Browsing by Author "Leloudas, G."
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Item Evidence for rapid disc formation and reprocessing in the X-ray bright tidal disruption event candidate AT 2018fyk(OXFORD UNIV PRESS INC, 2019-10) Wevers, T.; Pasham, D. R.; van Velzen, S.; Leloudas, G.; Schulze, Steve; Miller-Jones, J. C. A.; Jonker, P. G.; Gromadzki, M.; Kankare, E.; Hodgkin, S. T.; Wyrzykowski, L.; Kostrzewa-Rutkowska, Z.; Moran, S.; Berton, Marco; Maguire, K.; Onori, F.; Mattila, S.; Nicholl, M.; Metsähovi Radio Observatory; University of Cambridge; Massachusetts Institute of Technology; University of Maryland, Baltimore; Technical University of Denmark; Weizmann Institute of Science; Curtin University; SRON Netherlands Institute for Space Research; University of Warsaw; University of Turku; Trinity College Dublin; Istituto di Astrofisica e Planetologia Spaziali; University of EdinburghWe present optical spectroscopic and Swift UVOT/XRT observations of the X-ray and UV/optical bright tidal disruption event (TDE) candidate AT 2018fyk/ASASSN-18ul discovered by ASAS-SN. The Swift light curve is atypical for a TDE, entering a plateau after similar to 40d of decline from peak. After 80d the UV/optical light curve breaks again to decline further, while the X-ray emission becomes brighter and harder. In addition to broad H, He, and potentially O/Fe lines, narrow emission lines emerge in the optical spectra during the plateau phase. We identify both high-ionization (Oiii) and low-ionization (Feii) lines, which are visible for similar to 45d. We similarly identify Feii lines in optical spectra of ASASSN-15oi 330 d after discovery, indicating that a class of Fe-rich TDEs exists. The spectral similarity between AT 2018fyk, narrow-line Seyfert 1 galaxies, and some extreme coronal line emitters suggests that TDEs are capable of creating similar physical conditions in the nuclei of galaxies. The Feii lines can be associated with the formation of a compact accretion disc, as the emergence of low-ionization emission lines requires optically thick, high-density gas. Taken together with the plateau in X-ray and UV/optical luminosity this indicates that emission from the central source is efficiently reprocessed into UV/optical wavelengths. Such a two-component light curve is very similar to that seen in the TDE candidate ASASSN-15lh, and is a natural consequence of a relativistic orbital pericentre.Item SN 2017ens: The Metamorphosis of a Luminous Broadlined Type Ic Supernova into an SN IIn(2018-11-10) Chen, T. W.; Inserra, C.; Fraser, M.; Moriya, T. J.; Schady, P.; Schweyer, T.; Filippenko, A. V.; Perley, D. A.; Ruiter, A. J.; Seitenzahl, I.; Sollerman, J.; Taddia, F.; Anderson, J. P.; Foley, R. J.; Jerkstrand, A.; Ngeow, C. C.; Pan, Y. C.; Pastorello, A.; Points, S.; Smartt, S. J.; Smith, K. W.; Taubenberger, S.; Wiseman, P.; Young, D. R.; Benetti, S.; Berton, M.; Bufano, F.; Clark, P.; Valle, M. Della; Galbany, L.; Gal-Yam, A.; Gromadzki, M.; Gutiérrez, C. P.; Heinze, A.; Kankare, E.; Kilpatrick, C. D.; Kuncarayakti, H.; Leloudas, G.; Lin, Z. Y.; Maguire, K.; Mazzali, P.; McBrien, O.; Prentice, S. J.; Rau, A.; Rest, A.; Siebert, M. R.; Stalder, B.; Tonry, J. L.; Yu, P. C.; Metsähovi Radio Observatory; Max Planck Institute for Extraterrestrial Physics; University of Southampton; University College Dublin; National Astronomical Observatory of Japan; University of California, Berkeley; Liverpool John Moores University; University of New South Wales; Stockholm University; European Southern Observatory; University of California, Santa Cruz; Max Planck Institute for Astrophysics; National Central University; INAF - Osservatorio Astronomico di Padova; National Optical Astronomy Observatory; Queen's University Belfast; INAF - Osservatorio Astrofisico di Catania; Osservatorio Astronomico di Capodimonte; University of Pittsburgh; Weizmann Institute of Science; University of Warsaw; University of Hawai’i at Manoa; University of Turku; Technical University of Denmark; Space Telescope Science InstituteWe present observations of supernova (SN) 2017ens, discovered by the ATLAS survey and identified as a hot blue object through the GREAT program. The redshift z = 0.1086 implies a peak brightness of M g = -21.1 mag, placing the object within the regime of superluminous supernovae. We observe a dramatic spectral evolution, from initially being blue and featureless, to later developing features similar to those of the broadlined Type Ic SN 1998bw, and finally showing ∼2000 km s-1 wide Hα and Hβ emission. Relatively narrow Balmer emission (reminiscent of a SN IIn) is present at all times. We also detect coronal lines, indicative of a dense circumstellar medium. We constrain the progenitor wind velocity to ∼50-60 km s-1 based on P-Cygni profiles, which is far slower than those present in Wolf-Rayet stars. This may suggest that the progenitor passed through a luminous blue variable phase, or that the wind is instead from a binary companion red supergiant star. At late times we see the ∼2000 km s-1 wide Hα emission persisting at high luminosity (∼3 × 1040 erg s-1) for at least 100 day, perhaps indicative of additional mass loss at high velocities that could have been ejected by a pulsational pair instability.Item SN 2017gci: A nearby Type i Superluminous Supernova with a bumpy tail(OXFORD UNIV PRESS INC, 2021-04-01) Fiore, A.; Chen, T. W.; Jerkstrand, A.; Benetti, S.; Ciolfi, R.; Inserra, C.; Cappellaro, E.; Pastorello, A.; Leloudas, G.; Schulze, S.; Berton, M.; Burke, J.; McCully, C.; Fong, W.; Galbany, L.; Gromadzki, M.; Gutiérrez, C. P.; Hiramatsu, D.; Hosseinzadeh, G.; Howell, D. A.; Kankare, E.; Lunnan, R.; Müller-Bravo, T. E.; O' Neill, D.; Nicholl, M.; Rau, A.; Sollerman, J.; Terreran, G.; Valenti, S.; Young, D. R.; Metsähovi Radio Observatory; INAF - Osservatorio Astronomico di Padova; Stockholm University; Cardiff University; Technical University of Denmark; Weizmann Institute of Science; University of California, Santa Barbara; Las Cumbres Observatory; Northwestern University; Instituto Carlos I de Física Teórica y Computacional; University of Warsaw; University of Southampton; Harvard University; University of Turku; Queen's University Belfast; University of Birmingham; Max Planck Institute for Extraterrestrial Physics; University of California, DavisWe present and discuss the optical spectrophotometric observations of the nearby (z = 0.087) Type I superluminous supernova (SLSN I) SN 2017gci, whose peak K-corrected absolute magnitude reaches M-g = -21.5 mag. Its photometric and spectroscopic evolution includes features of both slow- and of fast-evolving SLSN I, thus favoring a continuum distribution between the two SLSN-I subclasses. In particular, similarly to other SLSNe I, the multiband light curves (LCs) of SN 2017gci show two re-brightenings at about 103 and 142 d after the maximum light. Interestingly, this broadly agrees with a broad emission feature emerging around 6520 angstrom after similar to 51 d from the maximum light, which is followed by a sharp knee in the LC. If we interpret this feature as H alpha, this could support the fact that the bumps are the signature of late interactions of the ejecta with a (hydrogen-rich) circumstellar material. Then we fitted magnetar- and CSM-interaction-powered synthetic LCs on to the bolometric one of SN 2017gci. In the magnetar case, the fit suggests a polar magnetic field B-p similar or equal to 6 x 10(14) G, an initial period of the magnetar P-initial similar or equal to 2.8 ms, an ejecta mass M-ejecta similar or equal to 9M(circle dot) and an ejecta opacity kappa similar or equal to 0.08 cm(2) g(-1). A CSM-interaction scenario would imply a CSM mass similar or equal to 5 M-circle dot and an ejecta mass similar or equal to 12M(circle dot). Finally, the nebular spectrum of phase + 187 d was modeled, deriving a mass of similar or equal to 10 M-circle dot for the ejecta. Our models suggest that either a magnetar or CSM interaction might be the power sources for SN 2017gci and that its progenitor was a massive (40 M-circle dot) star.
