Speaker
Description
Swift/BAT first reported the detection of the X-ray transient Swift J1727.8-1613 on 2023 August 24 (Page+2023). Optical observations revealed that Swift J1727.8-1613 has a black hole candidate larger than 3.2 Msun and a K4V donor (Mata Sanchez+2023). Black hole X-ray binaries have an accretion state responsible for the ejection of large-scale or compact jets. The formation process of these jets is one of the open questions in astronomy. Swift J1727.8-1613 has the resolved continuous jets reaching 20–40 mas in the north-south direction observed by the Very Long Baseline Array during the hard/hard-intermediate state (Wood+2024). However, the variabilities of the intensity and the spatial structure of the observed jets have not been revealed. We therefore carried out the flux density monitoring at 6/8 GHz of a jet of Swift J1727.8-1613 with the Yamaguchi Interferometer (YI) and the Japanese VLBI Network (JVN) simultaneously from September 19 to October 1 in 2023. A radio interferometer such as the YI and the JVN can not detect a jet component larger than their spatial resolutions, which are 1'1 arcmin and 8 mas at 8 GHz. This means that the observed flux density of the JVN is less than that of YI. As a result, we observed the variabilities increasing 35 and 40 mJy in the JVN and the YI at 8 GHz in an hour, respectively. The difference of 5 mJy represents a component spread to a few mas which the JVN can resolve. Another component showed the radio variabilities that the short radio flares and the persistent components exist together. The former is that the variability amplitude of the YI is equal to that of JVN for two hours so it represents that the size of the radio flare component is smaller than a few mas. The latter represents a steady component larger than a few mas for several hours.
