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Péter Veres

Publications and source records attributed to Péter Veres.

27 records · Page 2Linked to original sources
arXiv2012

The extremely high peak energy of GRB 110721A in the context of a dissipative photosphere synchrotron emission model

The Fermi observations of GRB 110721A (Axelsson et al. 2012) have revealed an unusually high peak energy ~ 15 MeV in the first time bin of the prompt emission. We find that an interpretation is unlikely in terms of internal shock models, and confirm that a standard black-body photospheric model also falls short. We show that dissipative photospheric synchrotron models ranging from extreme magnetically dominated to baryon dominated dynamics, on the other hand, are able to accommodate such high peak values.

astro-ph.HE↗
arXiv2012

Gamma Ray Bursts: recent results and connections to very high energy Cosmic Rays and Neutrinos

Gamma-ray bursts are the most concentrated explosions in the Universe. They have been detected electromagnetically at energies up to tens of GeV, and it is suspected that they could be active at least up to TeV energies. It is also speculated that they could emit cosmic rays and neutrinos at energies reaching up to the $10^{18}-10^{20}$ eV range. Here we review the recent developments in the photon phenomenology in the light of \swift and \fermi satellite observations, as well as recent IceCube upper limits on their neutrino luminosity. We discuss some of the theoretical models developed to explain these observations and their possible contribution to a very high energy cosmic ray and neutrino background.

astro-ph.HE↗
arXiv2011

Photometry of Some Recent Gamma-ray Bursts

We present the results of the optical, X-ray and gamma-ray analysis of some recent GRBs. The data were obtained by the automated P60 telescope and the Swift telescope (UVOT, XRT and BAT). We present some example fits for the lightcurves. The data reduction and the investigations were made by the Konkoly Observatory HEART group (http://www.konkoly.hu/HEART/index.html).

astro-ph.HE↗
arXiv2010

Directional Anisotropy of Swift Gamma-Ray Bursts

Swift satellite measurements contributed substantially to the gamma-ray burst (GRB) redshift observations through fast slewing to the source of the GRBs. Still, a large number of bursts are without redshift. We study the celestial distribution of bursts with various methods and compare them to a random catalog using Monte-Carlo simulations. We find an anisotropy in the distribution of the intermediate class of bursts and find that the short and long population are distributed isotropically.

astro-ph.HE↗
arXiv2010

Gamma-ray bursts: connecting the prompt emission with the afterglow

With the early afterglow localizations of gamma-ray burst positions made by Swift, the clear delimitation of the prompt phase and the afterglow is not so obvious any more. It is important to see weather the two phases have the same origin or they stem from different parts of the progenitor system. We will combine the two kinds of gamma-ray burst data from the Swift-XRT instrument (windowed timing and photon counting modes) and from BAT. A thorough desription of the applied procedure is given. We apply various binning techniques to the different data: Bayes blocks, exponential binning and signal-to-noise type of binning. We present a handful of flux curves and some possible applications.

astro-ph.HE↗
arXiv2010

Physical parameters of a relativistic jet at very high redshift: the case of the blazar J1430+4204

Context. The high-redshift (z = 4.72) blazar J1430+4204 produced a major radio outburst in 2005. Such outbursts are usually associated with the emergence of a new component in the inner radio jet. Aims. We searched for possible changes in the radio structure on milli-arcsecond angular scales, to determine physical parameters that characterise the relativistic jet ejected from the centre of this source. Methods. We analysed 15-GHz radio interferometric images obtained with the Very Long Baseline Array (VLBA) before and after the peak of the outburst. Results. We did not identify any significant new jet component over a period of 569 days. We estimated the Doppler factor, the Lorentz factor, and the apparent transverse speed of a putative jet component using three different methods. The likely small jet angle to the line of sight and our values of the apparent transverse speed are consistent with not detecting a new jet feature.

astro-ph.CO↗
arXiv2009

Gamma-Ray Burst Groups Observed by Different Satellites

Two classes of gamma-ray bursts have been identified in the BATSE catalogs characterized by durations shorter and longer than about 2 seconds. There are, however, some indications for the existence of a third one. Swift satellite detectors have different spectral sensitivity than pre-Swift ones for gamma-ray bursts. Therefore it is worth to reanalyze the durations and their distribution and also the classification of GRBs. In this paper we are going to analyze the bursts' duration distribution and also the duration-hardness bivariate distribution, published in The First BAT Catalog, whether it contains two, three or maybe more groups. Similarly to the BATSE data, to explain the BAT GRBs duration distribution three components are needed. Although, the relative frequencies of the groups are different than they were in the BATSE GRB sample, the difference in the instrument spectral sensitivities can explain this bias in a natural way. This means theoretical models may have to explain three different type of gamma-ray bursts.

astro-ph.CO↗
arXiv2007

Magnetic Field Structures of BL Lac Objects on Decaparsec Scales

Relatively few Very Long Baseline Interferometry (VLBI) polarization observations have been carried out at 18 cm. The importance of such observations lies in their ability to reveal information about the jet magnetic ({\bf B}) field structure and the environment of the jet on scales intermediate between those probed by higher-frequency VLBI and connected-element interferometers such as the Very Large Array. We have obtained polarization observations of 34 BL Lac objects with the Very Long Baseline Array (VLBA), at 4 separate wavelengths in the 18-20 cm band. The 18-cm jets typically extend to tens of parsecs. In some cases, the decaparsec jet is a continuation of the jet on smaller scales, while in others, we see appreciable bending. We have constructed Faraday rotation-measure maps and used them to study the jet {\bf B} field structures and distribution of thermal plasma around the jets. The Faraday rotation is typically large at these wavelengths, and knowledge of the rotation-measure distribution is essential to derive the {\bf B} field structures of the jets. The high sensitivity of these observations to Faraday rotation makes them an effective tool for studies of possible interactions between the jets and the media through which they propagate.

astro-ph↗