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

TL;DR

This study presents multi-wavelength observations of Sgr A* revealing correlated flares in near-IR, X-ray, and radio, with evidence of time delays and localization within the inner accretion region, advancing understanding of black hole emission mechanisms.

Contribution

It provides the first direct evidence of hour-scale flares localized within the inner 30×70 Schwarzschild radii of Sgr A* and demonstrates correlated multi-wavelength flare activity with time delays.

Findings

Detection of three new flares in near-IR and X-ray bands.

First direct evidence of radio flares localized within the inner accretion region.

Observation of time delays up to three hours between different wavelength peaks.

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.