High energy astrophysics (20)
The blazar PKS 1510-089 is one of the most variable active galactic nuclei (AGN) in the gamma-ray sky and well monitored over the full spectral range. However, using simultaneous data to describe the spectral energy distributions (SEDs) of AGN with steady-state scenarios is degenerate. Here, we introduce an approach to use the concept of dynamic SEDs involving the search for correlations between physical parameters and the overall shape of time-resolved SEDs. We find that between 2008 and 2018, the GeV flux is in general a good proxy of the integrated keV to GeV high-energy emission of PKS1510-089. In contrast to this, no such strong correlation is found for the X-ray emission. The gamma-ray spectrum shows a harder-when-brighter trend, reminiscent of the canonical behavior of X-ray binaries.
In two recent papers, we presented measurements by the Fermi/LAT and theoretical interpretation of the gamma-ray spectra from two Galactic microquasars, Cyg X-1 and Cyg X-3. In both sources, orbital modulation (due to Compton anisotropy of scattered stellar photons from the donor) has been measured, which has allowed us to estimate of the location of the bulk of the gamma-ray emission. The theoretical interpretation of the broad-band spectra (from radio to gamma-rays) is based on extended-jet and accretion models, developed earlier. We have also measured cross-correlations between the gamma-rays and both radio and X-ray emission, which put constraints on the respective emission sites and, in the case of Cyg X-3, implies the presence of extended periods of advection of magnetic fields through the accretion flow.
I will present some new features of a supermassive black hole at the center of the Milky Way in relation to the combined effects of strong gravity and external electromagnetic fields on the plasma matter surrounding black hole.
The Cosmological Principle is \"the assumption that the universe is spatially homogeneous and isotropic in the large-scale average\" (Peebles P.J.E., Principles of Physical Cosmology, Princeton Univ. Press, 1993, page 199). In year 1998 the author, together with his two colleagues, has shown that the BATSE\'s short gamma-ray bursts are not distributed isotropically on the sky.
This claim was followed by other papers confirming both the existence
of anisotropies in the angular distribution of bursts and the existence of huge Gpc structures in the spatial distribution. These observational facts are in contradiction with the Cosmological Principle, because the large scale averaging hardly can be provided. The aim of this lecture is to survey these publications.
Relativically broadened iron lines can be used to study the accretion of matter onto supermassive black holes in active galactic nuclei (AGN) via X-ray spectroscopy. Radio-loud AGN are particularly important targets for such studies, because combined X-ray and radio studies might allow us to probe the connection between accretion and jet production. Unfortunately, broad-iron lines are rare among radio-loud AGN.
A promising radio-loud candidate whose spectrum has been suggested to exhibit relativically broadened iron-line emission is the nearby two-sided jet system NGC 1052.
Using data from the XMM-Newton satellite, we studied the X-ray spectrum (0.5 - 10 keV) of the pn-detector and compared various modelling approaches in order to test the broad-iron-line scenario in this important object.
The late studies point out that some X-ray pulsars show uncharacteristic bimodal energy spectrum in the low luminous state. We developed the model of the magnetized neutron star polar cap emission at low accretion rate case to explain this spectral behavior. At such rates, no accretion column is formed above the surface of the neutron star and the accreted matter hits the atmosphere. We calculate polarized radiative transfer in the atmosphere with nonuniform temperature and density profiles to model the radiation field. The model is applied to fit the spectrum of the X-ray pulsars GX304-1 observed by NuSTAR and Swift/XRT.
General Monte Carlo methods are a broad class of algorithms that rely on repeated random sampling to obtain reliable numerical results in many (not only) physical problems. The underlying concept is to use randomness to solve problems that might be deterministic in principle. They are often used in problems with many coupled degrees of freedom. We present the possible use of these methods in the long known case of the analytical model of Fanaroff-Riley type II radio sources, proposed by Kaiser et al. (1997, MNRAS, 292, 723) and assuming `continuum injection’ process in the jet-IGM interaction. Since this model it is characterized by a large number of free parameters, and originally requires knowing the number of source parameters a priori unknown, the use of Monte Carlo methods seems optimal. We discuss the application of these methods and their effectiveness and reliability in the case of studying the selected real radio sources.
In this review I would like to present an updated panorama about the Frontier Research in Astrophysics with particular emphasis on the most important results obtained for a better knowledge of the physics governing our Universe, and on the open problems that probably will be solved with the next generation space- and ground based experiments.
Symbiotic variables belong to an interesting class of interacting binary stars. Since the beginning of this century, the systematic search for these objects has begun and such surveys have led to discoveries of many new objects and dozens of candidates in the Milky Way and the Local Group. As the latest catalog of symbiotic binaries is almost two decades old, we decided to prepare a new, online database of the galactic and extragalactic symbiotic systems. These objects are also known for their X-ray emission. For the purpose of this work, we have prepared a census of symbiotic binaries and their properties based on observations obtained by X-ray satellites in the previous decades. As our review has shown, the X-ray emission seems to be a common feature of symbiotics with a white dwarf, preferentially detected from nearby sources.
Detecting the afterglows of double neutron star merger events is a challenging
task because of the quick fading of the observed flux. In order to create an efficient
observing strategy for their observing process it is crucial to know their intrinsic rate. Unfortunately, the numerous models existing today predict this rate on a vary wide range. In my talk I will compare the different levels of kilonova approximations in order to determine their reliability. Also, I will show the effect of different ejecta mass lay-outs on the light curve shape and the estimated kilonova rate.
Diffusive shock acceleration has been the leading contender to explain particle acceleration in blazars for decades. Recent observations of short time-scale variability are in tension with the shock-acceleration mechanism but in agreement with theoretical predictions for \"magnetoluminescence\" driven by relativistic magnetic reconnection.
Using cosmic ray electron spectra measured by HESS, Magic, and Fermi-LAT, we
determine the region of their origin in our Galaxy. We infer the region by fitting the solution of the cosmic ray electron diffusion equation to the data. The energy losses lead to a distance-dependent turnover energy in the electron spectrum placing the boundary for the source distribution at a distance of 3 kiloparsecs from the solar system. The sources injecting cosmic ray electrons are also copious producers of gamma rays. Comparing the cumulative flux of gamma-ray sources within 3 kpc with the required injection rate of electrons, we can check the consistency of the model.
**Veřejná populární** přednáška o nedávném úspěchu astronomů, kteří poprvé “vyfotili” černou díru, a sice tu v centru kvasaru M87, a vlastně i tak trochu povídání o černých dírách obecně.
By applying different statistically robust methods, we analyze the time-lag between the continuum and ionized line-emission (Mg II line) light curves for the distant bright quasar CTS C30.10 (redshift z~0.9). The data were obtained by the SALT telescope. In detail, we demonstrate the application of several methods using discreet correlation function (DCF), z-transformed discreet correlation function (zDCF), von Neumann estimator, and the JAVELIN code package. In particular, we discuss the uncertainties of these methods. In conclusion, we find that the quasar lies on the broad-line region (BLR) size – monochromatic luminosity power-law scaling, which was already confirmed for low-redshift sources. In case the BLR size-luminosity relation holds for other distant sources, quasars could be used for probing cosmological models as “standard candles” complementary to supernovae Ia.
GRO J1744-28 (aka. the Bursting Pulsar) is a low-mass X-ray binary (LMXB) with a proposed cyclotron resonant scattering feature (CRSF) at 4.7keV. Typically LMXBs have relatively low magnetic field strengths - generally believed to be not sufficiently strong for CRSFs - and this claim belongs to the few CRSF reports in LMXBs at energies <10keV. This talk is about NuSTAR data of the forth reactivation phase in 2017 which does not show significant absorption features in its spectrum. I will show results from spectral fitting and present a rigorous search for a CRSF. Based on detailed Monte Carlo simulations we can rule out a significant line at the >2sigma level.
We successfully described the combined Swift/XRT and NuSTAR spectrum of Cen X-3 with empirical and physical models. For the
fitting procedure of the physical continuum model by Becker & Wolff (2007) we implemented a new approach to ensure energy
conservation during the χ 2 minimization. We found that this new method can simplify the usage of the model considerably.
To better understand the the phenomena of gamma ray bursts and the physical properties of the progenitors in high-redshift host galaxies we have to know not only the distance of the host galaxy itself but the host\'s location in its local galaxy cluster. Using deep Subaru Hyper Suprime-Cam observations for a chosen z=0.8 GRB we are giving constraints on photometric redshifts of the parent galaxy cluster via statistical methods.
Using Very Long Base Line Interferometry (VLBI) we can resolve the parsec-scale jet structure of blazars in the radio regime and measure the bulk velocity of the jet plasma. Apparent superluminal motion is a common phenomenon observed in many blazars due to bulk relativistic motions at small inclinations to the line of sight. However, many BL Lac objects whose gamma-ray emission extends up to TeV energies and whose strong gamma-ray variability indicates very high relativistic Doppler factors are known to have only relatively slow VLBI jets. This unresolved contradiction has become known as the Doppler crisis of TeV blazars. We present new VLBI results from the TANAMI program for one of the brightest and most variableTeV blazars in the sky, PKS 2155-304, and discuss the results in the context of the Doppler crisis.
In nuclei of galaxies strong tidal forces can destroy stars passing within critical distance from the central supermassive black hole (SMBH). Observational signatures of tidal disruption events depend on the environment around the SBMH horizon and the level of its accretion activity. We consider a system where the material remnant from the disrupted star forms a gaseous ring that circularises and gradually spreads in radius by viscous process. We consider the case of a remnant trail embedded in a hot environment and illuminated by X-rays from the surrounding corona or the base of a jet. The evolving spectral features provide a novel way to reveal the parameters of the system, namely, the distance of the remnant gas from the SMBH, the radial extent of the trail, and the spin of the SMBH.
Properties of charged particle motion in the field of magnetized BHs imply four possible regimes of behavior of ionized Keplerian disks: survival in regular epicyclic motion, transformation into chaotic toroidal state, destruction due to fall into BH, destruction due to escape to infinity along magnetic field lines (Kerr BH only). Due to extremely efficient magnetic Penrose process particles escaping to infinity could form UHECRs.
Real-Time Image Processing In Astronomy (5)
I will present three GRB optical afterglows detected by the 0.5m robotic telescope telescope in Ondrejov. While the afterglows themselves might be called rather boring - not much variability, faint, late detection - there is a story behind each of them that could be interesting to the audience.
The JWST space telescope will be hopefully launched and thanks to its great sensitivity it will, apart from many other astonishing scientific tasks, uncover the mysteries of the origin of the first stars, first galaxies and look in details at some of the hot exoplanet candidates for extraterrestrial life. I will summarise the mission, discuss the main scientific goals and focus to some of the work I am involved in, namely the JWST deep field.
A typical property of fish-eye lens is image distortion that complicates standard linear plate solving or even higher order polynomial fitting. A model that has to be used is dependent on lens projection type that can be extracted after elaborate catalog matching.
New and optimized algorithm for image registration and plate solving of all-sky images will be presented.
Presented algorithm for image registration is based on Generalized Hough Transformation GHT and provides multiple optimizations against previously used algorithm considering the speed of pattern detection and properties of image projection with a fish-eye lens to cover a wider area in the image. Astrometric calibration is obtained through precise catalog matching and exact model fitting.
Scientific CMOS image sensors are a modern alternative for a typical CCDs offering both low noise, large sensitive area and high frame rates, which make them promising devices for a modern wide-field sky surveys. However, the peculiarities of CMOS technology have to be properly taken into account when analyzing the data, and in this talk I will briefly summarize my experience of working with two generations of Andor scientific CMOS sensors.
The robotic telescope D50 in Ondřejov routinely follows-up the triggers of Gamma-Ray Bursts in order to study their optical counterparts. While the afterglows of long gamma-ray bursts are relatively bright, the optical emission of short bursts is much weaker and more difficult to detect. We present the first ever detected optical counterpart of a short burst detected by our robotic system and from the Czech Republic.
Session on digitization and astrophysical applications of astronomical photographic plate collections (3)
The paper focuses on creating a digital multidisciplinary virtual observatory. The virtual observatory includes: 1) Electronic databases of astrometric and astrophysical observations. 2) Digital data on modern star catalogues, planetary parameters, digital data on meteoroids, occultations and lunar objects. 3) Data system in the field of astronomical heritage according to UNESCO declaration (database on Russian astronomers, astroarchaeological objects, historical heritage of Russian space flights, etc.). 4) Creation of Astronomical Heritage Center. A virtual observatory of this kind is being developed for the first time in the world.
I will briefly present and discuss the recent status of astronomical photographic data archives worldwide, both photometric and spectroscopic, including digitization, pipelines, astrophysical use, and public access.
This paper focuses on determining the positions of lunar objects using the collection of digital astronomical photographs of the Moon’s surface produced at various optical librations in the star system. As a result, the selenographic coordinates for 1161 objects were obtained with accuracies 0,04 ± 0,13 arcseconds in declination and 0,05 ± 0,11 arcseconds in right ascension. The work also describes practical results on analyzing digital astronomical photographs in various phase spaces. The method allows transforming objects’ coordinates from the photographs into celestial coordinate system with a high accuracy. The results produced may be applied in the field of space geodesy and navigation when analyzing various systems of digital images.
Small satellites for astrophysics and Instrumental session (12)
The satellites of BRITE constellation observe chosen field on the sky during six months. This results in a large amount of gathered data with gaps every hundred minutes. Asteroseismologists are provided with reduced data in the form of light curves that however still contain some trends of instrumental origin. I will talk about decorrelation and analysis of these data using Python scripts.
The first Slovak satellite skCUBE, wholly designed and built in Slovakia, was successfully launched into its orbit on June 23rd 2017. After 14 days in orbit, the communication between the radio and other subsystems ceased to work. Since then, only limited access to the satellite functions remains. The last packet was received on 12th January 2019 after 569 days on orbit. The satellite sent more than 2 million packets with valuable datasets. From the collected information it can be confirmed that most of the systems worked as designed. Most valuable data are from attitude determination and control system as well as from satellite power and communication subsystem. The skCUBE project was run by many enthusiasts and students mostly working voluntarily for the non-profit organization SOSA. The main goal was to bring hands-on experience with space technologies and components to a new generation of Slovak engineers. Thanks to valuable experience with skCUBE and developing collaboration with the Czech Republic, SOSA and it\'s partners decides to start a new, more challenging project of international Czechoslovak 3U nanosatellite called CSCube. This mission emphasized educational activities for Slovak and Czech schools, will do interesting science thanks to GRB detection payload and bring innovative technologies from both countries to space through it\'s IOD program.
This study presents a background estimation for the Cubesats Applied for MEasuring and LOcalising Transients (CAMELOT), which is a proposed fleet of nanosatellites for the all-sky monitoring and timing based localisation of gamma-ray transients with precise localization capability at low Earth orbits. CAMELOT will allow to observe and precisely localize short gamma-ray bursts (GRBs) associated with kilonovae, long GRBs associated with core-collapse massive stars, magnetar outbursts, terrestrial gamma-ray flashes, and gamma-ray counterparts to gravitational wave sources. The fleet of at least nine 3U CubeSats is proposed to be equipped with large and thin CsI(Tl) scintillators read out by multi-pixel photon counters (MPPC). A careful study of the radiation environment in space is necessary to optimize the detector casing, estimate the duty cycle due to the crossing of the South Atlantic Anomaly and polar regions, and to minimize the effect of the radiation damage of MPPCs.
A paradigm change in spacecraft engineering can currently be observed: from traditional multi-functional, large spacecraft towards robust systems of networked, cooperating, distributed very small satellites. This will illustrated by pico-satellite formation examples in the application area of Earth observation. Appropriate baseline distances between detectors on-board raise challenging control requirements for attitude and orbit control. In combination with sensor data fusion in Earth observation, concrete examples under development in Wuerzburg include “TOM – Telematics earth Observation Mission”, a 3 pico-satellite formation for photogrammetric observations. It is part of the international missions TIM (Telematics International Mission), where partners from 5 continents contribute CubeSats for 3D Earth observation. In the CloudCT mission, clouds are characterized by computed tomography methods via 10 cooperating pico-satellites. Similar principles should be applicable for astrophysics missions, just by pointing away from Earth instead of towards Earth.
As scores of small satellites are built and launched, a number of small-scale groundstations are coming up across the world. Our research is on utilizing the resources available by pooling together groundstations to track one satellite for a longer period automatically. This talk will go into the scheduling and communication aspects of such an abstraction layer eventually also dealing with tricky security aspects.
All-sky coverage combined with a precise localization is an important direction for multi-messenger astronomy to perform follow-up
observations of the electromagnetic counterparts of gravitational wave sources. The idea of timing-based localization in the gamma-ray band
with multiple CubeSats is a simple, powerful, and possibly unique solution. We have found, that with 9 satellites, equipped with large CsI scintillators readout by the multi-pixel photon counters, ten-arcmin-scale localization is achievable. We are now developing a mission called \"Cubesats Applied for MEsureing and LOcalising Transients: CAMELOT\". Further detailed studies on localization feasibility, the effect of the expected in-orbit background environment and various stages of demonstration flight experiments using prototype models are now rapidly proceeding. In this contribution, we will introduce our mission concept and the current status as well as the future prospects of this project.
Recent Status of ESA SMILE project and Czech participation will be briefly presented and discussed.
Recent Status of ESA THESEUS project, a candidate mission selected by ESA within the M5 call, and recent and expected Czech participation in this project will be briefly presented and discussed.
RISESAT is a small Japanese experimental Earth-observing, science and technology demonstration satellite. One of the scientific instruments onboard is a miniature radiation monitor telescope with two Timepix detectors, developed and built at the Institute of Experimental and Applied Physics, CTU in Prague. After its successful launch in January 2019, it joined two other still operational satellites with our Timepix-based radiation monitors, SATRAM onboard the ESA satellite Proba-V (launched in 2013) and the Czech VZLUSAT-1 cubesat (launched 2017). In this work we present general technical and scientific details about the RISESAT satellite mission and a basic comparison of space weather monitoring from SATRAM and VZLUSAT-1 radiation monitors.
During the recent years stress-compensated chromium-iridium coatings for X-ray mirrors have been developed successfully at Aschaffenburg University, thereby facing challenging technical requirements. This work was partially embedded in several binational projects (JEUMICO, JODEXRA, TRILAMICO, AXROCO, COPAXRA), gratefully funded by the Bavarian-Czech Academic Agency (BTHA). Within this conference contribution measurement results on the surface micro-roughness and on the layer structure of these coatings as well as on the coatings stress and its temporal behavior are presented. X-ray reflectivity measurements performed recently at the PANTER test facility at these coatings are compared with corresponding simulations and found to be in good agreement. It is intended to transfer these laboratory development results now to real applications in scientific satellite payloads for X-ray astronomy.
Talk will describe the X-ray Lobster Eye (LE) telescope demonstrator for an all sky monitoring mission. The X-ray LE optics represents an alternative to recently used technologies, brings advantages and offers a cost-effective solution. The mission and payload are based on heritage and experience from the VZLUSAT-1 CubeSat and its 1D X-ray optics payload. Both the satellite platform and payload will be presented.
The new, small satellite based gamma-ray detectors, like CAMELOT, will provide a new way to detect gamma transients in the multi-messenger era. The efficiency and the detection capabilities of such a system will be compared with current missions, e.g. Fermi GBM. This can be used in the future to estimate the observable GRBs’ parameters as well as other EM transients.