The Unanticipated Phenomenology of the Blazar PKS 2131–021: A Unique Supermassive Black Hole Binary Candidate

S. O’neill; S. Kiehlmann; A. C. S. Readhead; M. F. Aller; R. D. Blandford; I. Liodakis; M. L. Lister; P. Mróz; C. P. O’dea; T. J. Pearson; V. Ravi; M. Vallisneri; K. A. Cleary; M. J. Graham; K. J. B. Grainge; M. W. Hodges; T. Hovatta; A. Lähteenmäki; J.W. Lamb; T. J. W. Lazio; W. Max-moerbeck; V. Pavlidou; T. A. Prince; R. A. Reeves; M. Tornikoski; P. Vergara De La Parra; J. A. Zensus

doi:10.3847/2041-8213/ac504b

The Unanticipated Phenomenology of the Blazar PKS 2131–021: A Unique Supermassive Black Hole Binary Candidate

S. O’neill, S. Kiehlmann, A. C. S. Readhead, M. F. Aller, R. D. Blandford, I. Liodakis, M. L. Lister, P. Mróz, C. P. O’dea, T. J. Pearson, V. Ravi, M. Vallisneri, K. A. Cleary, M. J. Graham, K. J. B. Grainge, M. W. Hodges, T. Hovatta, A. Lähteenmäki, J.W. Lamb, T. J. W. LazioW. Max-moerbeck, V. Pavlidou, T. A. Prince, R. A. Reeves, M. Tornikoski, P. Vergara De La Parra, J. A. Zensus

Astronomy and Astrophysics Theory Group

Owens Valley Radio Observatory

Research output: Contribution to journal › Article › peer-review

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 ∼ 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 ∼ 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 4.6σ significance level, that the periodicity in this object is not due to random fluctuations in flux density. The observed period translates to 2.082 ± 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 resultsconstitute a compelling demonstration that the phenomenology, not the theory, must provide the lead in this field.

Keywords: galaxies: active, galaxies: jets, galaxies: BL Lacertae objects: individual (PKS 2131−021)

Original language	English
Pages (from-to)	L35
Journal	The Astrophysical Journal Letters
Volume	926
Issue number	2
Early online date	23 Feb 2022
DOIs	https://doi.org/10.3847/2041-8213/ac504b
Publication status	Published - 23 Feb 2022

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https://iopscience.iop.org/article/10.3847/2041-8213/ac504b

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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., ... Zensus, J. A. (2022). The Unanticipated Phenomenology of the Blazar PKS 2131–021: A Unique Supermassive Black Hole Binary Candidate. The Astrophysical Journal Letters, 926(2), L35. Advance online publication. https://doi.org/10.3847/2041-8213/ac504b

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title = "The Unanticipated Phenomenology of the Blazar PKS 2131–021: A Unique Supermassive Black Hole Binary Candidate",

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 ∼ 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 ∼ 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 analysesdemonstrate conclusively, at the 4.6σ significance level, that the periodicity in this object is not due to random fluctuations in flux density. The observed period translates to 2.082 ± 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 toPKS 2131−021 and searches using the techniques we have developed are strongly motivated. These resultsconstitute a compelling demonstration that the phenomenology, not the theory, must provide the lead in this field.Keywords: galaxies: active, galaxies: jets, galaxies: BL Lacertae objects: individual (PKS 2131−021)",

author = "S. O{\textquoteright}neill and S. Kiehlmann and Readhead, {A. C. S.} and Aller, {M. F.} and Blandford, {R. D.} and I. Liodakis and Lister, {M. L.} and P. Mr{\'o}z and O{\textquoteright}dea, {C. P.} and Pearson, {T. J.} and V. Ravi and M. Vallisneri and Cleary, {K. A.} and Graham, {M. J.} and Grainge, {K. J. B.} and Hodges, {M. W.} and T. Hovatta and A. L{\"a}hteenm{\"a}ki and J.W. Lamb and Lazio, {T. J. W.} and W. Max-moerbeck and V. Pavlidou and Prince, {T. A.} and Reeves, {R. A.} and M. Tornikoski and {Vergara De La Parra}, P. and Zensus, {J. A.}",

year = "2022",

month = feb,

day = "23",

doi = "10.3847/2041-8213/ac504b",

language = "English",

volume = "926",

pages = "L35",

journal = "The Astrophysical Journal Letters",

issn = "2041-8205",

publisher = "IOP Publishing Ltd",

number = "2",

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O’neill, S, Kiehlmann, S, Readhead, ACS, Aller, MF, Blandford, RD, Liodakis, I, Lister, ML, Mróz, P, O’dea, CP, Pearson, TJ, Ravi, V, Vallisneri, M, Cleary, KA, Graham, MJ, Grainge, KJB, Hodges, MW, Hovatta, T, Lähteenmäki, A, Lamb, JW, Lazio, TJW, Max-moerbeck, W, Pavlidou, V, Prince, TA, Reeves, RA, Tornikoski, M, Vergara De La Parra, P & Zensus, JA 2022, 'The Unanticipated Phenomenology of the Blazar PKS 2131–021: A Unique Supermassive Black Hole Binary Candidate', The Astrophysical Journal Letters, vol. 926, no. 2, pp. L35. https://doi.org/10.3847/2041-8213/ac504b

TY - JOUR

T1 - The Unanticipated Phenomenology of the Blazar PKS 2131–021: A Unique Supermassive Black Hole Binary Candidate

AU - O’neill, S.

AU - Kiehlmann, S.

AU - Readhead, A. C. S.

AU - Aller, M. F.

AU - Blandford, R. D.

AU - Liodakis, I.

AU - Lister, M. L.

AU - Mróz, P.

AU - O’dea, C. P.

AU - Pearson, T. J.

AU - Ravi, V.

AU - Vallisneri, M.

AU - Cleary, K. A.

AU - Graham, M. J.

AU - Grainge, K. J. B.

AU - Hodges, M. W.

AU - Hovatta, T.

AU - Lähteenmäki, A.

AU - Lamb, J.W.

AU - Lazio, T. J. W.

AU - Max-moerbeck, W.

AU - Pavlidou, V.

AU - Prince, T. A.

AU - Reeves, R. A.

AU - Tornikoski, M.

AU - Vergara De La Parra, P.

AU - Zensus, J. A.

PY - 2022/2/23

Y1 - 2022/2/23

N2 - 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 ∼ 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 ∼ 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 analysesdemonstrate conclusively, at the 4.6σ significance level, that the periodicity in this object is not due to random fluctuations in flux density. The observed period translates to 2.082 ± 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 toPKS 2131−021 and searches using the techniques we have developed are strongly motivated. These resultsconstitute a compelling demonstration that the phenomenology, not the theory, must provide the lead in this field.Keywords: galaxies: active, galaxies: jets, galaxies: BL Lacertae objects: individual (PKS 2131−021)

AB - 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 ∼ 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 ∼ 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 analysesdemonstrate conclusively, at the 4.6σ significance level, that the periodicity in this object is not due to random fluctuations in flux density. The observed period translates to 2.082 ± 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 toPKS 2131−021 and searches using the techniques we have developed are strongly motivated. These resultsconstitute a compelling demonstration that the phenomenology, not the theory, must provide the lead in this field.Keywords: galaxies: active, galaxies: jets, galaxies: BL Lacertae objects: individual (PKS 2131−021)

U2 - 10.3847/2041-8213/ac504b

DO - 10.3847/2041-8213/ac504b

M3 - Article

SN - 2041-8205

VL - 926

SP - L35

JO - The Astrophysical Journal Letters

JF - The Astrophysical Journal Letters

IS - 2

ER -

The Unanticipated Phenomenology of the Blazar PKS 2131–021: A Unique Supermassive Black Hole Binary Candidate

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