New Tests of Milli-lensing in the Blazar PKS 1413 + 135

A. L. Peirson, I. Liodakis, A. C. S Readhead, M. L. Lister, E. S. Perlman, M. F. Aller, R. D. Blandford, K. J. B. Grainge, D. A. Green, M. A. Gurwell, M. W. Hodges, T. Hovatta, S. Kiehlmann, A. Lähteenmäki, W. Max-Moerbeck, T. Mcaloone, S. O’Neill, V. Pavlidou, T. J. Pearson, V. RaviR. A. Reeves, P. F. Scott, G. B. Taylor, D. J. Titterington, M. Tornikoski, H. K. Vedantham, P. N. Wilkinson, D. T. Williams, J. A. Zensus

Research output: Contribution to journalArticlepeer-review


Symmetric 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.

Original languageEnglish
Article number24
JournalThe Astrophysical Journal
Issue number1
Publication statusPublished - 1 Mar 2022


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