J0011+3443: a GPS compact symmetric object, gravitational lens, or dual AGN?
arXiv:2608.19928
Efthalia Traianou, Tingting Liu, Roman Gold, Richard Mushotzky
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New VLBA images of a gigahertz-peaked radio source favor a compact symmetric object—possibly relic—over a lens or dual black hole, unless future astrometry says otherwise.
Read free explainer →We present new multi-frequency VLBA observations of \object{J0011+3443} (TXS\,0008+344, $z=0.89$) at 2.3, 4.9, 8.5, and, for the first time, 23.6\,GHz. The source consists of two compact components A and B at a projected separation of $314\pm2$\,pc, plus a third feature C detected at 23.6\,GHz at $0.6$\,mas from A. Archival low-resolution radio measurements confirm an integrated gigahertz-peaked spectrum, with an observed-frame peak frequency of $ν_\mathrm{peak}=0.73\pm0.08$\,GHz and a peak flux density of $S_\mathrm{peak}=879\pm125$\,mJy. Comparison with nearly frequency-matched low-resolution measurements shows that the VLBA recovers $0.85\pm0.11$ of the 4.85\,GHz flux density and $0.50\pm0.06$ of the 8.46\,GHz flux density. The lower recovered fraction at 8.5\,GHz suggests that low-surface-brightness emission is resolved out or falls below the VLBA surface-brightness sensitivity. We therefore interpret the VLBA component spectra as spectra of the compact recovered emission only. The 23.6\,GHz morphology, the absence of a detected flat-spectrum core, the similar compact spectra of A and B, and the steep integrated GHz spectrum favor an interpretation of \object{J0011+3443} as a GPS-class compact symmetric object, possibly in a short-lived or relic phase, although a dual-AGN origin cannot be excluded without multi-epoch astrometry.