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Astronomy and Astrophysics 528 (2011) 140
Concurrent X-ray, near-infrared, sub-millimeter, and GeV gamma-ray observations of Sagittarius A*
G. Trap1, 2, A. Goldwurm1, 2, K. Dodds-Eden3, A. Weiss4, R. Terrier2, G. Ponti2, 5, S. Gillessen3, R. Genzel3, P. Ferrando1, 2, G. Bélanger6, Y. Clénet7, D. Rouan7, P. Predehl3, R. Capelli3, F. Melia, F. Yusef-Zadeh

Aims: The radiative counterpart of the supermassive black hole at the Galactic center (GC), Sgr A⋆, is subject to frequent flares that are visible simultaneously in X-rays and the near-infrared (NIR). Often, enhanced radio variability from centimeter to sub-millimeter wavelengths is observed to follow these X-ray/NIR eruptions. We present here a multi-wavelength campaign carried out in April 2009, with the aim of characterizing this broadband flaring activity. Methods: Concurrent data from the XMM-Newton/EPIC (2-10 keV), VLT/NACO (2.1 μm, 3.8 μm), APEX/LABOCA (870 μm), and Fermi/LAT (0.1-200 GeV) instruments are employed to derive light curves and spectral energy distributions of new flares from Sgr A⋆. Results: We detected two relatively bright NIR flares, both associated with weak X-ray activity, one of which was followed by a strong sub-mm outburst ~200 min later. Photometric spectral information on a NIR flare was obtained for the first time with NACO, giving a power-law photon index α = -0.4 ± 0.3 (Fν ∝ ν α). The first attempt to detect flaring activity from the Fermi GC source 1FGL J1745.6-2900 is also reported. We model NIR, X-ray, and sub-mm flares in the context of non-thermal emission processes. We find that the simplest scenario involving a single expanding plasmoid releasing synchrotron NIR/sub-mm and synchrotron self-Compton X-ray radiation is inadequate to reproduce the data, but we offer suggestions to reconcile the basic elements of the theory and the observations.
1 :  IRFU - Institut de Recherches sur les lois Fondamentales de l'Univers (ex DAPNIA)
2 :  APC - UMR 7164 - AstroParticule et Cosmologie
3 :  MPE - Max Planck Institute for Extraterrestrial Physics
4 :  MPIFR - Max-Planck-Institut für Radioastronomie
5 :  School of Physics and Astronomy [Southampton, UK]
6 :  ESA/ESAC - European Space Agency [Madrid]
7 :  LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
Physique/Astrophysique/Phénomènes cosmiques de haute energie

Planète et Univers/Astrophysique/Phénomènes cosmiques de haute energie
Galaxy: center – black hole physics – radiation mechanisms: non-thermal – X-rays: general – infrared: general – submillimeter: general
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