NuSTAR J033202-2746.8: direct constraints on the Compton reflection in a heavily obscured quasar at z ≈ 2

A. Del Moro, J. R. Mullaney, D. M. Alexander, A. Comastri, F. E. Bauer, E. Treister, D. Stern, F. Civano, P. Ranalli, C. Vignali, J. A. Aird, D. R. Ballantyne, M. Baloković, S. E. Boggs, W. N. Brandt, Finn Erland Christensen, W. W. Craig, P. Gandhi, R. Gilli, C. J. HaileyF. A. Harrison, R. C. Hickox, S. M. LaMassa, G. B. Lansbury, B. Luo, S. Puccetti, M. Urry, W. W. Zhang

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    We report Nuclear Spectroscopic Telescope Array (NuSTAR) observations of NuSTAR J033202-2746.8, a heavily obscured, radio-loud quasar detected in the Extended Chandra Deep Field-South, the deepest layer of the NuSTAR extragalactic survey (∼400 ks, at its deepest). NuSTAR J033202-2746.8 is reliably detected by NuSTAR only at E > 8 keV and has a very flat spectral slope in the NuSTAR energy band (Γ = 0.55−0.64+0.62; 3-30 keV). Combining the NuSTAR data with extremely deep observations by Chandra and XMM-Newton (4 Ms and 3 Ms, respectively), we constrain the broad-band X-ray spectrum of NuSTAR J033202-2746.8, indicating that this source is a heavily obscured quasar (NH = 5.6+−0.80.9 × 1023 cm−2) with luminosity L10-40 keV ≈ 6.4 × 1044 erg s−1. Although existing optical and near-infrared (near-IR) data, as well as follow-up spectroscopy with the Keck and VLT telescopes, failed to provide a secure redshift identification for NuSTAR J033202-2746.8, we reliably constrain the redshift z = 2.00 ± 0.04 from the X-ray spectral features (primarily from the iron K edge). The NuSTAR spectrum shows a significant reflection component (R = 0.55+−0.370.44), which was not constrained by previous analyses of Chandra and XMM-Newton data alone. The measured reflection fraction is higher than the R∼0 typically observed in bright radio-loud quasars such as NuSTAR J033202-2746.8, which has L1.4 GHz≈1027 W Hz−1. Constraining the spectral shape of active galactic nuclei (AGNs), including bright quasars, is very important for understanding the AGN population, and can have a strong impact on the modeling of the X-ray background. Our results show the importance of NuSTAR in investigating the broad-band spectral properties of quasars out to high redshift.
    Original languageEnglish
    Article number16
    JournalAstrophysical Journal
    Issue number1
    Number of pages13
    Publication statusPublished - 2014


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