2016A&A...585A..18K

The object PG0043+039 has been identified as a broad absorption line (BAL) quasar based on its UV spectra. However, this optical luminous quasar has not been detected before in deep X-ray observations, making it the most extreme X-ray weak quasar known today. This study aims to detect PG0043+039 in a deep X-ray exposure. The question is what causes the extreme X-ray weakness of PG0043+039? Does PG0043+039 show other spectral or continuum peculiarities? We took simultaneous deep X-ray spectra with XMM-Newton, far-ultraviolet (FUV) spectra with the Hubble Space Telescope (HST), and optical spectra of PG0043+039 with the Hobby-Eberly Telescope (HET) and Southern African Large Telescope (SALT) in July, 2013. We have detected PG0043+039 in our X-ray exposure taken in 2013. We presented our first results in a separate paper (Kollatschny et al., 2015A&A...577L...1K). PG0043+039 shows an extreme α_ox gradient (α_ox=-2.37). Furthermore, we were able to verify an X-ray flux of this source in a reanalysis of the X-ray data taken in 2005. At that time, it was fainter by a factor of 3.8±0.9 with α_ox=-2.55. The X-ray spectrum is compatible with a normal quasar power-law spectrum (Γ=1.70_–0.45^+0.57) with moderate intrinsic absorption (N_H=5.5_–3.9^+6.9x10²¹cm^–2) and reflection. The UV/optical flux of PG0043+039 has increased by a factor of 1.8 compared to spectra taken in the years 1990-1991. The FUV spectrum is highly peculiar and dominated by broad bumps besides Lyα. There is no detectable Lyman edge associated with the BAL absorbing gas seen in the CIV line. PG0043+039 shows a maximum in the overall continuum flux at around λ≃2500Å in contrast to most other AGN where the maximum is found at shorter wavelengths. All the above is compatible with an intrinsically X-ray weak quasar, rather than an absorbed X-ray emission. Besides strong FeII multiplets and broad Balmer and HeI lines in the optical band we only detect a narrow [OII]λ3727 emission line and a BAL system in the CaHλ3968, CaKλ3934 lines (blueshifted by 4900km/s) and in the HeIλ3889 line (blueshifted by 5600km/s).