TY - JOUR
T1 - The variable radio counterpart of Swift J1858.6-0814
AU - Van Den Eijnden, J.
AU - Degenaar, N.
AU - Russell, T. D.
AU - Buisson, D. J.K.
AU - Altamirano, D.
AU - Padilla, M. A.
AU - Bahramian, A.
AU - Castro Segura, N.
AU - Fogantini, F. A.
AU - Heinke, C. O.
AU - MacCarone, T.
AU - Maitra, D.
AU - Miller-Jones, J. C.A.
AU - Munoz-Darias, T.
AU - Ozbey Arabaci, M.
AU - Russell, D. M.
AU - Shaw, A. W.
AU - Sivakoff, G.
AU - Tetarenko, A. J.
AU - Vincentelli, F.
AU - Wijnands, R.
N1 - 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 Ramón 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 ‘The first step for High-Energy Astrophysics relations between Argentina and UK’. 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’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:
© 2020 The Author(s).
PY - 2020/8/1
Y1 - 2020/8/1
N2 - 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.
AB - 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.
KW - Accretion, accretion discs
KW - X-rays: binaries
KW - stars: individual (Swift J1858.6-0814)
UR - http://www.scopus.com/inward/record.url?scp=85095452067&partnerID=8YFLogxK
U2 - 10.1093/mnras/staa1704
DO - 10.1093/mnras/staa1704
M3 - Article
AN - SCOPUS:85095452067
VL - 496
SP - 4127
EP - 4140
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
SN - 0035-8711
IS - 4
ER -