The flaring X-ray corona in the quasar PDS 456
Monthly Notices of the Royal Astronomical Society, ISSN: 1365-2966, Vol: 500, Issue: 2, Page: 1974-1991
2020
- 16Citations
- 10Captures
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Article Description
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 109 M⊙ and the total flare energy exceeds 1051 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 Efold=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.
Bibliographic Details
http://www.scopus.com/inward/record.url?partnerID=HzOxMe3b&scp=85097484992&origin=inward; http://dx.doi.org/10.1093/mnras/staa3377; https://academic.oup.com/mnras/article/500/2/1974/5944131; http://academic.oup.com/mnras/article-pdf/500/2/1974/34463203/staa3377.pdf; http://academic.oup.com/mnras/advance-article-pdf/doi/10.1093/mnras/staa3377/34068295/staa3377.pdf; https://dx.doi.org/10.1093/mnras/staa3377
Oxford University Press (OUP)
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