Optical evolution of AT 2024wpp: the high-velocity outflows in Cow-like transients are consistent with high spherical symmetry

ABSTRACT We present the analysis of optical/near-infrared (NIR) data and host galaxy properties of a bright, extremely rapidly evolving transient, AT 2024wpp, which resembles the enigmatic AT 2018cow. AT 2024wpp rose to a peak brightness of $c=-21.9$ mag in 4.3 d and remained above the half-maximum brightness for only 6.7 d. The blackbody fits to the photometry show that the event remained persistently hot ($T\gtrsim 20\, 000$ K) with a rapidly receding photosphere ($v\sim 11\, 500$ km s$^{-1}$), similarly to AT 2018cow albeit with a several times larger photosphere. $JH$ photometry reveals an NIR excess over the thermal emission at $\sim +20$ d, indicating a presence of an additional component. The spectra are consistent with blackbody emission throughout our spectral sequence ending at $+21.9$ d, showing a tentative, very broad emission feature at $\sim 5500$ Å – implying that the optical photosphere is likely within a near-relativistic outflow. Furthermore, reports of strong X-ray and radio emission cement the nature of AT 2024wpp as a likely Cow-like transient. AT 2024wpp is the second event of the class with optical polarimetry. Our $BVRI$ observations obtained from $+6.1$ to $+14.4$ d show a low polarization of $P\lesssim 0.5$ per cent across all bands, similar to AT 2018cow that was consistent with $P\sim 0$ per cent during the same outflow-driven phase. In the absence of evidence for a preferential viewing angle, it is unlikely that both events would have shown low polarization in the case that their photospheres were aspherical. As such, we conclude that the near-relativistic outflows launched in these events are likely highly spherical, but polarimetric observations of further events are crucial to constrain their ejecta geometry and stratification in detail.

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Journal
Monthly Notices of the Royal Astronomical Society
Published
2025-02-07
DOI
https://doi.org/10.1093/mnras/staf232
Citations
6
Primary Topic
Astrophysical Phenomena and Observations
Type
article
Field-Weighted Citation Impact
6.93

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article

Optical evolution of AT 2024wpp: the high-velocity outflows in Cow-like transients are consistent with high spherical symmetry

D O’Neill, J. D. Lyman, T. Nagao, Danny T. H. Steeghs et al.
6 citations
Monthly Notices of the Royal Astronomical Society
Astrophysical Phenomena and Observations
6.93
article

Optical evolution of AT 2024wpp: the high-velocity outflows in Cow-like transients are consistent with high spherical symmetry

D O’Neill, J. D. Lyman, T. Nagao, Danny T. H. Steeghs, Kenta Taguchi, K. Ackley, M Pursiainen, P. Charalampopoulos, Gavin Ramsay, T. Kravtsov, Thomas L. Killestein, R. Kotak, Amit Kumar, D. L. Coppejans, Keiichi Maeda, H. Kuncarayakti, D. K. Galloway, Bob Warwick, V. S. Dhillon, G. Leloudas
article en
6 citations

Abstract

ABSTRACT We present the analysis of optical/near-infrared (NIR) data and host galaxy properties of a bright, extremely rapidly evolving transient, AT 2024wpp, which resembles the enigmatic AT 2018cow. AT 2024wpp rose to a peak brightness of $c=-21.9$ mag in 4.3 d and remained above the half-maximum brightness for only 6.7 d. The blackbody fits to the photometry show that the event remained persistently hot ($T\gtrsim 20\, 000$ K) with a rapidly receding photosphere ($v\sim 11\, 500$ km s$^{-1}$), similarly to AT 2018cow albeit with a several times larger photosphere. $JH$ photometry reveals an NIR excess over the thermal emission at $\sim +20$ d, indicating a presence of an additional component. The spectra are consistent with blackbody emission throughout our spectral sequence ending at $+21.9$ d, showing a tentative, very broad emission feature at $\sim 5500$ Å – implying that the optical photosphere is likely within a near-relativistic outflow. Furthermore, reports of strong X-ray and radio emission cement the nature of AT 2024wpp as a likely Cow-like transient. AT 2024wpp is the second event of the class with optical polarimetry. Our $BVRI$ observations obtained from $+6.1$ to $+14.4$ d show a low polarization of $P\lesssim 0.5$ per cent across all bands, similar to AT 2018cow that was consistent with $P\sim 0$ per cent during the same outflow-driven phase. In the absence of evidence for a preferential viewing angle, it is unlikely that both events would have shown low polarization in the case that their photospheres were aspherical. As such, we conclude that the near-relativistic outflows launched in these events are likely highly spherical, but polarimetric observations of further events are crucial to constrain their ejecta geometry and stratification in detail.

Monthly Notices of the Royal Astronomical SocietyVol. 537(4)
University of Turku (FI), Royal Holloway University of London (GB), Kyoto University (JP), Armagh Observatory & Planetarium (GB), University of Warwick (GB), Physical Sciences (United States) (US), Instituto de Astrofísica de Canarias (ES), Metsähallitus (Finland) (FI), Monash University (AU), University of Sheffield (GB), Technical University of Denmark (DK), Aalto University (FI)
National Science Foundation, U.S. Department of Energy, National Aeronautics and Space Administration, Stanford University, University of California, Albert Ellis Institute, University of Pennsylvania, Ohio State University, University of Chicago, University of Michigan, Aarhus Universitet, University of Arizona, Texas A and M University, University of Portsmouth, University of Illinois System, University of Leicester, University of Warwick, University College London, University of Nottingham, University of Sussex, University of Edinburgh, University of Sheffield, Københavns Universitet, Monash University, Academy of Finland, Chinese Academy of Sciences, Ministerio de Ciencia e Innovación, Universitetet i Oslo, Háskóli Íslands, Turun Yliopisto, Kyoto University, Stockholms Universitet, Turun Yliopistosäätiö, Science and Technology Facilities Council, Japan Society for the Promotion of Science
Openalex Percentile: Top 4%
Astrophysical Phenomena and Observations
6.93
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