NuSTAR J033202-2746.8: Direct Constraints on the Compton Reflection in a Heavily Obscured Quasar at z ≈ 2

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

Abstract

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 ($\Gamma =0.55^{+0.62}_{-0.64}$; 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 ($N_{\rm H}=5.6^{+0.9}_{-0.8}\times 10^{23}$ cm–2) with luminosity L 10-40 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 ($R=0.55^{+0.44}_{-0.37}$), 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 L 1.4 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.

Citation

Del Moro, A., Mullaney, J., Alexander, D., Comastri, A., Bauer, F., Treister, E., …Zhang, W. (2014). NuSTAR J033202-2746.8: Direct Constraints on the Compton Reflection in a Heavily Obscured Quasar at z ≈ 2. Astrophysical Journal, 786(1), https://doi.org/10.1088/0004-637x/786/1/16

• Journal Article Type: Article
• Publication Date: May 1, 2014
• Deposit Date: Jun 25, 2014
• Publicly Available Date: Aug 5, 2014
• Journal: Astrophysical Journal
• Print ISSN: 0004-637X
• Electronic ISSN: 1538-4357
• Publisher: American Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 786
• Issue: 1
• DOI: https://doi.org/10.1088/0004-637x/786/1/16
• Keywords: Galaxies: active, infrared: Galaxies, quasars: General, quasars: individual (NuSTAR J033202-2746.8), X-rays
• Public URL: https://durham-repository.worktribe.com/output/1424755