Multiwavelength continuum, emission line and BAL variability with prominent PV absorption in the X-ray-weakest quasar PG0043+039

TL;DR

This paper presents a tightly coordinated multiwavelength study of the X-ray-weak BAL quasar PG 0043+039, using simultaneous XMM-Newton and NuSTAR X-ray data with HST UV spectra and HET optical spectra in 2022. It documents extreme X-ray faintness (α_{ox} ≈ −2.47) and substantial UV line variability, notably dramatic changes in O VI 1038 and Si IV 1403, alongside persistent, broad PV BALs with saturated absorption. Across epochs (1991, 2013, 2022), UV BALs shift in velocity space while maintaining similar profiles, and no general continuum-BAL correlation is found; however, UV BAL maximum velocities increase when the X-ray flux drops, suggesting a link between the ionizing continuum and disk-wind dynamics. The derived Eddington ratios (≈0.12–0.16) and mass estimates place PG 0043+039 in a moderately high accretion regime, with a red-to-blue evolution of the far-UV spectrum indicating a evolving spectral energy distribution and potential changes in the shielding/absorption geometry. The work highlights the complex interplay between X-ray emission, BAL winds, and optical/UV emission-line regions in a highly unusual quasar, with implications for wind-launching mechanisms and accretion physics in extreme accretors.

Abstract

PG0043+039 has been identified as an extremely X-ray-weak quasar and as a peculiar broad-absorption-line quasar based on UV HST spectra. We took simultaneous deep X-ray observations of PG0043+039 with XMM-Newton and NuSTAR, UV spectra with the HST, and optical spectra with the HET telescope in 2022. PG0043+039 was an extreme low-X-ray-luminosity quasar in 2022. This AGN showed an extreme steep alpha_oX value of -2.47. 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 OVI_1038 and SiIV_1403 lines between 2013 and 2022. The other UV emission lines such as Ly_alpha only decreased by a factor of 1.4. We derived a black hole mass of M=6.95*10^{8} M_solar (based on H_beta). This corresponds to an Eddington ratio of L/L_edd = 0.115. PG0043+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. The PV absorption is very strong, with equivalent widths of 7 - 10 AA. PG0043+039 shows strong Ly_alpha emission despite strong PV absorption. All the strong absorption-line troughs in the UV varied in unison in velocity space back and forward (-2000.+-300.kms-1, +2740.+-200.kms-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.

Figures (24)

• Figure 1: Hubble Space Telescope UV spectrum of PG 0043+039 taken in July, 2022. The location of possible emission lines is indicated above the spectrum (in black). Absorption troughs are indicated below the spectrum (in red).
• Figure 2: Observed optical spectrum of PG 0043+039 from July, 2022
• Figure 3: Combined UV-optical spectrum of PG 0043+039 in 2022. A power-law model (in red) was fit to the continuum, giving a spectral index of $\alpha=1.317$. The spectral regions that were used for deriving the power-law slope of the continuum are shown in gray.
• Figure 4: Optical spectra of PG 0043+039 taken in 2022, as well as in the years 2013, 2019, and 2024.
• Figure 5: Mean optical spectrum of PG 0043+039 based on years 2013, 2019, 2022, and 2024. The mean spectrum shortward of 3173 Å (dashed line) is lower because it is based on three spectra only (2019, 2022, 2024).