ASKAP J005512.2−255834: A Luminous, Long-lived Radio Transient at <i>z</i> = 0.1—an Orphan Afterglow or an Off-nuclear TDE from an IMBH?

Abstract We report the discovery of a slowly evolving, extragalactic radio transient, ASKAP J005512.2–255834 (hereafter ASKAP J0055–2558), identified using the Australian SKA Pathfinder in a search for orphan afterglows associated with archival gravitational-wave events. Although discovered in this context, there is no evidence that the transient is associated with any known gravitational-wave event. Nonetheless, this source exhibits a 20-fold increase in flux density over &lt;250 days, and it remains in a declining yet detectable state more than 1000 days after the initial detection. Follow-up observations from 0.3 to 9 GHz reveal an evolving spectrum consistent with synchrotron emission. ASKAP J0055–2558 is spatially coincident with a low-mass, star-forming galaxy at redshift z = 0.116 ( d L = 543 Mpc), placing its peak radio luminosity at νL ν ∼ 10 39 erg s −1 . Analysis of its radio light curve, inferred blast-wave velocity, energetics, host-galaxy properties, and the absence of counterparts at other wavelengths suggests that ASKAP J0055–2558 is most consistent with either the late-time phase of an orphan long gamma-ray burst afterglow or a tidal disruption event involving an intermediate-mass black hole spatially offset from the galaxy nucleus. The radio discovery of either of these phenomena is extremely rare, with only a few or no confirmed examples to date.

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Publication Details

Journal
The Astrophysical Journal
Published
2026-03-17
DOI
https://doi.org/10.3847/1538-4357/ae4351
Primary Topic
Pulsars and Gravitational Waves Research
Type
article
Field-Weighted Citation Impact
0.00

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article

ASKAP J005512.2−255834: A Luminous, Long-lived Radio Transient at z = 0.1—an Orphan Afterglow or an Off-nuclear TDE from an IMBH?

A J Goodwin, K. Gourdji, G. E. Anderson, Artem V. Tuntsov et al.
The Astrophysical Journal
Pulsars and Gravitational Waves Research
article

ASKAP J005512.2−255834: A Luminous, Long-lived Radio Transient at z = 0.1—an Orphan Afterglow or an Off-nuclear TDE from an IMBH?

A J Goodwin, K. Gourdji, G. E. Anderson, Artem V. Tuntsov, Dougal Dobie, Stella Koch Ocker, Mark Suhr, Kavya Shaji, Ziteng Wang, Poonam Chandra, Jeff Cooke, Ashna Gulati, Claudio Ricci, James K. Leung, David L. Kaplan, Elaine M. Sadler, Tara Murphy, Manisha Caleb, Joshua Pritchard, Barnali Das, Om Sharan Salafia, Giancarlo Ghirlanda, Anais Möller, Adam Deller
article en

Abstract

Abstract We report the discovery of a slowly evolving, extragalactic radio transient, ASKAP J005512.2–255834 (hereafter ASKAP J0055–2558), identified using the Australian SKA Pathfinder in a search for orphan afterglows associated with archival gravitational-wave events. Although discovered in this context, there is no evidence that the transient is associated with any known gravitational-wave event. Nonetheless, this source exhibits a 20-fold increase in flux density over &lt;250 days, and it remains in a declining yet detectable state more than 1000 days after the initial detection. Follow-up observations from 0.3 to 9 GHz reveal an evolving spectrum consistent with synchrotron emission. ASKAP J0055–2558 is spatially coincident with a low-mass, star-forming galaxy at redshift z = 0.116 ( d L = 543 Mpc), placing its peak radio luminosity at νL ν ∼ 10 39 erg s −1 . Analysis of its radio light curve, inferred blast-wave velocity, energetics, host-galaxy properties, and the absence of counterparts at other wavelengths suggests that ASKAP J0055–2558 is most consistent with either the late-time phase of an orphan long gamma-ray burst afterglow or a tidal disruption event involving an intermediate-mass black hole spatially offset from the galaxy nucleus. The radio discovery of either of these phenomena is extremely rare, with only a few or no confirmed examples to date.

The Astrophysical JournalVol. 1000(1)
University of Geneva (CH), California Institute of Technology (US), Commonwealth Scientific and Industrial Research Organisation (AU), The University of Sydney (AU), Australia Telescope National Facility (AU), Pennsylvania State University (US), University of Toronto (CA), Carnegie Institution for Science (US), Hebrew University of Jerusalem (IL), Curtin University (AU), National Radio Astronomy Observatory (US), Brera Astronomical Observatory (IT), Manly Hospital (AU), Osservatorio Astrofisico di Torino (IT), Canadian Institute for Theoretical Astrophysics (CA), Carnegie Observatories (US), ARC Centre of Excellence for Gravitational Wave Discovery (AU), Istituto Nazionale di Fisica Nucleare, Sezione di Milano Bicocca (IT), International Centre for Radio Astronomy Research (AU), University of Wisconsin–Milwaukee (US), Swinburne University of Technology (AU), Universidad Diego Portales (CL)
National Aeronautics and Space Administration, W. M. Keck Foundation, California Institute of Technology, Science and Industry Endowment Fund, Australian Government, Commonwealth Scientific and Industrial Research Organisation, Swinburne University of Technology, Government of Western Australia
Openalex Percentile: Top 43%
Pulsars and Gravitational Waves Research
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