open access publication

Article, 2024

Swift/UVOT discovery of Swift J221951−484240: a UV luminous ambiguous nuclear transient

Monthly Notices of the Royal Astronomical Society, ISSN 1365-2966, 0035-8711, Volume 530, 2, Pages 1688-1710, 10.1093/mnras/stae795

Contributors

Oates, Samantha R 0000-0001-9309-7873 (Corresponding author) [1] [2] Kuin, N P M [3] Nicholl, Matt 0000-0002-2555-3192 [2] [4] Marshall, F [5] Ridley, Evan J 0009-0008-2579-1810 [2] Boutsia, Konstantina 0000-0003-4432-5037 [6] [7] Breeveld, Alice A 0000-0002-0001-7270 [3] Buckley, David A H 0000-0002-7004-9956 [8] [9] [10] Cenko, Stephen Bradley [5] [11] De Pasquale, M [12] Edwards, P G [13] Gromadzki, M [14] Gupta, R [15] [16] Laha, Sibasish [5] [17] [18] Morrell, Nidia Irene 0000-0003-2535-3091 [7] Orio, M [19] [20] Pandey, S B [16] Page, M J [3] Page, K L [21] Parsotan, Tyler M 0000-0002-4299-2517 [5] Rau, A [22] Schady, Patricia 0000-0002-1214-770X [23] Stevens, J [13] Brown, P J [24] Evans, P A [21] Gronwall, Caryl A 0000-0001-6842-2371 [25] Kennea, Jamie A 0000-0002-6745-4790 [25] Klingler, Noel J [5] [17] [18] Siegel, Michael H 0000-0003-1817-3009 [25] Tohuvavohu, Aaron A 0000-0002-2810-8764 [26] Ambrosi, E [27] Barthelmy, Scott D [5] Beardmore, A P [21] Bernardini, M G [28] Bonnerot, Clément [2] Campana, S [28] Caputo, R [5] Ciroi, Stefano 0000-0001-9539-3940 [29] Cusumano, G [27] D’Aì, A [27] D'Avanzo, Paolo 0000-0001-7164-1508 [28] D'Elia, Valerio 0000-0002-7320-5862 [30] [31] Giommi, P [30] Hartmann, Dieter H 0000-0002-8028-0991 [32] Krimm, Hans A 0000-0003-4348-6058 [33] Malesani, Daniele Bjørn 0000-0002-7517-326X [34] [35] Melandri, A [31] Nousek, J A [25] O’Brien, P T [21] Osborne, J P [21] Pagani, C [21] Palmer, D M [36] Perri, Matteo 0000-0003-3613-4409 [30] [31] Racusin, Judith L 0000-0002-4744-9898 [5] Sakamoto, T [37] Sbarufatti, Boris 0000-0001-6620-8347 [25] [27] Schlieder, J E [5] Tagliaferri, Gianpiero 0000-0003-0121-0723 [28] Troja, Eleonora 0000-0002-1869-7817 [38] [39] Xu, Dong [39] [40]

Affiliations

  1. [1] Lancaster University
    2. [NORA names: United Kingdom; Europe, Non-EU; OECD];
  2. [2] University of Birmingham
    3. [NORA names: United Kingdom; Europe, Non-EU; OECD];
  3. [3] University College London
    4. [NORA names: United Kingdom; Europe, Non-EU; OECD];
  4. [4] Queen's University Belfast
    5. [NORA names: United Kingdom; Europe, Non-EU; OECD];
  5. [5] Astrophysics Science Division
    6. [NORA names: United States; America, North; OECD];

Abstract

ABSTRACT We report the discovery of Swift J221951−484240 (hereafter: J221951), a luminous slow-evolving blue transient that was detected by the Neil Gehrels Swift Observatory Ultraviolet/Optical Telescope (Swift/UVOT) during the follow-up of gravitational wave alert S190930t, to which it is unrelated. Swift/UVOT photometry shows the UV spectral energy distribution of the transient to be well modelled by a slowly shrinking blackbody with an approximately constant temperature of T ∼ 2.5 × 104 K. At a redshift z = 0.5205, J221951 had a peak absolute magnitude of Mu,AB = −23 mag, peak bolometric luminosity $L_{max}=1.1\times 10^{45}~{\rm erg\, s}^{-1}$ and a total radiated energy of E > 2.6 × 1052 erg. The archival Wide-field Infrared Survey Explorer IR photometry shows a slow rise prior to a peak near the discovery date. Spectroscopic UV observations display broad absorption lines in N  v and O  vi, pointing towards an outflow at coronal temperatures. The lack of emission in the higher H α lines, N i and other neutral lines is consistent with a viewing angle close to the plane of the accretion or debris disc. The origin of J221951 cannot be determined with certainty but has properties consistent with a tidal disruption event and the turn-on of an active galactic nucleus.

Keywords

IR photometry, Neil, O VI, Swift/UVOT, UV, UV observations, UV spectral energy distribution, Ultraviolet/Optical Telescope, absorption, absorption lines, accretion, active galactic nuclei, angle, approximately constant temperature, approximation, archival, blackbody, certainty, constant temperature of T, coronal temperatures, date, debris, debris disks, determined with certainty, discovery, discovery date, disk, disruptive events, distribution, emission, energy distribution, erg\, events, follow-up, galactic nuclei, higher H, lack, lack of emission, lines, mag, magnitude, neutral line, nucleus, observations, origin, outflow, photometry, plane, properties, redshift, redshift z, rise, slow rise, slow-evolving, spectral energy distribution, s}^{-1}$, telescope, temperature, temperature of T, tidal disruption events, viewing angle

Funders

  • European Research Council
  • Indian Space Research Organisation
  • Danish National Research Foundation
  • National Aeronautics and Space Administration
  • Ministry of Education, Universities and Research
  • Agenzia Spaziale Italiana
  • Commonwealth Scientific and Industrial Research Organisation
  • Scientific and Technological Research Council of Turkey
  • National Science Foundation
  • Jet Propulsion Laboratory
  • Deutsche Forschungsgemeinschaft
  • Ministero degli Affari Esteri
  • United Kingdom Space Agency
  • European Commission
  • The Velux Foundations
  • Goddard Space Flight Center

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