Late-time HST UV and optical observations of AT 2018cow: extracting a cow from its background

Author:

Inkenhaag Anne12ORCID,Jonker Peter G12,Levan Andrew J13,Chrimes Ashley A1ORCID,Mummery Andrew4,Perley Daniel A5ORCID,Tanvir Nial R6

Affiliation:

1. Department of Astrophysics/IMAPP, Radboud University Nijmegen , P.O. Box 9010, NL-6500 GL Nijmegen , the Netherlands

2. SRON, Netherlands Institute for Space Research , Niels Bohrweg 4, NL-2333 CA Leiden , the Netherlands

3. Department of Physics, University of Warwick , Gibbet Hill Road, Coventry CV4 7AL , UK

4. Oxford Astrophysics, Denys Wilkinson Building , Keble Road, Oxford OX1 3RH , UK

5. Astrophysics Research Institute, Liverpool John Moores University , IC2, Liverpool Science Park, 146 Brownlow Hill, Liverpool L3 5RF , UK

6. School of Physics and Astronomy, University of Leicester, University Road , Leicester LE1 7RH , UK

Abstract

ABSTRACT The bright, blue, rapidly evolving AT 2018cow is a well-studied peculiar extragalactic transient. Despite an abundance of multiwavelength data, there still is no consensus on the nature of the event. We present our analysis of three epochs of Hubble Space Telescope (HST) observations spanning the period from 713 to 1474 d post-burst, paying particular attention to uncertainties of the transient photometry introduced by the complex background in which AT 2018cow resides. Photometric measurements show evident fading in the UV and more subtle but significant fading in the optical. During the last HST observation, the transient’s optical/UV colours were still bluer than those of the substantial population of compact, young, star-forming regions in the host of AT 2018cow, suggesting some continued transient contribution to the light. However, a compact source underlying the transient would substantially modify the resulting spectral energy distribution, depending on its contribution in the various bands. In particular, in the optical filters, the complex, diffuse background poses a problem for precise photometry. An underlying cluster is expected for a supernova occurring within a young stellar environment or a tidal-disruption event (TDE) within a dense older one. While many recent works have focused on the supernova interpretation, we note the substantial similarity in UV light-curve morphology between AT 2018cow and several tidal disruption events around supermassive black holes. Assuming AT 2018cow arises from a TDE-like event, we fit the late-time emission with a disc model and find MBH = 103.2 ± 0.8 M⊙. Further observations are necessary to determine the late-time evolution of the transient and its immediate environment.

Funder

NWO

Leverhulme Trust

MINECO

Publisher

Oxford University Press (OUP)

Subject

Space and Planetary Science,Astronomy and Astrophysics

Cited by 1 articles. 订阅此论文施引文献 订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献

1. AT2023fhn (the Finch): a luminous fast blue optical transient at a large offset from its host galaxy;Monthly Notices of the Royal Astronomical Society: Letters;2023-10-04

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