A1 Refereed original research article in a scientific journal
Multiwavelength observations of the extraordinary accretion event AT2021lwx
Authors: Wiseman P, Wang Y, Honig S, Castro-Segura N, Clark P, Frohmaier C, Fulton MD, Leloudas G, Middleton M, Muller-Bravo TE, Mummery A, Pursiainen M, Smartt SJ, Smith K, Sullivan M, Anderson JP, Pulido JAA, Charalampopoulos P, Banerji M, Dennefeld M, Galbany L, Gromadzki M, Gutierrez CP, Ihanec N, Kankare E, Lawrence A, Mockler B, Moore T, Nicholl M, Onori F, Petrushevska T, Ragosta F, Rest S, Smith M, Wevers T, Carini R, Chen TW, Chambers K, Gao H, Huber M, Inserra C, Magnier E, Makrygianni L, Toy M, Vincentelli F, Young DR
Publisher: OXFORD UNIV PRESS
Publication year: 2023
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: 522
Issue: 3
First page : 3992
Last page: 4002
Number of pages: 11
ISSN: 0035-8711
DOI: https://doi.org/10.1093/mnras/stad1000
Web address : https://doi.org/10.1093/mnras/stad1000
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/180214727
We present observations from X-ray to mid-infrared wavelengths of the most energetic non-quasar transient ever observed, AT2021lwx. Our data show a single optical brightening by a factor >100 to a luminosity of 7 x 10(45) erg s(-1) and a total radiated energy of 1.5 x 10(53) erg, both greater than any known optical transient. The decline is smooth and exponential and the ultraviolet-optical spectral energy distribution resembles a blackbody with a temperature of 1.2 x 10(4) K. Tentative X-ray detections indicate a secondary mode of emission, while a delayed mid-infrared flare points to the presence of dust surrounding the transient. The spectra are similar to recently discovered optical flares in known active galactic nuclei but lack some characteristic features. The lack of emission for the previous 7 yr is inconsistent with the short-term, stochastic variability observed in quasars, while the extreme luminosity and long time-scale of the transient disfavour the disruption of a single solar-mass star. The luminosity could be generated by the disruption of a much more massive star, but the likelihood of such an event occurring is small. A plausible scenario is the accretion of a giant molecular cloud by a dormant black hole of 10(8)-10(9) solar masses. AT2021lwx thus represents an extreme extension of the known scenarios of black hole accretion.
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