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Late-Time HST UV and optical observations of at 2018cow: Extracting a cow from its background

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posted on 2023-11-10, 09:45 authored by A Inkenhaag, PG Jonker, AJ Levan, AA Chrimes, A Mummery, DA Perley, NR Tanvir

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.

History

Author affiliation

School of Physics & Astronomy, University of Leicester

Version

  • VoR (Version of Record)

Published in

Monthly Notices of the Royal Astronomical Society

Volume

525

Issue

3

Pagination

4042 - 4056

Publisher

Oxford University Press (OUP)

issn

0035-8711

eissn

1365-2966

Copyright date

2023

Available date

2023-11-10

Language

en

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