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Concurrent X-ray, near-infrared, sub-millimeter, and GeV gamma-ray observations of Sagittarius A

Abstract : 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.
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http://hal.in2p3.fr/in2p3-00670177
Contributor : Régis Terrier <>
Submitted on : Tuesday, February 14, 2012 - 6:01:02 PM
Last modification on : Saturday, September 19, 2020 - 4:50:41 AM

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G. Trap, A. Goldwurm, K. Dodds-Eden, A. Weiss, R. Terrier, et al.. Concurrent X-ray, near-infrared, sub-millimeter, and GeV gamma-ray observations of Sagittarius A. Astronomy and Astrophysics - A&A, EDP Sciences, 2011, 528, pp.140. ⟨10.1051/0004-6361/201015157⟩. ⟨in2p3-00670177⟩

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