Comprehensive Radio Monitoring of the Black Hole X-ray Binary Swift J1727.8$-$1613 during its 2023$-$2024 Outburst

TL;DR

This paper provides an extensive multi-frequency radio light curve dataset of the 2023-2024 outburst of the black hole X-ray binary Swift J1727.8-1613, aiding multi-wavelength studies and understanding jet ejections.

Contribution

It offers the first comprehensive, multi-frequency radio monitoring dataset of Swift J1727.8-1613's outburst, including 197 epochs over 10 months, and encourages community data sharing.

Findings

Multiple radio flares indicating jet ejections.

Radio spectral indices show steepening and cooling effects.

Brightest flare reached approximately 1 Jy.

Abstract

This work presents comprehensive multi-frequency radio monitoring of the black hole low-mass X-ray binary Swift J1727.8$-$1613, which underwent its first recorded outburst after its discovery in August 2023. Through a considerable community effort, we have coalesced the data from multiple, distinct observing programs; the light curves include ${\sim} 10$ months and 197 epochs of monitoring from 7 radio facilities with observing frequencies ranging from (approximately) 0.3$-$230GHz. The primary purpose of this work is to provide the broader astronomical community with these light curves to assist with the interpretation of other observing campaigns, particularly non-radio observing frequencies. We discuss the phenomenological evolution of the source, which included: (i) multiple radio flares consistent with the launching of discrete jet ejections, the brightest of which reached $\sim$ 1 Jy; (ii) temporally evolving radio spectral indices ($\alpha$), reaching values steeper than expected for optically-thin synchrotron emission ($\alpha {<} -1$) and emission with significant radiative cooling ($\alpha < -1.5$). We have published a digital copy of the data and intend for this work to set a precedent for the community to continue releasing comprehensive radio light curves of future low-mass X-ray binary outbursts.