15616146
Soliton with a pion field in the global color symmetry model
We calculate the property of the global color symmetry soliton with the pion field being included explicitly. The calculated results indicate that the pion field provides a strong attraction so that the eigenenergy of a quark and the mass of a soliton reduce drastically, in contrast to those with only the sigma field.
24865622
Energy and momentum deposited into a QCD medium by a jet shower.
For a hard parton moving through a dense QCD medium, we compute self-consistently the energy loss and the fraction deposited into the medium due to showering and rescattering of the shower, assuming weak coupling between probe and medium. The same transport coefficients thus determine both the energy loss and its deposition into the medium. This allows a parameter free calculation of the latter once the former are computed or measured. We compute them for a weakly interacting medium. Assuming a short thermalization time for the deposited energy, we determine the medium's hydrodynamical response and obtain a conical pattern that is strongly enhanced by showering.
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.
119349636
Dissipative hydrodynamics for viscous relativistic fluids
Explicit equations are given for describing the space-time evolution of nonideal (viscous) relativistic fluids undergoing boost-invariant longitudinal and arbitrary transverse expansion. The equations are derived from the second-order Israel-Stewart approach which ensures causal evolution. Both azimuthally symmetric (1+1)dimensional and nonsymmetric (2+1)-dimensional transverse expansion are discussed. The latter provides the formal basis for the hydrodynamic computation of elliptic flow in relativistic heavy ion collisions including dissipative effects.
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.
73657451
Systematic parameter study of hadron spectra and elliptic flow from viscous hydrodynamic simulations of Au+Au collisions at √s_NN=200 GeV
Using the (2+1)-dimensional viscous hydrodynamic code vish2+1[H. Song and U. Heinz, Phys. Lett. B 658, 279 (2008); H. Song and U. Heinz, Phys. Rev. C 77, 064901 (2008); H. Song, Ph. D. thesis, The Ohio State University, 2009], we present systematic studies of the dependence of pion and proton transverse-momentum spectra and their elliptic flow in 200A GeV Au+Au collisions on the parameters of the hydrodynamic model (thermalization time, initial entropy density distribution, decoupling temperature, equation of state, and specific shear viscosity {eta}/s). We identify a tension between the slope of the proton spectra, which (within hydrodynamic simulations that assume a constant shear viscosity to entropy density ratio) prefer larger {eta}/s values, and the slope of the p{sub T} dependence of charged hadron elliptic flow, which prefers smaller values of {eta}/s. Changing other model parameters does not appear to permit dissolution of this tension.
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.
119209019
On the influence of the Sun on the rapid variability of compact extragalactic sources
Since December 2004, we have performed a program to monitor intraday variable sources at a frequency of 5 GHz at the Urumqi Observatory. We present our analysis of the variability characteristics of the flat-spectrum radio source AO 0235 + 164, which detects an annual cycle in the variability amplitude. This appears to correlate with the solar elongation of the source. A thorough analysis of the results of the MASIV IDV survey - which provides the variability characteristics of a large sample of compact radio sources confirms that there is a small but detectable component of the observed fractional modulation that increases with decreasing solar elongation. We discuss the hypothesis that the phenomenon is related to interplanetary scintillation.
17574064
Observations of IntraDay Variable sources with the Effelsberg and Urumqi Radio Telescopes
National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, PR ChinaE-mail: hjl@bao.ac.cnA sample of classical IntraDay Variable (IDV) and IDV candidate sources has been monitoredwith the Urumqi 25m telescope and the Effelsberg 100m telescope. Aim of the project is to inves-tigate the origin of IntraDay Variability, a phenomenon which has been observed in about 30%of ﬂat spectrum radio quasars. Simultaneous Effelsberg-Urumqi observations demonstrated thatthe Urumqi antenna, although relatively small in diameter, is well suitable for IDV experiments.A few Urumqi datasets, however, turned out to be affected by a spurious ˘24 hours modulation,an effect which has been removed by means of a new procedure for data reduction. In about 14months, 12 epochs of observation have been collected, for a total observing time of more than 45days. The epochs are regularly distributed over the whole year, in order to check for the presenceof systematic annual changes in the variability time scales - a crucial test for verifying the con-sistency of source-extrinsic models of the variability. Preliminary time-analysis of the monitoredsources revealed some hint for a slowing down of the characteristic time scales of S5 0716+714,a result that, if conﬁrmed, would be compatible with a source-extrinsic origin of the variability, incontrast to previous IDV studies. No signiﬁcant modulation of the time scales has been detectedfor S4 0954+658.Bursts, Pulses and Flickering:Wide-ﬁeld monitoring of the dynamic radio skyJune 12-15 2007Kerastari, Tripolis, Greece
118880227
A Broken Solar Type?II Radio Burst Induced by a Coronal Shock Propagating across the Streamer Boundary
We discuss an intriguing type II radio burst that occurred on 2011 March 27. The dynamic spectrum was featured by a sudden break at about 43 MHz on the well-observed harmonic branch. Before the break, the spectrum drifted gradually with a mean rate of about -0.05 MHz s(-1). Following the break, the spectrum jumped to lower frequencies. The post-break emission lasted for about 3 minutes. It consisted of an overall slow drift which appeared to have a few fast-drift sub-bands. Simultaneous observations from the Solar TErrestrial RElations Observatory and the Solar Dynamics Observatory were also available and are examined for this event. We suggest that the slow-drift period before the break was generated inside a streamer by a coronal eruption driven shock, and the spectral break as well as the relatively wide spectrum after the break is a consequence of the shock crossing the streamer boundary where density drops abruptly. It is suggested that this type of radio bursts can be taken as a unique diagnostic tool for inferring the coronal density structure, as well as the radio-emitting source region.
73710703
A seasonal cycle and an abrupt change in the variability characteristics of the intraday variable source S4 0954+65
The BLLac object S4 0954+65 is one of the main targets of the Urumqi monitoring program targeting intraday variable (IDV) sources. Between August 2005 and December 2009, the source was included in 41 observing sessions, carried out at a frequency of 4.8 GHz. The time analysis of the collected light curves, performed by applying both a structure function analysis and a specifically developed wavelet-based algorithm, discovered an annual cycle in the variability timescales, suggesting that there is a fundamental contribution by interstellar scintillation to the IDV pattern of the source. The combined use of the two analysis methods also revealed that there was a dramatic change in the variability characteristics of the source between February and March 2008, at the starting time of a strong outburst phase. The analysis' results suggest that the flaring state of the source coincides with the appearance of multiple timescales in its light curves, indicating that changes in the structure of the relativistically moving emitting region may strongly influence the variability observed on IDV timescales.