Time filter

Source Type

Krelowski J.,Torun Center for Astronomy
Planetary and Space Science | Year: 2017

Methods of measuring distances to distant objects, allowing to investigate structure of our Milky Way, are briefly discussed. The methods may be based on three principles: using standard rod, standard candle and column density of interstellar matter. Using of the first one is generally restricted to pretty nearby objects. The third one can be applied in the thin galactic disc only. The spectrophotometric method (standard candle) is the most universal one but it involves uncertainties related to calibration the "standard candle" parameters and the interstellar extinction effects. Weak and strong points of these three methods are presented. The presence of gray extinction towards some objects is suggested which makes the most universal method of standard candle very uncertain. It's difficult to say whether this extinction appears in the form of circumstellar debris discs or is present in the general interstellar medium. The application of the method of measuring column densities of interstellar gases suggests that the rotation curve of our Milky Way system is rather Keplerian than flat which creates doubts to whether any Dark Matter is present in our Galaxy. It is emphasized that the most universal method, i.e. that of standard candle, used to estimate distances to cosmological objects, may suffer serious errors because of improper subtraction of extinction effects. © 2017 Elsevier Ltd.

Van Weeren R.J.,Harvard - Smithsonian Center for Astrophysics | Williams W.L.,Leiden University | Williams W.L.,Netherlands Institute for Radio Astronomy | Tasse C.,Rhodes University | And 119 more authors.
Astrophysical Journal | Year: 2014

We present Low Frequency Array (LOFAR) Low Band observations of the Boötes and 3C 295 fields. Our images made at 34, 46, and 62 MHz reach noise levels of 12, 8, and 5 mJy beam-1, making them the deepest images ever obtained in this frequency range. In total, we detect between 300 and 400 sources in each of these images, covering an area of 17-52 deg2. From the observations, we derive Euclidean-normalized differential source counts. The 62 MHz source counts agree with previous GMRT 153 MHz and Very Large Array 74 MHz differential source counts, scaling with a spectral index of -0.7. We find that a spectral index scaling of -0.5 is required to match up the LOFAR 34 MHz source counts. This result is also in agreement with source counts from the 38 MHz 8C survey, indicating that the average spectral index of radio sources flattens toward lower frequencies. We also find evidence for spectral flattening using the individual flux measurements of sources between 34 and 1400 MHz and by calculating the spectral index averaged over the source population. To select ultra-steep spectrum (α < -1.1) radio sources that could be associated with massive high-redshift radio galaxies, we compute spectral indices between 62 MHz, 153 MHz, and 1.4 GHz for sources in the Boötes field. We cross-correlate these radio sources with optical and infrared catalogs and fit the spectral energy distribution to obtain photometric redshifts. We find that most of these ultra-steep spectrum sources are located in the 0.7 ≲ z ≲ 2.5 range. © 2014. The American Astronomical Society. All rights reserved.

Shulevski A.,University of Groningen | Shulevski A.,Netherlands Institute for Radio Astronomy | Morganti R.,University of Groningen | Morganti R.,Netherlands Institute for Radio Astronomy | And 23 more authors.
Astronomy and Astrophysics | Year: 2015

Context. Steep spectrum radio sources associated with active galactic nuclei (AGN) may contain remnants of past AGN activity episodes. Studying these sources gives us insight into the AGN activity history. Novel instruments like the LOw Frequency ARray (LOFAR) are enabling studies of these fascinating structures to be made at tens to hundreds of MHz with sufficient resolution to analyse their complex morphology. Aims. Our goal is to characterize the integrated and resolved spectral properties of VLSS J1431+1331 and estimate source ages based on synchrotron radio emission models, thus putting constraints on the AGN duty cycle. Methods. Using a broad spectral coverage, we have derived spectral and curvature maps, and used synchrotron ageing models to determine the time elapsed from the last time the source plasma was energized. We used LOFAR, Giant Metrewave Radio Telescope (GMRT) and Jansky Very Large Array (VLA) data. Results. We confirm the morphology and the spectral index values found in previous studies of this object. Based on our ageing analysis, we infer that the AGN that created this source currently has very low levels of activity or that it is switched off. The derived ages for the larger source component range from around 60 to 130 Myr, hinting that the AGN activity decreased or stopped around 60 Myr ago. We observe that the area around the faint radio core located in the larger source component is the youngest, while the overall age of the smaller source component shows it to be the oldest part of the source. Conclusions. Our analysis suggests that VLSS J1431.8+1331 is an intriguing, two-component source. The larger component seems to host a faint radio core, suggesting that the source may be an AGN radio relic. The spectral index we observe from the smaller component is distinctly flatter at lower frequencies than the spectral index of the larger component, suggesting the possibility that the smaller component may be a shocked plasma bubble. From the integrated source spectrum, we deduce that its shape and slope can be used as tracers of the activity history of this type of steep spectrum radio source. We discuss the implications this conclusion has for future studies of radio sources having similar characteristics. © ESO, 2015.

Kunert-Bajraszewska M.,Torun Center for Astronomy | Labiano A.,European Space Agency | Labiano A.,Harvard - Smithsonian Center for Astrophysics | Siemiginowska A.,Harvard - Smithsonian Center for Astrophysics | Guainazzi M.,European Space Agency
Monthly Notices of the Royal Astronomical Society | Year: 2014

We report on the first X-ray Chandra observations of a sample of seven low-luminosity compact sources, which belong to a class of young compact steep spectrum (CSS) radio sources. Four of these have been detected, while the other three have upper limit estimations for X-ray flux; one CSS galaxy is associated with an X-ray cluster. We have used the new observations, together with the observational data for known strong CSS and gigahertz-peaked spectrum (GPS) objects and large-scale Fanaroff-Riley types I and II objects (FR I and II), to study the relation between morphology, X-ray properties and excitation modes in radio-loud active galactic nuclei (AGNs). We have found the following. (i) The low-power objects fit well with the already established X-ray-radio luminosity correlation for AGNs and occupy the space among FR I objects, which are weaker in X-rays. (ii) The high-excitation and low-excitation galaxies occupy a distinct locus in the radio/X-ray luminosity plane, notwithstanding their evolutionary stage. This is in agreement with the postulated different origins of the X-ray emission in these two groups of objects. (iii) We have tested the AGN evolution models by comparing the radio/X-ray luminosity ratio with the size of the sources and, indirectly, with their age. We conclude that the division for two different X-ray emission modes, which originate in the base of the relativistic jet (FR Is) or in the accretion disc (FR IIs) is already present among the younger compact AGNs. (iv) Finally, we have found that the CSS sources are less obscured than the more compact GPS objects in X-rays. However, the anticorrelation between X-ray column density and radio size does not hold for the whole sample of GPS and CSS objects. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Migaszewski C.,Torun Center for Astronomy
Celestial Mechanics and Dynamical Astronomy | Year: 2012

We study the long-term dynamics of a planetary system composed of a star and a planet. Both bodies are considered as extended, non-spherical, rotating objects. There are no assumptions made on the relative angles between the orbital angular momentum and the spin vectors of the bodies. Thus, we analyze full, spatial model of the planetary system. Both objects are assumed to be deformed due to their own rotations, as well as due to the mutual tidal interactions. The general relativity corrections are considered in terms of the post-Newtonian approximation. Besides the conservative contributions to the perturbing forces, there are also taken into account non-conservative effects, i. e., the dissipation of the mechanical energy. This dissipation is a result of the tidal perturbation on the velocity field in the internal zones with non-zero turbulent viscosity (convective zones). Our main goal is to derive the equations of the orbital motion as well as the equations governing time-evolution of the spin vectors (angular velocities). We derive the Lagrangian equations of the second kind for systems which do not conserve the mechanical energy. Next, the equations of motion are averaged out over all fast angles with respect to time-scales characteristic for conservative perturbations. The final equations of motion are then used to study the dynamics of the non-conservative model over time scales of the order of the age of the star. We analyze the final state of the system as a function of the initial conditions. Equilibria states of the averaged system are finally discussed. © 2012 The Author(s).

Kunert-Bajraszewska M.,Torun Center for Astronomy | Siemiginowska A.,Harvard - Smithsonian Center for Astrophysics | Labiano A.,CSIC - National Institute of Aerospace Technology
Astrophysical Journal Letters | Year: 2013

We discovered an X-ray cluster in a Chandra observation of the compact steep spectrum (CSS) radio source 1321+045 (z = 0.263). CSS sources are thought to be young radio objects at the beginning of their evolution and can potentially test the cluster heating process. 1321+045 is a relatively low-luminosity source and its morphology consists of two radio lobes on the opposite sides of a radio core with no evidence for jets or hotspots. The optical emission line ratios are consistent with an interstellar medium dominated by active galactic nucleus photoionization with a small contribution from star formation, and no contributions from shocks. Based on these ratios, we classify 1321+045 as a low excitation galaxy (LEG) and suggest that its radioactivity is in a coasting phase. The X-ray emission associated with the radio source is detected with 36.1 ± 8.3 counts, but the origin of this emission is highly uncertain. The current X-ray image of the cluster does not show any signatures of a radio source impact on the cluster medium. Chandra detects the cluster emission at >3σ level out to ∼60″ (240 kpc). We obtain the best-fit beta model parameters of the surface brightness profile of β = 0.58 ± 0.2 and a core radius of 9.4 arcsec. The average temperature of the cluster is equal to keV, with a temperature and cooling profile indicative of a cooling core. We measure the cluster luminosity L (0.5-2 keV) = 3 × 1044 erg s-1 and mass 1.5 × 1014 M⊙. © 2013. The American Astronomical Society. All rights reserved.

Kunert-Bajraszewska M.,Torun Center for Astronomy
Astronomische Nachrichten | Year: 2016

There are numerous examples of radio sources with various sizes which surprisingly exhibit very similar morphology. This observational fact helped to create a standard evolutionary model in which young and small radio-loud active galactic nuclei (AGN), called gigahertz-peaked spectrum (GPS) sources and compact steep spectrum (CSS) sources, become largescale radio objects. However, many details of this evolutionary process are still unclear. We explored evolution scenarios of radio-loud AGN using new radio, optical and X-ray data of so far unstudied low luminosity compact (LLC) sources and we summarize the results in this paper. Our studies show that the evolutionary track is very "individualized" although we can mention common factors affecting it. These are interaction with the ambient medium and AGN power. The second feature affects the production of the radio jets which, if they are weak, are more vulnerable for instabilities and disruption. Thus not all GPS and CSS sources will be able to develop large scale morphologies. Many will fade away being middleaged (105 yr). It seems that only radio strong, high excitation compact AGN can be progenitors of large-scale FRII radio sources. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ceglowski M.,Torun Center for Astronomy | Kunert-bajraszewska M.,Torun Center for Astronomy | Roskowinski C.,Torun Center for Astronomy
Monthly Notices of the Royal Astronomical Society | Year: 2015

We present high-resolution observations, using both the European VLBI Network (EVN) at 1.7 GHz and the Very Long Baseline Array (VLBA) at 5 and 8.4 GHz, to image radio structures of 14 compact sources classified as broad absorption line (BAL) quasars based on the absorption index (AI). All sources but one were resolved, with the majority showing core-jet morphology typical for radio-loud quasars. We discuss in detail the most interesting cases. The high radio luminosities and small linear sizes of the observed objects indicate they are strong young active galactic nuclei. Nevertheless, the distribution of the radio-loudness parameter, logRI, of a larger sample of AI quasars shows that the objects observed by us constitute the most luminous, small subgroup of the AI population. Additionally, we report that for the radio-loudness parameter, the distribution of AI quasars and that for those selected using the traditional balnicity index differ significantly. Strong absorption is connected with lower log RI and thus probably larger viewing angles. Since the AI quasars have on average larger log RI, the orientation can mean that we see them less absorbed. However, we suggest that the orientation is not the only parameter that affects the detected absorption. That the strong absorption is associated with the weak radio emission is equally important and worth exploring. © 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Kunert-Bajraszewska M.,Torun Center for Astronomy | Katarzynski K.,Torun Center for Astronomy | Janiuk A.,Polish Academy of Sciences
Astronomy and Astrophysics | Year: 2015

Aims. We present modelling and interpretation of the continuum broadband emission of two broad absorption line (BAL) quasars. The X-ray weakness of BAL quasars in comparison to non-BAL objects is possibly caused by the absorption of X-ray emission by the shielding material near the equatorial plane. On the other hand, the radio-loud BAL quasars are more X-ray loud than the radio-quiet ones. This suggests that part of the X-ray emission may arise from the radio jet. To investigate this possibility, we modelled the nuclear spectra of two BAL quasars in the whole available energy range. Methods. We focus on the emission from the very centres of these two objects, not greater than several parsecs. The source of emission was approximated by a single, homogeneous component that produces synchrotron and inverse-Compton radiation. The simplicity of the model allowed us to estimate the basic physical parameters of the emitting regions, using a universal analytic approach. Such methods have already been proposed to estimate basic physical parameters in blazars. For the first time, in a simplified form we propose this solution for quasars. In addition, we modelled the radiation spectra of the accretion disk and its corona to compare them with the jets' spectra. Results. We find that in the case of radio and X-ray luminous high-redshift object 3C 270.1, the nuclear X-ray continuum is dominated by the non-thermal, inverse-Compton emission from the innermost parts of the radio jet. However, the radio core of the lobe-dominated PG 1004+130 is probably too weak to produce significant part of the observed X-ray emission. A large contribution from the X-ray emitting accretion disk and corona is produced in our model for a sufficiently high mass of the black hole. However, it then exceeds the observed flux. Because the large intrinsic absorption was postulated recently by the NuSTAR observations, we propose that the disk-corona component may still account for the X-rays produced in this source. This part of the spectrum must nevertheless be dominated by the X-ray jet. The results of our modelling show that the jet-linked X-ray emission is present in both strong and weak radio sources, but its fraction seems to scale with the radio jet power. © 2015 ESO.

Kunert-Bajraszewska M.,Torun Center for Astronomy | Ceglowski M.,Torun Center for Astronomy | Katarzynski K.,Torun Center for Astronomy | Roskowinski C.,Torun Center for Astronomy
Astronomy and Astrophysics | Year: 2015

Aims. Outflows manifest as broad absorption lines (BALs) in the quasars spectra. Although outflows are one of the most common astrophysical processes in the Universe, the BAL quasars are rare. Radio emission is another tool that can help to understand the phenomenon of BAL quasars. The aim of this paper is to study their orientation and age by very long baseline interferometry (VLBI) imaging and radio-loudness parameter distribution. Methods. We performed high resolution radio observations of a new sample of ten BAL quasars using both the Very Long Baseline Array (VLBA) and the European VLBI Network (EVN) at 5 GHz. All the selected sources have balnicity indices (BI) more than 0 and radio flux densities less than 80 mJy at 1.4 GHz. They are very compact with linear sizes of the order of a few tens of parsecs and radio luminosities at 1.4 GHz above the FR I-FR II luminosity threshold. Results. Most of the observed objects have been resolved at 5 GHz showing one-sided, probably core-jet structures, typical for quasars. We discuss in detail their age and orientation based on the radio observations. We then used the largest available sample of BAL quasars to study the relationships between the radio and optical properties in these objects. We found that (1) the strongest absorption (high values of the balnicity index BI) is connected with the lower values of the radio-loudness parameter, log RI< 1.5, and thus probably with large viewing angles; (2) the large span of the BI values in each bin of the radio-loudness parameter indicates that the orientation is only one of the factors influencing the measured absorption; (3) most of the radio-loud BAL quasars are compact, low luminosity objects with a wide range of jet power (although the highest values of BI seem to be associated with the lower values of jet power). In addition, we suggest that the short lifetime postulated for some compact active galactic nuclei could also explain the scarcity of the large-scale radio sources among BAL quasars. © ESO, 2015.

Loading Torun Center for Astronomy collaborators
Loading Torun Center for Astronomy collaborators