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http://hdl.handle.net/20.500.12386/32256
Title: | The flaring X-ray corona in the quasar PDS 456 | Authors: | Reeves, J. N. BRAITO, Valentina Porquet, D. Lobban, A. P. Matzeu, G. A. NARDINI, EMANUELE |
Issue Date: | 2021 | Journal: | MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY | Number: | 500 | Issue: | 2 | First Page: | 1974 | Abstract: | New Swift monitoring observations of the variable, radio-quiet quasar, PDS 456, are presented. A bright X-ray flare was captured in 2018 September, the flux increasing by a factor of 4 and with a doubling time-scale of 2 d. From the light crossing argument, the coronal size is inferred to be ≲30 gravitational radii for a black hole mass of 10<SUP>9</SUP> M<SUB>⊙</SUB> and the total flare energy exceeds 10<SUP>51</SUP> erg. A hardening of the X-ray emission accompanied the flare, with the photon index decreasing from Γ = 2.2 to Γ = 1.7 and back again. The flare is produced in the X-ray corona, the lack of any optical or UV variability being consistent with a constant accretion rate. Simultaneous XMM-Newton and NuSTAR observations were performed, 1-3 d after the flare peak and during the decline phase. These caught PDS 456 in a bright, bare state, where no disc wind absorption features are apparent. The hard X-ray spectrum shows a high energy roll-over, with an e-folding energy of $E_{\rm fold}=51^{+11}_{-8}$ keV. The deduced coronal temperature, of kT = 13 keV, is one of the coolest measured in any AGN and PDS 456 lies well below the predicted pair annihilation line in X-ray corona. The spectral variability, becoming softer when fainter following the flare, is consistent with models of cooling X-ray coronae. Alternatively, an increase in a non-thermal component could contribute towards the hard X-ray flare spectrum. | URI: | http://hdl.handle.net/20.500.12386/32256 | URL: | https://academic.oup.com/mnras/article/500/2/1974/5944131 http://arxiv.org/abs/2010.14295v1 |
ISSN: | 0035-8711 | DOI: | 10.1093/mnras/staa3377 | Bibcode ADS: | 2021MNRAS.500.1974R | Fulltext: | open |
Appears in Collections: | 1.01 Articoli in rivista |
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staa3377.pdf | Pdf editoriale | 2.08 MB | Adobe PDF | View/Open |
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