Browsing by Author "Hodges, M. W."
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Item New Tests of Milli-lensing in the Blazar PKS 1413 + 135(IOP Publishing Ltd., 2022-03-01) Peirson, A. L.; Liodakis, I.; Readhead, A. C.S.; Lister, M. L.; Perlman, E. S.; Aller, M. F.; Blandford, R. D.; Grainge, K. J.B.; Green, D. A.; Gurwell, M. A.; Hodges, M. W.; Hovatta, T.; Kiehlmann, S.; Lähteenmäki, A.; Max-Moerbeck, W.; McAloone, T.; O'Neill, S.; Pavlidou, V.; Pearson, T. J.; Ravi, V.; Reeves, R. A.; Scott, P. F.; Taylor, G. B.; Titterington, D. J.; Tornikoski, M.; Vedantham, H. K.; Wilkinson, P. N.; Williams, D. T.; Zensus, J. A.; Metsähovi Radio Observatory; Department of Electronics and Nanoengineering; Anne Lähteenmäki Group; Stanford University; University of Turku; California Institute of Technology; Purdue University; Florida Institute of Technology; University of Michigan, Ann Arbor; University of Manchester; University of Cambridge; Harvard University; Universidad de Chile; University of Crete; Universidad de Concepción; University of New Mexico; Netherlands Institute for Radio Astronomy; Max Planck Institute for Radio Astronomy; Foundation for Research and Technology - HellasSymmetric achromatic variability (SAV) is a rare form of radio variability in blazars that has been attributed to gravitational milli-lensing by a ∼102-105 M ⊙ mass condensate. Four SAVs have been identified between 1980 and 2020 in the long-term radio monitoring data of the blazar PKS 1413 + 135. We show that all four can be fitted with the same, unchanging, gravitational lens model. If SAV is due to gravitational milli-lensing, PKS 1413 + 135 provides a unique system for studying active galactic nuclei with unprecedented microarcsecond resolution, as well as for studying the nature of the milli-lens itself. We discuss two possible candidates for the putative milli-lens: a giant molecular cloud hosted in the intervening edge-on spiral galaxy, and an undetected dwarf galaxy with a massive black hole. We find a significant dependence of SAV crossing time on frequency, which could indicate a fast shock moving in a slower underlying flow. We also find tentative evidence for a 989 day periodicity in the SAVs, which, if real, makes possible the prediction of future SAVs: the next three windows for possible SAVs begin in 2022 August, 2025 May, and 2028 February.Item The Unanticipated Phenomenology of the Blazar PKS 2131-021: A Unique Supermassive Black Hole Binary Candidate(IOP Publishing Ltd., 2022-02-01) 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.; Vergara De La Parra, P.; Zensus, J. A.; Metsähovi Radio Observatory; Department of Electronics and Nanoengineering; Anne Lähteenmäki Group; California Institute of Technology; University of Michigan, Ann Arbor; Stanford University; University of Turku; Purdue University; University of Warsaw; University of Manitoba; Jet Propulsion Laboratory; University of Manchester; Universidad de Chile; University of Crete; Universidad de Concepción; Max Planck Institute for Radio AstronomyMost 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 similar to 0.001-0.01 pc. Our 45.1 yr radio light curve shows two epochs of strong sinusoidal variation with the same period and phase to within less than or similar to 2% and similar to 10%, respectively, straddling a 20 yr 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 +/- 0.003 yr 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 that 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.