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 $\Delta z \approx 0.33$. 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 $z \simeq 4$. For the the faint long bursts - which should be up to $z \simeq 20$ - 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&