A possible 35-minute periodicity in the OJ 287 active galactic nucleus at 7-mm wavelength

Abstract

BL Lacertids are a class of active galactic nuclei (AGNs) characterized in part by flat radio spectra and rapid flux variability on time scales of weeks to days, at centimetre to optical wavelengths1. One such object, OJ 287, exhibits very short time-scale (minutes) nonperiodic variations in infrared and centimetre flux, as well as in optical polarization^2–4. Over the past fifteen years, there have also been reports of short term (tens of minutes) periodic^{5 – 8} modulation of the emission from OJ287 at a variety of wavelengths; these periodicities have proved elusive to confirm^3,9, perhaps because they are inherently sporadic. Because the presence of periodic flux variations strongly constrains the nature of the central source within an AGN, the report of periodic variability in OJ287 with a stable 15.7-min period detected at multiple frequencies and using different telescopes⁸, prompted us to under-take observations of this object at 7-mm wavelength. In this letter, we report detection in February 1986 of a weak (4% amplitude), 35-min flux modulation of OJ 287, whose statistical significance we estimate to be ∼97%. Nearly one year later, observations of the same source revealed no periodicities between 4 and 300 min with amplitudes greater than 2%.