H. Bartko

Kinematics of the old stellar population at the Galactic centre

Aims. We aim at a detailed description of the kinematic properties of the old, (several Gyrs) late-type CO-absorption star population among the Galactic centre (GC) cluster stars. This cluster is composed of a central supermassive black hole (Sgr A*) and a selfgravitating system of stars. Understanding its kinematics thus offers the opportunity to understand the dynamical interaction between a central point mass and the surrounding stars in general, especially in view of understanding other galactic nuclei. Methods. We applied AO-assisted, near-infrared imaging and integral-field spectroscopy using the instruments NAOS/CONICA and SINFONI at the VLT. We obtained proper motions for 5445 stars, 3D velocities for 664 stars, and acceleration limits (in the sky plane) for 750 stars. Global kinematic properties were analysed using velocity and velocity dispersion distributions, phase-space maps, twopoint correlation functions, and the Jeans equation. Results. We detect for the first time significant cluster rotation in the sense of the general Galactic rotation in proper motions. Out of the 3D velocity dispersion, we derive an improved statistical parallax for the GC of R0 = 8.07 ± 0.32stat ± 0.13sys kpc. The distribution of 3D stellar speeds can be approximated by local Maxwellian distributions. Kinematic modelling provides deprojected 3D kinematic parameters, including the mass profile of the cluster. We find an upper limit of 4% for the amplitude of fluctuations in the phase-space distribution of the cluster stars compared to a uniform, spherical model cluster. Using upper limits on accelerations, we constrain the minimum line-of-sight distances from the plane of Sgr A* of five stars located within the innermost few (projected) arcsec. The stars within 0.7 �� radius from the star group IRS13E do not co-move with this group, making it unlikely that IRS13E is the core of a substantial star cluster. Overall, the GC late-type cluster is described well as a uniform, isotropic, rotating, dynamically relaxed, phase-mixed system.

SIMULTANEOUS MULTIWAVELENGTH OBSERVATIONS OF THE BLAZAR 1ES 1959+650 AT A LOW TeV FLUX

We present the resultsfroma multiwavelength campaignonthe TeVblazar1ES 1959+650, performed in2006May. Data from the optical, UV, soft- and hard-X-ray, and very high energy (VHE) gamma-ray (E > 100 GeV) bands were obtained with the Suzaku and Swift satellites, the MAGIC telescope, and other ground-based facilities. The source spectral energy distribution (SED), derived from Suzaku and MAGIC observations at the end of 2006 May, shows the usual double hump shape, with the synchrotron peak at a higher flux level than the Compton peak. With respect to historicalvalues,duringourcampaignthe sourceexhibiteda relatively highstateinX-raysand optical, while inthe VHEbanditwasatoneof thelowestlevelsofarrecorded.Wealsomonitoredthesourceforfluxspectralvariability onatimewindowof 10daysintheoptical-UVandX-raybandsand7daysintheVHEband.Thesourcevariesmorein the X-ray than in the optical band, with the 2Y10 keV X-ray flux varying by a factor of � 2. The synchrotron peak is locatedintheX-raybandandmovestohigherenergiesasthesourcegetsbrighter,withtheX-rayfluxesaboveitvarying more rapidly than the X-ray fluxes at lower energies. The variability behavior observed in the X-ray band cannot be

What is limiting near‐infrared astrometry in the Galactic Centre?

We systematically investigate the error sources for high-precision astrometry from adaptive optics (AO) based near-infrared imaging data. We focus on the application in the crowded stellar field in the Galactic Centre. We show that at the level of ≲ 100 μas a number of effects are limiting the accuracy. Most important are the imperfectly subtracted seeing haloes of neighbouring stars, residual image distortions and unrecognized confusion of the target source with fainter sources in the background. Further contributors to the error budget are the uncertainty in estimating the point-spread function, the signal-to-noise ratio induced statistical uncertainty, coordinate transformation errors, the chromaticity of refraction in Earths atmosphere, the post-AO differential tilt jitter and anisoplanatism. For stars as bright as m K = 14, residual image distortions limit the astrometry, for fainter stars the limitation is set by the seeing haloes of the surrounding stars. In order to improve the astrometry substantially at the current generation of telescopes, an AO system with high performance and weak seeing haloes over a relatively small field (r ≲ 3 arcsec) is suited best. Furthermore, techniques to estimate or reconstruct the seeing halo could be promising.

γ-ray emission from PWNe interacting with molecular clouds

We consider a situation in which a pulsar is formed inside or close to a high-density region of a molecular cloud. Right after birth, the pulsar was very active and accelerated hadrons and leptons to very high energies. Hadrons diffuse through the supernova remnant and some of them are trapped in the nearby cloud interacting with the matter. We extend a recent timedependent model for the γ radiation of pulsar wind nebulae (PWNe) to describe this more complicated astrophysical scenario. The typical calculations have been performed for two objects, IC 443 and W41, which have recently been discovered as sources of TeV γ -rays. In this model the low-energy TeV emission should be correlated with the birth place of the pulsar and the region of dense soft radiation rather than with its present position, provided that the injection rate of relativistic particles into the PWN has been much more efficient at early times. The high-energy TeV emission should be correlated with the location of dense clouds which were able to capture high-energy hadrons due to their strong magnetic fields.

On the possibility of a warped disc origin of the inclined stellar discs at the galactic centre

(Abridged) The Galactic Center (GC) hosts a population of young stars some of which seem to form mutually inclined discs of clockwise and counter clockwise rotating stars. We present a warped disc origin scenario for these stars assuming that an initially flat accretion disc becomes warped due to the Pringle instability, or due to Bardeen-Petterson effect, before it fragments to stars. We show that this is plausible if the star formation efficiency

GRAVITY Spectrometer Metrology laser blocking strategy at OD=12

\epsilon_{SF} \lesssim 1

Results from the VLTI-PRIMA fringe tracking testbed

, and the viscosity parameter

EVIDENCE FOR WARPED DISKS OF YOUNG STARS IN THE GALACTIC CENTER

\alpha \sim 0.1

Evidence for X-ray synchrotron emission from simultaneous mid-infrared to X-ray observations of a strong Sgr A* flare

. After fragmentation, we model the disc as a collection of concentric, circular, mutually tilted rings, and construct warped disc models for mass ratios and other parameters relevant to the GC environment, but also for more massive discs. We take into account the discs self-gravity and the torques exerted by a surrounding star cluster. We show that a self-gravitating low-mass disc (

GC-IRS13E—A Puzzling Association of Three Early-type Stars

M_d / M_{bh} \sim 0.001