Multiband counterparts of two eclipsing ultraluminous X-ray sources in M 51

Abstract

We present the discovery and interpretation of ionized nebulae around two ultraluminous X-ray sources in M 51; both sources share the rare property of showing X-ray eclipses by their companion stars, and are therefore prime targets for follow-up studies. Using archival Hubble Space Telescope images, we found an elongated, 100-pc-long emission-line structure associated with one X-ray source (CXOM51 J132940.0+471237; ULX-1 for simplicity), and a more circular, ionized nebula at the location of the second source (CXOM51 J132939.5+471244; ULX-2 for simplicity). We observed both nebulae with the Large Binocular Telescope's Multi-Object Double Spectrograph. From our analysis of the optical spectra, we argue that the gas in the ULX-1 bubble is shock-ionized, consistent with the effect of a jet with a kinetic power of $\approx$2 $\times 10^{39}$ erg s${}^{-1}$. Additional X-ray photo-ionization may also be present, to explain the strength of high-ionization lines such as He II $\lambda 4686$ and [Ne V] $\lambda 3426$. On the other hand, the emission lines from the ULX-2 bubble are typical for photoionization by normal O stars suggesting that the nebula is actually an H II region not physically related to the ULX but is simply a chance alignment. From archival Very Large Array data, we also detect spatially extended, steep-spectrum radio emission at the location of the ULX-1 bubble (consistent with its jet origin), but no radio counterpart for ULX-2 (consistent with the lack of shock-ionized gas around that source).

18 pages, 10 figures, 2 tables. Accepted for publication in MNRAS

References in corpus (19)

• The MAPPINGS III Library of Fast Radiative Shock Models
• An Ultraluminous X-ray Source Powered by An Accreting Neutron Star
• Super-critically accreting stellar-mass black holes as ultraluminous X-ray sources
• The Effects of Stellar Rotation. II. A Comprehensive Set of Starburst99 Models
• Discovery of a 0.42-s pulsar in the ultraluminous X-ray source NGC 7793 P13
• Discovery of coherent pulsations from the Ultraluminous X-ray Source NGC 7793 P13
• Reprocessing of X-rays in the outer accretion disc of the black hole binary XTE J1817--330
• Kinematics of Spiral Arm Streaming in M51
• The powerful jet of an off-nuclear intermediate-mass black hole in the spiral galaxy NGC 2276
• Spectral Changes in the Hyperluminous Pulsar in NGC 5907 as a Function of Super-Orbital Phase
• Optical Properties of the Ultraluminous X-ray Source Holmberg IX X-1 and its Stellar Environment
• A ULX microquasar in NGC 5408?
• Near-infrared counterparts of ultraluminous X-ray sources
• The ionizing radiation from massive stars and its impact on HII regions: results from modern model atmospheres
• Deep optical observations of the interaction of the SS 433 microquasar jet with the W 50 radio continuum shell
• Irradiated, colour-temperature-corrected accretion discs in ultraluminous X-ray sources
• Two eclipsing ultraluminous X-ray sources in M 51
• Jets of SS433 on scales of dozens parsecs
• Kinematics of the Nebular Complex MH9/10/11 Associated with HoIX X-1

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• Optical Counterparts of ULXs in NGC 1672
• A plausible link between dynamically unsettled molecular gas and the radio jet in NGC 6328
• Optical IFU spectroscopy of a bipolar microquasar jet in NGC 300
• Optical Counterparts of Two Candidate Ultraluminous X-ray Sources in NGC 4536