Milli-arcsecond scale rotation measure in the CSS quasars 0548+165 and 1524-136

¹ Istituto di Radioastronomia, CNR, via P. Gobetti 101, Bologna, Italy
² University of New Mexico, Albuquerque, New Mexico 87131, USA
³ Scuola Internazionale Superiore di Studi Avanzati, via Beirut 4, 34014 Trieste, Italy
⁴ National Centre for Radio Astrophysics, TIFR, Post Bag 3, Ganeshkhind, Pune, 411007, India
⁵ Arecibo Observatory, HC3 Box 53995, Arecibo, Puerto Rico PR 00612, USA

Corresponding author: F. Mantovani, fmantovani@ira.bo.cnr.it

Received: 18 December 2001
Accepted: 3 March 2002

Abstract

Two Compact Steep-spectrum Sources (CSSs), 0548+165 and 1524-136, chosen from a list of CSSs with polarization percentages that decrease with decreasing frequency and high rotation measure values ( rad m^-2) on arcsecond scales, were observed with the VLBA at 4.9 and 8.4 GHz. RM values up to ≈ 10⁴ rad m^-2 were found in several regions along the jets in both sources. We suggest that a thin screen of magneto-ionic material with about 1 kpc thickness is responsible for these high RMs. The observed depolarization may be due to beam depolarization and/or inhomogeneities in the magnetic field.