Simultaneous MITSuME g'RCIC monitoring of S5 0716+714

Abstract

We present the results of our intra-night optical flux monitoring observations of S5 0716+714 done simultaneously in g',RC and IC filters. The observations were done using the Multicolor Imaging Telescopes for Survey and Monstrous Explosions instrument on the 50 cm telescope at the Okayama Astrophysical Observatory over 30 nights between 2008 March 11 and 2008 May 8. Of these 30 nights, 22 nights have continuous (without any break) observations with the duration ranging from 1 to 6 h and hence were considered for intra-night optical variability (INOV). The remaining eight nights have continuous observations of less than 1 h and hence were considered only for long-term optical variability. In total, we have 4888 data points which were simultaneous in g',RC and IC filters. Of the 22 nights considered for INOV, the object showed flux variability on 19 nights with the amplitude of variability in the IC band ranging from ~4 per cent to ~55 per cent. The duty cycle for INOV was thus found to be 83 per cent. A good correlation between the light curves in all the three bands was found. No time lag between different bands was noticed on most of the nights, except for three nights where the variation in g' was found to lead that of the IC band by 0.3 to 1.5 h. On inter-night time-scales, no lag was found between g' and IC bands. On inter-night time-scales as well as intra-night time-scales on most of the nights, the amplitude of variability was found to increase towards shorter wavelengths. The flux variations in the different bands were not achromatic, with the blazar tending to become bluer when brighter on both inter-night and intra-night time-scales, and this might be attributed to the larger amplitude variation at shorter wavelengths. A clear periodic variation of 3.3 h was found on 2008 April 1 and a hint for another possible periodic variability of 4 h was found on 2008 March 31. During our 30 days of observations over a 2 month period, the source has varied with an amplitude of variability as large as ~80 per cent.