Optical evolution of AT 2024wpp: the high-velocity outflows in Cow-like transients are consistent with high spherical symmetry
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A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
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en
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12
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Monthly Notices of the Royal Astronomical Society, Volume 537, issue 4, pp. 3298-3309
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 ≳ 20 000 K) with a rapidly receding photosphere (v ∼ 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 ∼ +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 ∼ 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 ≲ 0.5 per cent across all bands, similar to AT 2018cow that was consistent with P ∼ 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.Description
Publisher Copyright: © 2025 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society.
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Pursiainen, M, Killestein, T L, Kuncarayakti, H, Charalampopoulos, P, Warwick, B, Lyman, J, Kotak, R, Leloudas, G, Coppejans, D, Kravtsov, T, Maeda, K, Nagao, T, Taguchi, K, Ackley, K, Dhillon, V S, Galloway, D K, Kumar, A, O’Neill, D, Ramsay, G & Steeghs, D 2025, 'Optical evolution of AT 2024wpp: the high-velocity outflows in Cow-like transients are consistent with high spherical symmetry', Monthly Notices of the Royal Astronomical Society, vol. 537, no. 4, pp. 3298-3309. https://doi.org/10.1093/mnras/staf232