The Great Markarian 421 Flare of 2010 February: Multiwavelength Variability and Correlation Studies

We report on variability and correlation studies using multiwavelength observations of the blazar Mrk 421 during the month of 2010 February, when an extraordinary flare reaching a level of ∼27 Crab Units above 1 TeV was measured in very high energy (VHE) γ-rays with the Very Energetic Radiation Imaging Telescope Array System (VERITAS) observatory. This is the highest flux state for Mrk 421 ever observed in VHE γ-rays. Data are analyzed from a coordinated campaign across multiple instruments, including VHE γ-ray (VERITAS, Major Atmospheric Gamma-ray Imaging Cherenkov), high-energy γ-ray (Fermi-LAT), X-ray (Swift, Rossi X-ray Timing Experiment, MAXI), optical (including the GASP-WEBT collaboration and polarization data), and radio (Metsahovi, Owens Valley Radio Observatory, University of Michigan Radio Astronomy Observatory). Light curves are produced spanning multiple days before and after the peak of the VHE flare, including over several flare "decline" epochs. The main flare statistics allow 2 minute time bins to be constructed in both the VHE and optical bands enabling a cross-correlation analysis that shows evidence for an optical lag of ∼25-55 minutes, the first time-lagged correlation between these bands reported on such short timescales. Limits on the Doppler factor (δ ⪆ 33) and the size of the emission region (δ-1RB≲ 3.8 × 1013cm) are obtained from the fast variability observed by VERITAS during the main flare. Analysis of 10 minute binned VHE and X-ray data over the decline epochs shows an extraordinary range of behavior in the flux-flux relationship, from linear to quadratic to lack of correlation to anticorrelation. Taken together, these detailed observations of an unprecedented flare seen in Mrk 421 are difficult to explain with the classic single-zone synchrotron self-Compton model.</p

XPS study of ammonia-exposed C₆₀ films both original and photopolymerized

Surface of C₆₀ films (original and photopolymerized with UV radiation) exposed to ammonia at different pressure was investigated by the method of X-ray photoelectron spectroscopy. Effect of X-ray stimulated interaction between films and adsorbed water, which resulted in bonds like C-O-H and enhanced by ammonia was detected. It was shown that ammonia unreacted chemically with C₆₀ films, both original and photo-polymerized.Методом рентгеновской фотоэлектронной спектроскопии исследована поверхность фуллереновых пленок (не полимеризованных и полимеризованных с помощью ультрафиолетового облучения), выдержанных в аммиаке при различных давлениях газа. Обнаружен эффект взаимодействия пленок с адсорбированной водой с образованием связей типа C-O-H, который стимулируется рентгеновским облучением и ускоряется аммиаком. Показано, что аммиак не взаимодействует химически с фуллереновой пленкой как полимеризованной, так и не полимеризованной.Методом рентгенівської фотоелектронної спектроскопії досліджено поверхню фуле-ренових плівок (не полімеризованих і полімеризованих за допомогою ультрафіолетового опромінення), витриманих в аміаку при різних тисках газу. Виявлено ефект взаємодії плівок з адсорбованою водою з утворенням зв’язків типу C-O-H, що стимулюється рентгенівським опроміненням і прискорюється аміаком. Показано, що аміак не взаємодіє хімічно з фулереновою плівкою як полімеризованою так і не полімеризо-ваною

Mutual influence of additives of Ca and Si on properties of Cr-doped YAG ceramics

Cr-doped yttrium aluminum garnet ceramics with different concentration of additives Ca and Si were synthesized by vacuum reaction sintering. It was established that simultaneous doping with Ca and Si effects crucially on morphology and optical ceramics properties. Average grain size of such ceramics can reach to 1.08±0.06 μm that is much more less against the ceramics without Ca dopant. The optical properties of the ceramics deteriorate significantly with increase of Ca concentration. The degree of Cr4+ transformation to Cr3+ under air annealing is not well due to competition between Cr⁴⁺ and Si⁴⁺ ions to be charge compensated by Ca²⁺. Sintering aid SiO₂, which used in widespread ceramic technology to produce the high optical quality ceramics based on YAG, cannot be applied to produce the Cr⁴⁺-doped YAG ceramics with Ca as a charge compensator

X-ray and photo-excited luminescence of ZnWO₄ nanoparticles with different size and morphology

X-ray and photoluminescence of ZnWO₄ nanocrystals with controlled size and morphology: grains with diameter of 10-20 nm; rods with diameter of 10-20 nm and length of 200-250 nm produced by microwave hydrothermal method were studied. Red luminescence with λmax = 700 nm was found in the samples. The intensity of the red luminescence increases with decreasing of the ZnWO₄ nanoparticles size due to increase of concentration of oxygen vacancies and creation of distorted WO₆ centers. It was shown that reduction in the X-ray luminescence intensity with decrease of the ZnWO₄ nanoparticles size is due to creation of the distorted WO₆ centers which are the nonradiative relaxation channel competing with the self-trapped excitons

Morphology of lead sulfide crystalline particles in size-limited state

Monocrystalline PbS particles of cubic structure ranging in size from 3 to 500 nm, were obtained. Influence of growth conditions on the final particles size and dispersion of lead sulfide nanocrystals, as well as effects of nanocrystals size on their shape have been studied. It was found that increasing of monocrystalline particles size more than 12 nm leads to transition of shape from spherical to cubic, that indicate predominance of surface energy influence on equilibrium geometry of nanocrystals