The flat-spectrum radio quasar 4C \(+\)71.07 is a high-redshift (\(z=2.172\)), \(\gamma\)-loud blazar whose optical emission is dominated by the thermal radiation from accretion disc. 4C \(+\)71.07 ...has been detected in outburst twice by the AGILE \(\gamma\)-ray satellite during the period end of October - mid November 2015, when it reached a \(\gamma\)-ray flux of the order of \(F_{\rm E>100\,MeV} = (1.2 \pm 0.3)\times 10^{-6}\) photons cm\(^{-2}\) s\(^{-1}\) and \(F_{\rm E>100\,MeV} = (3.1 \pm 0.6)\times 10^{-6}\) photons cm\(^{-2}\) s\(^{-1}\), respectively, allowing us to investigate the properties of the jet and of the emission region. We investigated its spectral energy distribution by means of almost simultaneous observations covering the cm, mm, near-infrared, optical, ultra-violet, X-ray and \(\gamma\)-ray energy bands obtained by the GASP-WEBT Consortium, the Swift and the AGILE and Fermi satellites. The spectral energy distribution of the second \(\gamma\)-ray flare (the one whose energy coverage is more dense) can be modelled by means of a one-zone leptonic model, yielding a total jet power of about \(4\times10^{47}\) erg s\(^{-1}\). During the most prominent \(\gamma\)-ray flaring period our model is consistent with a dissipation region within the broad-line region. Moreover, this class of high-redshift, large-mass black-hole flat-spectrum radio quasars might be good targets for future \(\gamma\)-ray satellites such as e-ASTROGAM.
We present a multi-wavelength spectral and temporal analysis of the blazar OJ 287 during its recent activity between December 2015 -- May 2016, showing strong variability in the near-infrared (NIR) ...to X-ray energies with detection at \(\gamma\)-ray energies as well. Most of the optical flux variations exhibit strong changes in polarization angle and degree. All the inter-band time lags are consistent with simultaneous emissions. Interestingly, on days with excellent data coverage in the NIR--UV bands, the spectral energy distributions (SEDs) show signatures of bumps in the visible--UV bands, never seen before in this source. The optical bump can be explained as accretion-disk emission associated with the primary black hole of mass \(\sim \rm 1.8 \times10^{10} M_{\odot}\) while the little bump feature in the optical-UV appears consistent with line emission. Further, the broadband SEDs extracted during the first flare and during a quiescent period during this span show very different \(\gamma\)-ray spectra compared to previously observed flare or quiescent spectra. The probable thermal bump in the visible seems to have been clearly present since May 2013, as found by examining all available NIR-optical observations, and favors the binary super-massive black hole model. The simultaneous multi-wavelength variability and relatively weak \(\gamma\)-ray emission that shows a shift in the SED peak is consistent with \(\gamma\)-ray emission originating from inverse Compton scattering of photons from the line emission that apparently contributes to the little blue bump.
Here we report on the results of the WEBT photo-polarimetric campaign targeting the blazar S5~0716+71, organized in March 2014 to monitor the source simultaneously in BVRI and near IR filters. The ...campaign resulted in an unprecedented dataset spanning \(\sim 110\)\,h of nearly continuous, multi-band observations, including two sets of densely sampled polarimetric data mainly in R filter. During the campaign, the source displayed pronounced variability with peak-to-peak variations of about \(30\%\) and "bluer-when-brighter" spectral evolution, consisting of a day-timescale modulation with superimposed hourlong microflares characterized by \(\sim 0.1\)\,mag flux changes. We performed an in-depth search for quasi-periodicities in the source light curve; hints for the presence of oscillations on timescales of \(\sim 3\)\,h and \(\sim 5\)\,h do not represent highly significant departures from a pure red-noise power spectrum. We observed that, at a certain configuration of the optical polarization angle relative to the positional angle of the innermost radio jet in the source, changes in the polarization degree led the total flux variability by about 2\,h; meanwhile, when the relative configuration of the polarization and jet angles altered, no such lag could be noted. The microflaring events, when analyzed as separate pulse emission components, were found to be characterized by a very high polarization degree (\(> 30\%\)) and polarization angles which differed substantially from the polarization angle of the underlying background component, or from the radio jet positional angle. We discuss the results in the general context of blazar emission and energy dissipation models.
We report the results of decade-long (2008-2018) \(\gamma\)-ray to 1 GHz radio monitoring of the blazar 3C 279, including GASP/WEBT, \(\it{Fermi}\) and \(\it{Swift}\) data, as well as polarimetric ...and spectroscopic data. The X-ray and \(\gamma\)-ray light curves correlate well, with no delay > 3 hours, implying general co-spatiality of the emission regions. The \(\gamma\)-ray-optical flux-flux relation changes with activity state, ranging from a linear to a more complex dependence. The behaviour of the Stokes parameters at optical and radio wavelengths, including 43 GHz VLBA images, supports either a predominantly helical magnetic field or motion of the radiating plasma along a spiral path. Apparent speeds of emission knots range from 10 to 37c, with the highest values requiring bulk Lorentz factors close to those needed to explain \(\gamma\)-ray variability on very short time scales. The Mg II emission line flux in the `blue' and `red' wings correlates with the optical synchrotron continuum flux density, possibly providing a variable source of seed photons for inverse Compton scattering. In the radio bands we find progressive delays of the most prominent light curve maxima with decreasing frequency, as expected from the frequency dependence of the \(\tau=1\) surface of synchrotron self-absorption. The global maximum in the 86 GHz light curve becomes less prominent at lower frequencies, while a local maximum, appearing in 2014, strengthens toward decreasing frequencies, becoming pronounced at \(\sim5\) GHz. These tendencies suggest different Doppler boosting of stratified radio-emitting zones in the jet.
We report the discovery and characterisation of a deeply eclipsing AM CVn-system, Gaia14aae (= ASSASN-14cn). Gaia14aae was identified independently by the All-Sky Automated Survey for Supernovae ...(ASAS-SN; Shappee et al. 2014) and by the Gaia Science Alerts project, during two separate outbursts. A third outburst is seen in archival Pan-STARRS-1 (PS1; Schlafly et al. 2012; Tonry et al. 2012; Magnier et al. 2013) and ASAS-SN data. Spectroscopy reveals a hot, hydrogen-deficient spectrum with clear double-peaked emission lines, consistent with an accreting double degenerate classification. We use follow-up photometry to constrain the orbital parameters of the system. We find an orbital period of 49.71 min, which places Gaia14aae at the long period extremum of the outbursting AM CVn period distribution. Gaia14aae is dominated by the light from its accreting white dwarf. Assuming an orbital inclination of 90 degrees for the binary system, the contact phases of the white dwarf lead to lower limits of 0.78 M solar and 0.015 M solar on the masses of the accretor and donor respectively and a lower limit on the mass ratio of 0.019. Gaia14aae is only the third eclipsing AM CVn star known, and the first in which the WD is totally eclipsed. Using a helium WD model, we estimate the accretor's effective temperature to be 12900+-200 K. The three out-burst events occurred within 4 months of each other, while no other outburst activity is seen in the previous 8 years of Catalina Real-time Transient Survey (CRTS; Drake et al. 2009), Pan-STARRS-1 and ASAS-SN data. This suggests that these events might be rebrightenings of the first outburst rather than individual events.
Envelopes of cometary orbits Mijajlović Ž.; Pejović N.; Damljanović G. ...
Serbian astronomical journal.,
01/2008, Letnik:
2008, Številka:
177
Journal Article
Odprti dostop
We discuss cometary orbits from the standpoint of Nonstandard (Leibnitz) analysis, a relatively new branch of mathematics. In particular, we consider parabolic cometary paths. It appears that, in a ...sense, every parabola is an ellipse.
We report on long-term multiwavelength monitoring of blazar Mrk 421 by the GLAST-AGILE Support Program of the Whole Earth Blazar Telescope (GASP-WEBT) collaboration and Steward Observatory, and by ...the Swift and Fermi satellites. We study the source behaviour in the period 2007-2015, characterized by several extreme flares. The ratio between the optical, X-ray and gamma-ray fluxes is very variable. The gamma-ray flux variations show a fair correlation with the optical ones starting from 2012. We analyse spectropolarimetric data and find wavelength-dependence of the polarization degree (P), which is compatible with the presence of the host galaxy, and no wavelength dependence of the electric vector polarization angle (EVPA). Optical polarimetry shows a lack of simple correlation between P and flux and wide rotations of the EVPA. We build broad-band spectral energy distributions with simultaneous near-infrared and optical data from the GASP-WEBT and ultraviolet and X-ray data from the Swift satellite. They show strong variability in both flux and X-ray spectral shape and suggest a shift of the synchrotron peak up to a factor of similar to 50 in frequency. The interpretation of the flux and spectral variability is compatible with jet models including at least two emitting regions that can change their orientation with respect to the line of sight.
Epitaxial RuSr2GdCu2O8 (Ru-1212) films have been synthesized by post-annealing of precursor films prepared by pulsed laser deposition (PLD). Two types of the precursors, i.e. chemically homogeneous ...and multilayered chemically structured, have been used. Nearly single phase (00l) oriented Ru-1212 films were produced by post-annealing of the precursors. The films obtained from multilayered precursors demonstrated semiconductor properties with ferromagnetic ordering below TCurie125K. The films obtained from homogeneous precursors had Curie temperature in a range of 130-150K. Those films had temperature dependence of resistance varying from semiconducting to superconducting behaviour. Appearance of superconductivity correlates with impurities level.
The paper proposes the framework for cross-layer Quality of Service (QoS) adaptation in Next Generation Networks (NGN) based on Service-Oriented Architecture (SOA) principles of system design. The ...aim of this framework is to establish efficient communication mechanisms among the layers that will be able to adapt dynamically to the diversity of user/application requirements, networking technologies, and provider capabilities. Moreover, the unified information structure contained in Web Ontology Language (OWL) ontologies and Semantic Web Rule Language (SWRL) rules provides the common understanding of concepts and relationships maintained and shared by the service providers and users in heterogeneous environment.
In this paper we have analysed the impact of running transactions at different isolation levels on application performance, more specifically on the execution time of the set of transactions. Three ...scenarios of transaction executions were defined, based on real applicative cases, and applied to different transaction sets and transaction isolation levels. Tests were performed using three actual DBMS: Oracle, Microsoft SQL Server and MySQL.
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