Ionised Emission and Absorption in a Large Sample of Ultraluminous X-ray Sources

Abstract

Most Ultraluminous X-ray sources (ULXs) are thought to be powered by super-Eddington accretion onto stellar-mass compact objects. Accretors in this extreme regime are naturally expected to ionise copious amounts of plasma in their vicinity and launch powerful radiation-driven outflows from their discs. High spectral resolution X-ray observations (with RGS gratings onboard XMM-Newton) of a few ULXs with the best datasets indeed found complex line spectra and confirmed such extreme (0.1-0.3c) winds. However, a search for plasma signatures in a large ULX sample with a rigorous technique has never been performed, thereby preventing us from understanding their statistical properties such as the rate of occurrence, to constrain the outflow geometry and its duty cycle. We developed a fast method for automated line detection in X-ray spectra and applied it to the full RGS ULX archive, rigorously quantifying the statistical significance of any candidate lines. Collecting the 135 most significant features detected in 89 observations of 19 objects, we created the first catalogue of spectral lines detected in soft X-ray ULX spectra. We found that the detected emission lines are concentrated around known rest-frame elemental transitions and thus originate from low-velocity material. The absorption lines instead avoid these transitions, suggesting they were imprinted by blueshifted outflows. Such winds therefore appear common among the ULX population. Additionally, we found that spectrally hard ULXs show fewer line detections than soft ULXs, indicating some difference in their accretion geometry and orientation, possibly causing over-ionisation of plasma by the harder spectral energy distributions of harder ULXs.

arXiv commentAccepted for publication in MNRAS. 22 pages, 6 figures and 3 tables

References in corpus (45)

• The European Photon Imaging Camera on XMM-Newton: The MOS Cameras
• The eROSITA X-ray telescope on SRG
• An Ultraluminous X-ray Source Powered by An Accreting Neutron Star
• Ultraluminous X-Ray Sources in External Galaxies
• Statistics: Handle with Care, Detecting Multiple Model Components with the Likelihood Ratio Test
• Evidence for ultra-fast outflows in radio-quiet AGNs: I - detection and statistical incidence of Fe K-shell absorption lines
• Super-critically accreting stellar-mass black holes as ultraluminous X-ray sources
• Ultraluminous X-Ray Sources
• An Intermediate-mass Black Hole of Over 500 Solar Masses in the Galaxy ESO 243-49
• Chandra X-Ray Observatory (CXO):Overview
• An accreting pulsar with extreme properties drives an ultraluminous x-ray source in NGC 5907
• The Ultraluminous State
• The Chandra High Energy Transmission Grating: Design, Fabrication, Ground Calibration and Five Years in Flight
• Discovery of a 0.42-s pulsar in the ultraluminous X-ray source NGC 7793 P13
• Discovery of coherent pulsations from the Ultraluminous X-ray Source NGC 7793 P13
• X-ray Spectroscopic Evidence for Intermediate Mass Black Holes: Cool Accretion Disks in Two Ultra--Luminous X-ray Sources
• Discovery of pulsations from NGC 300 ULX1 and its fast period evolution
• The ultraluminous state revisited: fractional variability and spectral shape as diagnostics of super-Eddington accretion
• Resolved atomic lines reveal outflows in two ultraluminous X-ray sources
• Masses, Beaming and Eddington Ratios in Ultraluminous X-ray Sources
• A spectral-timing model for ULXs in the super-critical regime
• The ultraluminous X-ray sources NGC 1313 X-1 and X-2: a broadband study with NuSTAR and XMM-Newton
• Cross-Correlation and Maximum Likelihood Analysis: A New Approach to Combine Cross-Correlation Functions
• The discovery of weak coherent pulsations in the ultraluminous X-ray source NGC 1313 X-2
• Discovery of a 2.8 s pulsar in a 2 d orbit High-Mass X-ray Binary powering the Ultraluminous X-ray source ULX-7 in M51
• The XMM-Newton EPIC Background and the production of Background Blank Sky Event Files
• Evidence for a Variable Ultrafast Outflow in the Newly Discovered Ultraluminous Pulsar NGC 300 ULX-1
• From ultraluminous X-ray sources to ultraluminous supersoft sources: NGC 55 ULX, the missing link
• ISM composition through X-ray spectroscopy of LMXBs
• Broadband X-ray Spectra of the Ultraluminous X-ray Source Holmberg IX X-1 observed with NuSTAR, XMM-Newton and Suzaku
• An Extremely Luminous and Variable Ultraluminous X-ray Source in the Outskirts of Circinus Observed with NuSTAR
• An Iron K Component to the Ultrafast Outflow in NGC 1313 X-1
• X-ray evidence for a mildly relativistic and variable outflow in the luminous Seyfert 1 galaxy Mrk509
• Thermal radiation processes
• Searching for Outflows in Ultraluminous X-ray Sources Through High-Resolution X-ray Spectroscopy
• A deep XMM-Newton observation of the ultraluminous X-ray source HoII X-1 : the case against a 1000 solar mass black hole
• On the structure and energetics of quasar broad absorption-line outflows
• The 2019 super-Eddington outburst of RX J0209.6-7427: Detection of pulsations and constraints on the magnetic field strength
• On the evidence for narrow, relativistically shifted X-ray lines
• XMM-Newton Campaign On Ultraluminous X-ray Source NGC 1313 X-1: Wind vs. State Variability
• Thermal stability of winds driven by radiation pressure in super-Eddington accretion disks
• Accreting, highly magnetized neutron stars at the Eddington limit: A study of the 2016 outburst of SMC X-3
• Chandra reveals a possible ultra-fast outflow in the super-Eddington Be/X-ray binary Swift J0243.6+6124
• An ionised accretion disc wind in Hercules X-1
• Detection of a variable ultra-fast outflow in the Narrow Line Seyfert 1 galaxy PG 1448+273

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• Propeller states in locally super-critical ULXs
• Constraints on the ultra-fast outflows in the narrow-line Seyfert 1 galaxy Mrk 1044 from high-resolution time- and flux-resolved spectroscopy
• The long stare at Hercules X-1 -- I. Emission lines from the outer disk, the magnetosphere boundary and the accretion curtain
• On the nature of the ultraluminous X-ray source Holmberg II X-1
• Winds in ultraluminous X-ray sources: new challenges
• The ultraluminous X-ray source M81 X-6: a weakly magnetised neutron star with a precessing accretion disc?
• Hard X-ray flares and spectral variability in NGC 4395 ULX1
• The largest bright ULX population in a galaxy: X-ray variability and Luminosity Function in the Cartwheel ring Galaxy
• The High Energy X-ray Probe (HEX-P): Studying Extreme Accretion with Ultraluminous X-ray Sources
• Constraint on the accretion of NGC 6946 X-1 using broadband X-ray data
• Bubble in the Whale: Identifying the Optical Counterparts and Extended Nebula for the Ultraluminous X-ray Sources in NGC 4631
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• A NuSTAR study of quasi-periodic oscillations from the ultraluminous X-ray sources in M82
• Long-Term X-Ray/UV Variability in ULXs
• XMM-Newton multi-year campaign on NGC 55 ULX-1: Resolving the wind and its variability with RGS
• A Study of Spectral Variability between flaring and non-flaring state in M74 X-1
• Unveiling the biconical geometry of the outflow in the ultraluminous X-ray source NGC 5204 X-1
• Spectral and Temporal Properties of Ultra-luminous X-ray Source NGC 55 ULX1
• Probing extreme black-hole outflows on short timescales via high spectral-resolution X-ray imagers
• Ultraluminous X-ray sources in the first eROSITA survey I. Candidate catalogs