No asymmetric outflows from Sagittarius A* during the pericenter passage of the gas cloud G2

The gas cloud G2 falling toward Sagittarius A* (Sgr A*), the supermassive black hole at the center of the Milky Way, is supposed to provide valuable information on the physics of accretion flows and the environment of the black hole. We observed Sgr A* with four European stations of the Global Millimeter Very Long Baseline Interferometry Array (GMVA) at 86 GHz on 1 October 2013 when parts of G2 had already passed the pericenter. We searched for possible transient asymmetric structure -- such as jets or winds from hot accretion flows -- around Sgr A* caused by accretion of material from G2. The interferometric closure phases remained zero within errors during the observation time. We thus conclude that Sgr A* did not show significant asymmetric (in the observer frame) outflows in late 2013. Using simulations, we constrain the size of the outflows that we could have missed to ~2.5 mas along the major axis, ~0.4 mas along the minor axis of the beam, corresponding to approximately 232 and 35 Schwarzschild radii, respectively; we thus probe spatial scales on which the jets of radio galaxies are suspected to convert magnetic into kinetic energy. As probably less than 0.2 Jy of the flux from Sgr A* can be attributed to accretion from G2, one finds an effective accretion rate eta*Mdot < 1.5*10^9 kg/s ~ 7.7*10^-9 Mearth/yr for material from G2. Exploiting the kinetic jet power--accretion power relation of radio galaxies, one finds that the rate of accretion of matter that ends up in jets is limited to Mdot < 10^17 kg/s ~ 0.5 Mearth/yr, less than about 20% of the mass of G2. Accordingly, G2 appears to be largely stable against loss of angular momentum and subsequent (partial) accretion at least on time scales < 1 year.Comment: 5 pages, 2 figures, 1 table; A&A Letter, in press (submitted 2015 February 26; accepted 2015 March 31

Dust in 3C324

The results of a deep submillimetre observation using SCUBA of the powerful radio galaxy 3C324, at redshift z=1.206, are presented. At 850 microns, emission from the location of the host radio galaxy is marginally detected at the 4.2 sigma level, 3.01 +/- 0.72 mJy, but there is no detection of emission at 450 microns to a 3 sigma limit of 21 mJy. A new 32 GHz radio observation using the Effelsberg 100m telescope confirms that the sub-millimetre signal is not associated with synchrotron emission. These observations indicate that both the mass of warm dust within 3C324, and the star formation rate, lie up to an order of magnitude below the values recently determined for radio galaxies at z = 3 to 4. The results are compared with dust masses and star formation rates derived in other ways for 3C324.Comment: 5 pages LaTeX, including 1 figure. Accepted for publication in MNRA

5 year Global 3-mm VLBI survey of Gamma-ray active blazars

The Global mm-VLBI Array (GMVA) is a network of 14 3\,mm and 7\,mm capable telescopes spanning Europe and the United States, with planned extensions to Asia. The array is capable of sensitive maps with angular resolution often exceeding 50\,$\mu$as. Using the GMVA, a large sample of prominent $\gamma$-ray blazars have been observed approximately 6 monthly from later 2008 until now. Combining 3\,mm maps from the GMVA with near-in-time 7\,mm maps from the VLBA-BU-BLAZAR program and 2\,cm maps from the MOJAVE program, we determine the sub-pc morphology and high frequency spectral structure of $\gamma$-ray blazars. The magnetic field strength can be estimated at different locations along the jet under the assumption of equipartition between magnetic field and relativistic particle energies. Making assumptions on the jet magnetic field configuration (e.g. poloidal or toroidal), we can estimate the separation of the mm-wave "core" and the jet base, and estimate the strength of the magnetic field there. The results of this analysis show that on average, the magnetic field strength decreases with a power-law $B \propto r^{-n}$, $n=0.3 \pm 0.2$. This suggests that on average, the mm-wave "core" is $\sim 1-3$\,pc downstream of the de-projected jet apex and that the magnetic field strength is of the order $B_{\rm{apex}} \sim 5-20$\,kG, broadly consistent with the predictions of magnetic jet launching (e.g. via magnetically arrested disks (MAD)).Comment: 6 pages, 1 figur

Long-term variations of the mesospheric wind field at mid-latitudes

Continuous MF radar observations at the station Juliusruh (54.6° N; 13.4° E) have been analysed for the time interval between 1990 and 2005, to obtain information about solar activity-induced variations, as well as long-term trends in the mesospheric wind field. Using monthly median values of the zonal and the meridional prevailing wind components, as well as of the amplitude of the semidiurnal tide, regression analyses have been carried out with a dependence on solar activity and time. The solar activity causes a significant amplification of the zonal winds during summer (increasing easterly winds) and winter (increasing westerly winds). The meridional wind component is positively correlated with the solar activity during summer but during winter the correlation is very small and non significant. Also, the solar influence upon the amplitude of the semidiurnal tidal component is relatively small (in dependence on height partly positive and partly negative) and mostly non-significant. The derived trends in the zonal wind component during summer are below an altitude of about 83 km negative and above this height positive. During the winter months the trends are nearly opposite compared with the trends in summer (transition height near 86 km). The trends in the meridional wind components are below about 85 km positive in summer (significant) and near zero (nonsignificant) in winter; above this height during both seasons negative trends have been detected. The trends in the semidiurnal tidal amplitude are at all heights positive, but only partly significant. The detected trends and solar cycle dependencies are compared with other experimental results and model calculations. There is no full agreement between the different results, probably caused by different measuring techniques and evaluation methods used. Also, different heights and observation periods investigated may contribute to the detected differences

Measuring the Virial Temperature of Galactic Halos Through Electron Scattering of Quasar Emission Lines

Semi-analytic models of galaxy formation postulate the existence of virialized gaseous halos around galaxies at high redshifts. A small fraction of the light emitted by any high-redshift quasar is therefore expected to scatter off the free electrons in the halo of its host galaxy. The broadening of the scattered emission lines of the quasar can be used to measure the temperature of these electrons. For gas in virial equilibrium, the velocity width of the scattered line profile is larger by a factor of (m_p/m_e)^{1/2}=43 than the velocity dispersion of the host galaxy and reaches >10,000 km/s for the massive galaxies and groups in which bright quasars reside. In these systems, the scattered width exceeds the intrinsic width of the quasar lines and hence can be used to measure the virial temperature of the quasar host. The high degree of polarization of the scattered radiation can help filter out the extended scattered light from the central emission by the quasar and its host galaxy. The signal-to-noise ratio of the spectral broadening can be enhanced by matching the full spectrum of the scattered radiation to a template of the unscattered quasar spectrum. Although the central fuzz around low-redshift quasars is dominated by starlight, the fuzz around high-redshift quasars might be dominated by scattering before galaxies have converted most of their gas reservoirs into stars.Comment: 10 pages, 1 figures, submitted to ApJ Letter

Reflectivity Anisotropy Spectra of Cu- and Ag- (110) surfaces from {\it ab initio} theory

We are able to disentagle the effects of the intraband and interband parts of the bulk dielectric function on the bare dielectric anisotropy of the surface. We show how the position, sign and amplitude of the structures observed in such spectra depend on the above quantities. The lineshape of all the calculated structures agree very well with the ones observed experimentally for samples treated by suitable surface cleaning. In particular, we reproduce the observed single peak structure of Ag at high energy, found to represent a state of the clean surface different from the one giving the originally observed double peak structure. This results is not reproduced by the 'local field' model.Comment: 4 pages, 3 figures. submitted to Phys. Rev. Let

The 1.4 GHz light curve of GRB 970508

We report on Westerbork 1.4 GHz radio observations of the radio counterpart to $\gamma$-ray burst GRB~970508, between 0.80 and 138 days after this event. The 1.4 GHz light curve shows a transition from optically thick to thin emission between 39 and 54 days after the event. We derive the slope $p$ of the spectrum of injected electrons ($dN/d\gamma_{e}\propto\gamma_{e}^{-p}$) in two independent ways which yield values very close to $p=2.2$. This is in agreement with a relativistic dynamically near-adiabatic blast wave model whose emission is dominated by synchrotron radiation and in which a significant fraction of the electrons cool fast.Comment: Paper I. Accepted for publication in the Astrophysical Journal Letter