We analyze the 11 yr long-term light curve of the Radio-loud Narrow-line Seyfert 1 galaxy J0849+5108 and the nearly simultaneous γ-ray data of the source. The data were obtained with the Owens Valley Radio Observatory 40 m telescope at 15GHz and with the Large Area Telescope onboard the Fermi Gamma-ray Space Telescope, respectively. A quasi-periodic oscillation (QPO) signal at a significance of >5σ is found in the radio light curve, but no similar modulation is seen in the γ-ray light curve. The QPO signal was present for 21 cycles, the longest among the reported radio QPOs, and likely disappeared after 2019 January 16. Different mechanisms proposed to explain the observed QPOs in active galactic nuclei (AGNs) are discussed for this QPO case. Either a secular instability in the inner accretion disk or a helical structure in the jet of J0849+5108 may explain the radio QPO, while for the latter scenario the jet has to be collimated up to ∼200pc, similar to that seen in the nearby AGN M87. It will be of interest to keep monitoring the source at radio frequencies, seeing whether similar QPO signals appear again.

我们分析了射电响亮窄线赛弗特 1 星系 J0849+5108 的 11 年长期光变曲线和源的几乎同时的γ射线数据。这些数据分别是通过欧文斯谷射电天文台 40 m 望远镜在 15GHz 和费米伽玛射线空间望远镜上的大面积望远镜获得的。在射电光曲线中发现了显着性大于 5 σ的准周期振荡 (QPO) 信号，但在γ 中没有看到类似的调制- 光线光线曲线。QPO 信号存在 21 个周期，是报告的无线电 QPO 中最长的一个，并且可能在 2019 年 1 月 16 日之后消失。针对这个 QPO 案例讨论了不同的机制来解释在活动星系核 (AGN) 中观察到的 QPO。内部吸积盘的长期不稳定性或 J0849+5108 射流中的螺旋结构可以解释射电 QPO，而对于后一种情况，射流必须准直至 200pc，类似于在附近的 AGN 中看到的M87。继续以无线电频率监视源，看看是否再次出现类似的 QPO 信号将很有趣。