Unveiling the enigma of ATLAS17aeu
Covino, S.; D'Avanzo, P.; Campana, S.; Della Valle, M.; Melandri, A.; Pian, E.; Salvaterra, R.; D'Elia, V.; Palazzi, E.; Lyman, J. D.; Stella, L.; Fruchter, A. S.; Masetti, N.; Longo, F.; Dadina, M.; Rossi, A.; Fan, X.; Benetti, S.; Testa, V.; Cusano, F.; Amati, L.; Castro-Tirado, A. J.; Pinamonti, M.; Levan, A. J.; Grado, A.; Tanvir, N. R.; Garnavich, P.; Hjorth, J.; Piranomonte, S.; Tomasella, L.; Stratta, G.; Branchesi, M.; Brocato, E.; Greco, G.; Hu, Y. -D.; Perego, A.; Yang, S.; Raimondo, G.; Giunta, A.; O'Brien, P.; Caballero-García, M. D.; Valeev, A. F.; Carini, R.; di Paola, A.; Sokolov, V. V.
Italy, United Kingdom, Spain, United States, Denmark, Chile, Czech Republic, Russia
Abstract
Aims: The unusual transient ATLAS17aeu was serendipitously detected within the sky localisation of the gravitational wave trigger GW 170104. The importance of a possible association with gravitational waves coming from a binary black hole merger led to an extensive follow-up campaign, with the aim of assessing a possible connection with GW 170104.
Methods: With several telescopes, we carried out both photometric and spectroscopic observations of ATLAS17aeu, for several epochs, between ∼3 and ∼230 days after the first detection.
Results: We studied in detail the temporal and spectroscopic properties of ATLAS17aeu and its host galaxy. Although at low significance and not conclusive, we found similarities to the spectral features of a broad-line supernova superposed onto an otherwise typical long-GRB afterglow. Based on analysis of the optical light curve, spectrum, and host galaxy spectral energy distribution, we conclude that the redshift of the source is probably z ≃ 0.5 ± 0.2.
Conclusions: While the redshift range we have determined is marginally compatible with that of the gravitational wave event, the presence of a supernova component and the consistency of this transient with the Ep-Eiso correlation support the conclusion that ATLAS17aeu was associated with the long gamma-ray burst GRB 170105A. This rules out the association of the GRB 170105A/ATLAS17aeu transient with the gravitational wave event GW 170104, which was due to a binary black hole merger.