Letter to the Editor

A quasi-periodic modulation of the radio light curve of the blazar PKS B0048-097

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany e-mail: mkadler@milkyway.gsfc.nasa.gov;ros@mpifr-bonn.mpg.de
² Exploration of the Universe Division, NASA Goddard Space Flight Center, Greenbelt Road, Greenbelt, MD 20771, USA
³ Astronomy Department, University of Michigan, Ann Arbor, MI 48109-1042, USA e-mail: [phughes;mfa;haller]@umich.edu

Received: 21 November 2005
Accepted: 23 May 2006

Abstract

In this letter we present the results of a wavelet analysis of the radio light curve of the BL Lac Object PKS B0048-097 from the University of Michigan Radio Astronomy Observatory monitoring program at 8 GHz during twenty-five years, from 1979 to 2004. The results show a remarkable periodicity of 450–470 days in the early 1980s that changed to a ~585 day periodicity in the late 1980s to early 1990s. A less pronounced ~400 day periodicity is found after . Very-long-baseline interferometry imaging at 15 GHz shows dramatic structural changes in the usually unresolved source between two epochs, 1995.57 and 2002.38. The pronounced northward directed jet seen in the 2002 image differs by more than 90° in direction from the source structure found in earlier epochs. These findings make PKS B0048-097 a primary target for multi-wavelength observations and intensive radio monitoring to decipher the blazar-variability phenomenon.