intrinsic
dispersion is much larger than the cosmological time dilatation and redshift
effects. We perform separate bivariate log-normal distribution fits to the
BATSE short and long burst samples. The bivariate log-normal behaviour results
in an ellipsoidal distribution, whose major axis determines an overall
statistical relation between the fluence and the duration. We show that this
fit provides evidence for a power-law dependence between the fluence and the
duration, with a statistically significant different index for the long and
short groups. We discuss possible biases, which might affect this result, and
argue that the effect is probably real. This may provide a potentially useful
constraint for models of long and short bursts.Comment: A.A. in press ; significantly revised version of astro-ph/0007438; 16
pages 5 PS figure
Length-scale-dependent phase transition in BSCCO single crystals
Electrical transport measurements using a multiterminal configuration are
presented, which prove that in BSCCO single crystals near the transition
temperature in zero external magnetic field the secondary voltage is induced by
thermally activated vortex loop unbinding. The phase transition between the
bound and unbound states of the vortex loops was found to be below the
temperature where the phase coherence of the superconducting order parameter
extends over the whole volume of the sample. We show experimentally that 3D/2D
phase transition in vortex dimensionality is a length-scale-dependent layer
decoupling process and takes place simultaneously with the 3D/2D phase
transition in superconductivity at the same temperature.Comment: 14 pages, 4 figures, to be published in Philos. Ma
Synthesis of Zinc Ferrites in RF Thermal Plasma Reactor
Formation of nanosized zinc ferrite spinels was studied
from iron- and zinc oxide powders and corresponding
nitrate solutions, respectively in a radiofrequency thermal
plasma reactor. From the viewpoint of applications,
the research was motivated by the potential use of these
materials in advanced magnetic devices on the one
hand, and by their biomedical applications such as drug
carriers or agents for cancer treatment by hyperthermia
on the other. In this work effects of synthesis conditions
on properties of products were studied in details. The
products were characterised for chemical composition,
phase conditions, particle size distribution, morphologies
and saturation magnetisation. Most products exhibited
ferrimagnetic behaviour. Correlations among domain-
and particle sizes were also investigated. Conditions
for the synthesis of nanosized, inverse zinc ferrites
of high saturation magnetisation were established. It
was proved that in thermal plasma conditions normal
and inverse ferrites could be produced in a single step
process
Synthesis of Spinel Ferrites in Radiofrequency Thermal Plasma Reactor
Formation of nanosized zinc-ferrites and nickel-zinc ferrites from iron- and
zinc oxide powders and corresponding nitrate solutions, respectively, was studied in RF
thermal plasma conditions. The products were characterized for chemical composition,
phase conditions, particle size distribution, morphologies and saturation magnetization.
Effects of synthesis conditions on properties of products were studied in details
Dependence of the optical brightness on the gamma and X-ray properties of GRBs
The Swift satellite made a real break through with measuring simultaneously
the gamma X-ray and optical data of GRBs, effectively. Although, the satellite
measures the gamma, X-ray and optical properties almost in the same time a
significant fractions of GRBs remain undetected in the optical domain. In a
large number of cases only an upper bound is obtained. Survival analysis is a
tool for studying samples where a part of the cases has only an upper (lower)
limit. The obtained survival function may depend on some other variables. The
Cox regression is a way to study these dependencies. We studied the dependence
of the optical brightness (obtained by the UVOT) on the gamma and X-ray
properties, measured by the BAT and XRT on board of the Swift satellite. We
showed that the gamma peak flux has the greatest impact on the afterglow's
optical brightness while the gamma photon index and the X-ray flux do not. This
effect probably originates in the energetics of the jet launched from the
central engine of the GRB which triggers the afterglow.Comment: 2012 Fermi Symposium proceedings - eConf C12102
Further Study of the Gamma-Ray Bursts Duration Distribution
Two classes of gamma-ray bursts have been identified so far, characterized by
durations shorter and longer than approximately 2 seconds. In 1998 two
independent papers indicated the existence of the third class of the bursts
roughly duration between 2 and 10 seconds. In this paper, using the full BATSE
Catalog, the maximum likelihood estimation is presented, which gives a 0.5%
probability to having only two subclasses. The Monte-Carlo simulation confirms
this probability, too.Comment: submitted to A&
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