An Extremely Luminous and Variable Ultraluminous X-ray Source in the Outskirts of Circinus Observed with NuSTAR

Abstract

Following a serendipitous detection with the NuSTAR observatory, we present a multi-epoch spectral and temporal analysis of an extreme ultraluminous X-ray source (ULX) located in the outskirts of the Circinus galaxy, hereafter Circinus ULX5, including coordinated follow-up observations with XMM-Newton and NuSTAR. The NuSTAR data presented here represent one of the first instances of a ULX reliably detected at hard (E>10 keV) X-rays. Circinus ULX5 is variable on long timescales by at least a factor of ~5 in flux, and was caught in a historically bright state during our 2013 observations (0.3-30.0 keV luminosity of 1.6e40 erg/s). During this epoch, the source displayed a curved 3-10 keV spectrum, broadly similar to other bright ULXs. While in many cases the interpretation of spectral components in ULXs is uncertain, the spectral and temporal properties of the all the high quality datasets currently available strongly support a simple disk-corona model reminiscent of that invoked for Galactic binaries, with the accretion disk becoming more prominent as the luminosity increases. However, although the disk temperature and luminosity are remarkably well correlated across all timescales currently probed, the observed luminosity follows T^(1.70+/-0.17), flatter than that expected for simple blackbody radiation. The spectral variability displayed by Circinus ULX5 is highly reminiscent of that observed from some known Galactic black hole binaries (BHBs) at high luminosities. This comparison would imply a black hole mass of ~90 Msun for Circinus ULX5. However, given the diverse behavior observed from Galactic BHB accretion disks, this mass estimate is still uncertain. Finally, the limits placed on any undetected iron absorption features with the 2013 dataset imply that we are not viewing the central regions of Circinus ULX5 through any extreme super-Eddington outflow. [abridged]

18 pages, 15 figures, accepted for publication in ApJ

References in corpus (18)

• X-ray Properties of Black-Hole Binaries
• Modelling the behaviour of accretion flows in X-ray binaries
• Super-critically accreting stellar-mass black holes as ultraluminous X-ray sources
• XMM-Newton observations of the brightest Ultraluminous X-ray sources
• The magnetic nature of disk accretion onto black holes
• Masses, Beaming and Eddington Ratios in Ultraluminous X-ray Sources
• The ultraluminous X-ray sources NGC 1313 X-1 and X-2: a broadband study with NuSTAR and XMM-Newton
• X-ray observations of ultraluminous X-ray sources
• On the size and location of the X-ray emitting coronae around black holes
• Spectral State Transitions of the Ultraluminous X-ray Sources X-1 and X-2 in NGC 1313
• Supernova 1996cr: SN 1987A's Wild Cousin?
• Full Spectral Survey of Active Galactic Nuclei in the Rossi X-ray Timing Explorer Archive
• Optical Counterparts of Ultra-Luminous X-ray Sources identified from Archival Hubble Space Telescope/WFPC2
• X-ray Outflows and Super-Eddington Accretion in the Ultraluminous X-ray Source Holmberg IX X-1
• A bright ultraluminous X-ray source in NGC 5907
• Simultaneous X-ray and Radio Observations of Rotating Radio Transient J1819-1458
• Effects of local dissipation profiles on magnetized accretion disk spectra
• VLT/FORS2 observations of four high-luminosity ULX candidates

Cited by in corpus (71)

• The Evolution of Normal Galaxy X-ray Emission Through Cosmic History: Constraints from the 6 Ms Chandra Deep Field-South
• A spectral-timing model for ULXs in the super-critical regime
• NuSTAR Spectroscopy of Multi-Component X-ray Reflection from NGC 1068
• Evidence for Pulsar-like Emission Components in the Broadband ULX Sample
• NuSTAR catches the unveiling nucleus of NGC 1068
• The 2-79 keV X-ray Spectrum of the Circinus Galaxy with NuSTAR, XMM-Newton and Chandra: a Fully Compton-Thick AGN
• The Soft State of Cygnus X-1 Observed with NuSTAR: A Variable Corona and a Stable Inner Disk
• Diagnosing the accretion flow in ultraluminous X-ray sources using soft X-ray atomic features
• Broadband X-ray Spectra of the Ultraluminous X-ray Source Holmberg IX X-1 observed with NuSTAR, XMM-Newton and Suzaku
• NuSTAR and XMM-Newton Observations of NGC 1365: Extreme Absorption Variability and a Constant Inner Accretion Disk
• ULX spectra revisited: Accreting, highly magnetized neutron stars as the engines of ultraluminous X-ray sources
• Spectra of Black Hole Accretion Models of Ultra-Luminous X-ray Sources
• Determining the covering factor of Compton-thick active galactic nuclei with NuSTAR
• Spectral Changes in the Hyperluminous Pulsar in NGC 5907 as a Function of Super-Orbital Phase
• Super-Eddington Accretion onto the Neutron Star NGC 7793 P13: Broadband X-ray Spectroscopy and Ultraluminous X-ray Sources
• The Broadband XMM-Newton and NuSTAR X-ray Spectra of Two Ultraluminous X-ray Sources in the Galaxy IC 342
• Hot Dust Obscured Galaxies with Excess Blue Light: Dual AGN or Single AGN Under Extreme Conditions?
• Spectral and temporal properties of the ultra-luminous X-ray pulsar in M82 from 15 years of Chandra observations and analysis of the pulsed emission using NuSTAR
• NuSTAR Observations of the Compton-thick Active Galactic Nucleus and Ultraluminous X-ray Source Candidate in NGC 5643
• A tale of two periods: determination of the orbital ephemeris of the super-Eddington pulsar NGC 7793 P13
• Spatially Resolving a Starburst Galaxy at Hard X-ray Energies: NuSTAR, Chandra, AND VLBA Observations of NGC 253
• NuSTAR, XMM-Newton and Suzaku Observations of the Ultraluminous X-ray Source Holmberg II X-1
• NuSTAR and XMM-Newton observations of the extreme ultraluminous X-ray source NGC 5907 ULX1: A Vanishing Act
• A Hard X-Ray Study of Ultraluminous X-ray Source NGC 5204 X-1 with NuSTAR and XMM-Newton
• The Unusual Broadband X-ray Spectral Variability of NGC 1313 X-1 seen with XMM$-$Newton, Chandra and NuSTAR
• The X-ray spectral evolution of the ultraluminous X-ray source Holmberg IX X-1
• Anatomy of the AGN in NGC 5548: III. The high-energy view with NuSTAR and INTEGRAL
• Exploring the Overabundance of ULXs in Metal- and Dust-poor Local Lyman Break Analogs
• Ionised Emission and Absorption in a Large Sample of Ultraluminous X-ray Sources
• Revisiting the ultraluminous supersoft source in M101: an optically thick outflow model
• Nature of the Extreme Ultraluminous X-ray Sources
• The dust-gas AGN torus as constrained from X-ray and mid-infrared observations
• Periodic signals from the Circinus region: two new cataclysmic variables and the ultraluminous X-ray source candidate GC X-1
• The Broadband Spectral Variability of Holmberg IX X-1
• A Focused, Hard X-ray Look at Arp 299 with NuSTAR
• A new candidate pulsating ULX in NGC 7793
• X-ray time lags and nonlinear variability in the ultraluminous X-ray sources NGC 5408 X-1 and NGC 6946 X-1
• X-Ray Spectral Variability of Ultraluminous X-Ray Sources in Extragalactic Globular Clusters
• A Hard X-ray Study of the Normal Star-Forming Galaxy M83 with NuSTAR
• $NuSTAR$ Observations of Four Nearby X-ray Faint AGN: Low Luminosity or Heavy Obscuration?
• The hyperluminous X-ray source candidate in IC 4320: another HLX bites the dust
• CG X-1: an eclipsing Wolf-Rayet ULX in the Circinus galaxy
• Ultraluminous X-ray sources: three exciting years
• Patchy Accretion Disks in Ultraluminous X-ray Sources
• Black Holes and Neutron Stars in Nearby Galaxies: Insights from NuSTAR
• A search for hyperluminous X-ray sources in the XMM-Newton source catalog
• The ultraluminous X-ray source NGC 5643 ULX1: a large stellar mass black hole accreting at super-Eddington rates?
• Super-Eddington accretion onto a stellar mass ultraluminous X-ray source NGC 4190 ULX1
• Average bolometric corrections and optical to X-ray flux measurements as a function of accretion rate for X-ray binaries
• The two Ultraluminous X-ray sources in the galaxy NGC 925
• Hard X-ray/Soft gamma-ray experiments and missions: overview and prospects
• On the X-ray Spectral Energy Distributions of Star-Forming Galaxies: the 0.3-30 keV Spectrum of the Low-Metallicity Starburst Galaxy VV 114
• Identification of the Hard X-ray Source Dominating the E > 25 keV Emission of the Nearby Galaxy M31
• NuSTAR and XMM-Newton observations of the ultraluminous X-ray source NGC 5643 X-1
• Variability in Ultra-luminous X-ray Sources
• Spectral state transitions in Circinus ULX5
• Investigating the nature of the ultraluminous X-ray sources in the galaxy NGC 925
• NuSTAR observations of the ultraluminous X-ray source M33 X-8: a black hole in a very high state?
• Origins of the UV/X-ray Relation in Arakelian 120
• Simultaneous NICER and NuSTAR observations of the Ultraluminous source NGC 4190 ULX-1
• Multi-epoch hard X-ray view of Compton-thick AGN Circinus Galaxy
• Hard X-ray flares and spectral variability in NGC 4395 ULX1
• The High Energy X-ray Probe (HEX-P): Studying Extreme Accretion with Ultraluminous X-ray Sources
• The largest bright ULX population in a galaxy: X-ray variability and Luminosity Function in the Cartwheel ring Galaxy
• Ultra Luminous X-ray sources - new distance indicators?
• NGC 2403 XMM4: evidence for a super-Eddington neutron star with a possible transient pulsation
• Synchrotron cutoff in Ultraluminous X-ray sources
• Spectral variability in NGC 1042 ULX1
• A NuSTAR Census of the X-ray Binary Population of the M31 Disk
• A Multi-Mission Catalogue of Ultraluminous X-ray Source Candidates
• Time Domain Astronomy with the THESEUS Satellite