ASKAP Discovery of a Giant Odd Radio Circle at z=0.15
Abstract
Odd radio circles (ORCs) are a recently recognized class of faint, roughly circular diffuse radio sources, typically a few hundred kiloparsecs across, whose origin is still debated. We report the serendipitous discovery of a giant ORC, ORC~J1928−5056, in 856~MHz continuum data from the ASKAP observations. The emission forms a single, mildly elliptical structure 4′ across, corresponding to $0.63$~Mpc at the redshift z=0.1507 of the central galaxy LEDA~140850, the brightest cluster galaxy of Abell~3639, which makes it one of the largest single ORCs known. After subtracting the radio nucleus associated with the host galaxy, the ORC has a flux density of 73~mJy integrated within an area of ∼ 12~arcmin2, i.e.\ a mean surface brightness of only $1.7μ$Jy~arcsec−2, and a rest-frame luminosity of L1.4=2×1024~W~Hz−1, comparable to those of the most luminous ORCs. Including its nucleus, the system reaches L1.4=6.6×1024~W~Hz−1, higher than that of any other ORC reported so far. The host is a massive (M∗∼1011 M⊙), passive elliptical galaxy with negligible star formation. It contains an AGN jet with a power-law spectrum of index α=−0.877±0.089 between 856 and 1656~MHz. Finally, we discuss the implications for ORC formation models and the observations needed to establish the nature of this system.
Related
- Evidence for the binary nature of the long-period radio transient ASKAP/DART J1832-0911
- The 943 MHz radio-SFR relation of nearby galaxies observed with ASKAP
- The long period radio transient ASKAP J1448-68 is a cataclysmic variable
- The long period radio transient ASKAP J1448−68 is a cataclysmic variable
- A Unified Mass-Loading Model for ASKAP J1745-5051: Linking Long-Period Radio Transients to Magnetic Cataclysmic Variables
BibTeX
@misc{su2026askap,
title = {{ASKAP Discovery of a Giant Odd Radio Circle at $z=0.15$}},
author = {Renzhi Su and Minfeng Gu},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.36512},
eprint = {2610.36512},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.36512},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - UNPB
TI - ASKAP Discovery of a Giant Odd Radio Circle at z=0.15
AU - Renzhi Su
AU - Minfeng Gu
PY - 2026
DA - 2026/10/27
PB - arXiv
DO - 10.48550/arxiv.2610.36512
UR - https://arxiv.org/abs/2610.36512
AB - Odd radio circles (ORCs) are a recently recognized class of faint, roughly circular diffuse radio sources, typically a few hundred kiloparsecs across, whose origin is still debated. We report the serendipitous discovery of a giant ORC, ORC~J1928−5056, in 856~MHz continuum data from the ASKAP observations. The emission forms a single, mildly elliptical structure 4^′ across, corresponding to $0.63$~Mpc at the redshift z=0.1507 of the central galaxy LEDA~140850, the brightest cluster galaxy of Abell~3639, which makes it one of the largest single ORCs known. After subtracting the radio nucleus associated with the host galaxy, the ORC has a flux density of 73~mJy integrated within an area of ∼ 12~arcmin^2, i.e.\ a mean surface brightness of only $1.7μ$Jy~arcsec^−2, and a rest-frame luminosity of L_1.4=2×10^24~W~Hz^−1, comparable to those of the most luminous ORCs. Including its nucleus, the system reaches L_1.4=6.6×10^24~W~Hz^−1, higher than that of any other ORC reported so far. The host is a massive (M_∗∼10^11 M_⊙), passive elliptical galaxy with negligible star formation. It contains an AGN jet with a power-law spectrum of index α=−0.877±0.089 between 856 and 1656~MHz. Finally, we discuss the implications for ORC formation models and the observations needed to establish the nature of this system.
ER -