e-MERLIN observations of the candidate binary supermassive black hole in SDSS J143016.05+230344.4

ATel #15306; G. Bruni (INAF-IAPS), J. Rodi (INAF-IAPS), F. Panessa (INAF-IAPS), L. Hernandez-Garcia (U. Valparaiso), M. Molina (INAF-IASF), A. Malizia (INAF-OAS), A. Bazzano (INAF-IAPS), P. Ubertini (INAF-IAPS)
on 1 Apr 2022; 09:24 UT
Credential Certification: Gabriele Bruni (gabriele.bruni@inaf.it)

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Recent studies suggest that the Seyfert 1 galaxy SDSS J143016.05+230344.4 is potentially hosting a merging supermassive black hole (SMBH) system (Jiang et al. 2022). Analyses of the source’s long-term light curves in optical, UV, and X-ray wavelengths show a decaying period that decreases from 1 year to 1 month over the span of 3 years. The authors interpret the decreasing period as signature of in-spiral of two SMBHs with an uneven mass ratio.

In the radio band, the source is detected in the FIRST survey at 1.4 GHz, showing an unresolved component with an integrated flux density of 0.98+/-0.22 mJy (dating back to 1995). Its radio power (~1.4x10^22 W/Hz) is just below the threshold between radio-loud and radio-quiet AGN (10^23 W/Hz, Condon et al. 1992), still consistent with either a star-formation or an AGN origin. More recently, the source has been detected in the VLASS survey (3 GHz, 2017) at a position corresponding with the FIRST detection, with a flux density of 0.6+/-0.1 mJy/beam.

On March 28th, 2022, we performed e-MERLIN observations at 1.5 GHz to test the compactness of such emission. A single 12-hour observation was carried out, reaching an RMS of 34 uJy/beam. The angular resolution with natural weighting was 0.209x0.119 arcsec, at a position angle of 21.7 deg. The source was detected as a single component with an integrated flux density of 0.73+/-0.09 mJy/beam, lower though consistent within errors with the one from the FIRST survey. At the resolution of our observations the source shows a deconvolved size of 85x34 mas, resulting in a brightness temperature of ~10^5 K, consistent with thermal emission (see e.g. Baldi et al. 2018).

We plan to monitor the source with e-MERLIN to spot any variability similar to the X-ray and optical one induced by the spiralling binary system.

e-MERLIN image at 1.5 GHz