Radio and optical observations of the possible microlensed BL Lac source MS 0205.7+3509 were obtained simultaneously with ASCA x–ray measurements in February 1997 .
A single power law model , with a photon index of 2.61 , is an adequate fit to the ASCA data , once hydrogenic absorption in excess of the Galactic value is permitted , confirming a previous ROSAT measurement .
On the basis of our simultaneous data we have determined MS 0205.7+3509 to be a typical x–ray selected BL Lac , with \alpha _ { xox } = -0.82 .
There is no indication of an inverse Compton ( IC ) component in the ASCA spectrum up to 10 keV .
No evidence for variability on hour-long timescales is present in either the x–ray or the optical data .
We discuss these results in the context of a gravitational microlensing scenario for MS 0205.7+3509 .