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Published June 2016 | Published
Journal Article Open

NuSTAR reveals the extreme properties of the super-Eddington accreting supermassive black hole in PG 1247+267

Abstract

PG1247+267 is one of the most luminous known quasars at z ~ 2 and is a strongly super-Eddington accreting supermassive black hole (SMBH) candidate. We obtained NuSTAR data of this intriguing source in December 2014 with the aim of studying its high-energy emission, leveraging the broad band covered by the new NuSTAR and the archival XMM-Newton data. Several measurements are in agreement with the super-Eddington scenario for PG1247+267: the soft power law (Γ = 2.3 ± 0.1); the weak ionized Fe emission line; and a hint of the presence of outflowing ionized gas surrounding the SMBH. The presence of an extreme reflection component is instead at odds with the high accretion rate proposed for this quasar. This can be explained with three different scenarios; all of them are in good agreement with the existing data, but imply very different conclusions: i) a variable primary power law observed in a low state, superimposed on a reflection component echoing a past, higher flux state; ii) a power law continuum obscured by an ionized, Compton thick, partial covering absorber; and iii) a relativistic disk reflector in a lamp-post geometry, with low coronal height and high BH spin. The first model is able to explain the high reflection component in terms of variability. The second does not require any reflection to reproduce the hard emission, while a rather low high-energy cutoff of ~100 keV is detected for the first time in such a high redshift source. The third model require a face-on geometry, which may affect the SMBH mass and Eddington ratio measurements. Deeper X-ray broad-band data are required in order to distinguish between these possibilities.

Additional Information

© 2016 ESO. Received 17 February 2016. Accepted 21 March 2016. Published online 13 May 2016. We thank the anonymous referee for constructive comments that have helped us to improve the quality of the paper. G.L. thanks F. Gastaldello for useful insights on NuSTAR background issues, E. Dalessandro for advice about HST data, and O. Shemmer for help with the Swift data. G.L. acknowledges financial support from the CIG grant "eEASY" No. 321913 and from ASI-INAF 2014-045-R.0 and ASI/INAF I/037/12/0–011/13 grants. A.C.F. acknowledges support from ERC grant 340442. FEB acknowledges support from CONICYT-Chile (Basal-CATA PFB-06/2007, FONDECYT Regular 1141218, "EMBIGGEN" Anillo ACT1101), the Ministry of Economy, Development, and Tourism's Millennium Science Initiative through grant IC120009, awarded to The Millennium Institute of Astrophysics, MAS.W.N.B. and B.L. acknowledges support from Caltech NuSTAR subcontract 44A-1092750. This work made use of data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by NASA. This research also made use of the NuSTAR Data Analysis Software (NuSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (USA).

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August 20, 2023
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October 20, 2023