Comparative intranight optical variability of X-ray and γ-ray-detected narrow-line Seyfert 1 galaxies

In a systematic program to characterize the intranight optical variability (INOV) of different classes of narrow-line Seyfert 1 (NLSy1s) galaxies, we report here the first comparative INOV study of NLSy1 sets detected in the X-ray and γ-ray bands. Our sample consists of 18 sources detected in X-rays but not in γ-rays (hereafter x_NLSy1s) and seven sources detected in γ-rays (hereafter g_NLSy1s), out of which five are detected also in X-rays. We have monitored these two sets of NLSy1s, respectively, in 24 and 21 sessions of a minimum of 3-h duration each. The INOV duty cycles for these two sets are found to be 12 per cent and 53 per cent, respectively (at a 99 per cent confidence level). In the set of 18 x_NLSy1s, INOV duty cycle is found to be zero for the 13 radio-quiet members (monitored in 14 sessions) and 43 per cent for the five radio-loud members (10 sessions). The latter is very similar to the aforementioned duty cycle of 53 per cent found here for the set of g_NLSy1s (all of which are radio-loud). Thus, it appears that the radio-loudness level is the prime factor behind the INOV detection and the pattern of the high-energy radiation plays only a minor role.