VLITE Light Curve for Swift J1727.8-1613

ATel #16279; W. M. Peters (U. S. Naval Research Laboratory), E. Polisensky (U. S. Naval Research Laboratory), T. E. Clarke (U. S. Naval Research Laboratory), S. Giacintucci (U. S. Naval Research Laboratory), N. E. Kassim (U. S. Naval Research Laboratory)
on 10 Oct 2023; 14:40 UT
Credential Certification: Wendy Peters (wendy.peters@nrl.navy.mil)

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Swift J1727.8-1613 is a low-mass black hole X-ray binary (XRB) candidate originally identified on 24 August 2023 as GRB 230824A (GCN #34536, #34537), and subsequently reported at X-ray (ATEL #16205, #16206, #16207, #16210) and optical (ATEL #16208, #16209) wavelengths. Radio observations at GHz frequencies (ATEL #16211, #16228, #16230, #16231), identified a nearly flat-spectrum source with a compact jet which brightened rapidly in the days after the initial detection.

We present radio measurements of the XRB Swift J1727.8-1613 at 338 MHz with the VLA Low-band Ionosphere and Transient Experiment (VLITE). VLITE is a commensal instrument which records data from 18 antennae during all routine Karl G. Jansky Very Large Array (VLA) observations. Measurements of Swift J1727.8-1613 were made during two independent VLA programs (22B-069, PI: A. Tetarenko and 23A-260, PI: J. Miller-Jones) on 15 days between 2023-08-25 and 2023-10-09. The data in August and September were taken with the VLA in its largest (A) configuration (maximum baseline of 36 km). In October the VLA was moving to its most compact (D) configuration. All data were processed with a 6 klambda minimum baseline cut to provide a more uniform result; the final resolutions were approximately 5". The data have been calibrated using the standard VLITE calibration and imaging pipeline (Polisensky et al. 2016). The flux density is calibrated to 3c286 on the Perley & Butler (2017) scale.

Within the uncertainties, the VLITE measurements are consistent with published spectral indices from GHz measurements (ATEL #16211, #16271). A small flare is seen for a few days starting on 2023-09-20; this overlaps a similar flare in the MAXI 2-20 keV X-ray light curve (Veledina et al. 2023; Figure 1a). The VLITE measurements on 2023-10-05 and 2023-10-06 show the same quenching and subsequent flaring reported at GHz frequencies (ATEL #16271), possibly due to the ejection of transient, relativistic jets, and coincident with the X-ray transition to the soft or soft intermediate state (ATEL #16273). That flare has dimmed by the final observation on 2023-10-09, when the source also re-transitioned to a hard X-ray state (ATEL #16276).

VLITE measurements are listed below. The quoted errors include a standard VLITE 15% flux density calibration uncertainty and the fit errors, summed in quadrature.


Date: Start MJD: VLITE Flux
2023-08-25: 60181.98205: 15.7 ± 8.4 mJy
2023-08-29: 60185.99742: 111.6 ± 18.7 mJy
2023-09-03: 60190.09856: 86.4 ± 13.4 mJy
2023-09-09: 60196.07773: 93.4 ± 14.8 mJy
2023-09-14: 60201.56898: 89.0 ± 13.6 mJy
2023-09-15: 60202.99030: 80.2 ± 17.4 mJy
2023-09-17: 60204.03606: 76.9 ± 11.9 mJy
2023-09-20: 60207.03606: 169.0 ± 25.6 mJy
2023-09-22: 60209.99326: 180.8 ± 29.0 mJy
2023-09-24: 60211.02565: 166.9 ± 25.3 mJy
2023-10-05: 60222.01868: 51.0 ± 21.7 mJy
2023-10-06: 60223.03575: 332.0 ± 50.6 mJy
2023-10-06: 60223.95528: 245.3 ± 37.3 mJy
2023-10-07: 60224.98987: 86.4 ± 14.1 mJy
2023-10-09: 60225.99023: 53.2 ± 12.0 mJy


Basic research in radio astronomy at the U.S. Naval Research Laboratory (NRL) is supported by 6.1 Base funding. Construction and installation of VLITE was supported by the NRL Sustainment Restoration and Maintenance fund. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.