Allen Telescope Array Detection of the black hole candidate Swift J1727.8-1613

ATel #16228; Joe Bright (Oxford), Wael Farah (SETI Institute), Rob Fender (Oxford), Andrew Siemion, Alexander Pollak, Dave DeBoer (Berkeley, Breakthrough Listen)
on 5 Sep 2023; 10:52 UT
Credential Certification: Joe Bright (joe.bright@physics.ox.ac.uk)

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We observed the field of the candidate black hole X-ray binary Swift J1727.8-1613 with the Allen Telescope Array (ATA) between UT 00:15:54 and 03:11:39 on 30/08/2023, and between UT 23:22:01 and 00:24:55 on 30/08/2023 and 31/08/2023. The ATA has a flexible backend which allows for two 672 MHz spectral windows to be tuned independently anywhere between 1 and 10 GHz, which we placed centred at 5 and 8 GHz for the first observation, and 3 and 8 GHz for the second observation (Farah et al. in prep., Pollak et al. in prep.). The flux density calibrator 3C286 was used to calibrate the absolute flux scale and bandpass response of the array, while interleaved observations of 1733-130 were used to calibrate the time dependent complex gains, with a 10 minute observation per 30 minutes on source. Calibration and imaging were performed in CASA using standard techniques.

We detect significant emission at the position of Swift J1727.8-1613, at both 5 and 8 GHz on 30/08/2023 (107 +/- 11 mJy and 105 +/- 11 mJy, respectively) and at 3 and 8 GHz on 30/08/2023 (104 +/- 11 mJy and 110 +/- 11 mJy, respectively). We have assumed a conservative 10% calibration uncertainty added in quadrature to the statistical error on the fit. This represents a significant radio brightening compared to observations reported in ATel #16211. These preliminary measurements suggest a very bright flat-spectrum compact jet associated with the source, and we encourage both higher-resolution radio observations and higher frequency (mm and infrared) observations.

Further monitoring is ongoing. We thank the staff at the Hat Creek Radio Observatory for maintaining and operating the ATA. The Allen Telescope Array (ATA) refurbishment program and its ongoing operations receive substantial support from Franklin Antonio. Additional contributions from Frank Levinson, Jill Tarter, Jack Welch, the Breakthrough Listen Initiative and other private donors have been instrumental in the renewal of the ATA. Breakthrough Listen is managed by the Breakthrough Initiatives, sponsored by the Breakthrough Prize Foundation. The Paul G. Allen Family Foundation provided major support for the design and construction of the ATA, alongside contributions from Nathan Myhrvold, Xilinx Corporation, Sun Microsystems, and other private donors. The ATA has also been supported by contributions from the US Naval Observatory and the US National Science Foundation.