TY - JOUR
T1 - Evidence for X-ray synchrotron emission from simultaneous mid-infrared to X-ray observations of a strong Sgr A* flare
AU - Dodds-Eden, K.
AU - Porquet, D.
AU - Trap, G.
AU - Quataert, E.
AU - Haubois, X.
AU - Gillessen, S.
AU - Grosso, N.
AU - Pantin, E.
AU - Falcke, H.
AU - Rouan, D.
AU - Genzel, R.
AU - Hasinger, G.
AU - Goldwurm, A.
AU - Yusef-Zadeh, F.
AU - Clenet, Y.
AU - Trippe, S.
AU - Lagage, P. O.
AU - Bartko, H.
AU - Eisenhauer, F.
AU - Ott, T.
AU - Paumard, T.
AU - Perrin, G.
AU - Yuan, F.
AU - Fritz, T. K.
AU - Mascetti, L.
PY - 2009
Y1 - 2009
N2 - 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, as well as with XMM-Newton at X-ray (2-10 keV) wavelengths. On 2007 April 4, a very bright flare was observed from Sgr A* simultaneously at L′ band and X-ray wavelengths. No emission was detected using VISIR. The resulting spectral energy distribution has a blue slope (β>0 for νL ν νβ, consistent with νL ν ν0.4) between 12 μm and 3.8 μm. For the first time, our high-quality data allow a detailed comparison of infrared (IR) 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 μm light curve are clearly not seen in the X-ray data. From the shortest timescale variations in the L′-band light curve, we find that the flaring region must be no more than 1.2RS in size. The high X-ray to IR 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.
AB - 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, as well as with XMM-Newton at X-ray (2-10 keV) wavelengths. On 2007 April 4, a very bright flare was observed from Sgr A* simultaneously at L′ band and X-ray wavelengths. No emission was detected using VISIR. The resulting spectral energy distribution has a blue slope (β>0 for νL ν νβ, consistent with νL ν ν0.4) between 12 μm and 3.8 μm. For the first time, our high-quality data allow a detailed comparison of infrared (IR) 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 μm light curve are clearly not seen in the X-ray data. From the shortest timescale variations in the L′-band light curve, we find that the flaring region must be no more than 1.2RS in size. The high X-ray to IR 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.
KW - Accretion, accretion disks
KW - Black hole physics
KW - Galaxy: center
KW - Infrared: general
KW - Radiation mechanisms: general
KW - X-rays: general
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U2 - 10.1088/0004-637X/698/1/676
DO - 10.1088/0004-637X/698/1/676
M3 - Article
AN - SCOPUS:66649094185
SN - 0004-637X
VL - 698
SP - 676
EP - 692
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 1
ER -