412156
Coordinated mm/sub-mm observations of Sagittarius A* in May 2007
At the center of the Milky Way, with a distance of ~8 kpc, the compact source Sagittarius A* (SgrA*) can be associated with a super massive black hole of ~4x10^6 solar masses. SgrA* shows strong variability from the radio to the X-ray wavelength domains. Here we report on simultaneous NIR/sub-millimeter/X-ray observations from May 2007 that involved the NACO adaptive optics (AO) instrument at the European Southern Observatory's Very Large Telescope, the Australian Telescope Compact Array (ATCA), the US mm-array CARMA, the IRAM 30m mm-telescope, and other telescopes. We concentrate on the time series of mm/sub-mm data from CARMA, ATCA, and the MAMBO bolometer at the IRAM 30m telescope.
2297347
Radio Observations of AGN in Low Surface Brightness Galaxies
We present preliminary results of a study of the low frequency radio continuum emission from the nuclei of Giant Low Surface Brightness (LSB) galaxies. We have mapped the emission and searched for extended features such as radio lobes/jets associated with AGN activity. LSB galaxies are poor in star formation and generally less evolved compared to nearby bright spirals. This paper presents low frequency observations of 3 galaxies; PGC 045080 at 1.4 GHz, 610 MHz, 325MHz, UGC 1922 at 610 MHz and UGC 6614 at 610 MHz. The observations were done with the GMRT. Radio cores as well as extended structures were detected and mapped in all three galaxies; the extended emission may be assocated with jets/lobes associated with AGN activity. Our results indicate that although these galaxies are optically dim, their nuclei can host AGN that are bright in the radio domain.
14401845
Coordinated NIR/mm observations of flare emission from Sagittarius A*
Context. We report on a successful, simultaneous observation and modelling of the millimeter (mm) to near-infrared (NIR) flare emission of the Sgr A* counterpart associated with the supermassive (4 × 10^6 M_☉) black hole at the Galactic centre (GC). We present a mm/sub-mm light curve of Sgr A* with one of the highest quality continuous time coverages. 
 
Aims. We study and model the physical processes giving rise to the variable emission of Sgr A*. 
 
Methods. Our non-relativistic modelling is based on simultaneous observations carried out in May 2007 and 2008, using the NACO adaptive optics (AO) instrument at the ESO's VLT and the mm telescope arrays CARMA in California, ATCA in Australia, and the 30 m IRAM telescope in Spain. We emphasize the importance of multi-wavelength simultaneous fitting as a tool for imposing adequate constraints on the flare modelling. We present a new method for obtaining concatenated light curves of the compact mm-source Sgr A* from single dish telescopes and interferometers in the presence of significant flux density contributions from an extended and only partially resolved source. 
 
Results. The observations detect flaring activity in both the mm domain and the NIR. Inspection and modelling of the light curves show that in the case of the flare event on 17 May 2007, the mm emission follows the NIR flare emission with a delay of 1.5±0.5 h. On 15 May 2007, the NIR flare emission is also followed by elevated mm-emission. We explain the flare emission delay by an adiabatic expansion of source components. For two other NIR flares, we can only provide an upper limit to any accompanying mm-emission of about 0.2 Jy. The derived physical quantities that describe the flare emission give a source component expansion speed of ν_(exp) ~ 0.005c–0.017c, source sizes of about one Schwarzschild radius, flux densities of a few Janskys, and spectral indices of α = 0.6 to 1.3. These source components peak in the THz regime. 
 
Conclusions. These parameters suggest that either the adiabatically expanding source components have a bulk motion greater than ν_(exp) or the expanding material contributes to a corona or disk, confined to the immediate surroundings of Sgr A*. Applying the flux density values or limits in the mm- and X-ray domain to the observed flare events constrains the turnover frequency of the synchrotron components that are on average not lower than about 1 THz, such that the optically thick peak flux densities at or below these turnover frequencies do not exceed, on average, about ~1 Jy.
4805836
Coordinated multi-wavelength observations of Sgr A*
We report on recent near-infrared (NIR) and X-ray observations of Sagittarius A* (Sgr A*), the electromagnetic manifestation of the !4" 10 6 M! super-massive black hole (SMBH) at the Galactic Center. The goal of these coordinated multi-wavelength observations is to investigate the variable emission from Sgr A* in order to obtain a better understanding of the underlying physical processes in the accretion flow/outflow. The observations have been carried out using the NACO adaptive optics (AO) instrument at the European Southern Observatory's Very Large Telescope (July 2005, May 2007) and the ACIS-I instrument aboard the Chandra X- ray Observatory (July 2005). We report on a polarized NIR flare synchronous to a 8" 10 33 erg/s X-ray flare in July 2005, and a further flare in May 2007 that shows the highest sub-flare to flare contrast observed until now. The observations can be interpreted in the framework of a model involving a temporary disk with a short jet. In the disk component flux density variations can be explained due to hot spots on relativistic orbits around the central SMBH. The variations of the sub-structures of the May 2007 flare are interpreted as a variation of the hot spot structure due to di! erential rotation within the disk.
122683216
Resonance Multiplicities in a Hadron Transport Approach
In this article we focus on the multiplicities of resonances, ratios of resonant over non-resonant states and rescattering processes in heavy ion collisions. Therefore we utilize a hadron transport model (UrQMD vl.3). We find that rescattering of decay particles is of great importance when studying resonances in a hadronic medium.
119008128
Transverse pressure and strangeness dynamics in relativistic heavy-ion reactions
Transverse hadron spectra from proton–proton, proton–nucleus and nucleus–nucleus collisions from 2 A GeV to 21.3 A TeV are investigated within two independent transport approaches (HSD and UrQMD). For central Au+Au (Pb+Pb) collisions at energies above Elab ~ 5 A GeV, the measured K± transverse mass spectra have a larger inverse slope parameter than expected from the default calculations. The additional pressure—as suggested by lattice QCD calculations at finite quark chemical potential μq and temperature T—might be generated by strong interactions in the early pre-hadronic/partonic phase of central Au+Au (Pb+Pb) collisions. This is supported by a non-monotonic energy dependence of v2/pT in the present transport model.
118400528
Evidence for the a(1) meson being a difficult messenger for the restoration of chiral symmetry
We perform a theoretical analysis of the ${a}_{1}$ resonance mass spectrum in ultrarelativistic heavy ion collisions within a hadron/string transport approach. Predictions for the ${a}_{1}$ yield and its mass distribution are given for the GSI-FAIR and the critRHIC energy regime. The potential of the ${a}_{1}$ meson as a signal for chiral symmetry restoration is explored. In view of the latest discussion, we investigate the decay channel ${a}_{1}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\pi}$ in detail and find a strong bias toward low ${a}_{1}$ masses. This apparent mass shift of the ${a}_{1}$, if observed in the $\ensuremath{\gamma}\ensuremath{\pi}$ channel, might render a possible mass shift due to chiral symmetry restoration very difficult to disentangle from the decay kinematics.
119346840
Elliptic flow fluctuations in heavy ion collisions and the perfect fluid hypothesis
We analyze the recently measured v2 fluctuation in the context of establishing the degree of fluidity of the matter produced in heavy ion collisions. We argue that flow observables within systems with a non-negligible mean free path should acquire a “dynamical” fluctuation, due to the random nature of each collision between the system’s degrees of freedom. Because of this, v2 fluctuations can be used to estimate the Knudsen number of the system produced at the relativistic heavy ion collider (RHIC). To illustrate this quantitatively, we apply the UrQMD model, with scaled cross sections, to show that collisions at RHIC have a Knudsen number at least one order of magnitude below the expected value for an interacting hadron gas. Furthermore, we argue that the Knudsen number is also bound from below by the v2 fluctuation data, because too small a Knudsen number would break the observed scaling of v2 fluctuations due to the onset of turbulent flow. We propose, therefore that v2 fluctuation measurements, together with an understanding of the turbulent regime for relativistic hydrodynamics, will provide an upper as well as a lower limit for the Knudsen number. We also argue that an energy scan of v2 fluctuations could shed light on the onset of the fluid regime.