Entity

Time filter

Source Type

Budapest, Hungary

Kobori J.,Eotvos Lorand University | Bagoly Z.,Eotvos Lorand University | Balazs L.G.,MTA CSFK Konkoly Observatory | Balazs L.G.,Eotvos Lorand University | Horvath I.,National Public Service University
Astronomische Nachrichten | Year: 2013

Gamma-ray bursts (GRBs) can be divided into three groups: short-, intermediate- and long-duration bursts. While the progenitors of the short and long ones are relatively known, the progenitors of the intermediate-duration bursts (IBs) are generally unknown. However, recent statistical studies suggest that they can be related to the long-duration bursts. Another types of GRBs are the so-called X-ray flashes (XRFs) and X-ray rich GRBs (XRRs). The former ones radiate more intensively in the X-ray bands than common GRBs, but in the cases of XRFs the main component of the emission is produced entirely at X-ray wavelengths. Also, the XRFs and IBs show some similarities regarding their prompt- and afterglow properties. In this work we investigate whether there is a difference between the global parameters of the X-ray flashes and intermediate-duration group of gamma-ray bursts. The statistical tests do not show any significant discrepancy regarding most of the parameters, except the BAT photon index, which is only a consequence of the definition of the XRFs. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Gutierrez P.J.,Institute Astrofisica Of Andalucia Csic | Jorda L.,Aix - Marseille University | Gaskell R.W.,Planetary Science Institute | Davidsson B.J.R.,Uppsala University | And 54 more authors.
Astronomy and Astrophysics | Year: 2016

Context. Data derived from the reconstruction of the nucleus shape of comet 67P/Churyumov-Gerasimenko (67P) from images of the OSIRIS camera onboard ROSETTA show evidence that the nucleus rotates in complex mode. First, the orientation of the spin axis is not fixed in an inertial reference frame, which suggests a precessing motion around the angular momentum vector with a periodicity of approximately 257 h ± 12 h.Second, periodograms of the right ascension and declination (RA/Dec) coordinates of the body-frame Z axis show a very significant (higher than 99.99%) periodicity at 276 h ± 12 h, different from the rotational period of 12.40 h as previously determined from light-curve analysis. Aims. The main goal is to interpret the data and associated periodicities of the spin axis orientation in space. Methods. We analyzed the spin axis orientation in space and associated periodicities and compared them with solutions of Euler equations under the assumption that the body rotates in torque-free conditions. Statistical tests comparing the observationally derived spin axis orientation with the outcome from simulations were applied to determine the most likely inertia moments, excitation level, and periods. Results. Under the assumption that the body is solid-rigid and rotates in torque-free conditions, the most likely interpretation is that 67P is spinning around the principal axis with the highest inertia moment with a period of about 13 h. At the same time, the comet precesses around the angular momentum vector with a period of about 6.35 h. While the rotating period of such a body would be about 12.4 h, RA/Dec coordinates of the spin axis would have a periodicity of about 270 h as a result of the combination of the two aforementioned motions. Conclusions. The most direct and simple interpretation of the complex rotation of 67P requires a ratio of inertia moments significantly higher than that of a homogeneous body. © ESO, 2016. Source


Ip W.-H.,National Central University | Ip W.-H.,Macau University of Science and Technology | Lai I.-L.,National Central University | Lee J.-C.,National Central University | And 55 more authors.
Astronomy and Astrophysics | Year: 2016

Aims. We aim to characterize the circular depressions of comet 67P/Churyumov-Gerasimenko and investigate whether such surface morphology of a comet nucleus is related to the cumulative sublimation effect since becoming a Jupiter family comet (JFC). Methods. The images from the Rosetta/OSIRIS science camera experiment are used to construct size frequency distributions of the circular depression structures on comet 67P and they are compared with those of the JFCs 81P/Wild 2, 9P/Tempel 1, and 103P/Hartley 2. The orbital evolutionary histories of these comets over the past 100 000 yr are analyzed statistically and compared with each other. Results. The global distribution of the circular depressions over the surface of 67P is charted and classified. Descriptions are given to the characteristics and cumulative size frequency distribution of the identified features. Orbital statistics of the JFCs visited by spacecraft are derived. Conclusions. The size frequency distribution of the circular depressions is found to have a similar power law distribution to those of 9P/Tempel 1 and 81P/Wild 2. This might imply that they could have been generated by the same process. Orbital integration calculation shows that the surface erosion histories of 81P/Wild 2, and 9P/Tempel 1 could be shorter than those of 67P, 103 P/Hartley 2 and 19P/Borrelly. From this point of view, the circular depressions could be dated back to the pre-JFC phase or the transneptunian phase of these comets. The north-south asymmetry in the distribution of the circular depressions could be associated with the heterogeneous structure of the nucleus of comet 67P and/or the solar insolation history. © ESO, 2016. Source


Balazs L.G.,MTA CSFK Konkoly Observatory | Balazs L.G.,Eotvos Lorand University | Bagoly Z.,Eotvos Lorand University | Bagoly Z.,National Public Service University | And 5 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2015

According to the cosmological principle (CP), Universal large-scale structure is homogeneous and isotropic. The observable Universe, however, shows complex structures even on very large scales. The recent discoveries of structures significantly exceeding the transition scale of 370 Mpc pose a challenge to the CP. We report here the discovery of the largest regular formation in the observable Universe; a ring with a diameter of 1720 Mpc, displayed by 9 gamma-ray bursts (GRBs), exceeding by a factor of 5 the transition scale to the homogeneous and isotropic distribution. The ring has a major diameter of 43° and a minor diameter of 30° at a distance of 2770 Mpc in the 0.78 < z < 0.86 redshift range, with a probability of 2 × 10-6 of being the result of a random fluctuation in the GRB count rate. Evidence suggests that this feature is the projection of a shell on to the plane of the sky. Voids and string-like formations are common outcomes of large-scale structure. However, these structures have maximum sizes of 150 Mpc, which are an order of magnitude smaller than the observed GRB ring diameter. Evidence in support of the shell interpretation requires that temporal information of the transient GRBs be included in the analysis. This ring-shaped feature is large enough to contradict the CP. The physical mechanism responsible for causing it is unknown. © 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

Discover hidden collaborations