119173058
Hadron spectra and elliptic flow for 200 A GeV Au + Au collisions from viscous hydrodynamics coupled to a Boltzmann cascade
It is shown that the recently developed hybrid code VISHNU, which couples a relativistic viscous fluid dynamical description of the quark-gluon plasma (QGP) with a microscopic Boltzmann cascade for the late hadronic rescattering stage, yields an excellent description of charged and identified hadron spectra and elliptic flow measured in 200 A GeV Au+Au collisions at the Relativistic Heavy-Ion Collider (RHIC). Using initial conditions that incorporate event-by-event fluctuations in the initial shape and orientation of the collision fireball and values {eta}/s for the specific shear viscosity of the quark-gluon plasma that were recently extracted from the measured centrality dependence of the eccentricity-scaled, p{sub T}-integrated charged hadron elliptic flow v{sub 2,ch}/{epsilon}, we obtain universally good agreement between theory and experiment for the p{sub T} spectra and differential elliptic flow v{sub 2}(p{sub T}) for both pions and protons at all collision centralities.
118788264
Hydrodynamic modeling and the QGP shear viscosity
In this article, we will briefly review the recent progress on hydrodynamic modeling and the extraction of the quark-gluon plasma (QGP) specific shear viscosity with an emphasis on the results obtained from the hybrid model VISHNU that couples viscous hydrodynamics for the macroscopic expansion of the QGP to the hadron cascade model for the microscopic evolution of the late hadronic stage.
28563606
200 A GeV Au + Au collisions serve a nearly perfect quark-gluon liquid.
A new robust method to extract the specific shear viscosity (η/s)(QGP) of a quark-gluon plasma (QGP) at temperatures T(c) < T ≲ 2T(c) from the centrality dependence of the eccentricity-scaled elliptic flow v2/ε measured in ultrarelativistic heavy-ion collisions is presented. Coupling viscous fluid dynamics for the QGP with a microscopic transport model for hadronic freeze-out we find for 200 A GeV Au + Au collisions that v2/ε is a universal function of multiplicity density (1/S)(dN(ch)/dy) that depends only on the viscosity but not on the model used for computing the initial fireball eccentricity ε. Comparing with measurements we find 1<4π(η/s)(QGP) < 2.5 where the uncertainty range is dominated by model uncertainties for the values of ε used to normalize the measured v2.
119257437
Very Long Baseline Array observations of the intraday variable source J1128+592
Context. Short timescale flux density variations in flat spectrum radio sources are often explained by the scattering of radio waves in the turbulent ionized interstellar medium of the Milky Way. One of the most convincing observational arguments in favor of this is the annual modulation of the variability timescale caused by the orbital motion of Earth around the Sun. J1128+5925 is a recently discovered IDV source with a possible annual modulation in its variability timescale. New observations suggest a change in its variability characteristics.
119312762
Structure, spectra and variability of some GPS radio sources
We report the results of multifrequency-VLBI observations of GHz-Peaked-Spectrum (GPS) radio sources. The VLBI structure and component spectra of some GPS sources are presented. Our VLBI results show that about 80% of the GPS galaxies exhibit a compact double or CSO-like structure, white the GPS quasars tend to show a core-jet. The component spectra of the GPS galaxies are often steep/convex, and the core has a flat spectrum but it is usually hidden or weak. In addition, we studied the variability of GPS sources by comparing new flux density measures, acquired with the Urumqi 25-m telescope at 4.85 GHz, with previous 87GB data. The results show that 44% of the GPS quasars varied higher than 10% in passed 20 years, while the fraction is only 12% for the GPS galaxies meaning that the GPS quasars are much more variable than GPS galaxies. In total, 25% of GPS sources show > 10% variability at 4.85 GHz in our sample.
118516843
Intra-day variability observations of S5 0716+714 over 4.5 years at 4.8 GHz
Aims. We aim to search for evidence of annual modulation in the time scales of the BL Lac object S5 0716+714.
16178268
The radio lightcurve of SN 2008iz in M82 revealed by Urumqi observations
We report on a set of 5 GHz Urumqi observations of the galaxy M82, made between August 2005 and May 2009. From the resulting flux densities, we detect a strong flare, starting in March or April and peaking in June 2008. We identify this flare with supernova SN 2008iz. The time sampling of the radio light curve allows us to obtain information on the precursor mass-loss rate, the strength of the magnetic field in the radiating region, the explosion date, and the deceleration of the expanding shock. We also check the possible contribution of synchrotron self absorption to the radio light curve and compare our model with other observations of the supernova at 22 GHz.
117018554
Bursty Variations of Jovian 6cm Radio Emissions and Quasi-Periodic Jupiter's Polar Activities
In reference to Jupiter south polar quasi-periodic 40-50 min (QP-40) activities and the model scenario for global QP-40 oscillations of the Jovian inner radiation belt (IRB), we validate relevant predictions and confirmations by amassing empirical evidence from Ulysses, Cassini, Chandra, Galileo, XMM-Newton, and Advanced Composition Explorer for Jupiter north polar QP-40 activities. We report ground 6cm radio observations of Jupiter by Urumqi 25m telescope for synchrotron intensity bursty variations of the Jovian IRB and show their likely correlations with the recurrent arrival of high-speed solar winds at Jupiter.