Coordinated multi-wavelength observations of Sgr A*

TL;DR

This paper presents coordinated near-infrared and X-ray observations of Sgr A* revealing polarized flares and sub-flare structures, supporting models of a temporary accretion disk with hot spots and jet activity around the supermassive black hole.

Contribution

It provides new multi-wavelength observational evidence of Sgr A*'s variable emission and supports a model involving a transient disk with hot spots and jet features.

Findings

Detection of polarized NIR flare synchronous with X-ray flare

Observation of the highest sub-flare contrast to date

Evidence supporting a temporary disk with hot spots and jets

Abstract

We report on recent near-infrared (NIR) and X-ray observations of Sagittarius A* (Sgr A*), the electromagnetic manifestation of the ~4x10^6 solar masses super-massive black hole (SMBH) at the Galactic Center. The goal of these coordinated multi-wavelength observations is to investigate the variable emission from Sgr A* in order to obtain a better understanding of the underlying physical processes in the accretion flow/outflow. The observations have been carried out using the NACO adaptive optics (AO) instrument at the European Southern Observatory's Very Large Telescope (July 2005, May 2007) and the ACIS-I instrument aboard the Chandra X-ray Observatory (July 2005). We report on a polarized NIR flare synchronous to a 8x1033 erg/s X-ray flare in July 2005, and a further flare in May 2007 that shows the highest sub-flare to flare contrast observed until now. The observations can be interpreted in the framework of a model involving a temporary disk with a short jet. In the disk component flux density variations can be explained due to hot spots on relativistic orbits around the central SMBH. The variations of the sub-structures of the May 2007 flare are interpreted as a variation of the hot spot structure due to differential rotation within the disk.