Interstellar scintillation measurements of pulsars at 326.5 MHz

We have measured the decorrelation frequency (f _v ) and decorrelation time (t _v ) for 15 pulsars. We show by combining our data with those of others thatfv∫ DM^-1.79±0.14 andt _v ∫ DM^-0.80±0.15 up to a dispersion measure (DM) of about 60 cm³ pc. The combined data set does not form a complete sample, but the relations obtained from our measurements on 14 pulsars, which form almost a complete sample up to 41 cm³ pc, are consistent with the above relations, suggesting that these relations are not seriously affected by selection effects. The relations are broadly in agreement with those expected from a homogeneous interstellar medium and are in disagreement with earlier conclusions by others that these relations steepen even for low-DM pulsars. The agreement suggests that the local interstellar medium is homogeneous at least up to a distance of about 2 kpc.