On the importance of special relativistic effects in modelling ultra-fast outflows

Abstract

Outflows are observed in a variety of astrophysical sources. Remarkably, ultra-fast ($v\ge 0.1c$), outflows in the UV and X-ray bands are often seen in AGNs. Depending on their energy and mass outflow rate, respectively ${\dot{E}}_{out},{\dot{M}}_{out}$, such outflows may play a key role in regulating the AGN-host galaxy co-evolution process through cosmic time. It is therefore crucial to provide accurate estimates of the wind properties. Here, we concentrate on special relativistic effects concerning the interaction of light with matter moving at relativistic speed relatively to the source of radiation. Our aim is to assess the impact of these effects on the observed properties of the outflows and implement a relativistic correction in the existing spectral modelling routines. We define a simple procedure to incorporate relativistic effects in radiative transfer codes. Following this procedure, we run a series of simulations to explore the impact of these effects on the simulated spectra, for different $v$ and column densities of the outflow. The observed optical depth is usually considered a proxy for the wind $N_H$, independently on its velocity. However, our simulations show that the observed optical depth of an outflow with a given column density $N_H$ decreases rapidly as the velocity of the wind approaches relativistic values. This, in turn, implies that when estimating $N_H$ from the optical depth, it is necessary to include a velocity-dependent correction, already for moderate velocities (e.g. $v\ge 0.05c$). This correction linearly propagates to the derived ${\dot{M}}_{out},{\dot{E}}_{out}$. As an example of these effects, we calculate the relativistically corrected values of ${\dot{M}}_{out}$ and ${\dot{E}}_{out}$ for a sample of $\sim 30$ Ultra-Fast Outflows taken from the literature, and find correction factors of $20-120\%$ within the observed range of outflowing velocities.

6 pages, 5 figures. Accepted for publication in A&A

References in corpus (5)

• First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole
• Wind from the black-hole accretion disk driving a molecular outflow in an active galaxy
• Feedback from Active Galactic Nuclei: Energy- versus momentum-driving
• A Compton-thick Wind in the High Luminosity Quasar, PDS 456
• The impact of accretion disk winds on the X-ray spectrum of AGN: Part 1 - XSCORT

Cited by in corpus (26)

• Ionized outflows from active galactic nuclei as the essential elements of feedback
• Structured ionized winds shooting out from a quasar at relativistic speeds
• Location and energetics of the ultra-fast outflow in PG 1448+273
• Tell-Tale Spectral Signatures of MHD-driven Ultra-Fast Outflows in AGNs
• Speed limits for radiation driven SMBH winds
• The WISSH quasars project X. Discovery of a multi-component and highly-variable UV ultra-fast outflow in a z=3.6 quasar
• Supermassive Black Hole Winds in X-rays -- SUBWAYS. III. A population study on ultra-fast outflows
• A New Emulated Monte Carlo Radiative Transfer Disk-Wind Model: X-Ray Accretion Disk-wind Emulator -- XRADE
• Impact of the disk magnetization on MHD disk wind signature
• Unraveling the structure of the stratified ultra-fast outflows in PDS 456 with XRISM
• The lively accretion disc in NGC 2992. III. Tentative evidence of rapid Ultra Fast Outflow variability
• Delving into the depths of NGC 3783 with XRISM III. Birth of an ultrafast outflow during a soft flare
• Ultra-high-energy cosmic rays from ultra-fast outflows of active galactic nuclei
• On the connection between AGN radiative feedback and massive black hole spin
• The XMM-Newton and NuSTAR view of IRASF11119+3257. I Detection of multiple UFO components and a very cold corona
• Black hole-galaxy co-evolution and the role of feedback
• XMM-Newton --NuSTAR monitoring campaign of the Seyfert 1 galaxy IC 4329A
• Winds of change: the nuclear and galaxy-scale outflows and the X-ray variability of 2MASS 0918+2117
• Poynting-Robertson effect on black-hole-driven winds
• Effect of radiation drag on the line-force-driven winds
• Leading-order gravitational time delay of massive particles by a moving Schwarzschild lens
• Multiphase Powerful Outflows Detected in High-z Quasars
• A New Member of the Fast and Furious Family: A Relativistic and Time-Variable UV Outflow in a Luminous Quasar
• Numerical simulations of the line-force-driven winds from active galactic nuclei: The special relativistic effects
• Wind-luminosity evolution in NLS1 AGN 1H 0707-495
• The extreme properties of the nearby hyper-Eddington accreting Active Galactic Nucleus in IRAS 04416+1215