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Description
We present the results of the multiwavelength study of the flaring activity of the supermassive black hole named Sgr A* is located at the dynamical center of the Milky Way. We detected two X-ray flares on 2014 Mar. 10 and Apr. 2 with XMM-Newton, three near-infrared (NIR) flares with HST on 2014 Mar. 10 and Apr. 2, and two NIR flares on 2014 Apr. 3 and 4 with VLT. The X-ray flare on 2014 Mar. 10 is characterized by a long rise and a rapid decay. Its total duration is one of the longest detected so far in X-rays. Its NIR counterpart peaked well before the X-ray maximum, implying a dramatic change in the X-ray-to-NIR flux ratio during this event. This NIR/X-ray flare is interpreted as either a single flare where variation in the X-ray-to-NIR flux ratio is explained by the adiabatic compression of a plasmon, or two distinct flaring components separated by 1.2h with simultaneous peaks in X-rays and NIR. We identified an increase in the rising radio flux density at 13.37GHz on 2014 Mar. 10 with the VLA that could be the delayed radio emission from a NIR/X-ray flare that occurred before the start of our observation. The X-ray flare on 2014 Apr. 2 occurred for HST during the occultation of Sgr A* by the Earth, therefore we only observed the start of its NIR counterpart. With NIR synchrotron emission from accelerated electrons and assuming X-rays from synchrotron self-Compton emission, the region of this NIR/X-ray flare has a size of 0.03-7 times the Schwarzschild radius and an electron density of 10^8.5-10^10.2cm^-3^, assuming a synchrotron spectral index of 0.3-1.5. When Sgr A* reappeared to the HST view, we observed the decay phase of a distinct bright NIR flare with no detectable counterpart in X-rays. On 2014 Apr. 3, two 95GHz flares were observed with CARMA, where the first may be the delayed emission of a NIR flare observed with VLT.
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