The peculiar optical-UV X-ray spectra of the X-ray weak quasar PG 0043+039

Context. The object PG 0043+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. Aims. This study aims to detect PG 0043+039 in a deep X-ray exposure. The question is what causes the extreme X-ray weakness of PG 0043+039? Does PG 0043+039 show other spectral or continuum peculiarities? Methods. We took simultaneous deep X-ray spectra with XMM-Newton , far-ultraviolet (FUV) spectra with the Hubble Space Telescope (HST), and optical spectra of PG 0043+039 with the Hobby-Eberly Telescope (HET) and Southern African Large Telescope (SALT) in July, 2013. Results. We have detected PG 0043+039 in our X-ray exposure taken in 2013. We presented our first results in a separate paper (Kollatschny et al. ). PG 0043+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 +6.9 × 10 21 cm -2 ) and reflection. The UV/optical flux of PG 0043+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 Ly α . There is no detectable Lyman edge associated with the BAL absorbing gas seen in the CIV line. PG 0043+039 shows a maximum in the overall continuum flux at around λ ≈ 2500 A 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 [O ii] λ 3727 emission line and a BAL system in the CaH λ 3968, CaK λ 3934 lines (blueshifted by 4900 km s -1 ) and in the He i λ 3889 line (blueshifted by 5600 km s -1 ).