UNUSUAL INCREASE IN THE 325 MHZ FLUX-DENSITY OF PSR-B0655+64

We report on the detection of a large amplification of the flux densit y of PSR B0655+64 at 325 MHz (a factor of similar to 43) that lasted a bout one hour. To the best of our knowledge such a large amplification has not been reported before. The phenomenon is restricted to a very narrow bandwidth (50 % decorrelation half-width of 3.6 +/- 0.4 MHz). T he decorrelation bandwidth and characteristic time scale of the variat ion are in agreement with the values expected for diffractive interste llar scintillation. However, the observed amplification of the flux de nsity of PSR B0655+64 is rather large. The observations suggest that a mplifications of a factor up to 8 are not uncommon for PSR 0655+64 at 92 cm. The extreme flux density amplification of PSR 0655+64 might be explained in terms of caustics. We consider it unlikely that this even t can be explained by intrinsic variability.