Sep 8 – 13, 2019
Europe/Rome timezone
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First measurement of coronal properties in two luminous, high-z QSOs

Sep 11, 2019, 10:40 AM
15m

Speaker

Dr Giorgio Lanzuisi (INAF-OAS)

Description

X-ray emission from AGN is believed to be produced via Comptonization of optical/UV seed photons emitted by the accretion disk, up-scattered by hot electrons in a corona surrounding the black hole. A critical compactness vs. temperature threshold is predicted above which any increase in the source luminosity would generate positron-electron pairs rather than continue heating the coronal plasma.
Current observations seem to confirm that all AGN populate the region below this critical line. Pair production models, however, have never been probed by observations in the high-luminosity regime, where the critical line is expected to reach low temperatures.
To fill this observational gap, we selected two luminous (log(LBol)>47.5 erg/s) quasars, 2MASSJ1614 (z=1.86) and B1422 (z=3.62), and obtained XMM and NuSTAR deep observations. We performed detailed spectral analysis of their quasi-simultaneous soft and hard X-ray data, in order to constrain the parameters of their coronae.
Using a phenomenological cut-off power-law model plus reflection, we derived rest-frame values of the high energy cut-off of Ecut=106+102-37 keV and Ecut=66+17-12 keV, respectively. Comptonization models consistently give as best-fit parameters electron temperatures of ∼45 keV and ∼28 keV, and optically thick coronae (τ >1). These low coronal temperatures fall in the limited region allowed at these luminosities to avoid runaway pair production.

Affiliation INAF-OAS
Topic Active Galactic Nuclei: accretion physics and evolution across cosmic time

Primary author

Dr Giorgio Lanzuisi (INAF-OAS)

Co-authors

Stefano Bianchi (Università degli Studi Roma Tre) Prof. Niel Brandt (Penn State University) Marcella Brusa (Istituto Nazionale di Astrofisica (INAF)) Massimo Cappi (Istituto Nazionale di Astrofisica (INAF)) Prof. George Chartas (Department of Physics and Astronomy, College of Charleston) Dr Francesca Civano (Harvard-Smithsonian centre for Astrophysics) Andrea Comastri (Istituto Nazionale di Astrofisica (INAF)) Mauro Dadina (Istituto Nazionale di Astrofisica (INAF)) Massimo Gaspari (Princeton University) Roberto Gilli (Istituto Nazionale di Astrofisica (INAF)) Andrea Marinucci (Università Roma Tre) Riccardo Middei (Università degli Studi Roma Tre) Enrico Piconcelli (Istituto Nazionale di Astrofisica (INAF)) Francesco Tombesi (University of Rome "Tor Vergata") Cristian Vignali (Dipartimento di Fisica e Astronomia, Università di Bologna)

Presentation materials