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Multi-wavelength polarimetry and radio observations of Swift J1727. 8-1613 at the beginning of its recent 2023 outburst suggested the presence of a bright compact jet aligned in the north-south direction, which could not be confirmed without high angular resolution images. Using the Very Long Baseline Array and the Long Baseline Array, we imaged Swift J1727. 8-1613, during the hard/hard-intermediate state, revealing a bright core and a large, two-sided, asymmetrical, resolved jet. The jet extends in the north-south direction, at a position angle of -0. 600. 07 East of North. At 8. 4 GHz, the entire resolved jet structure is 110 (d/2. 7\, kpc) / i AU long, with the southern approaching jet extending 80 (d/2. 7\, kpc) / i AU from the core, where d is the distance to the source and i is the inclination of the jet axis to the line of sight. These images reveal the most resolved continuous X-ray binary jet, and possibly the most physically extended continuous X-ray binary jet ever observed. Based on the brightness ratio of the approaching and receding jets, we put a lower limit on the intrinsic jet speed of 0. 27 and an upper limit on the jet inclination of i74. In our first observation we also detected a rapidly fading discrete jet knot 66. 890. 04 mas south of the core, with a proper motion of 0. 660. 05 mas hour^-1, which we interpret as the result of a downstream internal shock or a jet-ISM interaction, as opposed to a transient relativistic jet launched at the beginning of the outburst.
Wood et al. (Mon,) studied this question.