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

Journal Article · 18 March 2024 · Monthly Notices of the Royal Astronomical Society

DOI: https://doi.org/10.1093/mnras/stae795 · OSTI ID:2340879

Oates, S. R.  ^[1]; Kuin, N. M.  ^[2]; Nicholl, M.  ^[3]; Marshall, F. ^[4]; Ridley, E.  ^[5]; Boutsia, K.  ^[6]; Breeveld, A. A. ^[2]; Buckley, D. H.  ^[7]; Cenko, S. B. ^[8]; De Pasquale, M. ^[9]; Edwards, P. G. ^[10]; Gromadzki, M.  ^[11]; Gupta, R. ^[12]; Laha, S. ^[13]; Morrell, N. ^[14]; Orio, M.  ^[15]; Pandey, S. B. ^[16]; Page, M. J.  ^[2]; Page, K. L. ^[17]; Parsotan, T.  ^[4] ; Rau, A. ^[18]; Schady, P.  ^[19]; Stevens, J. ^[20]; Brown, P. J. ^[21]; Evans, P. A.  ^[17]; Gronwall, C. ^[22]; Kennea, J. A.  ^[23]; Klingler, N. J. ^[13]; Siegel, M. H. ^[23]; Tohuvavohu, A. ^[24]; Ambrosi, E.  ^[25]; Barthelmy, S. D. ^[4]; Beardmore, A. P.  ^[17]; Bernardini, M. G. ^[26]; Bonnerot, C.  ^[5]; Campana, S.  ^[26]; Caputo, R. ^[4]; Ciroi, S. ^[27]; Cusumano, G.  ^[25]; D’Aì, A.  ^[25]; D’Avanzo, P. ^[26]; D’Elia, V. ^[28]; Giommi, P.  ^[29]; Hartmann, D. H. ^[30]; Krimm, H. A. ^[31]; Malesani, D. B.  ^[32]; Melandri, A.  ^[33]; Nousek, J. A. ^[23]; O’Brien, P. T. ^[17]; Osborne, J. P. ^[17]; Pagani, C. ^[17]; Palmer, D. M.  ^[34]; Perri, M. ^[35]; Racusin, J. L. ^[4]; Sakamoto, T. ^[36]; Sbarufatti, B. ^[37]; Schlieder, J. E. ^[4]; Tagliaferri, G. ^[26]; Troja, E.  ^[38]; Xu, D. ^[39]

---

1. Department of Physics, Lancaster University , Lancaster LA1 4YB , UK; School of Physics and Astronomy & Institute for Gravitational Wave Astronomy, University of Birmingham , Birmingham, B15 2TT , UK
2. University College London, Mullard Space Science Laboratory , Holmbury St Mary, Dorking RH5 6NT , UK
3. School of Physics and Astronomy & Institute for Gravitational Wave Astronomy, University of Birmingham , Birmingham, B15 2TT , UK; Astrophysics Research Centre, School of Mathematics and Physics, Queens University Belfast , Belfast BT7 1NN , UK
4. Astrophysics Science Division, NASA Goddard Space Flight Center , Greenbelt, MD 20771 , USA
5. School of Physics and Astronomy & Institute for Gravitational Wave Astronomy, University of Birmingham , Birmingham, B15 2TT , UK
6. Cerro Tololo Inter-American Observatory/NSFs NOIRLab , Casilla 603, La Serena , Chile; Las Campanas Observatory , Carnegie Observatories, Colina El Pino, Casilla 601, La Serena , Chile
7. South African Astronomical Observatory , PO Box 9, Observatory 7935, Cape Town , South Africa; Department of Astronomy, University of Cape Town , Private Bag X3, Rondebosch 7701 , South Africa; Department of Physics, University of the Free State , PO Box 339, Bloemfontein 9300 , South Africa
8. Astrophysics Science Division, NASA Goddard Space Flight Center , Greenbelt, MD 20771 , USA; Joint Space-Science Institute, Computer and Space Sciences Building, University of Maryland , College Park, MD 20742 , USA
9. University of Messina, MIFT Department , Polo Papardo, Viale F.S. D’Alcontres 31, I-98166 Messina , Italy
10. Australia Telescope National Facility, CSIRO Space and Astronomy , PO Box 76, Epping, NSW 1710 , Australia
11. Astronomical Observatory, University of Warsaw , Al. Ujazdowskie 4, PL-00-478 Warszawa , Poland
12. Aryabhatta Research Institute of Observational Sciences (ARIES) , Manora Peak, Nainital-263002 , India; Department of Physics, Deen Dayal Upadhyaya Gorakhpur University , Gorakhpur-273009 , India
13. Astrophysics Science Division, NASA Goddard Space Flight Center , Greenbelt, MD 20771 , USA; Center for Space Science and Technology, University of Maryland Baltimore County , 1000 Hilltop Circle, Baltimore, MD 21250 , USA; Center for Research and Exploration in Space Science and Technology, NASA/GSFC , Greenbelt, MD 20771 , USA
14. Las Campanas Observatory , Carnegie Observatories, Colina El Pino, Casilla 601, La Serena , Chile
15. Department of Astronomy, University of Wisconsin , 475 N. Charter Str, Madison, WI 53704 , USA; INAF-Osservatorio di Padova , vicolo dell Osservatorio 5, I-35122 Padova , Italy
16. Aryabhatta Research Institute of Observational Sciences (ARIES) , Manora Peak, Nainital-263002 , India
17. School of Physics and Astronomy, University of Leicester , Leicester LE1 7RH , UK
18. Max-Planck-Institut für Extraterrestrische Physik , Giessenbachstraße 1, D-85748 Garching , Germany
19. Department of Physics, University of Bath , Bath BA2 7AY , UK
20. Australia Telescope National Facility, CSIRO Space and Astronomy , 1828 Yarrie Lake Road, Narrabri, NSW 2390 , Australia
21. George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Mitchell Physics Building, Texas A&M University, Department of Physics and Astronomy , College Station, TX 77843 , USA
22. Department of Astronomy and Astrophysics, The Pennsylvania State University , University Park, PA 16802 , USA; Institute for Gravitation and the Cosmos, The Pennsylvania State University , University Park, PA 16802 , USA
23. Department of Astronomy and Astrophysics, The Pennsylvania State University , University Park, PA 16802 , USA
24. Department of Astronomy and Astrophysics, University of Toronto , Toronto, ON, M5S 3H4 , Canada
25. INAF – IASF Palermo , Via Ugo La Malfa 153, I-90146 Palermo , Italy
26. INAF – Osservatorio Astronomico di Brera , Via Bianchi 46, I-23807 Merate , Italy
27. Dipartimento di Fisica e Astronomia, Universitá di Padova , 35122 Padova , Italy
28. INAF–Osservatorio Astronomico di Roma , Via Frascati 33, I-00040 Monteporzio Catone , Italy; Space Science Data Center (SSDC) – Agenzia Spaziale Italiana (ASI) , I-00133 Roma , Italy
29. Space Science Data Center (SSDC) – Agenzia Spaziale Italiana (ASI) , I-00133 Roma , Italy
30. Department of Physics and Astronomy, Clemson University , Kinard Lab of Physics, Clemson, SC 29634-0978 , USA
31. National Science Foundation , Alexandria, VA 22314 , USA
32. Department of Astrophysics/IMAPP, Radboud University , NL-6525 AJ Nijmegen , the Netherlands; Cosmic Dawn Center (DAWN) , Denmark; Niels Bohr Institute, University of Copenhagen , Jagtvej 128, DK-2200 Copenhagen N , Denmark
33. INAF–Osservatorio Astronomico di Roma , Via Frascati 33, I-00040 Monteporzio Catone , Italy
34. Los Alamos National Laboratory , B244, Los Alamos, NM 87545 , USA
35. Space Science Data Center (SSDC) – Agenzia Spaziale Italiana (ASI) , I-00133 Roma , Italy; INAF–Osservatorio Astronomico di Roma , Via Frascati 33, I-00040 Monteporzio Catone , Italy
36. Department of Physics and Mathematics, Aoyama Gakuin University , Sagamihara, Kanagawa, 252-5258 , Japan
37. INAF – IASF Palermo , Via Ugo La Malfa 153, I-90146 Palermo , Italy; Department of Astronomy and Astrophysics, The Pennsylvania State University , University Park, PA 16802 , USA
38. Department of Physics, University of Rome Tor Vergata , via della Ricerca Scientifica 1, I-00100 Rome , Italy; INAF, Via del Fosso del Cavaliere , 100, I-00133 Rome , Italy
39. INAF, Via del Fosso del Cavaliere , 100, I-00133 Rome , Italy; Key Laboratory of Space Astronomy and Technology, National Astronomical Observatories, Chinese Academy of Sciences , Beijing 100101 , China

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 M_u,AB = −23 mag, peak bolometric luminosity Lmax = 1.1 x 10⁴⁵ ergs^-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.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA); National Aeronautics and Space Administration (NASA); National Science Foundation (NSF); Scientific and Technological Research Council of Turkey (TÜBITAK); United Kingdom Space Agency; Italian Space Agency; Italian Ministry of Foreign Affairs and International Cooperation; European Union’s Horizon 2020; Danish National Research Foundation
• Contributing Organization: LIGO Scientific Collaboration; Virgo Scientific Collaboration
• Grant/Contract Number: 89233218CNA000001
• OSTI ID: 2340879
• Report Number(s): LA-UR--23-24498
• Journal Information: Monthly Notices of the Royal Astronomical Society, Journal Name: Monthly Notices of the Royal Astronomical Society Journal Issue: 2 Vol. 530; ISSN 0035-8711
• Publisher: Oxford University PressCopyright Statement
• Country of Publication: United States
• Language: English