Detection of compact radio emission from Circinus X-1 with the first Southern hemisphere e-VLBI experiment
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Version 1 2023-05-16, 19:46Version 1 2023-05-16, 19:46
journal contribution
posted on 2024-09-17, 02:08authored byCJ Phillips, A Deller, SW Amy, SJ Tingay, AK Tzioumis, JE Reynolds, DL Jauncey, JB Stevens, Simon EllingsenSimon Ellingsen, John DickeyJohn Dickey, RP Fender, V Tudose, GD Nicolson
Abstract
Circinus X-1 has recently returned to a state of strong radio flaring. Here we report on the first VLBI observations, and detection, undertaken in the 25 years since the 1975–1985 period of strong recurrent flaring activity. We detected Circinus X-1 with the first observations conducted by a recently developed Southern hemisphere e-VLBI array, at both 1.6 and 8.4 GHz, over a three-day period. At 1.6 GHz, the compact source has a total flux density of 11 mJy and a size of 60 ± 15 mas (Gaussian model full width at half maximum). At 8.4 GHz, the compact source is less than 60 mas. The size variation with frequency is consistent with a broadened image due to scattering in the turbulent, ionized interstellar medium of our Galaxy. However, these size measurements appear inconsistent with the λ2.2 variation expected for strong interstellar scattering and previous VLBI observations made at 2.3 GHz in the early 1980s. To explain this apparent inconsistency, we suggest that Circinus X-1 supports a weak, non-varying component of 35 mas extent (175 au at 5 kpc distance), corresponding to compact structure in the extended radio nebula. No significant variation in the flux density at 1.6 GHz is evident between two observations 24 h apart. No jet-like structures are evident on scales of tens of mas, simply a scatter broadened source, presumably coincident with the suggested neutron star in the binary system.
Funding
Australian Research Council
History
Publication title
Monthly Notices of the Royal Astronomical Society: Letters
Volume
380
Issue
1
Pagination
L11-L14
ISSN
1745-3933
Department/School
School of Natural Sciences
Publisher
Blackwell Publishing
Publication status
Published
Place of publication
Oxford, England
Socio-economic Objectives
280120 Expanding knowledge in the physical sciences