A double-period oscillation signal in millimeter emission of the radio
  galaxy NGC 1275
  The nearby Seyfert type galaxy NGC 1275 contains a bright radio nucleus at
its center, revealed through high-spatial resolution imaging to be the source
of the jets emanating from the galaxy. Coincident with the emergence of a new
component C3 in the nucleus since 2005, flux densities from NGC 1275, at least
at radio, millimeter (mm), and gamma-ray frequencies, had been increasing up
through 2017 and leveled off afterwards. We analyze the long-term light curves
of the nucleus that span the rising trend to 2015 July, and find a pair of
approximately year-long quasi-periodic oscillations, with periods of $P_l\simeq
345$\,d and $P_h\simeq 386$\,d respectively, in emission at 1.3-mm wavelength.
We discuss the case that there would be a long precession period $P_{\rm
prec}\simeq 9$\,yr, causing the appearance of $P_h$ that is slightly higher
than $P_l$. The accretion disk around the central supermassive black hole
(SMBH) would be precessing at $P_{\rm prec}$, induced by either the
Lense-Thirring effect or the existence of a companion SMBH. In the two
scenarios, $P_l$ would be the jet wobbling timescale or the SMBH binary period
respectively. The finding, which could be verified through high-spatial
resolution mm imaging, would not only identify the nature of the jet variation
but also help reveal the full features of the galaxy.
