Lunch talk on Oct. 23, 2023

Soft X-ray excess in AGNs  - The “warm corona” interpretation

Speaker: Zeyuan Tang (Guanzhou University)

Venue: SWIFAR Building 2111

Time: 12:30 PM, Monday, Oct. 23, 2023

Abstract: 

AGN is one of the most powerful X-ray sources in the universe. Most AGN spectra show a soft X-ray excess (SE) above the 2–10 keV power law extrapolation. One popular interpretation is that, the formation of SE is due to the Comptonisation of disc photons in an optically-thick (τ ~10–40), warm (kT~0.1–1 keV) plasma (“warm corona”). While the warm corona has been widely used to explain the SE, its observed radiation flux in the actually physical environment has yet to be further studied. (1) For the first time, we calculate the relativistic warm coronal flux in high-accretion-rate systems. The numerical results show that the warm coronal flux generally rises first and then drops with increasing inclination. The flux rise is more significant for a compact and low-temperature warm corona and can reach 1–2 dexes. Meanwhile, the flux drop is significant if and only if the warm corona is heavily obscured due to the finite thickness. (2) We Monte Carlo simulate the Comptonisation process and then post-fit the output spectra by the popular code THCOMP. We find that a high seed photon temperature (>0.01 keV) will lead to underestimation of warm coronal temperature and optical depth, and an extreme high seed photon temperature (~0.07 keV) will lead to a blackbody-like SE.

Report PPT:  SWIFAR_Zeyuan Tang.pdf