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.
118545612
A Statistical Study on the Morphology of Rays and Dynamics of Blobs in the Wake of Coronal Mass Ejections
In this paper, with a survey through the Large Angle and Spectrometric Coronagraph (LASCO) data from 1996 to 2009, we present 11 events with plasma blobs flowing outwards sequentially along a bright coronal ray in the wake of a coronal mass ejection. The ray is believed to be associated with the current-sheet structure that formed as a result of solar eruption, and the blobs are products of magnetic reconnection occurring along the current sheet. The ray morphology and blob dynamics are investigated statistically. It is found that the apparent angular widths of the rays at a fixed time vary in a range of 2.1 – 6.6○ (2.0 – 4.4○) with an average of 3.5○ (2.9○) at 3R⊙ (4R⊙), respectively, and the observed durations of the events vary from 12 h to a few days with an average of 27 h. It is also found, based on the analysis of blob motions, that 58% (26) of the blobs were accelerated, 20% (9) were decelerated, and 22% (10) moved with a nearly constant speed. Comparing the dynamics of our blobs and those that are observed above the tip of a helmet streamer, we find that the speeds and accelerations of the blobs in these two cases differ significantly. It is suggested that these differences of the blob dynamics stem from the associated magnetic reconnection involving different magnetic field configurations and triggering processes.
119279322
Interplay of shear and bulk viscosity in generating flow in heavy-ion collisions
We perform viscous hydrodynamic calculations in 2+1 dimensions to investigate the influence of bulk viscosity on the viscous suppression of elliptic flow in noncentral heavy-ion collisions at Relativistic Heavy Ion Collider energies. Bulk and shear viscous effects on the evolution of radial and elliptic flow are studied with different model assumptions for the transport coefficients. We find that the temperature dependence of the relaxation time for the bulk viscous pressure, especially its critical slowing-down near the quark-hadron phase transition at T{sub c}, partially offsets effects from the strong growth of the bulk viscosity itself near T{sub c} and that even small values of the specific shear viscosity eta/s of the fireball matter can be extracted without large uncertainties from poorly controlled bulk viscous effects.
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
13994103
Causal relativistic hydrodynamics for viscous fluids
We report on recent results from VISH2+1, a code that solves the relativistic Israel–Stewart equations for causal viscous hydrodynamics for heavy-ion collisions with longitudinal boost invariance. We find that even 'minimal' shear viscosity η/s = /(4π) leads to a large reduction of elliptic flow compared to ideal fluid dynamics. We explore systematically the sensitivity of this reduction to the equation of state, system size, initial conditions and the microscopic relaxation time in different formulations of the Israel–Stewart equations.
119119786
Radio observations of the first three-months of Fermi AGN at 4.8 GHz
Using the Urumqi 25 m radio telescope, sources from the first t hree months of the Fermi-large area telescope detected active galactic nuclei (AGN) catalog with a declination of > 0 ◦ were observed in 2009 at 4.8 GHz. The radio flux density ap- peared to correlate with the -ray intensity. Intra-day variability (IDV) observations were performed in March, April and May 2009 for 42 selected -ray bright blazars, and ∼60% of them showed evidence of flux variability at 4.8 GHz duri ng the IDV observations. The IDV detection rate was higher than that in previous flat-spectrum AGN samples. IDV appeared more often in the very long baseline interferometry-core dominant blazars, and the non-IDV blazars showed relatively "steeper" spectral in- dices than the IDV blazars. Pronounced inter-month variability was also found in two BL Lac objects: J0112+2244 and J0238+1636.
53557649
Multiplicity scaling in ideal and viscous hydrodynamics
Using numerical results from ideal and viscous relativistic hydrodynamic simulations with three different equations of state, for Au+Au and Cu+Cu collisions at different centralities and initial energy densities, we explore the dependence of the eccentricity-scaled elliptic flow, v{sub 2}/{epsilon}, and the produced entropy fraction, {delta}S/S{sub 0}, on the final charged hadron multiplicity density dN{sub ch}/dy per unit transverse overlap area S,(1/S)dN{sub ch}/dy. The viscous hydrodynamic simulations are performed with two different versions of the Israel-Stewart kinetic evolution equations, and in each case we investigate the dependence of the physical observables on the kinetic relaxation time. We find approximate scaling of v{sub 2}/{epsilon} and {delta}S/S{sub 0} with (1/S)dN{sub ch}/dy, with scaling functions that depend on the EOS and, in particular, on the value of the specific shear viscosity {eta}/s. Small scaling violations are seen even in ideal hydrodynamics, caused by a breaking of the scale invariance of ideal fluid dynamics by the freeze-out condition. Viscous hydrodynamics shows somewhat larger scale-breaking effects that increase with increasing {eta}/s and decreasing system size and initial energy density. We propose to use precision studies of these scaling violations to help constrain the shear viscosity {eta}/s of the quark-gluon plasma created in relativistic heavy ion collisions.