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

The Astrophysical Journal (Impact Factor: 6.28). 10/2009; 706(1):348. DOI: 10.1088/0004-637X/706/1/348
Source: arXiv

ABSTRACT We report the detection of variable emission from Sgr A* in almost all
wavelength bands (i.e. centimeter, millimeter, submillimeter, near-IR and
X-rays) during a multi-wavelength observing campaign. Three new moderate flares
are detected simultaneously in both near-IR and X-ray bands. The ratio of X-ray
to near-IR flux in the flares is consistent with inverse Compton scattering of
near-IR photons by submillimeter emitting relativistic particles which follow
scaling relations obtained from size measurements of Sgr A*. We also find that
the flare statistics in near-IR wavelengths is consistent with the probability
of flare emission being inversely proportional to the flux. At millimeter
wavelengths, the presence of flare emission at 43 GHz (7mm) using VLBA with
milli-arcsecond spatial resolution indicates the first direct evidence that
hourly time scale flares are localized within the inner 30$\times$70
Schwarzschild radii of Sgr A*. We also show several cross correlation plots
between near-IR, millimeter and submillimeter light curves that collectively
demonstrate the presence of time delays between the peaks of emission up to
three hours. The evidence for time delays at millimeter and submillimeter
wavelengths are consistent with the source of emission being optically thick
initially followed by a transition to an optically thin regime. In particular,
there is an intriguing correlation between the optically thin near-IR and X-ray
flare 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 delayed
with respect to the near-IR and X-ray flare emission.


Available from: Howard Bushouse, Jun 07, 2015