COORDINATED VISIBLE AND INFRARED MONITORING OF RAPID VARIATIONS OF MARKARIAN 501 - 1ST RESULTS WITH FOVIA

We present simultaneous monitoring of the BL Lacertae object Markarian 501 obtained in the visible and near infrared using a double photomet er system on the 1.5m Carlos Sanchez Telescope situated in El Observat orio del Teide, Tenerife and CCD photometry in U and B taken with the lm Jacobus Kapteyn Telescope of El Observatorio del Roque de los Mucha chos, La Palma. We see evidence of coordinated variability on time sca les of hours in the variations in the visible and infrared. A brief in frared flare is seen on one night which has a formal probability of re ality of approximately 99 % and which is not seen in the B light curve . If real, this flare presents considerable difficulties within the fr amework of existing models. The results demonstrate the value of havin g a single telescope equipped to observe simultaneously in two differe nt ranges of the spectrum. These data are compared with CCD photometry in U and B taken at other epochs.