Simultaneous Multi-Wavelength Observations of Sgr A* during 2007 April 1-11

摘要

We report the detection of variable emission from Sgr A* in almost allwavelength bands (i.e. centimeter, millimeter, submillimeter, near-IR andX-rays) during a multi-wavelength observing campaign. Three new moderate flaresare detected simultaneously in both near-IR and X-ray bands. The ratio of X-rayto near-IR flux in the flares is consistent with inverse Compton scattering ofnear-IR photons by submillimeter emitting relativistic particles which followscaling relations obtained from size measurements of Sgr A*. We also find thatthe flare statistics in near-IR wavelengths is consistent with the probabilityof flare emission being inversely proportional to the flux. At millimeterwavelengths, the presence of flare emission at 43 GHz (7mm) using VLBA withmilli-arcsecond spatial resolution indicates the first direct evidence thathourly time scale flares are localized within the inner 30$\times$70Schwarzschild radii of Sgr A*. We also show several cross correlation plotsbetween near-IR, millimeter and submillimeter light curves that collectivelydemonstrate the presence of time delays between the peaks of emission up tothree hours. The evidence for time delays at millimeter and submillimeterwavelengths are consistent with the source of emission being optically thickinitially followed by a transition to an optically thin regime. In particular,there is an intriguing correlation between the optically thin near-IR and X-rayflare and optically thick radio flare at 43 GHz that occurred on 2007 April 4.This would be the first evidence of a radio flare emission at 43 GHz delayedwith respect to the near-IR and X-ray flare emission.