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Tautenburg, Germany

Singal A.K.,Physical Research Laboratory | Rajpurohit K.,Thuringer Landessternwarte TLS
Monthly Notices of the Royal Astronomical Society

We examine the possibility that a claimed dependence of the Fanaroff-Riley type I/II (FR I/II) break value in radio luminosity on the absolute magnitude of the optical host galaxy could be due to the Malmquist bias, where a redshift-luminosity correlation appears in a flux-limited sample because of an observational selection effect. In such a sample, the redshift dependence of a phenomenon could appear as a luminosity-dependent effect and may not be really representing an intrinsic property of the radio sample. We test this on the radio-complete MRC (Molonglo Reference Catalog) sample, where Spearman rank correlation and Kendall rank correlation tests showthat the correlations are indeed stronger between the redshift and the optical luminosity than that between the radio luminosity and the optical luminosity, suggesting that the latter correlation perhaps arises because of the Malmquist Bias. We further show that similar effects of the Malmquist bias could also be present elsewhere in other correlations claimed in the literature between the radio luminosity and other observed properties of FR I and II sources. © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

Stroe A.,Leiden University | Shimwell T.,Leiden University | Rumsey C.,Astrophysics Group | Van Weeren R.,Harvard - Smithsonian Center for Astrophysics | And 8 more authors.
Monthly Notices of the Royal Astronomical Society

Radio relics are patches of diffuse synchrotron radio emission that trace shock waves. Relics are thought to form when intracluster medium electrons are accelerated by cluster mergerinduced shock waves through the diffusive shock acceleration mechanism. In this paper, we present observations spanning 150 MHz to 30 GHz of the 'Sausage' and 'Toothbrush' relics from the Giant Metrewave and Westerbork telescopes, the Karl G. Jansky Very Large Array, the Effelsberg telescope, the Arcminute Microkelvin Imager and Combined Array for Research in Millimeter-wave Astronomy.We detect both relics at 30 GHz, where the previous highest frequency detection was at 16 GHz. The integrated radio spectra of both sources clearly steepen above 2 GHz, at the ≳6σ significance level, supporting the spectral steepening previously found in the 'Sausage' and the Abell 2256 relic. Our results challenge the widely adopted simple formation mechanism of radio relics and suggest more complicated models have to be developed that, for example, involve re-acceleration of aged seed electrons. © 2015 The Authors. Source

Singal A.K.,Physical Research Laboratory | Rajpurohit K.,Thuringer Landessternwarte TLS
Astrophysics and Space Science

We investigate the dependence of the Fanaroff-Riley (FR) 1/2 dichotomy of radio galaxies on their luminosities and redshifts. Because of a very strong redshift-luminosity correlation (Malmquist bias) in a flux-limited sample, any redshift-dependent effect could appear as a luminosity-related effect and vice versa. A question could then arise-do all the morphological differences seen in the two classes (FR 1 and 2 types) of sources, usually attributed to the differences in their luminosities, could as well be primarily a redshift-dependent effect? A sharp break in luminosity, seen among the two classes, could after all reflect a sharp redshift dependence due to a rather critical ambient density value at some cosmic epoch. A doubt on these lines does not seem to have been raised in past and things have never been examined with this particular aspect in mind. We want to ascertain the customary prevalent view in the literature that the systematic differences in the two broad morphology types of FR 1 and 2 radio galaxies are indeed due to the differences in their luminosities, and not due to a change in redshift. Here we investigate the dependence of FR 1/2 dichotomy of radio galaxies on luminosity and redshift by using the 3CR sample, where the FR 1/2 dichotomy was first seen, supplemented by data from an additional sample (MRC), that goes about a factor of 5 or more deeper in flux-density than the original 3CR sample. This lets us compare sources with similar luminosities but at different redshifts as well as examine sources at similar redshifts but with different luminosities, thereby allowing us a successful separation of the otherwise two intricately entangled effects. We find that the morphology type is not directly related to redshift and the break between the two types of morphologies seems to depend only upon the radio luminosity. © 2014 Springer Science+Business Media Dordrecht. Source

Drabent A.,Thuringer Landessternwarte TLS | Hoeft M.,Thuringer Landessternwarte TLS | Pizzo R.F.,Netherlands Institute for Radio Astronomy | Bonafede A.,Hamburger Sternwarte | And 2 more authors.
Astronomy and Astrophysics

Context. Galaxy clusters with signs of a recent merger in many cases show extended diffuse radio features. This emission originates from relativistic electrons that suffer synchrotron losses due to the intracluster magnetic field. The mechanisms of particle acceleration and the properties of the magnetic field are still poorly understood. Aims. We search for diffuse radio emission in galaxy clusters. Here, we study the complex galaxy cluster Abell2069, for which X-ray observations indicate a recent merger. Methods. We investigate the cluster's radio continuum emission by deep Westerbork Synthesis Radio Telescope (WSRT) observations at 346 MHz and Giant Metrewave Radio Telescope (GMRT) observations at 322MHz. Results. We find an extended diffuse radio feature roughly coinciding with the main component of the cluster. We classify this emission as a radio halo and estimate its lower limit flux density at 25 ± 9 mJy. Moreover, we find a second extended diffuse source located at the cluster's companion and estimate its flux density at 15 ± 2 mJy. We speculate that this is a small halo or a mini-halo. If true, this cluster is the first example of a double-halo in a single galaxy cluster. © ESO, 2015. Source

Tkachenko A.,Thuringer Landessternwarte TLS | Lehmann H.,Thuringer Landessternwarte TLS | Mkrtichian D.,Crimean Astrophysical Observatory
Astronomical Journal

TWDra is a well-known short-period Algol-type system. It belongs to the class of oEA stars (Algol-type systems with a δScuti-like oscillating primary component). We investigate the TWDra system based on high-resolution spectra taken in 2007 and in 2008 to derive precise stellar and system parameters and to check for phases of active mass transfer. We derived a precise orbital solution and the extracted spectra of the stellar components of the TWDra system. The analysis of the spectrum of the primary shows that it is a normal A5-type star with a chemical composition close to solar. By means of the Shellspec07-inverse program we calculated precise stellar and system parameters from the composite spectra. All results agree with those from the most recent photometric study. During both epochs of observations, the system can be well modeled without counting for mass transfer effects, assuming a spherical configuration of the primary and a Roche-lobe filling secondary. Thus, we conclude that the star was in quiet phases during both epochs of observations. © 2010 The American Astronomical Society. Source

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