The Antennae Ultraluminous X-Ray Source, X-37, Is A Background Quasar

Abstract

In this paper we report that a bright, X-ray source in the Antennae galaxies (NGC 4038/9), previously identified as an ultra-luminous X-ray source, is in fact a background quasar. We identify an isolated infrared and optical counterpart within 0.3+/-0.5 arcseconds the X-ray source X-37. After acquiring an optical spectrum of its counterpart, we use the narrow [OIII] and broad H_alpha emission lines to identify X-37 as a quasar at a redshift of z=0.26. Through a U, V, and K_s photometric analysis, we demonstrate that most of the observable light along this line of sight is from the quasar. We discuss the implications of this discovery and the importance of acquiring spectra for optical and IR counterparts to ULXs.

11 pages, 3 Postscript figures, accepted by ApJL

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Cited by in corpus (17)

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• Ultraluminous X-ray Sources in the Chandra and XMM-Newton Era
• Optical emission from massive donors in ULX binary systems
• On the association of the ultraluminous X-ray sources in the Antennae galaxies with young stellar clusters
• Testing the Paradigm that Ultraluminous X-ray Sources as a Class Represent Accreting Intermediate-Mass Black Holes
• A Redshift for the Intermediate Mass Black Hole Candidate HLX-1: Confirmation of its Association with the Galaxy ESO 243-49
• Optical Counterparts of Ultra-Luminous X-ray Sources identified from Archival Hubble Space Telescope/WFPC2
• Optical Counterparts of Ultra Luminous X-ray Sources
• Optical Counterparts of Ultraluminous X-Ray Sources
• X-Ray Sources in the Star Forming Galaxies NGC 4194 and NGC 7541
• A Comparison of Ultraluminous X-ray Sources in NGC 1399 and the Antennae Galaxies (NGC 4038/4039)
• X-ray Binaries and Star Clusters in the Antennae: Optical Cluster Counterparts
• Toward a Clean Sample of Ultra-Luminous X-ray Sources
• Infrared Counterparts to Chandra X-Ray Sources in the Antennae
• Multiwavelength Study of Chandra X-Ray Sources in the Antennae
• A First Estimate Of The X-Ray Binary Frequency As A Function Of Star Cluster Mass In A Single Galactic System
• Optical Counterparts of Two Candidate Ultraluminous X-ray Sources in NGC 4536