@article{46e3319273544bbbac3e0b7f27c31695,
title = "The variable radio counterpart of Swift J1858.6-0814",
abstract = "Swift J1858.6-0814 is a transient neutron star X-ray binary discovered in 2018 October. Multiwavelength follow-up observations across the electromagnetic spectrum revealed many interesting properties, such as erratic flaring on minute time-scales and evidence for wind outflows at both X-ray and optical wavelengths, strong and variable local absorption, and an anomalously hard X-ray spectrum. Here, we report on a detailed radio observing campaign consisting of one observation at 5.5/9 GHz with the Australia Telescope Compact Array, and nine observations at 4.5/7.5 GHz with the Karl G. Jansky Very Large Array. A radio counterpart with a flat to inverted radio spectrum is detected in all observations, consistent with a compact jet being launched from the system. Swift J1858.6-0814 is highly variable at radio wavelengths in most observations, showing significant variability when imaged on 3-to-5-min time-scales and changing up to factors of 8 within 20 min. The periods of brightest radio emission are not associated with steep radio spectra, implying they do not originate from the launching of discrete ejecta. We find that the radio variability is similarly unlikely to have a geometric origin, be due to scintillation, or be causally related to the observed X-ray flaring. Instead, we find that it is consistent with being driven by variations in the accretion flow propagating down the compact jet. We compare the radio properties of Swift J1858.6-0814 with those of Eddington-limited X-ray binaries with similar X-ray and optical characteristics, but fail to find a match in radio variability, spectrum, and luminosity.",
keywords = "Accretion, accretion discs, X-rays: binaries, stars: individual (Swift J1858.6-0814)",
author = "{Van Den Eijnden}, J. and N. Degenaar and Russell, {T. D.} and Buisson, {D. J.K.} and D. Altamirano and Padilla, {M. A.} and A. Bahramian and {Castro Segura}, N. and Fogantini, {F. A.} and Heinke, {C. O.} and T. MacCarone and D. Maitra and Miller-Jones, {J. C.A.} and T. Munoz-Darias and {Ozbey Arabaci}, M. and Russell, {D. M.} and Shaw, {A. W.} and G. Sivakoff and Tetarenko, {A. J.} and F. Vincentelli and R. Wijnands",
note = "Funding Information: The authors thank the VLA director and schedulers for approving, rapidly scheduling, and coordinating the DDT observation included in this study. This research made use of ASTROPY,7 a community-developed core Python package for Astronomy (Astropy Collaboration 2013; Price-Whelan et al. 2018). JvdE and ND are supported by an NWO Vidi grant awarded to ND. TDR is supported by an NWO Veni grant. DA and DJKB acknowledge support from the Royal Society. MAP is funded by the Juan de la Cierva Fellowship IJCI– 2016-30867. TMD is funded by the Ram{\'o}n y Cajal Fellowship RYC-2015-18148. MAP and TMD acknowledge support by the Spanish MINECO grant AYA2017-83216-P. FF and DD acknowledges support from the Royal Society International Exchanges {\textquoteleft}The first step for High-Energy Astrophysics relations between Argentina and UK{\textquoteright}. MOA acknowledges support from the Royal Society through Newton International Fellowship program. GRS acknowledges support from an NSERC Discovery Grant (RGPIN-2016-06569). This research has made use of data and software provided by the High Energy Astrophysics Science Archive Research Center (HEASARC) and NASA{\textquoteright}s Astrophysics Data System Bibliographic Services. The Australia Telescope Compact Array (ATCA) is part of the Australia Funding Information: Telescope, which is funded by the Commonwealth of Australia for operation as a National Facility managed by CSIRO. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. Publisher Copyright: {\textcopyright} 2020 The Author(s).",
year = "2020",
month = aug,
day = "1",
doi = "10.1093/mnras/staa1704",
language = "English (US)",
volume = "496",
pages = "4127--4140",
journal = "Monthly Notices of the Royal Astronomical Society",
issn = "0035-8711",
publisher = "Oxford University Press",
number = "4",
}