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

Research output: Contribution to journalArticlepeer-review

  • External authors:
  • A. L. Peirson
  • I. Liodakis
  • A. C. S Readhead
  • M. L. Lister
  • E. S. Perlman
  • M. F. Aller
  • R. D. Blandford
  • 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. Ravi
  • R. A. Reeves
  • P. F. Scott
  • G. B. Taylor
  • D. J. Titterington
  • M. Tornikoski
  • H. K. Vedantham
  • P. N. Wilkinson
  • J. A. Zensus


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.

Bibliographical metadata

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