The Nature of the IMBH Candidate CXO~J133815.6+043255: High-Frequency Radio Emission

TL;DR

This study presents high-frequency radio observations of the ULX candidate CXO~J133815.6+043255, revealing a steep-spectrum jet consistent with an intermediate-mass black hole producing radio jets similar to quasars.

Contribution

The paper provides the first 22 GHz radio data for this ULX candidate, supporting its classification as an intermediate-mass black hole with jet properties akin to low-luminosity AGN.

Findings

Spectral slope of -0.66 indicating optically-thin synchrotron emission

Radio to X-ray luminosity ratio of ~10^-3 consistent with LLAGN

Supports the IMBH nature with jet activity similar to quasars

Abstract

The ultra-luminous X-ray source CXO~J133815.6+043255 is a strong candidate for a bona-fide intermediate mass black hole, residing in the outskirts of NGC~5252. We present 22~GHz radio observations of this source obtained serendipitously in an ongoing high-frequency imaging survey of radio-quiet Active Galactic Nuclei (AGN), and use this new data point to construct the broad-band radio spectral energy distribution (SED). We find that the SED exhibits a spectral slope of $\alpha=-0.66\pm0.02$, consistent with a steep spectrum from optically-thin synchrotron emission from an unresolved jet. We also find that the $L_R / L_X$ ratio is approximately $10^{-3}$, inconsistent with radio-quiet AGN and many ULXs but consistent with low-luminosity AGN (LLAGN) and radio-loud quasars. Together, these observations support the conclusion that CXO~J133815.6+043255 is an intermediate-mass black hole producing a low-mass analog of radio jets seen in classical quasars.