Longterm Optical Monitoring of Bright BL Lacertae Objects with ATOM: Spectral Variability and Multiwavelength Correlations

Blazars are the established sources of an intense and variable non-thermal radiation extending from radio wavelengths up to HE and VHE gamma-rays. Understanding the spectral evolution of blazars in selected frequency ranges, as well as multi-frequency correlations in various types of blazar sources, is of a primary importance for constraining the blazar physics. Here we present the results of a long-term optical monitoring of a sample of 30 blazars of the BL Lac type. We study the optical color-magnitude correlation patterns emerging in the analyzed sample, and compare the optical properties of the targets with the high-energy gamma-ray and high-frequency radio data. The optical observations were carried out in R and B filters using ATOM telescope. Each object was observed during at least 20 nights in the period 2007-2012. We find significant global color-magnitude correlations in 40 % of the sample. The sources which do not display any clear chromatism often do exhibit bluer-when-brighter (bwb) behavior but only in isolated shorter time intervals. We also discovered spectral state transitions at optical wavelengths in several sources. Finally, we find that the radio, optical, and gamma-ray luminosities of the sources obey almost linear correlations, which seem however induced, at least partly, by the redshift dependance, and may be also affected by non-simultaneousness of the analyzed dataset. We argue that the observed bwb behavior is intrinsic to the jet emission regions, at least for some of the analyzed blazars, rather than resulting from the contamination of the measured flux by the starlight of host galaxies. We also conclude that the significance of color-magnitude scalings does not correlate with the optical color, but instead seems to depend on the source luminosity, in a sense that these are the lowest-luminosity BL Lac objects which display the strongest correlations.Comment: 16 pages, 9 figures, accepted for publication in Astronomy & Astrophysic

Three-dimensional stratigraphy reconstruction and GIS - postprocessing issues in archaeological field 3D documentation

This paper aims to present the results of experiments which allowed us to propose up-to-date method of 3D visual representation of explored archaeological layers. Considering the destructive nature of excavations, the correct documentation of an exploration, which offers an insight both into the decision-making process taking place on site, and into the most faithful representation of the examined material, presents a fundamental challenge for a field archaeologist. The aim of the experiments presented here was to test three methods of creating 3D models of successive archaeological layers (contexts) recorded during an exploration. The presented findings show that the method of editing point clouds using open-source software prior to importing the model of the reconstruction of the explored layer into GIS software, is the best solution from the point of view of both the effort and time required, and it can definitely be suggested as the standard procedure of creating the graphical bases for an archaeological database

The X-ray Jet in Centaurus A: Clues on the Jet Structure and Particle Acceleration

We report detailed studies of the X-ray emission from the kpc scale jet in the nearest active galaxy, Cen A. 41 compact sources were found within the jet, 13 of which were newly identified. We construct the luminosity function for the detected jet-knots and argue that the remaining emission is most likely to be truly diffuse, rather than resulting from the pile-up of unresolved faint knots. The transverse jet profile reveals that the extended emission has the intensity peak at the jet boundaries. We note that limb-brightened jet morphologies have been observed previously at radio frequencies in some jet sources, but never so clearly at higher photon energies. Our result therefore supports a stratified jet model, consisting of a relativistic outflow including a boundary layer with a velocity shear. In addition, we found that the X-ray spectrum of the diffuse component is almost uniform across and along the jet. We discuss this spectral behavior within a framework of shock and stochastic particle acceleration processes. We note some evidence for a possible spectral hardening at the outer sheath of the jet. Due to the limited photon statistics of the present data, further deep observations of Cen A are required to determine the reality of this finding, however we note that the existence of the hard X-ray features at outer jet boundaries would provide an important challenge to theories for the evolution of ultra-relativistic particles within the jets.Comment: 27page, 8 figures, ver2, accepted for publication in the Ap

Cherenkov Telescope Array : the World’s largest VHE gamma-ray observatory

Very-High Energy (VHE) gamma-ray astroparticle physics is a relatively young field, and observations over the past decade have surprisingly revealed almost two hundred VHE emitters which appear to act as cosmic particle accelerators. These sources are an important component of the Universe, influencing the evolution of stars and galaxies. At the same time, they also act as a probe of physics in the most extreme environments known - such as in supernova explosions, and around or after the merging of black holes and neutron stars. However, the existing experiments have provided exciting glimpses, but often falling short of supplying the full answer. A deeper understanding of the TeV sky requires a significant improvement in sensitivity at TeV energies, a wider energy coverage from tens of GeV to hundreds of TeV and a much better angular and energy resolution with respect to the currently running facilities. The next generation gamma-ray observatory, the Cherenkov Telescope Array Observatory (CTAO), is the answer to this need. In this talk I will present this upcoming observatory from its design to the construction, and its potential science exploitation. CTAO will allow the entire astronomical community to explore a new discovery space that will likely lead to paradigm changing breakthroughs. In particular, CTA has an unprecedented sensitivity to short (sub-minute) timescale phenomena, placing it as a key instrument in the future of multi-messenger and multi-wavelength time domain astronomy. I will conclude the talk presenting the first scientific results obtained by the LST-1, the prototype of one CTA telescope type - the Large Sized Telescope, that is currently under commission

Technical elements for minimising of vibration effects in special vehicles

The paper presents chosen solutions and technical elements for minimising of vibration effects in special vehicles. Due to volume and scope of the impact, forces and load generated in special vehicle during operating these elements are extremely important for isolation and absorbing of vibration affecting human or load. As the example of such solutions frame, suspension of car-body and cabin adopt in high mobility wheeled platform were described

An Analysis of Soft X-ray Structures at Kiloparsec Distances from the Active Nucleus of Centaurus A Galaxy

Here we re-analyze the archival {\it Chandra} data for the central parts of the Centaurus\,A radio galaxy, aiming for a systematic investigation of the X-ray emission associated with the inner radio lobes in the system, and their immediate surroundings. In particular, we focus on four distinct features characterized by the soft excess with respect to the adjacent fields. Those include the two regions located at kpc distances from the nucleus to the West and East, the extended bow-shock structure to the South, and a fragment of a thin arc North from the center. The selected North, West, and South features coincide with the edges of the radio lobes, while the East structure is seemingly displaced from the radio-emitting plasma. Our X-ray spectral analysis reveals (i) a power-law emission component with photon index $\Gamma \sim 2$ in the North, East, and South regions, and (ii) a dense (number density $\sim 0.3$\,cm$^{-3}$) and relatively cold (temperature $\sim 0.2$\,keV) gas in the East and West regions. The power-law emission is consistent with the synchrotron continuum generated at the edges of the radio structure, and implies that the efficiency of the electron acceleration at the terminal bow-shock does not vary dramatically over the inner lobes' extension. The presence of gaseous condensations, on the other hand, could possibly be understood in terms of a massive outflow from the central regions of the galaxy.Comment: Accepted for publication in The Astrophysical Journa

X-ray spectral analysis of the jet termination shock in pictor A on subarcsecond scales with Chandra

Hot spots observed at the edges of extended radio lobes in high-power radio galaxies and quasars mark the position of mildly relativistic termination shock, where the jet bulk kinetic energy is converted to the internal energy of the jet particles. These are the only astrophysical systems where mildly relativistic shocks can be directly resolved at various wavelengths of the electromagnetic spectrum. The western hot spot in the radio galaxy Pictor A is an exceptionally good target in this respect, due to the combination of its angular size and high surface brightness. In our previous work, after a careful Chandra image deconvolution, we resolved this hot spot into a disk-like feature perpendicular to the jet axis, and identified it as the front of the jet termination shock. We argued for a synchrotron origin of the observed X-ray photons, which implied electron energies reaching at least 10–100 TeV at the shock front. Here, we present a follow-up on that analysis, proposing, in particular, a novel method for constraining the shape of the X-ray continuum emission with subarcsecond resolution. The method is based on a Chandra hardness map analysis, using separately deconvolved maps in the soft and hard X-ray bands. In this way, we have found there is a systematic, yet statistically significant gradient in the hardness ratio across the shock, such that the implied electron energy index ranges from s $\leq$ 2.2 at the shock front to s > 2.7 in the near downstream. We discuss the implications of the obtained results for a general understanding of particle acceleration at mildly relativistic shocks

The impact of the mineral composition of Carboniferous claystones on the water-induced changes of their geomechanical properties

In this article, the authors describe the characteristics and changes of geomechanical properties of Carbonifeorus claystones as related to their mineral composition and the time of soaking in water. Geomechanical properties, including bulk density, Young modulus, Poisson ratio, unconfined compressive strength, durability index, and swelling index were examined in dry rock samples, and in water-soaked samples after 3 hours of soaking, and 6 hours of soaking respectively. Changes in the geomechanical properties of rocks were also examined as a function of their mineralogical composition. In particular, the properties of rocks were examined in relation to present aluminosilicates and layered aluminosilicates, respectively. Changes in the geomechanical properties were also examined relative to the presence of minerals anatase and siderite. Correlation coefficients between physical parameters and mineral composition were examined. It was determined that the total quantity of aluminosilcates is a better predictor of geomechanical properties after soaking, than only the content of layered aluminosilicates. Calculated correlation coefficients were generally higher for most samples after 6 hours of soaking than after 3 hours of soaking. It was also determined that the increase of bulk density correlates much better with the mineral anatase content, than with the siderite content

Low-frequency high-resolution radio observations of theTeV-emitting blazar SHBL J001355.9−185406

Context. In the framework of the unification scheme of radio-loud active galactic nuclei, BL Lac objects and quasars are the beamed end-on counterparts of low-power (FR I) and high-power (FR II) radio galaxies, respectively. Aims. Some BL Lacs have been found to possess the FR II-type, large-scale radio morphology, suggesting that the parent population of BL Lacs is a mixture of low- and high-power radio galaxies. This seems to apply only to “low frequency-peaked” BL Lacs, since all the “high frequency-peaked” BL Lacs studied so far were shown to host the FR I-type radio jets, exclusively. While analyzing the NRAO VLA Sky Survey (NVSS) maps of the TeV detected BL Lacs, we have discovered, however, that the high frequency-peaked object SHBL J001355.9−185406 is associated uniquely with the one-sided, arcmin-scale, and edge-brightened jet/lobe-like feature extending to the south-west from the blazar core. Methods. In order to investigate the large-scale morphology of SHBL J001355.9−185406 in detail, we have performed low-frequency and high-resolution observations of the source at 156, 259, and 629 MHz using the Giant Metrewave Radio Telescope (GMRT). Results. Our analysis indicates that no diffuse arcmin-scale emission is present around the unresolved blazar core, and that the arcmin-scale structure seen on the NVSS map breaks into three distinct features unrelated to the blazar, but instead associated with background AGN. Conclusions. The upper limits for the extended radio halo around the TeV-emitting BL Lac object SHBL J001355.9−185406 read as <10%−1% at 156−629 MHz. The fact that the integrated radio spectrum of the unresolved blazar core is flat down to 156 MHz indicates that a self-similar character of the jet in the source holds up to relatively large distances from the jet base