Polarimetric signatures of hot spots in black hole accretion flows

Vol. 668
2. Astrophysical processes

Polarimetric signatures of hot spots in black hole accretion flows

The back hole at the center of our Galaxy, Sagittarius A*, shows the occurrence of random flares that last several tens of minutes at X-ray and near-infrared wavelengths. One possible interpretation involves the emission of bright spots in the accretion flow close to the back hole event horizon. In this paper, Vos and collaborators adopt a semi-analytic approach to compute the polarimetric signature of these emitting blobs immersed in a tenuous accretion disk, including all the relativistic effects due to the closeness to the central black hole. They find characteristic loop structures in the polarization plane, depending on the disk inclination, the black hole spin, and the structure of the magnetic field. Simulations for the blob emission were carried out at millimeter wavelengths where polarimetric variability from Sagittarius A* has already been observed with the Atacama Large Millimetre/submillimetre Array. These simulations show that the identified characteristic loopsin the polarization plane are particularly informative on the magnetic field topology, a quantity otherwise difficult to measure.