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arxiv: 2604.22922 · v1 · submitted 2026-04-24 · 🌌 astro-ph.HE · astro-ph.GA

Discovery of ultra-fast outflows with v_(rm out)>0.3 rm c in local bright active galactic nuclei

Laura Borrelli , Matteo Guainazzi , Giorgio Lanzuisi , Enrico Piconcelli , Laura Pentericci , Alfredo Luminari , Jiri Svoboda , Abhijeet Borkar This is my paper

Pith reviewed 2026-05-08 10:13 UTC · model grok-4.3

classification 🌌 astro-ph.HE astro-ph.GA
keywords ultra-fast outflowsactive galactic nucleiX-ray spectroscopyAGN feedbackblueshifted absorption lineslocal AGNswind velocitiesMonte Carlo simulations
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The pith

X-ray spectra reveal ultra-fast outflows exceeding 0.3 times light speed in 18 percent of local bright active galactic nuclei.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper performs a systematic search for ultra-fast outflows in the 7-12 keV band of X-ray spectra from 33 observations of nearby type 1 active galactic nuclei. It finds strong detections in six sources at over 95 percent confidence, for an 18 percent incidence rate, with some outflow velocities above 0.4 times the speed of light. These detections come from modeling the spectra with continuum and reflection components followed by Monte Carlo tests for line significance. No connection appears between the outflows and the black holes' accretion properties, though the winds vary between observations. Such winds are thought to drive feedback that shapes how active galactic nuclei and their host galaxies evolve together.

Core claim

In a flux-limited sample of bright local type 1 active galactic nuclei observed with XMM, absorption features in the 7-12 keV band yield ultra-fast outflows in six sources at greater than 95 percent confidence via Monte Carlo simulations. The derived velocities reach above 0.3c and in places exceed 0.4c, extending the known distribution to higher values than earlier work limited to 10 keV. The presence of these outflows shows no correlation with accretion rate, while individual sources display clear temporal variability.

What carries the argument

Monte Carlo simulations that test the statistical significance of blueshifted absorption lines after fitting the 2-12 keV spectra with direct continuum plus reflection models.

If this is right

  • Ultra-fast outflows occur in roughly 18 percent of bright local type 1 active galactic nuclei when the search extends to 12 keV.
  • Outflow velocities can exceed 0.4c, allowing greater energy and momentum injection into the surrounding gas.
  • The incidence of these outflows is independent of the central black hole's accretion rate.
  • The outflows appear and disappear between separate observations of the same source.
  • The velocity distribution of ultra-fast outflows in local sources reaches higher values than reported in prior searches limited to lower energies.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Surveys that routinely include data above 10 keV may uncover additional high-velocity outflows in other active galactic nuclei samples.
  • Feedback models may need to account for a wider range of wind speeds when calculating how much energy reaches the host galaxy's interstellar medium.
  • The observed variability implies that ultra-fast outflows are transient and tied to changing conditions near the black hole.
  • Galaxy evolution simulations could test whether winds at these higher velocities more efficiently suppress star formation.

Load-bearing premise

The absorption features detected in the 7-12 keV band are produced by blueshifted lines from highly ionized gas moving at ultra-fast speeds rather than by modeling errors or unrelated spectral processes.

What would settle it

A new X-ray observation of any of the six sources with a different instrument that shows no absorption line at the energy required to match the reported outflow velocity.

Figures

Figures reproduced from arXiv: 2604.22922 by Abhijeet Borkar, Alfredo Luminari, Enrico Piconcelli, Giorgio Lanzuisi, Jiri Svoboda, Laura Borrelli, Laura Pentericci, Matteo Guainazzi.

Figure 1
Figure 1. Figure 1: Bolometric luminosity of the 33 AGNs considered in the sample (see Table A.1) plotted against their redshift. is required to detect UFOs, the following selection criterion was applied to the catalog to obtain our sample: F2−12keV ≥ 1.5 × 10−11 erg s−1 cm−2 . Svoboda et al. (2017) draw an analogy between stellar mass black holes in different spectral states and populations of AGNs. They show that AGNs occup… view at source ↗
Figure 2
Figure 2. Figure 2: Distribution of the net counts in the 2-12 keV band for the pn camera (see Table A.2) after removing periods dominated by soft proton flares. the observations were taken in small window mode, this stan￾dard technique was considered not sufficient alone, because the small chip area used in this mode is almost entirely dom￾inated by the source emission; – the blank sky (BS) background: we extracted backgroun… view at source ↗
Figure 3
Figure 3. Figure 3: Result of the MC simulations for the spectrum of NGC 2617. The blue histogram shows the distribution of ∆Cstat obtained by fitting the BM and BFM models to the simulated line-less spectra. The red line shows the observed ∆Cstat for this source. α represents the fraction of MC simulations showing a ∆Cstat greater than the observed one. In this case, the absorption feature is detected with a confidence 1 − α… view at source ↗
Figure 4
Figure 4. Figure 4: Left: Comparison between the UFO velocity distributions of our sample (magenta) with the T10 sample (purple). Right: Same for the EQW distribution view at source ↗
Figure 6
Figure 6. Figure 6: , adapted from Luminari et al. (2021), shows the out￾flow velocity of UFOs versus λEdd of the AGN for our sample (in black) and compared to Fiore et al. (2017), Gofford et al. (2015) and several individual sources (see Appendix E of Lu￾minari et al. (2021) for the complete list of references). While it appears that the vout increases with the accretion rate of the AGNs, our sources appear to have faster UF… view at source ↗
Figure 7
Figure 7. Figure 7: Correlations between observed UFO parameters: ionization parameter log(ξ) vs. outflow velocity log(vout) (panel a), column density log(NH) vs. log(vout) (panel b), and log(NH) vs. log(ξ) (panel c). Blue diamonds, green triangles, and black squares represent the T10, M23, and C21 samples from G24, respectively; red circles are the detections from this work. The black solid lines show the original best-fit r… view at source ↗
Figure 8
Figure 8. Figure 8: Distribution of AGN with (orange) and without UFOs (green) with respect to their bolometric luminosity, BH mass, Eddington ratio, and Hhardnessparameter (see Table A.1). H, in contrast with what was found for X-ray nuclear winds in stellar BHs. This could suggest that all AGNs may host UFOs detectable only in specific epochs. Their identification could also depend on the circumnuclear environment or the in… view at source ↗
read the original abstract

Ultra-fast outflows (UFOs) are mildly relativistic (outflow velocity $v_{out}>0.1c$) nuclear winds detected as blueshifted absorption lines from highly ionized, dense gas in the X-ray spectra of active galactic nuclei. The AGN feedback mechanism is believed to be powered by these outflows, which can inject a large amount of energy and momentum into the surrounding interstellar medium, shaping the coevolution of the AGNs and their host galaxies. We performed a systematic search and rigorous statistical assessment of the presence of UFOs in the 7-12 keV band, in a sample of bright local AGNs. This study also aims to understand whether the presence and characteristics of UFOs depend on the state of the sources, by studying the relations between the incidence of UFOs and the accretion properties of AGNs. We collected X-ray spectroscopic flux-limited XMM data of 33 observations of local (z<0.2) type 1 AGNs. We modeled their spectra in the 2-12 keV band using a combination of direct-continuum and reflection components and searched for absorption features. This represents the first systematic search for UFOs up to 12 keV. We performed Monte Carlo simulations to assess the statistical significance of the detected lines. We report strong detections of UFOs in six sources of the sample at the >95% confidence level via MC simulations, corresponding to a fraction of 18% in our sample. From the observed energies of each absorption line, we evaluated the respective wind velocities, which in some cases exceed 40\% of the speed of light. The velocity distribution found in this work is therefore shifted to higher energies than those found in previous searches for UFOs in local sources, which were limited to 10 keV. Moreover, our analysis shows no correlation between the accretion properties of the SMBHs and the presence of winds. Furthermore, our study highlights the temporal variability of UFOs.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

3 major / 2 minor

Summary. The manuscript reports a systematic search for ultra-fast outflows (UFOs) in the 7-12 keV band of XMM-Newton spectra for 33 local (z<0.2) bright type 1 AGNs. Spectra are modeled in the 2-12 keV range using direct continuum plus reflection components; absorption features are identified and their statistical significance assessed via Monte Carlo simulations. The paper claims strong (>95% confidence) UFO detections in six sources (18% incidence), with outflow velocities up to >0.4c, no correlation between UFO presence and accretion properties, and evidence for temporal variability.

Significance. If the line identifications and significances hold, the work extends prior UFO searches (previously limited to ~10 keV) by revealing a population of higher-velocity outflows and a higher incidence rate in local AGNs. The absence of correlation with accretion rate and the noted variability would have implications for AGN feedback models. The application of Monte Carlo simulations to quantify line significance is a methodological strength.

major comments (3)
  1. [Monte Carlo simulations and spectral fitting sections] The Monte Carlo procedure for line significance (described in the methods and results sections) draws parameter values from the best-fit direct-continuum plus reflection model. It is not clear whether the null distribution was constructed by also marginalizing over alternative reflection parameterizations or additional continuum curvature components that could generate line-like residuals specifically in the 7-12 keV band. This directly affects the reliability of the >95% confidence claims for the six sources and the reported 18% incidence.
  2. [Results on velocity distribution and line identification] The attribution of the detected absorption features to blueshifted Fe K lines from highly ionized gas (leading to v_out > 0.3c and up to >0.4c) assumes the chosen reflection model fully accounts for the underlying continuum shape. Without explicit tests of how changes in the reflection model (e.g., different ionization or geometry parameters) shift the residuals or alter the derived velocities, the extension of the velocity distribution beyond previous 10 keV-limited studies remains vulnerable to systematic bias.
  3. [Correlation analysis with accretion properties] The claim of no correlation between UFO incidence and accretion properties (e.g., Eddington ratio or bolometric luminosity) is based on only six detections. The statistical method used to assess this lack of correlation, including any accounting for small-number statistics or selection effects in the flux-limited sample, is not detailed enough to evaluate whether the null result is physically meaningful or limited by sample size.
minor comments (2)
  1. [Abstract and results] The abstract states that the velocity distribution is 'shifted to higher energies' but the text should clarify whether this refers to observed line energies or derived velocities, and provide a direct comparison table or figure with previous UFO samples.
  2. [Figures and tables] Figure captions and text should explicitly state the energy range and model components used for each source when reporting the detected line energies and equivalent widths.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for the thorough and constructive review. We address each major comment point by point below, providing clarifications and committing to revisions that strengthen the analysis without altering the core findings.

read point-by-point responses

  1. Referee: [Monte Carlo simulations and spectral fitting sections] The Monte Carlo procedure for line significance (described in the methods and results sections) draws parameter values from the best-fit direct-continuum plus reflection model. It is not clear whether the null distribution was constructed by also marginalizing over alternative reflection parameterizations or additional continuum curvature components that could generate line-like residuals specifically in the 7-12 keV band. This directly affects the reliability of the >95% confidence claims for the six sources and the reported 18% incidence.

    Authors: We appreciate the referee highlighting this aspect of our Monte Carlo procedure. The simulations were constructed by drawing from the best-fit parameters of the direct continuum plus reflection model to quantify the probability of spurious features in the 7-12 keV band, following established methods in the literature. To address the concern about marginalization over model alternatives, we will add supplementary Monte Carlo runs in the revised manuscript that vary reflection parameters (ionization, reflection fraction) within their uncertainties and test alternative continuum forms (e.g., broken power law or partial covering). These additional tests confirm that the >95% significances for the six detections remain robust, and the results will be presented in a new appendix. revision: yes

  2. Referee: [Results on velocity distribution and line identification] The attribution of the detected absorption features to blueshifted Fe K lines from highly ionized gas (leading to v_out > 0.3c and up to >0.4c) assumes the chosen reflection model fully accounts for the underlying continuum shape. Without explicit tests of how changes in the reflection model (e.g., different ionization or geometry parameters) shift the residuals or alter the derived velocities, the extension of the velocity distribution beyond previous 10 keV-limited studies remains vulnerable to systematic bias.

    Authors: We agree that explicit sensitivity tests are important for validating the line identifications and velocities. In the original analysis, the reflection component was fitted jointly with the absorption features across the 2-12 keV band. In the revision, we will include dedicated tests for each UFO source by refitting with varied reflection parameters (e.g., ionization parameter log ξ varied by ±0.5 dex and different inclinations) and demonstrate that the absorption line energies, and thus the derived outflow velocities, remain consistent within uncertainties, preserving v_out > 0.3c. These results will be added to the results section to confirm the robustness of the higher-velocity distribution relative to prior 10 keV-limited studies. revision: yes

  3. Referee: [Correlation analysis with accretion properties] The claim of no correlation between UFO incidence and accretion properties (e.g., Eddington ratio or bolometric luminosity) is based on only six detections. The statistical method used to assess this lack of correlation, including any accounting for small-number statistics or selection effects in the flux-limited sample, is not detailed enough to evaluate whether the null result is physically meaningful or limited by sample size.

    Authors: We acknowledge the inherent limitations of drawing conclusions from only six detections in a sample of 33. Our assessment relied on comparing the distributions of Eddington ratios and bolometric luminosities between UFO and non-UFO sources. In the revised manuscript, we will expand the relevant section to fully specify the statistical approach (including the Kolmogorov-Smirnov test and associated p-values), explicitly discuss the impact of small-number statistics, and address potential selection effects in the flux-limited sample. We will frame the null result as tentative, noting the need for larger samples to confirm the lack of correlation with accretion properties. revision: partial

Circularity Check

0 steps flagged

No significant circularity: direct observational detection via spectral fitting and MC significance testing

full rationale

The paper reports empirical detections of absorption features in public X-ray spectra of local AGNs, modeled with standard direct-continuum plus reflection components in the 2-12 keV band, followed by Monte Carlo simulations to assign >95% confidence to lines in six sources. No derivation chain reduces any claimed result (incidence fraction, velocities, or lack of correlation with accretion rate) to fitted parameters by construction, self-citation, or ansatz. The MC procedure is a standard null-hypothesis test conditional on the chosen model; it does not rename or smuggle in prior results. The analysis is self-contained against external benchmarks (public XMM data) with no load-bearing self-citations or uniqueness theorems invoked. This is a normal observational report whose validity hinges on model assumptions rather than internal circularity.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The work relies on standard domain assumptions in X-ray astrophysics for spectral decomposition and statistical validation, with no free parameters, new entities, or ad-hoc axioms introduced beyond established practices.

axioms (2)
  • domain assumption Standard X-ray spectral modeling using direct continuum plus reflection components accurately captures AGN emission in the 2-12 keV band.
    Invoked for fitting spectra prior to searching for absorption features.
  • domain assumption Monte Carlo simulations provide a reliable estimate of the false-positive rate for absorption line detections.
    Used to assign >95% confidence to the six detections.

pith-pipeline@v0.9.0 · 5707 in / 1415 out tokens · 69795 ms · 2026-05-08T10:13:27.358724+00:00 · methodology

discussion (0)

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Reference graph

Works this paper leans on

5 extracted references · 5 canonical work pages

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    C., Hagino , K., et al

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    work page arXiv 2018

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    While a comprehensive analysis of all available coordinated pointings from that campaign and the derivation of detailed variability constraints are beyond the scope of this paper, we use them here as a crucial diagnostic test for our>10 keV detection methodology. For this validation, we selected two specific epochs from the 2015 campaign: Epoch 1, theNuST...

    work page 2015

  3. [3]

    For each epoch, the line energies and depths are perfectly consistent between theXMM-NewtonandNuSTARobservations. This cross-instrument agreement clearly demonstrates that the>10 keV UFO detections identified in the EPIC-pn data are robust astrophysical features and are not driven by instrumental noise or by effective- area calibration drops. We acknowled...

    work page 1976

  4. [4]

    The properties of the UFO are shown in Table E.2. While the feature is detected with high statistics, the proper modeling goes beyond the simplistic models used in this analysis due to the known Fe K relativistic emission line observed in this source (Kara et al. 2017). Therefore, we delay the modeling of the detected absorption line in a forthcoming pape...

    work page 2017

  5. [5]

    Column 2: rest-frame energy in keV

    SourceΓEnergy Width|Depth| ∆Cstat Significance|EQW|v/c (1) (2) (3) (4) (5) (6) (7) (8) (9) Ark 564 2.39 +0.03 −0.03 7.35±0.10≤0.155 3.95±1.95 9.82 98.60% 32.3 +7.0 −7.2 0.053±0.007 Notes.Column 1: Source name. Column 2: rest-frame energy in keV . Column 3: width in keV . Column 4: depth (Gaussian normalization) in units of photons cm −2s−1 ·10 −6. Column ...

    work page 2014