Upper limits on optical microvariabilities in a large sample of 22 Seyfert galaxies have been obtained, using differential photometry. We have developped a new method of analysis minimizing the influence of possible variability of the comparison stars. We thus obtain precision on our variability detection smaller than 1% and in most cases about 0.5%. We do not detect variability in any of our objects, with a possible trend of several hours in Mkn 359. In the hypothesis where variable optical emission would be due to synchrotron radiation from the non-thermal electron population which we suppose to be responsible for the X-ray emission, these results enable us to constraint intrinsic properties of the local environment of the non thermal source. Upper limits on our variability detection and equipartition hypothesis between magnetic field and particle, restrain the possible values of the size R of the non thermal source, its distance Z from the UV emission region and fix upper and lower limits for the magnetic field.
© European Southern Observatory (ESO) 1999
Online publication: February 23, 1999