Examinando por Autor "Leloudas G."

Mostrando 1 - 5 de 5
  • No hay miniatura disponible
    Ítem
    A long life of excess: The interacting transient SN 2017hcc
    (EDP Sciences, 2023-01) Moran S.; Fraser M.; Kotak R.; Pastorello A.; Benetti S.; Brennan S.J.; Gutiérrez C.P.; Kankare E.; Kuncarayakti H.; Mattila S.; Reynolds T.M.; Anderson J.P.; Brown P.J.; Campana S.; Chambers K.C.; Chen T.-W.; Della Valle M.; Dennefeld M.; Elias-Rosa N.; Galbany L.; Galindo-Guil F.J.; Gromadzki M.; Hiramatsu D.; Inserra C.; Leloudas G.; Müller-Bravo T.E.; Nicholl M.; Reguitti A.; Shahbandeh M.; Smartt S.J.; Tartaglia L.; Young D.R.
    In this study we present the results of a five-year follow-up campaign of the long-lived type IIn supernova SN 2017hcc, found in a spiral dwarf host of near-solar metallicity. The long rise time (57 ± 2 days, ATLAS o band) and high luminosity (peaking at -20.78 ± 0.01 mag in the ATLAS o band) point towards an interaction of massive ejecta with massive and dense circumstellar material (CSM). The evolution of SN 2017hcc is slow, both spectroscopically and photometrically, reminiscent of the long-lived type IIn, SN 2010jl. An infrared (IR) excess was apparent soon after the peak, and blueshifts were noticeable in the Balmer lines starting from a few hundred days, but appeared to be fading by around +1200 d. We posit that an IR light echo from pre-existing dust dominates at early times, with some possible condensation of new dust grains occurring at epochs ≳;+800 d. © The Authors 2023.
  • No hay miniatura disponible
    Ítem
    A study in scarlet: I. Photometric properties of a sample of intermediate-luminosity red transients
    (EDP Sciences, 2025-03) Valerin G.; Pastorello A.; Reguitti A.; Benetti S.; Cai Y.-Z.; Chen T.-W.; Eappachen D.; Elias-Rosa N.; Fraser M.; Gangopadhyay A.; Hsiao E.Y.; Howell D.A.; Inserra C.; Izzo L.; Jencson J.; Kankare E.; Kotak R.; Mazzali P.A.; Misra K.; Pignata G.; Prentice S.J.; Sand D.J.; Smartt S.J.; Stritzinger M.D.; Tartaglia L.; Valenti S.; Anderson J.P.; Andrews J.E.; Amaro R.C.; Brennan S.; Bufano F.; Callis E.; Cappellaro E.; Dastidar R.; Della Valle M.; Fiore A.; Fulton M.D.; Galbany L.; Heikkilä T.; Hiramatsu D.; Karamehmetoglu E.; Kuncarayakti H.; Leloudas G.; Lundquist M.; Mccully C.; Müller-Bravo T.E.; Nicholl M.; Ochner P.; Padilla Gonzalez E.; Paraskeva E.; Pellegrino C.; Rau A.; Reichart D.E.; Reynolds T.M.; Roy R.; Salmaso I.; Singh M.; Turatto M.; Tomasella L.; Wyatt S.
    Aims. We investigate the photometric characteristics of a sample of intermediate-luminosity red transients (ILRTs), a class of elusive objects with peak luminosity between that of classical novae and standard supernovae. Our goal is to provide a stepping stone in the path to reveal the physical origin of such events, thanks to the analysis of the datasets collected. Methods. We present the multi-wavelength photometric follow-up of four ILRTs, namely NGC 300 2008OT-1, AT 2019abn, AT 2019ahd, and AT 2019udc. Through the analysis and modelling of their spectral energy distribution and bolometric light curves, we inferred the physical parameters associated with these transients. Results. All four objects display a single-peaked light curve which ends in a linear decline in magnitudes at late phases. A flux excess with respect to a single blackbody emission is detected in the infrared domain for three objects in our sample, a few months after maximum. This feature, commonly found in ILRTs, is interpreted as a sign of dust formation. Mid-infrared monitoring of NGC 300 2008OT-1 761 days after maximum allowed us to infer the presence of ∼10-3-10-5 M⊙ of dust, depending on the chemical composition and the grain size adopted. The late-time decline of the bolometric light curves of the considered ILRTs is shallower than expected for 56Ni decay, hence requiring an additional powering mechanism. James Webb Space Telescope observations of AT 2019abn prove that the object has faded below its progenitor luminosity in the mid-infrared domain, five years after its peak. Together with the disappearance of NGC 300 2008OT-1 in Spitzer images seven years after its discovery, this supports the terminal explosion scenario for ILRTs. With a simple semi-analytical model we tried to reproduce the observed bolometric light curves in the context of a few solar masses ejected at few 103 km s-1 and enshrouded in an optically thick circumstellar medium. © The Authors 2025.
  • Miniatura
    Ítem
    An outflow powers the optical rise of the nearby, fast-evolving tidal disruption event AT2019qiz
    (Oxford University Press, 2020-11) Nicholl M.; Wevers T.; Oates S.R.; Alexander K.D.; Leloudas G.; Onori F.; Jerkstrand A.; Gomez S.; Campana S.; Arcavi I.; Charalampopoulos P.; Gromadzki M.; Ihanec N.; Jonker P.G.; Lawrence A.; Mandel I.; Schulze S.; Short P.; Burke J.; McCully C.; Hiramatsu D.; Howell D.A.; Pellegrino C.; Abbot H.; Anderson J.P.; Berger E.; Blanchard P.K.; Cannizzaro G.; Chen T.-W.; Dennefeld M.; Galbany L.; Gonzalez-Gaitan S.; Hosseinzadeh G.; Inserra C.; Irani I.; Kuin P.; Muller-Bravo T.; Pineda J.; Ross N.P.; Roy R.; Smartt S.J.; Smith K.W.; Tucker B.; Wyrzykowski L.; Young D.R.
    At 66 Mpc, AT2019qiz is the closest optical tidal disruption event (TDE) to date, with a luminosity intermediate between the bulk of the population and the faint-and-fast event iPTF16fnl. Its proximity allowed a very early detection and triggering of multiwavelength and spectroscopic follow-up well before maximum light. The velocity dispersion of the host galaxy and fits to the TDE light curve indicate a black hole mass ~106M⊙, disrupting a star of ~1M⊙. By analysing our comprehensive UV, optical, and X-ray data, we show that the early optical emission is dominated by an outflow, with a luminosity evolution L α t2, consistent with a photosphere expanding at constant velocity (≥2000 km s-1), and a line-forming region producing initially blueshifted H and He II profiles with v = 3000-10000 km s-1. The fastest optical ejecta approach the velocity inferred from radio detections (modelled in a forthcoming companion paper from K. D. Alexander et al.), thus the same outflow may be responsible for both the fast optical rise and the radio emission - the first time this connection has been observed in a TDE. The light-curve rise begins 29 ± 2 d before maximum light, peaking when the photosphere reaches the radius where optical photons can escape. The photosphere then undergoes a sudden transition, first cooling at constant radius then contracting at constant temperature. At the same time, the blueshifts disappear from the spectrum and Bowen fluorescence lines (N III) become prominent, implying a source of far-UV photons, while the X-ray light curve peaks at ~1041erg s-1. Assuming that these X-rays are from prompt accretion, the size and mass of the outflow are consistent with the reprocessing layer needed to explain the large optical to X-ray ratio in this and other optical TDEs, possibly favouring accretion-powered over collision-powered outflow models. © 2020 Oxford University Press. All rights reserved.
  • Miniatura
    Ítem
    Investigating the diversity of supernovae type Iax: A MUSE and NOT spectroscopic study of their environments
    (Oxford University Press, 2018) Lyman J.D.; Taddia F.; Stritzinger M.D.; Galbany L.; Leloudas G.; Anderson J.P.; Eldridge J.J.; James P.A.; Krühler T.; Levan A.J.; Pignata G.; Stanway E.R.
    SN 2002cx-like Type Ia supernovae (also known as SNe Iax) represent one of the most numerous peculiar SN classes. They differ from normal SNe Ia by having fainter peak magnitudes, faster decline rates and lower photospheric velocities, displaying awide diversity in these properties. We present both integral-field and long-slit visual-wavelength spectroscopy of the host galaxies and explosion sites of SNe Iax to provide constraints on their progenitor formation scenarios. The SN Iax explosion-site metallicity distribution is similar to that of core-collapse SNe and metal poor compared to either normal SNe Ia or SN 1991T-like events. Fainter members, speculated to form distinctly from brighter SN Iax, are found at a range of metallicities, extending to very metal poor environments. Although the SN Iax explosion-sites' ages and star formation rates are comparatively older and less intense than the distribution of star-forming regions across their host galaxies, we confirm the presence of young stellar populations (SPs) at explosion environments for most SNe Iax, expanded here to a larger sample. Ages of the young SPs (several × 107 to 108 yr) are consistent with predictions for young thermonuclear and electron-capture SN progenitors. The lack of extremely young SPs at the explosion sites disfavours very massive progenitors such as Wolf-Rayet explosions with significant fallback. We find weak ionized gas in the only SN Iax host without obvious signs of star formation. The source of the ionization remains ambiguous but appears unlikely to be mainly due to young, massive stars. © 2017 The Authors.
  • No hay miniatura disponible
    Ítem
    Panning for gold, but finding helium: Discovery of the ultra-stripped supernova SN 2019wxt from gravitational-wave follow-up observations
    (EDP Sciences, 2023-07) Agudo I.; Amati L.; An T.; Bauer F.E.; Benetti S.; Bernardini M.G.; Beswick R.; Bhirombhakdi K.; De Boer T.; Branchesi M.; Brennan S.J.; Brocato E.; Caballero-García M.D.; Cappellaro E.; Castro Rodríguez N.; Castro-Tirado A.J.; Chambers K.C.; Chassande-Mottin E.; Chaty S.; Chen T.-W.; Coleiro A.; Covino S.; Da'ammando F.; Da'avanzo P.; Da'elia V.; Fiore A.; Flörs A.; Fraser M.; Frey S.; Frohmaier C.; Fulton M.; Galbany L.; Gall C.; Gao H.; García-Rojas J.; Ghirlanda G.; Giarratana S.; Gillanders J.H.; Giroletti M.; Gompertz B.P.; Gromadzki M.; Heintz K.E.; Hjorth J.; Hu Y.-D.; Huber M.E.; Inkenhaag A.; Izzo L.; Jin Z.P.; Jonker P.G.; Kann D.A.; Kool E.C.; Kotak R.; Leloudas G.; Levan A.J.; Lin C.-C.; Lyman J.D.; Magnier E.A.; Maguire K.; Mandel I.; Marcote B.; Mata Sánchez D.; Mattila S.; Mattila S.; Michaåà  Owski M.J.; Moldon J.; Nicholl M.; Nicuesa Guelbenzu A.; Oates S.R.; Onori F.; Orienti M.; Paladino R.; Paragi Z.; Perez-Torres M.; Pian E.; Pignata G.; Piranomonte S.; Quirola-Vásquez J.; Ragosta F.; Rau A.; Ronchini S.; Rossi A.; Sánchez-Ramírez R.; Salafia O.S.; Schulze S.; Smartt S.J.; Smith K.W.; Sollerman J.; Srivastav S.; Starling R.L.C.; Steeghs D.; Stevance H.F.; Tanvir N.R.; Testa V.; Torres M.A.P.; Valeev A.; Vergani S.D.; Vescovi D.; Wainscost R.; Watson D.; Wiersema K.; Wyrzykowski L.; Yang J.; Yang S.; Young D.R.
    We present the results from multi-wavelength observations of a transient discovered during an intensive follow-up campaign of S191213g, a gravitational wave (GW) event reported by the LIGO-Virgo Collaboration as a possible binary neutron star merger in a low latency search. This search yielded SN 2019wxt, a young transient in a galaxy whose sky position (in the 80% GW contour) and distance (∼150 Mpc) were plausibly compatible with the localisation uncertainty of the GW event. Initially, the transienta's tightly constrained age, its relatively faint peak magnitude (Mi ∼ -16.7 mag), and the r-band decline rate of ∼1 mag per 5 days appeared suggestive of a compact binary merger. However, SN 2019wxt spectroscopically resembled a type Ib supernova, and analysis of the optical-near-infrared evolution rapidly led to the conclusion that while it could not be associated with S191213g, it nevertheless represented an extreme outcome of stellar evolution. By modelling the light curve, we estimated an ejecta mass of only ∼0.1 M·, with 56Ni comprising ∼20% of this. We were broadly able to reproduce its spectral evolution with a composition dominated by helium and oxygen, with trace amounts of calcium. We considered various progenitor channels that could give rise to the observed properties of SN 2019wxt and concluded that an ultra-stripped origin in a binary system is the most likely explanation. Disentangling genuine electromagnetic counterparts to GW events from transients such as SN 2019wxt soon after discovery is challenging: in a bid to characterise this level of contamination, we estimated the rate of events with a volumetric rate density comparable to that of SN 2019wxt and found that around one such event per week can occur within the typical GW localisation area of O4 alerts out to a luminosity distance of 500 Mpc, beyond which it would become fainter than the typical depth of current electromagnetic follow-up campaigns. © 2023 Authors