Compact radio emission in Ultraluminous X-ray sources

Abstract

We present results from our studies of radio emission from selected Ultraluminous X-ray (ULX) sources, using archival Giant Metrewave Radio Telescope (GMRT) data and new European VLBI Network (EVN) observations. The GMRT data are used to find possible faint radio emission from ULX sources located in late-type galaxies in the Chandra Deep Fields. No detections are found at 235, 325 and 610 MHz, and upper limits on the radio flux densities at these frequencies are given. The EVN observations target milliarcsecond-scale structures in three ULXs with known radio counterparts (N4449- X1, N4088-X1, and N4861-X2). We confirm an earlier identification of the ULX N4449-X1 with a supernova remnant and obtain the most accurate estimates of its size and age. We detect compact radio emission for the ULX N4088-X1, which could harbour an intermediate mass black hole (IMBH) of 10^5 M\odot accreting at a sub-Eddington rate. We detect a compact radio component in the ULX N4861-X2, with a brightness temperature > 10^6 K and an indication for possible extended emission. If the extended structure is confirmed, this ULX could be an HII region with a diameter of 8.6 pc and surface brightness temperature \geq 10^5 K. The compact radio emission may be coming from a ~ 10^5 M\odot black hole accreting at 0.1M_Edd.

5 pages, 6 figures. Accepted for publication in the Astronomische Nachrichten

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• Ultraluminous X-ray sources
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• The powerful jet of an off-nuclear intermediate-mass black hole in the spiral galaxy NGC 2276
• Radio jets from AGN in dwarf galaxies in the COSMOS survey: mechanical feedback out to redshift $\sim$3.4
• Black Hole Powered Nebulae and a Case Study of the Ultraluminous X-ray Source IC342 X-1
• Radio observations of extreme ULXs: revealing the most powerful ULX radio nebula ever or the jet of an intermediate-mass black hole?
• The extended radio jet of an off-nuclear low-mass AGN in NGC 5252
• Milliarcsec-scale radio emission of ultraluminous X-ray sources: steady jet emission from an intermediate-mass black hole?
• Discovery of a Luminous Radio Transient 460 pc from the Central Supermassive Black Hole in Cygnus A
• Self-regulation of black hole accretion via jets in early protogalaxies
• The resolved structure of the extragalactic supernova remnant SNR 4449-1
• Revealing the nature of the ULX and X-ray population of the spiral galaxy NGC 4088
• Spectral study of X-ray sources in some galaxies recently observed by Chandra