Low-redshift absorption in the Seyfert galaxy PG 1211+143 -- a distant inflow maintaining off-plane accretion or the gravitational redshift of matter orbiting the SMBH?

Abstract

The detection of a high velocity (~ 0.3c) inflow of highly ionized matter during an extended XMM-Newton observation of the luminous Seyfert galaxy PG 1211+143 in 2014 provided the first direct evidence of a short-lived accretion event, and an explanation for the powerful winds (UFOs) now recognised as a common property of many luminous Seyfert galaxies. Although the ultra-fast inflow - observed at a redshift of 0.483 - was detected in only one of seven spacecraft orbits, weaker (lower column) but more persistent absorption is seen - at a redshift of 0.123 - in the high exposure, soft X-ray (RGS) spectra summed over all 7 individual spacecraft orbits. Similar stacking of the higher energy (pn camera) spectra reveals underlying absorption at a redshift of 0.148. Interpreted, conventionally, as a Doppler redshift, the RGS observation indicates a line-of-sight inflow velocity v ~ 0.038c and (free-fall) radial location at 1400 R_g, with the higher redshift and ionization in pn camera spectra perhaps detecting that inflow closer to the black hole. A very different explanation would be absorption in matter subject to the strong gravity close to the SMBH, an interpretation supported by the launch of a new UFO in the final spacecraft orbit.