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Detection of low-redshift absorption in the luminous Seyfert galaxy PG 1211+143 -- a slow, distant inflow feeding accretion or the gravitational redshift from a ring of matter close to the SMBH ?

Ken PoundsKim Page (University of Leicester)
Nov 2023
The detection of a high velocity (~ 0.3c) inflow of highly ionized matter during a long XMM-Newton observation of the luminous Seyfert galaxy PG 1211+143 in 2014 offered the first direct observational evidence of a short-lived accretion event, where matter approaching at a high inclination to the black hole spin plane may result in warping and tearing of the inner accretion disc, with subsequent inter-ring collisions producing shocks, loss of rotational support and rapid mass infall. In turn, such accretion events provide an explanation for the ultrafast outflows (UFOs) now recognised as a common property of many luminous Seyfert galaxies. While the ultra-fast inflow in PG 1211+143 was detected in only one of 7 spacecraft orbits, a weaker (lower column density) inflow, at a much lower redshift of ~ 0.123, is revealed in the soft x-ray spectrum by summing RGS data over the full 5-weeks XMM-Newton campaign. Modelling of the simultaneous, stacked pn data finds evidence for a similar low redshift absorption component in a previously unexplained feature on the low energy wing of the Fe K emission line complex near 6 keV. We briefly consider Doppler and strong gravity explanations for the observed redshift, with the former indicating a distant inflow feeding off-plane accretion, where an infall velocity of v ~ 0.038c and (free-fall) radius at 1400 R$_{g}$ lies beyond the tearing radius for PG 1211+143, but still within the sphere of influence of the SMBH. An intriguing alternative, recently given added credence, might be as the gravitational redshift of absorption in matter orbiting the SMBH at a radius of ~ 27 R_g. In the latter case the narrow RGS absorption line spectrum constrains the thickness of the orbiting ring due to the strong velocity shear so close to the hole.
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