Discovery of an optical counterpart to the hyperluminous X-ray source in ESO 243-49

Abstract

The existence of black holes of masses ~ 10^2-10^5 Msun has important implications for the formation and evolution of star clusters and supermassive black holes. One of the strongest candidates to date is the hyperluminous X-ray source HLX1, possibly located in the S0-a galaxy ESO243-49, but the lack of an identifiable optical counterpart had hampered its interpretation. Using the Magellan telescope, we have discovered an unresolved optical source with R = (23.80 +/- 0.25) mag and V = (24.5 +/- 0.3) mag within HLX1's positional error circle. This implies an average X-ray/optical flux ratio ~ 500. Taking the same distance as ESO243-49, we obtain an intrinsic brightness M_R = (-11.0 +/- 0.3) mag, comparable to that of a massive globular cluster. Alternatively, the optical source is consistent with a main-sequence M star in the Galactic halo (for example an M4.4 star at ~ 2.5 kpc). We also examined the properties of ESO243-49 by combining Swift/UVOT observations with stellar population modelling. We found that the overall emission is dominated by a ~5 Gyr old stellar population, but the UV emission at ~2000 Ang is mostly due to ongoing star-formation at a rate of ~ 0.03 Msun/yr. The UV emission is more intense (at least a 9-sigma enhancement above the mean) North East of the nucleus, in the same quadrant as HLX1. With the combined optical and X-ray measurements, we put constraints on the nature of HLX1. We rule out a foreground star and a background AGN. Two alternative scenarios are still viable. HLX1 could be an accreting intermediate-mass black hole in a star cluster, which may itself be the stripped nucleus of a dwarf galaxy that passed through ESO243-49, an event which might have caused the current episode of star formation. Or, it could be a neutron star in the Galactic halo, accreting from an M4-M5 donor star.

7 pages, accepted by MNRAS. Several improvements from Oct 7 version: stronger evidence of the optical counterpart; more accurate estimate of its brightness (a factor of 2 brighter than previously estimated); use of a larger set of Swift/UVOT data to measure the recent star formation rate in ESO243-49; improved discussion and comparison of the competing scenarios

References in corpus (16)

• The ACS Virgo Cluster Survey. VIII. The Nuclei of Early-Type Galaxies
• Super-critically accreting stellar-mass black holes as ultraluminous X-ray sources
• The Second-Generation Guide Star Catalog: Description and Properties
• An Intermediate-mass Black Hole of Over 500 Solar Masses in the Galaxy ESO 243-49
• The Donor Stars of Cataclysmic Variables
• Quantifying the Coexistence of Massive Black Holes and Dense Nuclear Star Clusters
• New Limits on an Intermediate Mass Black Hole in Omega Centauri: II. Dynamical Models
• Masses, Beaming and Eddington Ratios in Ultraluminous X-ray Sources
• The Coincidence of Nuclear Star Clusters and Active Galactic Nuclei
• X-ray observations of ultraluminous X-ray sources
• On the evolution and fate of supermassive stars
• Recurrent gas accretion by massive star clusters, multiple stellar populations and mass thresholds for spherical stellar systems
• First evidence for spectral state transitions in the ESO243-49 hyper luminous X-ray source HLX-1
• Identification of the X-Ray Thermal Dominant State in an Ultraluminous X-Ray Source in M82
• On the compact nature of the most luminous ULX in the Cartwheel ring
• Study of NGC 5128 Globular Clusters Under Multivariate Statistical Paradigm

Cited by in corpus (46)

• Ultraluminous X-Ray Sources
• An expanded M_bh-sigma diagram, and a new calibration of active galactic nuclei masses
• The (black hole mass)-(host spheroid luminosity) relation at high and low masses, the quadratic growth of black holes, and intermediate-mass black hole candidates
• MOCCA Code for Star Cluster Simulations - IV. A new Scenario for Intermediate Mass Black Hole Formation in Globular Clusters
• Radio Detections During Two State Transitions of the Intermediate Mass Black Hole HLX-1
• X-ray Variability and Hardness of ESO 243-49 HLX-1: Clear Evidence for Spectral State Transitions
• Wandering Black Holes in Bright Disk Galaxy Halos
• Limits on intermediate-mass black holes in six Galactic globular clusters with integral-field spectroscopy
• Periodic Fast Radio Bursts from Luminous X-ray Binaries
• A Young Massive Stellar Population Around the Intermediate Mass Black Hole ESO 243-49 HLX-1
• Beyond Ellipse(s): Accurately Modelling the Isophotal Structure of Galaxies with $Isofit$ and $Cmodel$
• X-ray spectral variability in the ultraluminous X-ray source Holmberg IX X-1
• The M_BH - sigma relation for intermediate-mass black holes in globular clusters
• Detection of a $\sim$100,000 M${}_{\odot }$ black hole in M31's most massive globular cluster: A tidally stripped nucleus
• A new globular cluster black hole in NGC 4472
• Optical counterpart of HLX-1 during the 2010 outburst
• Kinematics of the intermediate mass black hole candidate HLX-1
• Linking the X-ray and infrared properties of star-forming galaxies at z<1.5
• The nature of the bright ULX X-2 in NGC3921: a Chandra position and HST candidate counterpart
• Combined Analysis of Hubble and VLT Photometry of the Intermediate Mass Black Hole ESO 243-49 HLX-1
• Expected intermediate mass black holes in the Virgo cluster. II. Late-type galaxies
• Outbursts of the intermediate-mass black hole HLX-1: a wind instability scenario
• Does the intermediate mass black hole in LEDA 87300 (RGG 118) follow the near-quadratic (M_bh)-(M_spheroid) relation?
• Optical variability of the accretion disk around the intermediate mass black hole ESO 243-49 HLX-1 during the 2012 outburst
• Searching for Intermediate Mass Black Holes in galaxies with Low Luminosity AGN: A multiple-method approach
• X-ray study of HLX1: intermediate-mass black hole or foreground neutron star?
• ESO 243-49 HLX-1: scaling of X-ray spectral properties and black hole mass determination
• The Second Nucleus of NGC 7727: Direct Evidence for the Formation and Evolution of an Ultracompact Dwarf Galaxy
• Understanding the environment around the intermediate mass black hole candidate ESO 243-49 HLX-1
• Eccentricity of HLX-1
• A minor merger scenario for the ultraluminous X-ray source ESO 243-49 HLX-1 - II. Constraints from photometry
• Investigation of X-ray timing and spectral properties of ESO 243-49 HLX-1 with long-term Swift Monitoring
• A Very Large Array Search for Intermediate-Mass Black Holes in Globular Clusters in M81
• Potential Black Hole Seeding of the Spiral Galaxy NGC 4424 via an Infalling Star Cluster
• Exploring the Nature of the Brightest Hyper-luminous X-ray Source
• A Multi-Wavelength Analysis of NGC 4178: A Bulgeless Galaxy with an AGN
• Optical study of the hyper-luminous X-ray source 2XMM J011942.7+032421
• Variability in Ultra-luminous X-ray Sources
• Refining the mass estimate for the intermediate-mass black hole candidate in NGC 3319
• HI study of the environment around ESO 243-49, the host galaxy of an intermediate mass black hole
• The Brightest Cluster X-ray Sources
• Relics of Galaxy Merging: Observational Predictions for a Wandering Massive Black Hole and Accompanying Star Cluster in the Halo of M31
• On the nature of high X-ray luminosities in SDSS galaxies
• Identification of Intermediate-mass Black Hole Candidates Among a Sample of Sd Galaxies
• Accretion disk parameters in HLX-1
• Radio Nebulæ from Hyper-Accreting X-ray Binaries as Common Envelope Precursors and Persistent Counterparts of Fast Radio Bursts