This paper reports measurements of Sgr A* made with NACO in L ′ -band (3.80 µm), Ks-band (2.12 µm) and H-band (1.66 µm) and with VISIR in N-band (11.88 µm) at the ESO VLT 1 , as well as with XMM-Newton at X-ray (2-10 keV) wavelengths. On 4 April, 2007, a very bright flare was observed from Sgr A* simultaneously at L ′ -band and X-ray wavelengths. No emission was detected 1 The Very Large Telescope (VLT) at the European Southern Observatory (ESO) on Paranal, Chile: Program IDs 179.B-0261(A) and Program ID: 079.B-0929(A).using VISIR. The resulting SED has a blue slope (β > 0 for νL ν ∝ ν β , consistent with νL ν ∝ ν 0.4 ) between 12 micron and 3.8 micron.For the first time our high quality data allow a detailed comparison of infrared and X-ray light curves with a resolution of a few minutes. The IR and X-ray flares are simultaneous to within 3 minutes. However the IR flare lasts significantly longer than the X-ray flare (both before and after the X-ray peak) and prominent substructures in the 3.8 micron light curve are clearly not seen in the X-ray data. From the shortest timescale variations in the L ′ -band lightcurve we find that the flaring region must be no more than 1.2 R S in size.The high X-ray to infrared flux ratio, blue νL ν slope MIR to L ′ -band, and the soft νL ν spectral index of the X-ray flare together place strong constraints on possible flare emission mechanisms. We find that it is quantitatively difficult to explain this bright X-ray flare with inverse Compton processes. A synchrotron emission scenario from an electron distribution with a cooling break is a more viable scenario.

Context. The study of dynamical processes in protoplanetary disks is essential to understand planet formation. In this context, transition disks are prime targets because they are at an advanced stage of disk clearing and may harbor direct signatures of disk evolution. Aims. We aim to derive new constraints on the structure of the transition disk MWC 758, to detect non-axisymmetric features and understand their origin. Methods. We obtained infrared polarized intensity observations of the protoplanetary disk MWC 758 with VLT/SPHERE at 1.04 µm to resolve scattered light at a smaller inner working angle (0.093 ) and a higher angular resolution (0.027 ) than previously achieved. Results. We observe polarized scattered light within 0.53 (148 au) down to the inner working angle (26 au) and detect distinct nonaxisymmetric features but no fully depleted cavity. The two small-scale spiral features that were previously detected with HiCIAO are resolved more clearly, and new features are identified, including two that are located at previously inaccessible radii close to the star. We present a model based on the spiral density wave theory with two planetary companions in circular orbits. The best model requires a high disk aspect ratio (H/r ∼ 0.20 at the planet locations) to account for the large pitch angles which implies a very warm disk. Conclusions. Our observations reveal the complex morphology of the disk MWC 758. To understand the origin of the detected features, the combination of high-resolution observations in the submillimeter with ALMA and detailed modeling is needed.