Multiwavelength continuum, emission line and BAL variability with prominent P V absorption in the X-ray-weakest quasar PG 0043+039^⋆

¹ Institut für Astrophysik und Geophysik, Universität Göttingen, Friedrich-Hund Platz 1, D-37077 Göttingen, Germany
² XMM-Newton Science Operations Centre, ESA, Villafranca del Castillo, Apartado 78, 28691 Villanueva de la Cañada, Spain
³ TPZ for ESA/ESAC, 28691 Villanueva de la Canada, Madrid, Spain

^⋆⋆ Corresponding author: wkollat@gwdg.de

Received: 1 April 2025
Accepted: 3 September 2025

Abstract

Context. PG 0043+039 has been identified as an extremely X-ray-weak quasar and as a peculiar broad-absorption-line quasar (BALQ) based on UV HST spectra.

Aims. This study aims to investigate the spectral properties and their variation in PG 0043+039 in more detail.

Methods. We took simultaneous deep X-ray observations of PG 0043+039 with XMM-Newton & NuSTAR, UV spectra with the HST, and optical spectra with the HET telescope in 2022.

Results. PG 0043+039 was an extreme low-X-ray-luminosity quasar in 2022. This AGN showed an extreme steep α_ox value of −2.47. These values are similar to those measured in 2005. The X-ray luminosity was a factor of 3.4 higher in the meantime in 2013. The optical and UV continuum only decreased by a factor of 1.3–1.5 from 2013 to 2022. Very strong emission-line intensity variations by factors of eight or more were observed in the O VI λ 1038 and Si IV λ 1403 lines between 2013 and 2022. The other UV emission lines such as Lyα only decreased by a factor of 1.4. The optical emission lines showed only minor intensity variations. We derive black hole masses of M = 6.95 × 10⁸ M_⊙ (based on Hβ) and M = 3.53 × 10⁸ M_⊙ (based on Mg IIλ2800). This corresponds to Eddington ratios of L/L_edd = 0.115 (Hβ) and 0.157 (Mg IIλ2800). PG 0043+039 exhibits strong and broad absorption lines in the UV. The highly ionized absorption lines show the largest velocity blueshifts in their broad absorption lines (BALs). Lower ionized BALs have smaller blueshifts. The P V absorption is very strong, with equivalent widths of 7–10 Å. PG 0043+039 shows strong Lyα emission despite strong P V absorption. PG 0043+039 is the only source with strong Lyα in the sample of strong P V absorbers. All the strong absorption-line troughs in the UV varied in unison in velocity space back and forward (−2000. ± 300. km s⁻¹, +2740. ± 200. km s⁻¹) without any major changes in absorption strength or in their profiles for the years 1991, 2013, and 2022. We found no general correlations of X-ray/opt/UV continuum variations with the broad absorption line variations. However, based on the simultaneous UV and X-ray observations – taken in 2013 and 2022 – we see higher maximum velocities of the blueshifted broad absorption lines in the UV when the X-ray flux was lower.