Chandra observations of five ultraluminous X-ray sources in nearby galaxies

Abstract

We report the results of a programme of dual-epoch Chandra ACIS-S observations of five ultraluminous X-ray sources (ULXs) in nearby spiral galaxies. All five ULXs are detected as unresolved, point-like X-ray sources by Chandra, though two have faded below the 10^39 erg/s luminosity threshold used to first designate these sources as ULXs. Using this same criterion, we detect three further ULXs within the imaged regions of the galaxies. The ULXs appear to be related to the star forming regions of the galaxies, indicating that even in ``normal'' spiral galaxies the ULX population is predominantly associated with young stellar populations. A detailed study of the Chandra ACIS-S spectra of six of the ULXs shows that five are better described by a powerlaw continuum than a multi-colour disc blackbody model, though there is evidence for additional very soft components to two of the powerlaw continua. The measured photon indices in four out of five cases are consistent with the low/hard state in black hole binaries, contrary to the suggestion that powerlaw-dominated spectra of ULXs originate in the very high state. A simple interpretation of this is that we are observing accretion onto intermediate-mass black holes, though we might also be observing a spectral state unique to very high mass accretion rates in stellar-mass black hole systems. Short-term flux variability is only detected in one of two epochs for two of the ULXs, with the lack of this characteristic arguing that the X-ray emission of this sample of ULXs is not dominated by relativistically-beamed jets. The observational characteristics of this small sample suggest that ULXs are a distinctly heterogeneous source class.

arXiv comment19 pages, 8 figures, accepted for publication in MNRAS. Version including full resolution figures available from http://www.star.le.ac.uk/~tro/papers/fiveulxs.pdf

References in corpus (62)

• Advection-Dominated Accretion and the Spectral States of Black Hole X-Ray Binaries: Application to Nova Muscae 1991
• A Search for "Dwarf" Seyfert Nuclei. III. Spectroscopic Parameters and Properties of the Host Galaxies
• Massive Black Holes as Population III Remnants
• Sources of Relativistic Jets in the Galaxy
• Ultraluminous X-Ray Sources in External Galaxies
• The runaway growth of intermediate-mass black holes in dense star clusters
• The Nature of Accreting Black Holes in Nearby Galaxy Nuclei
• Correlated X-ray Spectral and Timing Behavior of the Black Hole Candidate XTE J1550-564: A New Interpretation of Black Hole States
• The Nature of Ultra-Luminous Compact X-Ray Sources in Nearby Spiral Galaxies
• Production of Intermediate-Mass Black Holes in Globular Clusters
• The Updated Zwicky Catalog (UZC)
• Super-Eddington Fluxes from Thin Accretion Disks?
• Black Hole Winds
• Missing Link Found? --- The ``runaway'' path to supermassive black holes
• X-ray Spectroscopic Evidence for Intermediate Mass Black Holes: Cool Accretion Disks in Two Ultra--Luminous X-ray Sources
• Chandra High-Resolution Camera Observations of the Luminous X-Ray Source in the Starburst Galaxy M82
• Hubble Space Telescope Evidence for an Intermediate-Mass Black Hole in the Globular Cluster M15: II. Kinematical Analysis and Dynamical Modeling
• Chandra Observations of "The Antennae" Galaxies (NGC 4038/39)
• A ROSAT HRI survey of bright nearby galaxies
• A 20 Thousand Solar Mass Black Hole in the Stellar Cluster G1
• Population X: Are the super-Eddington X-ray sources beamed jets in microblazars or intermediate mass black holes?
• Long Term Variability of Cyg X-1 I. X-ray spectral-temporal correlations in the hard state
• A Catalog of Candidate Intermediate-luminosity X-ray Objects
• X-ray Spectral Properties of Low-Mass X-ray Binaries in Nearby Galaxies
• The X-ray Globular Cluster Population in NGC 1399
• Radio Emission from an Ultraluminous X-Ray Source
• The X-ray Source Population of "The Antennae" Galaxies: X-ray Properties from Chandra and Multiwavelength Associations
• On the central structure of M15
• Non-Nuclear Hyper/Ultraluminous X-Ray Sources in the Starbursting Cartwheel Ring Galaxy
• Chandra Observations of the Luminous IR Galaxy NGC3256
• External Compton emission from relativistic jets in Galactic black hole candidates and ultraluminous X-ray sources
• The X-ray Luminosity Function of "The Antennae" Galaxies (NGC4038/39) and the Nature of Ultra-Luminous X-ray Sources
• Discovery of Spectral Transitions from Two Ultra-Luminous Compact X-Ray Sources in Ic342
• Hubble Space Telescope Evidence for an Intermediate-Mass Black Hole in the Globular Cluster M15: I. STIS Spectroscopy and WFPC2 Photometry
• The optical counterpart of a Ultraluminous X-Ray Object in M81
• Blunting the Spike: the CV Minimum Period
• The unusual supernova remnant surrounding the ultraluminous X-ray source IC 342 X-1
• The runaway black hole GRO J1655-40
• The Ultra-luminous M81 X-9 source: 20 years variability and spectral states
• A Chandra observation of the interacting pair of galaxies NGC 4485/NGC 4490
• Ultraluminous X-ray Sources and Star Formation
• Chandra observations of the X-ray luminous star-forming galaxy merger Arp~299
• Another intermediate mass black hole in a starburst galaxy?: The luminous X-ray source in NGC 3628 reappears
• The Time-Variable Ultra-Luminous X-ray Sources of "The Antennae"
• Spectral variability of Ultra Luminous Compact X-ray Sources in Nearby Spiral Galaxies
• The identification of an optical counterpart to the super-Eddington X-ray source, NGC 5204 X-1
• A Chandra Study of the Circinus Galaxy Point-Source Population
• The Luminous X-ray Source Population in M51 Observed with Chandra
• A Variable Ultraluminous Supersoft X-ray Source in "The Antennae": Stellar-Mass Black Hole or White Dwarf?
• Chandra Observation of Luminous and Ultraluminous X-ray Binaries in M101
• The optical counterpart of the ultra-luminous x-ray source NGC 5204 X-1
• Chandra reveals a black-hole X-ray binary within the ultraluminous supernova remnant MF 16
• Another Interpretation of the Power-law type Spectrum of an Ultraluminous Compact X-ray Source in IC 342
• ASCA observations of the nearby galaxies Dwingeloo 1 and Maffei 1
• An Ultra-luminous X-Ray Object with a 2 hour period in M51
• The nature of ultra-luminous X-ray sources in NGC4565
• Multiwavelength study of the nuclei of a volume-limited sample of galaxies I: X-ray observations
• A Possible X-Ray Periodicity at Several Tens Hours of a Ultra-Luminous Compact X-Ray Source in IC 342
• Spectral variability of the nucleus of M33 in a Chandra-ACIS observation
• Multiple Components of the Luminous Compact X-ray Source at the Edge of Holmberg II observed by ASCA and ROSAT
• The dynamics of the nebula M1-67 around the run-away Wolf-Rayet star WR 124
• Flux enhancement in the inner region of a geometrically and optically thick accretion disk

Cited by in corpus (52)

• Ultraluminous X-Ray Sources
• The Ultraluminous State
• The Mid-IR Properties of Starburst Galaxies from Spitzer-IRS Spectroscopy
• X-ray source populations in galaxies
• The Ultra-Luminous X-ray Source Population from the Chandra Archive of Galaxies
• XMM-Newton observations of the brightest Ultraluminous X-ray sources
• Old and Young X-ray Point Source Populations in Nearby Galaxies
• A Complete Sample of ULX Host Galaxies
• X-ray observations of ultraluminous X-ray sources
• Low metallicity natal environments and black hole masses in Ultraluminous X-ray Sources
• The hard X-ray spectral evolution in X-ray binaries and its application to constrain the black hole mass of ultraluminous X-ray sources
• XMM-Newton Archival Study of the ULX Population in Nearby Galaxies
• Broad absorption features in wind-dominated ULXs?
• The star-forming environment of a ULX in NGC 4559: an optical study
• ULX spectra revisited: Accreting, highly magnetized neutron stars as the engines of ultraluminous X-ray sources
• Optical counterparts of the nearest ultraluminous X-ray sources
• On the weakness of disc models in bright ULXs
• On Relativistic Disk Spectroscopy in Compact Objects with X-ray CCD Cameras
• Testing the Paradigm that Ultraluminous X-ray Sources as a Class Represent Accreting Intermediate-Mass Black Holes
• A Hard X-Ray Study of Ultraluminous X-ray Source NGC 5204 X-1 with NuSTAR and XMM-Newton
• Near-infrared counterparts of ultraluminous X-ray sources
• New Hubble Space Telescope imaging of the counterparts to six ultraluminous X-ray sources
• Chandra monitoring observations of the ultraluminous X-ray source NGC 5204 X-1
• The Ultraluminous X-ray Sources near the Center of M82
• XMM-Newton view of the ultra-luminous X-ray sources in M51
• Geometrical Effect of Supercritical Accretion Flows: Observational Implications of Galactic Black-Hole Candidates and Ultraluminous X-ray Sources
• XMM-Newton observations of the starburst merger galaxies NGC 3256 & NGC 3310
• M74 X-1 (CXOU J013651.1+154547): An Extremely Variable Ultraluminous X-Ray Source
• The ultraluminous X-ray source population of NGC 4485/4490
• Investigating ULX accretion flows and cyclotron resonance in NGC 300 ULX1
• Two eclipsing ultraluminous X-ray sources in M 51
• An XMM-Newton view of M101 - II. Global X-ray source properties
• Non-LTE Spectra of Accretion Disks Around Intermediate-Mass Black Holes
• Uncovering Red and Dusty Ultraluminous X-ray Sources with Spitzer
• XMM-Newton Spectroscopy of Bright ULX Sources in the Antennae Galaxies (NGC 4038/4039)
• Detailed Atmosphere Model Fits to Disk-Dominated ULX Spectra
• Are Ultra-Luminous X-ray Sources Intermediate Mass Black Holes Accreting from Molecular Clouds?
• A Two Hour Quasi-Period in an Ultra-luminous X-Ray source in NGC628
• Young Crab-like pulsars and luminous X-ray sources in starbursts and optically dull galaxies
• Evolution of Intermediate-Mass Black Hole X-Ray Binaries
• An Inverse Look at the Center of M15
• Ultraluminous X-ray sources out to z~0.3 in the COSMOS field
• The Diffuse and Compact X-ray Components of the Starburst Galaxy Henize~2-10
• Spectral State Transitions of the Ultraluminous X-ray Source IC 342 X-1
• XMM-Newton observations of the interacting galaxy pairs NGC7771/0 and NGC2342/1
• Accretion of helium and metal-rich gas onto neutron stars and black holes at high luminosities
• Two Power-Law States of the Ultraluminous X-ray Source IC342 X-1
• Discovery of multiple ultraluminous X-ray sources in the galaxy KUG 0214-057
• Detection of Late-Time Optical Emission from SN 1941C in NGC 4136
• Direct Gravitational Imaging of Intermediate Mass Black Holes in Extragalactic Halos
• Ultraluminous X-ray sources in the group-centric elliptical galaxy NGC 5813
• Optical Light Curves of Luminous Eclipsing Black Hole X-ray Binaries