ATCA observations of J1430+2303

ATel #15267; Tao An, Xiang Zhang, Ailing Wang, Yingkang Zhang, Zhenya Zheng, Xiang Ji (SHAO), George Heald (CSIRO), Xinwen Shu (AHU), Ning Jiang, Tinggui Wang (USTC), Huan Yang, Zhen Pan (PITP), Liming Dou (GZU)
on 10 Mar 2022; 05:27 UT
Credential Certification: Tao An (antao@shao.ac.cn)

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SDSS J143016.05+230344.4 (in short, J1430+2303) is recently discovered as a SMBH binary candidate predicted to merge within years by Jiang et al. (2022). Radio emission is critical for probing the jet, energy and environment and associated physics to happen during the final inspiraling stage of the SMBH binary merger. This source has been detected by the VLA FIRST at 1.4 GHz and VLASS at 3 GHz. The VLASS data show a sign of variability but need to be confirmed. The source was not detected in the ASKAP RACS image, likely hinting at a self-absorbed spectrum.

We conducted ATCA observations in the 16 cm and 4 cm bands to determine the radio spectrum of this source. The observations were made on 2022 February 28th, UT15-21. The central frequency of the 16-cm band is 2.13 GHz with a bandwidth of 2 GHz. The broad frequency coverage of the 4-cm band allows us to split into two sub-bands with the central frequencies of 5.48 and 7.48 GHz, respectively, each with 2-GHz bandwidth. We performed an analysis of the data using 1934-638 as a flux density calibrator and using 1442+101 and 1404+286 as gain calibrators.

A single point source is detected at RA=14 30 16.04, DEC=+23 03 44.86 (derived from the 7.48 GHz image), consistent with the reported optical position of J1430+2303 and the radio positions obtained from FIRST and VLASS images. We report here preliminary flux density measurements:
0.76+/-0.05 mJy at 2.13 GHz, beamsize=23.6"x3.6"
0.71+/-0.04 mJy at 5.48 GHz, beamsize=11.2"x1.3"
0.58+/-0.03 mJy at 7.48 GHz, beamsize= 7.6"x0.9"
Note that the error bars of the flux densities only take into account formal fitting errors.

The preliminary data show a steep spectral index between 5.5 and 7.5 GHz and a flat spectrum between 2.1 and 5 GHz, suggesting a possible radio spectral evolution. We plan to continue monitoring this source at radio bands including high-resolution VLBI observations and encourage multi-wavelength follow-up observations, especially high cadence optical and X-ray monitoring to investigate its physical nature.

We thank Dr. Jamie Stevens for approving and supporting this DDT observation.

References:
Jiang et al. 2022, arXiv:2201.11633