We report the results of radio flux-monitoring and high resolution observations at 3.6 cm with the VLA, of the central condensation in G 10.0−0.3, the radio nebula surrounding the soft gamma ray repeater (SGR) 1806−20. The quiescent X–ray source AX 1805.7−2025 is coincident with the radio core suggesting that G 10.0−0.3 is a plerionic supernova remnant. The monitoring experiment was performed i...

We present general relativistic magnetohydrodynamic (GRMHD) numerical simulations of the accretion flow around the supermassive black hole in the Galactic centre, Sagittarius A* (Sgr A∗). The simulations include for the first time radiative cooling processes (synchrotron, bremsstrahlung, and inverse Compton) selfconsistently in the dynamics, allowing us to test the common simplification of igno...

One of the most interesting results of the X-ray observations with the ASCA satellite of the Galactic center (GC) is the spatial distribution and the intensity of the Fe line at 6.4 keV. Up to now the morphology and the intensity of this line have been a puzzle. In this letter we present a map of the GC in the J=1→0 line of SiO covering the same region than the ASCA observations. The SiO emissi...

The silhouette cast by the horizon of the supermassive black hole in M87 can now be resolved with the emerging millimeter very-long baseline interferometry (VLBI) capability. Despite being ∼ 2× 10 times farther away than Sgr A* (the supermassive black hole at the center of the Milky-Way and the primary target for horizon-scale imaging), M87’s much larger black hole mass results in a horizon ang...

Context. The near-infrared emission from the black hole at the Galactic center (Sgr A*) has unique properties. The most striking feature is a suggestive periodic sub-structure that has been observed in a couple of flares so far. Aims. Using near-infrared polarimetric observations and modelling the quasi-periodicity in terms of an orbiting blob, we try to constrain the three dimensional orientat...

Variable emission from SgrA, the luminous counterpart to the super-massive black hole at the center of our Galaxy, arises from the innermost portions of the accretion flow. Better characterization of the variability is important for constraining models of the low-luminosity accretion mode powering SgrA, and could further our ability to use variable emission as a probe of the strong gravitatio...

We have performed monitoring observations of the 3-mm flux density toward the Galactic Center compact radio source Sgr A* with the Australia Telescope Compact Array since 2005 October. Careful calibrations of both elevationdependent and time-dependent gains have enabled us to establish the variability behavior of Sgr A*. Sgr A* appeared to undergo a high and stable state in 2006 June session, a...

A study of the metastable (J, K)=(18,18) line of ammonia (NH3) is presented aiming at better defining the physical properties of molecular gas in extreme environments. The spectra were collected with the Effelsberg 100-m telescope and are analyzed in combination with other data using a rotation diagram (Boltzmann plot). The first astronomical detection of the metastable (J, K) = (18,18) line of...

Sgr A* is a compact radio source at the Galactic Center, thought to be the radiative manifestation of a 2.6 × 106 M⊙ supermassive black hole. At least a portion of its spectrum—notably the mm/sub-mm “bump”—appears to be produced within the inner portion (r < 10 rS) of a hot, magnetized Keplerian flow, whose characteristics are also consistent with the ∼ 10% linear polarization detected from thi...

The pulsed radio emission from the Galactic Center (GC) magnetar SGR J1745-29 probes the turbulent, magnetized plasma of the GC hyperstrong scattering screen through both angular and temporal broadening. We present the first measurements of the angular size of SGR J1745-29, obtained with the Very Long Baseline Array and the phased Very Large Array at 8.7 and 15.4 GHz. The source sizes are consi...