Pulsars, transients and relativistic astrophysics

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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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SN 2023zaw: The Low-energy Explosion of an Ultrastripped Star

The Astrophysical Journal Letters American Astronomical Society 980:2 (2025) l44

Authors:

T Moore, JH Gillanders, M Nicholl, ME Huber, SJ Smartt, S Srivastav, HF Stevance, T-W Chen, KC Chambers, JP Anderson, MD Fulton, SR Oates, C Angus, G Pignata, N Erasmus, H Gao, J Herman, C-C Lin, T Lowe, EA Magnier, P Minguez, C-C Ngeow, X Sheng, SA Sim, KW Smith, R Wainscoat, S Yang, DR Young, K-J Zeng
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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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Reduction of the type Ia supernova host galaxy step in the outer regions of galaxies

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

Authors:

M Toy, P Wiseman, M Sullivan, D Scolnic, M Vincenzi, D Brout, TM Davis, C Frohmaier, L Galbany, C Lidman, J Lee, L Kelsey, R Kessler, A Möller, B Popovic, BO Sánchez, P Shah, M Smith, S Allam, M Aguena, O Alves, D Bacon, D Brooks, DL Burke, A Carnero Rosell, J Carretero, LN da Costa, MES Pereira, S Desai, HT Diehl, P Doel, A Drlica-Wagner, S Everett, I Ferrero, B Flaugher, J Frieman, J García-Bellido, M Gatti, E Gaztanaga, G Giannini, RA Gruendl, G Gutierrez, SR Hinton, DL Hollowood, K Honscheid, DJ James, O Lahav, S Lee, JL Marshall, J Mena-Fernández, R Miquel, A Palmese, A Pieres, AA Plazas Malagón, AK Romer, S Samuroff, E Sanchez, D Sanchez Cid, M Schubnell, E Suchyta, MEC Swanson, G Tarle, DL Tucker, V Vikram, AR Walker, N Weaverdyck

Abstract:

Abstract Using 1533 type Ia supernovae (SNe Ia) from the five-year sample of the Dark Energy Survey (DES), we investigate the relationship between the projected galactocentric separation of the SNe and their host galaxies and their light curves and standardization. We show, for the first time, that the difference in SN Ia post-standardization brightnesses between high and low-mass hosts reduces from 0.078 ± 0.011 mag in the full sample to 0.036 ± 0.018 mag for SNe Ia located in the outer regions of their host galaxies, while increasing to 0.100 ± 0.014 mag for SNe in the inner regions. The difference in the size of the mass step between inner and outer regions is 0.064 ± 0.023 mag. In these inner regions, the step can be reduced (but not removed) using a model where the RV of dust along the line-of-sight to the SN changes as a function of galaxy properties. We investigate the remaining difference using the distributions of the SN Ia stretch parameter to test the inferred age of SN progenitors. Comparing red (older) environments only, outer regions have a higher proportion of high-stretch SNe and a more homogeneous stretch distribution. However, this effect cannot explain the reduction in significance of any Hubble residual step in outer regions. We conclude that the standardized distances of SNe Ia located in the outer regions of galaxies are less affected by their global host galaxy properties than those in the inner regions.
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