학술논문
The Unanticipated Phenomenology of the Blazar PKS~2131$-$021: A Unique Super-Massive Black Hole Binary Candidate
Document Type
Working Paper
Author
O'Neill, S.; Kiehlmann, S.; Readhead, A. C. S.; Aller, M. F.; Blandford, R. D.; Liodakis, I.; Lister, M. L.; Mróz, P.; O'Dea, C. P.; Pearson, T. J.; Ravi, V.; Vallisneri, M.; Cleary, K. A.; Graham, M. J.; Grainge, K. J. B.; Hodges, M. W.; Hovatta, T.; Lähteenmäki, A.; Lamb, J. W.; Lazio, T. J. W.; Max-Moerbeck, W.; Pavlidou, V.; Prince, T. A.; Reeves, R. A.; Tornikoski, M.; de la Para, P. Vergara; Zensus, J. A.
Source
Subject
Language
Abstract
Most large galaxies host supermassive black holes in their nuclei and are subject to mergers, which can produce a supermassive black hole binary (SMBHB), and hence periodic signatures due to orbital motion. We report unique periodic radio flux density variations in the blazar PKS~2131$-$021, which strongly suggest an SMBHB with an orbital separation of $\sim 0.001-0.01$ pc. Our 45.1-year radio light curve shows two epochs of strong sinusoidal variation with the same period and phase to within $<2\%$ and $\sim 10\%$, respectively, straddling a 20-year period when this variation was absent. Our simulated light curves accurately reproduce the ``red noise'' of this object, and Lomb-Scargle, weighted wavelet Z-transform, and least-squares sine wave analyses demonstrate conclusively, at the $4.6\sigma$ significance level, that the periodicity in this object is not due to random fluctuations in flux density. The observed period translates to $2.082\pm 0.003$ years in the rest frame at the $z=1.285$ redshift of PKS~2131$-$021. The periodic variation in PKS~2131$-$021 is remarkably sinusoidal. We present a model in which orbital motion, combined with the strong Doppler boosting of the approaching relativistic jet, produces a sine-wave modulation in the flux density which easily fits the observations. Given the rapidly-developing field of gravitational wave experiments with pulsar timing arrays, closer counterparts to PKS~2131$-$021 and searches using the techniques we have developed are strongly motivated. These results constitute a compelling demonstration that the phenomenology, not the theory, must provide the lead in this field.
Comment: 24 pages, 13 figure, 3 Tables, accepted for publication in APJL
Comment: 24 pages, 13 figure, 3 Tables, accepted for publication in APJL