We searched a short-term radio variability in an active galactic nucleus PKS
1510-089. A daily flux monitoring for 143 days at 8.4 GHz was performed, and
VLBI observations at 8.4, 22, and 43 GHz were carried out 4 times during the
flux monitoring period. As a result, variability with time scale of 20 to 30
days was detected. The variation patterns were well alike on three frequencies,
moreover those at 22 and 43 GHz were synchronized. These properties support
that this short-term variability is an intrinsic one. The Doppler factor
estimated from the variability time scale is 47. Since the Doppler factor is
not extraordinary large for AGN, such intrinsic variability with time scale
less than 30 days would exist in other AGNs.Comment: 14 pages, 4 figure