A1 Refereed original research article in a scientific journal
Multiwavelength analysis of AT 2023sva: a luminous orphan afterglow with evidence for a structured jet
Authors: Srinivasaragavan, Gokul P.; Perley, Daniel A.; Ho, Anna Y. Q.; O'Connor, Brendan; Postigo, Antonio de Ugarte; Sarin, Nikhil; Cenko, S. Bradley; Sollerman, Jesper; Rhodes, Lauren; Green, David A.; Svinkin, Dmitry S.; Bhalerao, Varun; Waratkar, Gaurav; Nayana, A. J.; Chandra, Poonam; Miller, M. Coleman; Malesani, Daniele B.; Ryan, Geoffrey; Srijan, Suryansh; Bellm, Eric C.; Burns, Eric; Titterington, David J.; Stone, Maria B.; Purdum, Josiah; Ahumada, Tomas; Anupama, G. C.; Barway, Sudhanshu; Coughlin, Michael W.; Drake, Andrew; Fender, Rob; Fernandez, Jose F. Aguei; Frederiks, Dmitry D.; Geier, Stefan; Graham, Matthew J.; Kasliwal, Mansi M.; Kulkarni, S. R.; Kumar, Harsh; Li, Maggie L.; Laher, Russ R.; Lysenko, Alexandra L.; Parwani, Gopal; Perley, Richard A.; Ridnaia, Anna, V; Salgundi, Anirudh; Smith, Roger; Sravan, Niharika; Swain, Vishwajeet; Thoene, Christina C.; Tsvetkova, Anastasia E.; Ulanov, Mikhail, V; Vail, Jada; Wise, Jacob L.; Wold, Avery
Publisher: Oxford University Press (OUP)
Publishing place: OXFORD
Publication year: 2025
Journal: Monthly Notices of the Royal Astronomical Society
Journal name in source: Monthly Notices of the Royal Astronomical Society
Journal acronym: MON NOT R ASTRON SOC
Volume: 538
Issue: 1
First page : 351
Last page: 372
Number of pages: 22
ISSN: 0035-8711
eISSN: 1365-2966
DOI: https://doi.org/10.1093/mnras/staf290
Web address : https://doi.org/10.1093/mnras/staf290
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/491603607
We present multiwavelength analysis of ZTF23abelseb (AT 2023sva), an optically discovered fast-fading (Delta m(r)=2.2 mag in Delta t=0.74 d), luminous (M-r similar to-30.0 mag), and red (g-r=0.50 mag) transient at z=2.28 with accompanying luminous radio emission. AT 2023sva does not possess a gamma-ray burst (GRB) counterpart to an isotropic equivalent energy limit of E-gamma,(iso)<1.6x10(52) erg, determined through searching gamma-ray satellite archives between the last non-detection and first detection, making it the sixth example of an optically discovered afterglow with a redshift measurement and no detected GRB counterpart. We analyse AT 2023sva's optical, radio, and X-ray observations to characterize the source. From radio analyses, we find the clear presence of strong interstellar scintillation (ISS) 72 d after the initial explosion, allowing us to place constraints on the source's angular size and bulk Lorentz factor. When comparing the source sizes derived from ISS of orphan events to those of the classical GRB population, we find orphan events have statistically smaller source sizes. We also utilize Bayesian techniques to model the multiwavelength afterglow. Within this framework, we find evidence that AT 2023sva possesses a shallow power-law structured jet viewed slightly off-axis (theta(v)=0.07 +/- 0.02) just outside of the jet's core opening angle (theta(c)=0.06 +/- 0.02). We determine this is likely the reason for the lack of a detected GRB counterpart, but also investigate other scenarios. AT 2023sva's evidence for possessing a structured jet stresses the importance of broadening orphan afterglow search strategies to a diverse range of GRB jet angular energy profiles, to maximize the return of future optical surveys.
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GPS thanks Isiah Holt for useful discussions on nested sampling techniques, Tony Piro for reading the paper on request, and Simi Bhullar for her moral support through out the paper-writing process. AYQH was supported in part by NASA grant number 80NSSC23K1155. MWC acknowledges support from the National Science Foundation with grant numbers PHY-2308862 and PHY-2117997. MBS acknowledges the Finnish Cultural Foundation grant number 00231098 and Finnish Centre for Astronomy with ESO (FINCA) grant. GCA thanks the Indian National Science Academy for support under the INSA Senior Scientist Programme. MMK acknowledges generous support from the David and Lucille Packard Foundation. BO is supported by the McWilliams Postdoctoral Fellowship at Carnegie Mellon University. AT acknowledges the financial support from 'ASI-INAF Accordo Attuativo HERMES Pathinder operazioni n.2022-25-HH.0'.
