Aims: Intranight variation (or microvariation) is a common phenomenon of
radio-loud BL Lac objects. However, it is not clear whether the recently found
radio-quiet BL Lac objects have the same properties. The occurrence rate of
intranight variation is helpful in distinguishing the mechanism of the
continuum of radio-quiet BL Lac objects.
Methods: We conducted a photometric monitoring of 8 radio-quiet BL Lac
objects by the Xinglong 2.16m and Lijiang 2.4m telescopes. The differential
light curves are calculated between each target and two comparison stars. To
quantify the variation, the significance of variation is examined by a scaled
F-test.
Results: No significant variation is found in the 11 sessions of light curves
of 8 radio-quiet BL Lac objects (one galactic source is excluded). The lack of
microvariation in radio-quiet BL Lac objects is consistent with the detection
rate of microvariation in normal radio-quiet AGNs, but much lower than for
radio-loud AGNs. This result indicates that the continua of the radio-quiet BL
Lac objects are not dominated by jets that will induce frequent
microvariations.Comment: Accepted for publication in Astronomy and Astrophysics; 7 pages, 1
figure, 3 table
