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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 notbeen detected before in deep X-ray observations, making it the most extremeX-ray weak quasar known today. This study aims to detect PG 0043+039 in a deepX-ray exposure. The question is what causes the extreme X-ray weakness of PG0043+039? Does PG 0043+039 show other spectral or continuum peculiarities? Wetook 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 LargeTelescope (SALT) in July, 2013. We have detected PG 0043+039 in our X-rayexposure taken in 2013. We presented our first results in a separate paper(Kollatschny et al. 2015). PG 0043+039 shows an extreme {\alpha}_ox gradient({\alpha}_ox =-2.37). Furthermore, we were able to verify an X-ray flux of thissource in a reanalysis of the X-ray data taken in 2005. At that time, it wasfainter by a factor of 3.8 +- 0.9 with {\alpha}_ox=-2.55. The X-ray spectrum iscompatible with a normal quasar power-law spectrum ({\Gamma}=1.70_-0.45^+0.57)with moderate intrinsic absorption (N_H=5.5_-3.9^+6.9 +- 10^21cm^-2) andreflection. The UV/optical flux of PG 0043+039 has increased by a factor of 1.8compared to spectra taken in the years 1990-1991. The FUV spectrum is highlypeculiar and dominated by broad bumps besides Ly{\alpha}. There is nodetectable Lyman edge associated with the BAL absorbing gas seen in the CIVline. PG 0043+039 shows a maximum in the overall continuum flux at around{\lambda} 2500{\AA} in contrast to most other AGN where the maximum is found atshorter wavelengths. All the above is compatible with an intrinsically X-rayweak quasar, rather than an absorbed X-ray emission.

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