A Systematic Study of Variability in a Sample of Ultraluminous X-ray Sources

Abstract

We present results from a study of short term variability in 19 archival observations by XMM-Newton of 16 Ultraluminous X-ray Sources (ULXs). Eight observations (six sources) showed intrinsic variability with power spectra in the form of either a power law or broken power law-like continuum and in some cases quasi-periodic oscillations (QPOs). The remaining observations were used to place upper limits on the strength of possible variability hidden within. Seven observations (seven sources) yielded upper limits comparable to, or higher than, the values measured from those observations with detectable variations. These represented the seven faintest sources all with f_x < 3x10^-12 erg cm^-2 s^-1. In contrast there are four observations (three sources) that gave upper limits significantly lower than both the values measured from the ULX observations with detectable variations, and the values expected by comparison with luminous Galactic black hole X-ray binaries (BHBs) and Active Galactic Nuclei (AGN) in the observed frequency bandpass (10^-3 - 1 Hz). This is the case irrespective of whether one assumes characteristic frequencies appropriate for a stellar mass (10 M_sun) or an intermediate mass (1000 M_sun) black hole, and means that in some ULXs the variability is significantly suppressed compared to bright BHBs and AGN. We discuss ways to account for this unusual suppression in terms of both observational and intrinsic effects and whether these solutions are supported by our results.

12 pages, 5 figures, accepted by MNRAS

References in corpus (11)

• XMM-Newton observations of the brightest Ultraluminous X-ray sources
• X-ray observations of ultraluminous X-ray sources
• The variability plane of accreting compact objects
• A 62 Day X-Ray Periodicity and an X-Ray Flare from the Ultraluminous X-Ray Source in M82
• X-ray Variability of the Seyfert 1 Markarian 335: Power Spectrum and Time Lags
• A ULX microquasar in NGC 5408?
• Quasi Periodic Oscillations and Strongly Comptonized X-ray emission from Holmberg IX X-1
• Confirmation of the 62 Day X-Ray Periodicity from M82
• Chandra monitoring observations of the ultraluminous X-ray source NGC 5204 X-1
• Detailed Atmosphere Model Fits to Disk-Dominated ULX Spectra
• On the artificial nature of aperiodic variability in XMM-Newton observations of M31 X-ray sources and the ultraluminous X-ray source NGC 4559 ULX-7

Cited by in corpus (80)

• Ultraluminous X-Ray Sources
• Ultraluminous X-ray Sources in the Chandra and XMM-Newton Era
• Observational evidence for intermediate-mass black holes
• The ultraluminous state revisited: fractional variability and spectral shape as diagnostics of super-Eddington accretion
• 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
• Low metallicity natal environments and black hole masses in Ultraluminous X-ray Sources
• Ultraluminous X-ray sources
• The most extreme ultraluminous X-ray sources: evidence for intermediate-mass black holes?
• X-ray Variability and Hardness of ESO 243-49 HLX-1: Clear Evidence for Spectral State Transitions
• From ultraluminous X-ray sources to ultraluminous supersoft sources: NGC 55 ULX, the missing link
• Challenging times: a re-analysis of NGC 5408 X-1
• Broad absorption features in wind-dominated ULXs?
• Ultraluminous X-Ray Sources
• An Extremely Luminous and Variable Ultraluminous X-ray Source in the Outskirts of Circinus Observed with NuSTAR
• Optical counterparts of the nearest ultraluminous X-ray sources
• A new, clean catalogue of extragalactic non-nuclear X-ray sources in nearby galaxies
• Timing properties of ULX pulsars: optically thick envelopes and outflows
• A Tidal Flare Candidate in Abell 1795
• X-ray spectral evolution in M33 X-8
• The linear rms-flux relation in an Ultraluminous X-ray Source
• The Birth of an Ultra-Luminous X-ray Source in M83
• The origin of pulsating ultra-luminous X-ray sources: Low- and intermediate-mass X-ray binaries containing neutron star accretors
• Radio observations of extreme ULXs: revealing the most powerful ULX radio nebula ever or the jet of an intermediate-mass black hole?
• Ultra Luminous X-ray Sources: a deeper insight into their spectral evolution
• Lense-Thirring precession in ULXs as a possible means to constrain the neutron star equation-of-state
• The X-ray spectral evolution of the ultraluminous X-ray source Holmberg IX X-1
• A long-term X-ray monitoring of the ultraluminous X-ray source NGC 5408 X-1 with Swift reveals the presence of dips but no orbital period
• Time lags in the ultraluminous X-ray source NGC 5408 X-1: implications for the black hole mass
• Detection of Strong Short-Term Variability in NGC 6946 X-1
• A variable ULX and possible IMBH candidate in M51a
• Milliarcsec-scale radio emission of ultraluminous X-ray sources: steady jet emission from an intermediate-mass black hole?
• Comparing Spectral Models for ULXs with NGC 4517 ULX1
• Searching for Massive Outflows in Holmberg IX X-1 and NGC 1313 X-1: The Iron K Band
• X-ray time lags and nonlinear variability in the ultraluminous X-ray sources NGC 5408 X-1 and NGC 6946 X-1
• Discovery of a recurrent spectral evolutionary cycle in the ultra-luminous X-ray sources Holmberg II X-1 and NGC 5204 X-1
• NuSTAR and Chandra Insight into the Nature of the 3-40 keV Nuclear Emission in NGC 253
• The scaling of X-ray variability with luminosity in Ultra-luminous X-ray sources
• Uncovering Red and Dusty Ultraluminous X-ray Sources with Spitzer
• Evolution of the spectral curvature in the ULX Holmberg II X-1
• No Strong Geometric Beaming in the Ultraluminous Neutron Star Binary NGC 300 ULX-1 (SN 2010da) from Swift and Gemini
• Ultraluminous X-ray sources with flat-topped noise and QPO
• Discovery of a soft X-ray lag in the Ultraluminous X-ray Source NGC 1313 X-1
• Associated Spectral and Temporal State Transition of the bright ULX NGC1313 X-1
• Quasi-periodic dipping in the ultraluminous X-ray source, NGC 247 ULX-1
• Discovery of a Quasi-Periodic Oscillation in the Ultraluminous X-ray Source IC 342 X-1: XMM-Newton Results
• Hard and soft spectral states of ULXs
• Searching for coherent pulsations in ultraluminous X-ray sources
• Spectral variability in Swift and Chandra observations of the Ultraluminous source NGC 55 ULX1
• The ultraluminous X-ray source NGC 5643 ULX1: a large stellar mass black hole accreting at super-Eddington rates?
• The Ultraluminous X-ray sources population of the galaxy NGC 7456
• On the Nature of the mHz X-Ray Quasi-periodic Oscillations from Ultraluminous X-Ray Source M82 X-1: Search for Timing-Spectral Correlations
• Long-term X-ray Variability of Ultraluminous X-ray Sources
• Super-Eddington Accretion in the Ultraluminous X-ray Source NGC1313 X-2: An Ephemeral Feast
• Geometrical beaming of stellar mass ULXs
• The two Ultraluminous X-ray sources in the galaxy NGC 925
• The X-ray Properties of the Cometary Blue Compact Dwarf galaxies Mrk 59 and Mrk 71
• X-ray variability and energy spectra from NGC5408 X-1 with XMM-Newton
• Unveiling the disc structure in ultraluminous X-ray source NGC 55 ULX-1
• In-depth studies of the NGC 253 ULXs with XMM-Newton: remarkable variability in ULX1, and evidence for extended coronae
• Spectral state transitions in Circinus ULX5
• Investigating the nature of the ultraluminous X-ray sources in the galaxy NGC 925
• Measuring the black hole mass in Ultraluminous X-ray Sources with the X-ray Scaling Method
• Key results from an XMM-Newton and Chandra study of a new sample of extreme ULXs from the 2XMM catalogue
• X-ray properties of two transient ULX candidates in galaxy NGC 7090
• Revealing the nature of the ULX and X-ray population of the spiral galaxy NGC 4088
• The largest bright ULX population in a galaxy: X-ray variability and Luminosity Function in the Cartwheel ring Galaxy
• A transient ultraluminous X-ray source in NGC 55
• Evidence for Fe K${}_{\alpha }$ line and soft X-ray lag in NGC 7456 ULX-1
• Black-hole states in external galaxies
• Digging a little deeper: characterising three new extreme ULX candidates
• New Transient ULX Candidate in NGC 4254: Evidence of Circumbinary Disk?
• A search for periodicities from a ULX in the LINER galaxy NGC 4736
• Optical Counterparts of ULXs in Two Dwarf Galaxies: NGC 4861 and NGC 4449
• On the Black Hole Masses In Ultra-luminous X-ray Sources
• The hunt for new pulsating ultraluminous X-ray sources: a clustering approach
• The kilo-second variability of X-ray sources in nearby galaxies
• The aperiodic variability of the Ultraluminous X-ray source in NGC 5408
• Probing extreme black-hole outflows on short timescales via high spectral-resolution X-ray imagers
• The black hole in NGC 1313 X-2