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Mykolayiv, Ukraine

Tello J.C.,Institute Astrofisica Of Andalucia Iaa Csic | Castro-Tirado A.J.,Institute Astrofisica Of Andalucia Iaa Csic | Gorosabel J.,Institute Astrofisica Of Andalucia Iaa Csic | Perez-Ramirez D.,University of Jaen | And 6 more authors.
Astronomy and Astrophysics | Year: 2012

Context. Since the early 1990s, gamma ray bursts (GRB) have been accepted to be of extra-Galactic origin because of the isotropic distribution observed by BATSE and the redshifts observed via absorption line spectroscopy. Nevertheless, upon closer examination at least one case turned out to be of Galactic origin. This particular event presented a fast rise and exponential decay (FRED) structure, which leads us to believe that other FRED sources might also be Galactic. Aims. This study was set out to estimate the most probable degree of contamination by Galactic sources that certain samples of FREDs have. Methods. To quantify the degree of anisotropy, the average dipolar and quadripolar moments of each sample of GRBs with respect to the Galactic plane were calculated. This was then compared to the probability distribution of simulated samples comprising a combination of isotropically generated sources and Galactic sources. Results. We observe that the dipolar and quadripolar moments of the selected subsamples of FREDs are found more than two standard deviations outside those of random isotropically generated samples. The most probable degree of contamination by Galactic sources for the FRED GRBs of the Swift catalog detected until February 2011 that do not have a known redshift is about 21 out of 77 sources, which represents roughly 27%. Furthermore, we observe that by removing from this sample those bursts that have any type of indirect redshift indicator and multiple peaks, the most probable contamination increases to 34% (17 out of 49 sources). Conclusions. It is probable that a high degree of contamination by Galactic sources occurs among the single-peak FREDs observed by Swift. Accordingly, we encourage additional studies on these types of events to determine the nature of what could be an exotic type of Galactic source. © ESO, 2012.

Zauderer B.A.,Harvard University | Berger E.,Harvard University | Margutti R.,Harvard University | Levan A.J.,University of Warwick | And 22 more authors.
Astrophysical Journal | Year: 2013

We present X-ray, optical, near-infrared (IR), and radio observations of gamma-ray bursts (GRBs) 110709B and 111215A, as well as optical and near-IR observations of their host galaxies. The combination of X-ray detections and deep optical/near-IR limits establish both bursts as "dark." Sub-arcsecond positions enabled by radio detections lead to robust host galaxy associations, with optical detections that indicate z ≲ 4 (110709B) and z 1.8-2.9 (111215A). We therefore conclude that both bursts are dark due to substantial rest-frame extinction. Using the radio and X-ray data for each burst we find that GRB 110709B requires mag and GRB 111215A requires mag (assuming z = 2). These are among the largest extinction values inferred for dark bursts to date. The two bursts also exhibit large neutral hydrogen column densities of NH, int ≳ 1022 cm-2 (z = 2) as inferred from their X-ray spectra, in agreement with the trend for dark GRBs. Moreover, the inferred values are in agreement with the Galactic AV -N H relation, unlike the bulk of the GRB population. Finally, we find that for both bursts the afterglow emission is best explained by a collimated outflow with a total beaming-corrected energy of E γ + E K (7-9) × 1051 erg (z = 2) expanding into a wind medium with a high density, Myr-1(n 100-350 cm -3 at 1017 cm). While the energy release is typical of long GRBs, the inferred density may be indicative of larger mass-loss rates for GRB progenitors in dusty (and hence metal rich) environments. This study establishes the critical role of radio observations in demonstrating the origin and properties of dark GRBs. Observations with the JVLA and ALMA will provide a sample with sub-arcsecond positions and robust host associations that will help to shed light on obscured star formation and the role of metallicity in GRB progenitors. © 2013. The American Astronomical Society. All rights reserved.

Caballero-Garcia M.D.,Czech Technical University | Simon V.,Czech Technical University | Simon V.,Academy of Sciences of the Czech Republic | Jelinek M.,Institute Astrofisica Of Andalucia Iaa Csic | And 25 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2015

DG Canum Venaticorum (DG CVn) is a binary system in which one of the components is an M-type dwarf ultrafast rotator, only three of which are known in the solar neighbourhood. Observations of DG CVn by the Swift satellite and several ground-based observatories during its superflare event on 2014 allowed us to perform a complete hard X-ray-optical follow-up of a superflare from the red-dwarf star. The observations support the fact that the superflare can be explained by the presence of (a) large active region(s) on the surface of the star. Such activity is similar to the most extreme solar flaring events. This points towards a plausible extrapolation between the behaviour from the most active red-dwarf stars and the processes occurring in the Sun. © 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Flin P.,Jan Kochanowski University | Panko E.,Nikolaev National University
Baltic Astronomy | Year: 2011

Tadeusz Banachiewicz (1882-1954) was an outstanding Polish astronomer, mathematician and geodesist. He was a professor at the Jagiel-lonian University in Cracow and director of the Astronomical Observatory (1919-1954), and had a strong influence on Polish astronomy. His achievements led to honorary degrees at universities, fellowships in academies of sciences, and the prestige of high positions in international organizations, such as the International Astronomical Union and the Baltic Geodetic Commission. He is known from both his theoretical and observational studies, his famous motto being: "observo ergo sum". Here we recall three years of his activity in Tartu, where Tadeusz Banachiewicz made the most important steps in his career. He arrived at Yuryev in October of 1915, employed as a young assistant. In March 1918 he became the extraordinary professor and director of the Astronomical Observatory.

Panko E.,Nikolaev National University
Baltic Astronomy | Year: 2011

The Modified Catalog of Galaxy Clusters and Groups (Panko & Flin 2006, PF), covering an area of 5000 square degrees in the southern sky, was used as the input for the search of galaxy superclusters. Only the estimated redshifts could be used, since the PF catalog is a 2D catalog, with the calibration correlating the redshift of galaxy clusters with the magnitude of the tenth brightest cluster galaxy. Only galaxy clusters containing more than 50 galaxies were considered, and the FoF method was applied. The nearest neighbour distances for 1711 input clusters were calculated and analyzed, and 20 isolated clusters were found with the nearest neighbour at a distance greater than 68 h -1 Mpc. A distance of 24 h -1 Mpc between clusters was selected for the supercluster search, and 49 superclusters containing from 4 to 9 galaxy clusters were detected. Calculations for each supercluster include: its inferred center, RA, Dec, z est, the maximum distance between supercluster members and the estimated supercluster shapes. A typical size of superclusters identified here is about 55h -1 Mpc, and they appear mainly as elongated pancakes, with a weak correlation between the axes c/a and b/a, without a strong dependence on multiplicity.

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