Abstract
Blueshifted absorption lines in the X-ray spectra of AGN show that ultra-fast outflows with typical velocities $v \sim 0.1c$ are a common feature of these luminous objects. Such powerful AGN winds offer an explanation of the observed M-$\sigma$ relation linking the mass of the supermassive black hole and the velocity dispersion in the galaxy's stellar bulge. An extended XMM-Newton study of the luminous Seyfert galaxy PG1211+143 recently revealed a variable multi-velocity wind. Here we report the detection of a short-lived, ultra-fast inflow during the same observation. Previous reports of inflows used single absorption lines with uncertain identifications, but this new result identifies an array of resonance absorption lines of highly ionised Fe, Ca, Ar, S and Si, sharing a common redshift when compared with a grid of realistic photoionization spectra. The redshifted absorption arises in a column of highly ionized matter close to the black hole, with a line-of-sight velocity, $v \sim 0.3c$, inconsistent with the standard picture of a plane circular accretion disc. This may represent the first direct evidence for chaotic accretion in AGN, where accretion discs are generally misaligned to the black hole spin. For sufficient inclinations, the Lense-Thirring effect can break the discs into discrete rings, which then precess, collide and shock, causing near free-fall of gas towards the black hole. The observed accretion rate for the reported infall is comparable to the hard X-ray luminosity in PG1211+143, suggesting that direct infall may be a significant contributor to inner disc accretion.
Highlights
It is well established that a supermassive black hole (SMBH) lies in the centre of most galaxies, and further that it accretes material through a disc
Over the past 15 yr, observations with a new generation of X-ray observatories (Jansen 2001; Mitsuda 2007) have revealed ultrafast outflows (UFOs), probably launched from regions of the disc accreting at super-Eddington rates (King & Pounds 2003) where the momentum in the radiation field released by accretion can overcome the inward pull from the black hole’s gravity
While the observation is of high significance only in the XMM–Newton orbit rev2659, the extreme redshift (∼0.48) and inflow velocity (∼0.3c) indicate absorption in a significant body of matter plunging towards the SMBH at ∼20 Rg
Summary
It is well established that a supermassive black hole (SMBH) lies in the centre of most galaxies, and further that it accretes material through a disc. Of particular relevance to this study are unidentified absorption lines at ∼4.56 and ∼5.33 keV in the Chandra observation of PG1211+143 (Reeves et al 2005) While these earlier reports hint at fast evolving and complicated dynamics in the inner disc, so far none has provided compelling evidence for a high-velocity inflow that could represent a direct challenge to the standard picture of a circular, planar disc slowly accreting on to the central black hole. Their opposed velocity fields create shocks that rob the gas of rotational support, allowing it to fall inwards towards the black hole where residual angular momentum causes the gas to re-circularize at a smaller radius Motivated by these theoretical ideas and the paucity of relevant observations, we have carried out a thorough search for rapidly inflowing matter, on a range of time-scales, as part of an ongoing orbit-by-orbit analysis of the hard X-ray data from the 2014 XMM– Newton observation of PG1211+143
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