X-ray and γ-ray spectra and variability of the black hole candidate GX 339–4     

Grzegorz Wardzi&#;ski  rzej A. Zdziarski  Marek Gierli&#;ski  J. Eric Grove  Keith Jahoda  W. Neil Johnson 《Monthly notices of the Royal Astronomical Society》2002,337(3):829-839

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Validation of Galileo orbits using SLR with a focus on satellites launched into incorrect orbital planes     

Krzysztof Sośnica  Lars Prange  Kamil Kaźmierski  Grzegorz Bury  Mateusz Drożdżewski  Radosław Zajdel  Tomasz Hadas 《Journal of Geodesy》2018,92(2):131-148

The space segment of the European Global Navigation Satellite System (GNSS) Galileo consists of In-Orbit Validation (IOV) and Full Operational Capability (FOC) spacecraft. The first pair of FOC satellites was launched into an incorrect, highly eccentric orbital plane with a lower than nominal inclination angle. All Galileo satellites are equipped with satellite laser ranging (SLR) retroreflectors which allow, for example, for the assessment of the orbit quality or for the SLR–GNSS co-location in space. The number of SLR observations to Galileo satellites has been continuously increasing thanks to a series of intensive campaigns devoted to SLR tracking of GNSS satellites initiated by the International Laser Ranging Service. This paper assesses systematic effects and quality of Galileo orbits using SLR data with a main focus on Galileo satellites launched into incorrect orbits. We compare the SLR observations with respect to microwave-based Galileo orbits generated by the Center for Orbit Determination in Europe (CODE) in the framework of the International GNSS Service Multi-GNSS Experiment for the period 2014.0–2016.5. We analyze the SLR signature effect, which is characterized by the dependency of SLR residuals with respect to various incidence angles of laser beams for stations equipped with single-photon and multi-photon detectors. Surprisingly, the CODE orbit quality of satellites in the incorrect orbital planes is not worse than that of nominal FOC and IOV orbits. The RMS of SLR residuals is even lower by 5.0 and 1.5 mm for satellites in the incorrect orbital planes than for FOC and IOV satellites, respectively. The mean SLR offsets equal \(-44.9, -35.0\), and \(-22.4\) mm for IOV, FOC, and satellites in the incorrect orbital plane. Finally, we found that the empirical orbit models, which were originally designed for precise orbit determination of GNSS satellites in circular orbits, provide fully appropriate results also for highly eccentric orbits with variable linear and angular velocities.  相似文献   

Model for prediction of sea dike breaching initiated by breaking wave impact     

Stanczak  Grzegorz  Oumeraci  Hocine 《Natural Hazards》2012,61(2):673-687

A computational model system is proposed for the prediction of sea dike breaching initiated from the seaward side by breaking wave impact with the focus on the application of the model system for the estimation failure probability of the defence structure. The described model system is built using a number of existing models for the calculation of grass, clay, and sand erosion. The parameters identified as those having the most significant influence on the estimation of the failure have been described stochastically. Monte Carlo simulations to account for uncertainties of the relevant input parameters and the model itself have been performed and the probabilities of the breach initiation and of the full dike breaching have been calculated. This will form the basis to assess the coastal flood risk due to dike breaching.  相似文献   

Effects of non-thermal tails in Maxwellian electron distributions on synchrotron and Compton processes     

Grzegorz Wardzi&#;ski  rzej A. Zdziarski 《Monthly notices of the Royal Astronomical Society》2001,325(3):963-971

We investigate how the presence of a non-thermal tail beyond a Maxwellian electron distribution affects the synchrotron process as well as Comptonization in plasmas with parameters typical for accretion flows on to black holes. We find that the presence of the tail can significantly increase the net (after accounting for self-absorption) cyclo-synchrotron emission of the plasma, which then provides seed photons for Compton upscattering. Thus, the luminosity in the thermally Comptonized spectrum is enhanced as well. The importance of these effects increases with both increasing Eddington ratio and black hole mass. The enhancement of the Comptonized synchrotron luminosity can be as large as ∼10³ and ∼10⁵ for stellar and supermassive black holes, respectively, when the energy content in the non-thermal tail is 1 per cent.
The presence of the tail only weakly hardens the thermal Comptonization spectrum but it leads to the formation of a high-energy tail beyond the thermal cut-off, which two effects are independent of the nature of the seed photons. Since observations of high-energy tails in Comptonization spectra can constrain the non-thermal tails in the electron distribution and thus the Comptonized synchrotron luminosity, they provide upper limits on the strength of magnetic fields in accretion flows. In particular, the measurement of an MeV tail in the hard state of Cyg X-1 by McConnell et al. implies the magnetic field strength in this source to be at most an order of magnitude below equipartition.  相似文献   

Erratum: Effects of non-thermal tails in Maxwellian electron distributions on synchrotron and Compton processes     

Grzegorz Wardzi&#;ski  rzej A. Zdziarski  by 《Monthly notices of the Royal Astronomical Society》2001,327(1):351-352

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Analysis and modeling of spatial correlation structure in small-scale rainfall in Central Oklahoma   总被引：1，自引：0，他引：1  

Grzegorz J. Ciach  Witold F. Krajewski 《Advances in water resources》2006

Spatial correlation structure in small-scale rainfall is analyzed based on a dense cluster of raingauges in Central Oklahoma. This cluster, called the EVAC PicoNet, consists of 53 gauges installed in 25 measurement stations covering an area of about 3 km by 3 km. Two raingauges are placed in 24 stations and five in the central station. Three aspects of the estimated spatial correlation functions are discussed: dependence on time-scale ranging from 1 min to 24 h, inter-storm variability, and dependence on rainfall intensity. The results show a regular dependence of the correlogram parameters on the averaging time-scale, large differences of the correlograms in the individual storms, and the dominance of storms with high spatial variability on the average large sample characteristics. The authors also demonstrate and discuss the ambiguities in correlation estimates conditioned on rainfall intensities. The findings of this study have implications for raingauge network design, rainfall modeling, and conclusive evaluation of radar and satellite estimates of rainfall.  相似文献   

Crisis or recovery? Recent developments in the regional processes in Poland     

Dr. Grzegorz Gorzelak 《GeoJournal》1987,15(1):113-119

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Screening reactive materials for a permeable barrier to treat TCE-contaminated groundwater: laboratory studies     

S. Johana Grajales-Mesa  Grzegorz Malina 《Environmental Earth Sciences》2016,75(9):772

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Estimation of radar-rainfall error spatial correlation     

Pradeep V. Mandapaka  Witold F. Krajewski  Grzegorz J. Ciach  Gabriele Villarini  James A. Smith 《Advances in water resources》2009

The study presents a theoretical framework for estimating the radar-rainfall error spatial correlation (ESC) using data from relatively dense rain gauge networks. The error is defined as the difference between the radar estimate and the corresponding true areal rainfall. The method is analogous to the error variance separation that corrects the error variance of a radar-rainfall product for gauge representativeness errors. The study demonstrates the necessity to consider the area–point uncertainties while estimating the spatial correlation structure in the radar-rainfall errors. To validate the method, the authors conduct a Monte Carlo simulation experiment with synthetic fields with known error spatial correlation structure. These tests reveal that the proposed method, which accounts for the area–point distortions in the estimation of radar-rainfall ESC, performs very effectively. The authors then apply the method to estimate the ESC of the National Weather Service’s standard hourly radar-rainfall products, known as digital precipitation arrays (DPA). Data from the Oklahoma Micronet rain gauge network (with the grid step of about 5 km) are used as the ground reference for the DPAs. This application shows that the radar-rainfall errors are spatially correlated with a correlation distance of about 20 km. The results also demonstrate that the spatial correlations of radar–gauge differences are considerably underestimated, especially at small distances, as the area–point uncertainties are ignored.  相似文献   

Thermal synchrotron radiation and its Comptonization in compact X-ray sources     

Grzegorz Wardzi&#;ski  Andrzej A. Zdziarski 《Monthly notices of the Royal Astronomical Society》2000,314(1):183-198

We investigate the process of synchrotron radiation from thermal electrons at semirelativistic and relativistic temperatures. We find an analytic expression for the emission coefficient for random magnetic fields with an accuracy significantly higher than those derived previously. We also present analytic approximations to the synchrotron turnover frequency, treat Comptonization of self-absorbed synchrotron radiation, and give simple expressions for the spectral shape and the emitted power. We also consider modifications of the above results by bremsstrahlung.
We then study the importance of Comptonization of thermal synchrotron radiation in compact X-ray sources. We first consider emission from hot accretion flows and active coronae above optically thick accretion discs in black hole binaries and active galactic nuclei (AGNs). We find that for plausible values of the magnetic field strength, this radiative process is negligible in luminous sources, except for those with hardest X-ray spectra and stellar masses. Increasing the black hole mass results in a further reduction of the maximum Eddington ratio from this process. Then, X-ray spectra of intermediate-luminosity sources, e.g. low-luminosity AGNs, can be explained by synchrotron Comptonization only if they come from hot accretion flows, and X-ray spectra of very weak sources are always dominated by bremsstrahlung. On the other hand, synchrotron Comptonization can account for power-law X-ray spectra observed in the low states of sources around weakly magnetized neutron stars.  相似文献