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Published May 10, 2023 | Published
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A Flat-spectrum Radio Transient at 122 Mpc Consistent with an Emerging Pulsar Wind Nebula


We report the discovery and follow-up observations of VT 1137–0337, an unusual radio transient found in our systematic search for extragalactic explosions in the Very Large Array Sky Survey. It is located in the brightest region of a dwarf starburst galaxy at a luminosity distance of 121.6 Mpc. Its 3 GHz luminosity is comparable to luminous radio supernovae associated with dense circumstellar interaction and relativistic outflows. However, its broadband radio spectrum—proportional to ν^(−0.35) over a range of ≳10× in frequency and fading at a rate of 5% yr⁻¹—cannot be directly explained by the shock of a stellar explosion. Jets launched by various classes of accreting black holes also struggle to account for VT 1137–0337's combination of observational properties. Instead, we propose that VT 1137–0337 is a decades-old pulsar wind nebula that has recently emerged from within the free–free opacity of its surrounding supernova ejecta. If the nebula is powered by spin-down, the central neutron star should have a surface dipole field of ∼10¹³–10¹⁴ G and a present-day spin period of ∼10–100 ms. Alternatively, the nebula may be powered by the release of magnetic energy from a magnetar. Magnetar nebulae have been proposed to explain the persistent radio sources associated with the repeating fast radio bursts FRB 121102 and FRB 190520B. These FRB persistent sources have not previously been observed as transients but do bear a striking resemblance to VT 1137–0337 in their radio luminosity, spectral index, and host galaxy properties.

Additional Information

© 2023. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. D.Z.D. thanks Brian Metzger for helpful comments and Jim Cordes, Navin Sridhar, Jean Somalwar, Casey Law, Kristina Nyland, Vikram Ravi, and Bryan Gaensler for insightful conversations that helped shape this paper. This material is based upon work supported by the National Science Foundation under grant No. AST-1654815 and the United States–Israel Binational Science Foundation grant 2018154. This work is based on data taken with the Very Large Array, operated by the National Radio Astronomy Observatory (NRAO). The NRAO is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. Some of the data presented here were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. We wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are very thankful to have the opportunity to conduct observations from this sacred mountain. Facilities: VLA - Very Large Array, Keck. - Software: astropy (Astropy Collaboration et al. 2013, 2018), numpy (van der Walt et al. 2011; Harris et al. 2020), scipy (Jones et al. 2001; Virtanen et al. 2020), APLpy (Robitaille & Bressert 2012), PyBDSF (Mohan & Rafferty 2015), CASA (McMullin et al. 2007), LPIPE (Perley 2019), emcee (Foreman-Mackey et al. 2013).

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August 22, 2023
October 20, 2023