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The Radio Counterpart to the Fast X-Ray Transient EP240414a

The Astrophysical Journal American Astronomical Society 981:1 (2025) 48-48

Authors:

Joe S Bright, Francesco Carotenuto, Rob Fender, Carmen Choza, Andrew Mummery, Peter G Jonker, Stephen J Smartt, David R DeBoer, Wael Farah, James Matthews, Alexander W Pollak, Lauren Rhodes, Andrew Siemion

Abstract:

Abstract Despite being operational for only a short time, the Einstein Probe mission, with its large field of view and rapid localization capabilities, has already significantly advanced the study of rapid variability in the soft X-ray sky. We report the discovery of luminous and variable radio emission from the Einstein Probe fast X-ray transient EP240414a, the second such source with a radio counterpart. The radio emission at 3 GHz peaks at ∼30 days postexplosion and with a spectral luminosity ∼2 × 1030 erg s−1 Hz−1, similar to what is seen from long gamma-ray bursts, and distinct from other extragalactic transients including supernovae and tidal disruption events, although we cannot completely rule out emission from engine driven stellar explosions, e.g., the fast blue optical transients. An equipartition analysis of our radio data reveals that an outflow with at least a moderate bulk Lorentz factor (Γ ≳ 1.6) with a minimum energy of ∼1048 erg is required to explain our observations. The apparent lack of a reported gamma-ray counterpart to EP240414a could suggest that an off-axis or choked jet could be responsible for the radio emission, although a low-luminosity gamma-ray burst may have gone undetected. Our observations are consistent with the hypothesis that a significant fraction of extragalactic fast X-ray transients are associated with the deaths of massive stars.
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Radio observations of the ultra-long GRB 220627A reveal a hot cocoon supporting the blue supergiant progenitor scenario

ArXiv 2502.13435 (2025)

Authors:

James K Leung, Om Sharan Salafia, Cristiana Spingola, Giancarlo Ghirlanda, Stefano Giarratana, Marcello Giroletti, Cormac Reynolds, Ziteng Wang, Tao An, Adam Deller, Maria R Drout, David L Kaplan, Emil Lenc, Tara Murphy, Miguel Perez-Torres, Lauren Rhodes
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Multi-Wavelength Analysis of AT 2023sva: a Luminous Orphan Afterglow With Evidence for a Structured Jet

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) (2025) staf290

Authors:

Gokul P Srinivasaragavan, Daniel A Perley, Anna YQ Ho, Brendan O’Connor, Antonio de Ugarte Postigo, Nikhil Sarin, S Bradley Cenko, Jesper Sollerman, Lauren Rhodes, David A Green, Dmitry S Svinkin, Varun Bhalerao, Gaurav Waratkar, AJ Nayana, Poonam Chandra, M Coleman Miller, Daniele B Malesani, Geoffrey Ryan, Suryansh Srijan, Eric C Bellm, Eric Burns, David J Titterington, Maria B Stone, Josiah Purdum, Tomás Ahumada, GC Anupama, Sudhanshu Barway, Michael W Coughlin, Andrew Drake, Rob Fender, José F Agüí Fernández, Dmitry D Frederiks, Stefan Geier, Matthew J Graham, Mansi M Kasliwal, SR Kulkarni, Harsh Kumar, Maggie L Li, Russ R Laher, Alexandra L Lysenko, Gopal Parwani, Richard A Perley, Anna V Ridnaia, Anirudh Salgundi, Roger Smith, Niharika Sravan, Vishwajeet Swain, Christina C Thöne, Anastasia E Tsvetkova, Mikhail V Ulanov, Jada Vail, Jacob L Wise, Avery Wold
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The Observed Phase Space of Mass-loss History from Massive Stars Based on Radio Observations of a Large Supernova Sample

The Astrophysical Journal American Astronomical Society 979:2 (2025) 189

Authors:

Itai Sfaradi, Assaf Horesh, Rob Fender, Lauren Rhodes, Joe Bright, David Williams-Baldwin, Dave A Green
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Multi-band study of the flaring mode emission in the transitional millisecond pulsar PSR J1023+0038

Astronomy & Astrophysics EDP Sciences 694 (2025) L19-L19

Authors:

MC Baglio, F Coti Zelati, AK Hughes, F Carotenuto, S Campana, D de Martino, SE Motta, A Papitto, N Rea, DM Russell, DF Torres, A Di Marco, F La Monaca, S Covino, S Giarratana, G Illiano, A Miraval Zanon, K Alabarta, P D’Avanzo, MM Messa

Abstract:

We present a comprehensive study of the flaring mode of the transitional millisecond pulsar (tMSP) PSR J1023+0038 during its X-ray sub-luminous state, using strictly simultaneous X-ray, UV, optical, and radio observations. The X-ray flares exhibit UV and optical counterparts and coincide with the brightest radio flare observed in the past decade, reaching 1.2 mJy at 6 GHz and lasting ∼1 hour. During the flare, the optical polarisation drops from ≃1.4% to ≃0.5%, indicating the emergence of an unpolarised component. We propose that the thickening of the disc, which enlarges the shock region between the pulsar wind and the accretion flow and may drive the X-ray flaring observed in tMSPs, enhances the ionisation level of the disc, thereby generating an increased number of free electrons. These electrons could then be channelled by magnetic field lines into the jet. This increased jet mass-loading could drive the associated radio and optical variability. The radio spectral evolution during flares is consistent with synchrotron self-absorption in jet ejecta or internal shocks within the compact jet. We infer radio polarisation upper limits (< 8.7%, < 2.3%, and < 8.2%, before, during, and after the radio flare) that further support a compact jet origin but do not rule out discrete ejections. Our findings suggest that tMSPs could serve as essential laboratories for investigating jet-launching mechanisms, mainly because they operate under very low mass accretion rates. This accretion regime has not been explored before in the context of accretion-ejection coupling.
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