Proving strong magnetic fields near to the central black hole in the quasar PG0043+039 via cyclotron lines

¹ Institut für Astrophysik, Universität Göttingen, Friedrich-Hund Platz 1, 37077 Göttingen, Germany
e-mail: wkollat@astro.physik.uni-goettingen.de
² XMM-Newton Science Operations Centre, ESA, Villafranca del Castillo, Apartado 78, 28691 Villanueva de la Cañada, Spain
³ Osservatorio Astronomico di Brera (INAF), via Brera 28, 20121 Milano, Italy

Received: 27 February 2015
Accepted: 9 April 2015

Abstract

Context. The optical luminous quasar PG0043+039 has not been detected before in deep X-ray observations indicating the most extreme optical-to-X-ray slope index α_ox of all quasars.

Aims. This study aims to detect PG0043+039 in a deep X-ray exposure. Furthermore, we wanted to check out whether this object shows specific spectral properties in other frequency bands.

Methods. We took deep X-ray (XMM-Newton), far-ultraviolet (HST), and optical (HET, SALT telescopes) spectra of PG0043+039 simultaneously in July 2013.

Results. We just detected PG0043+039 in our deep X-ray exposure. The steep α_ox = −2.37 ± 0.05 gradient is consistent with an unusual steep gradient F_ν ~ ν^α with α = −2.67 ± 0.02 seen in the UV/far-UV continuum. The optical/UV continuum flux has a clear maximum near 2500 Å. The UV spectrum is very peculiar because it shows broad humps in addition to known emission lines. A modeling of these observed humps with cyclotron lines can explain their wavelength positions, their relative distances, and their relative intensities. We derive plasma temperatures of T ~ 3 keV and magnetic field strengths of B ~ 2 × 10⁸ G for the line-emitting regions close to the black hole.