Yaherlyn Diaz – Constraining the X-ray reflection in low accretion rate AGN using XMM-Newton, NuSTAR and Swift

Titre: Constraining the X-ray reflection in low accretion rate AGN using XMM-Newton, NuSTAR and Swift

Par : Yaherlyn Diaz

Abstract:
An interesting feature in AGN accreting at low rate is the weakness of the reflection features in their X-ray spectra, which can result from the gradual disappearance of the torus with decreasing accretion rates. It has been suggested that low luminosity AGN (LLAGN) would have a different reflector configuration compared with high luminosity AGN. Our purpose is to constrain the geometry and column density of the reflector in a sample of LLAGN covering a broad X-ray range of energy combining data from XMM-Newton + NuSTAR+Swift. We use XMM-Newton + NuSTAR + Swift observations of a hard X-ray-flux limited sample of 17 LLAGN from BASS/DR2 with accretion rates λ_Edd<10^−3. We fit all spectra using a reflection model for torus and accretion disk reflectors. We found a tentative correlation between the torus column density and the accretion rate, LLAGN shows a lower column density compared with the high-luminosity objects. We also confirm the relation between Γ and λ_Edd, with a smaller scatter than previously reported, thanks to the inclusion of high-energy data and the reflection models. Our results are consistent with a break at λ_Edd ~10^−3, suggestive of a different accretion mechanism compared with higher accretion AGN.