Browsing by Author "Kankare, E."

Filter results by typing the first few letters
Now showing 1 - 12 of 12
  • Asfalttipäällysteisen tieosan korjaaminen rakenteelliset ja taloudelliset näkökohdat huomioonottaen
    (1988) Matilainen, Erkki
     Helsinki University of Technology | Licentiate thesis
  • AT 2017gbl: A dust obscured TDE candidate in a luminous infrared galaxy
    (2020-10-01) Kool, E. C.; Reynolds, T. M.; Mattila, S.; Kankare, E.; Pérez-Torres, M. A.; Efstathiou, A.; Ryder, S.; Romero-Cañizales, C.; Lu, W.; Heikkilä, T.; Anderson, G. E.; Berton, M.; Bright, J.; Cannizzaro, G.; Eappachen, D.; Fraser, M.; Gromadzki, M.; Jonker, P. G.; Kuncarayakti, H.; Lundqvist, P.; Maeda, K.; Mcdermid, R. M.; Medling, A. M.; Moran, S.; Reguitti, A.; Shahbandeh, M.; Tsygankov, S.; Lebouteiller, V.; Wevers, T.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We present the discovery with Keck of the extremely infrared (IR) luminous transient AT 2017gbl, coincident with the Northern nucleus of the luminous infrared galaxy (LIRG) IRAS 23436+5257. Our extensive multiwavelength follow-up spans ∼900 d, including photometry and spectroscopy in the optical and IR, and (very long baseline interferometry) radio and X-ray observations. Radiative transfer modelling of the host galaxy spectral energy distribution and long-term pre-outburst variability in the mid-IR indicate the presence of a hitherto undetected dust obscured active galactic nucleus (AGN). The optical and near-IR spectra show broad ∼2000 km s-1 hydrogen, He i, and O i emission features that decrease in flux over time. Radio imaging shows a fast evolving compact source of synchrotron emission spatially coincident with AT 2017gbl. We infer a lower limit for the radiated energy of 7.3 × 1050 erg from the IR photometry. An extremely energetic supernova would satisfy this budget, but is ruled out by the radio counterpart evolution. Instead, we propose AT 2017gbl is related to an accretion event by the central supermassive black hole, where the spectral signatures originate in the AGN broad line region and the IR photometry is consistent with re-radiation by polar dust. Given the fast evolution of AT 2017gbl, we deem a tidal disruption event (TDE) of a star a more plausible scenario than a dramatic change in the AGN accretion rate. This makes AT 2017gbl the third TDE candidate to be hosted by a LIRG, in contrast to the so far considered TDE population discovered at optical wavelengths and hosted preferably by post-starburst galaxies.
  • Core-collapse supernova subtypes in luminous infrared galaxies
    (2021-05-27) Kankare, E.; Efstathiou, A.; Kotak, R.; Kool, E. C.; Kangas, T.; O'Neill, D.; Mattila, S.; Väisänen, P.; Ramphul, R.; Mogotsi, M.; Ryder, S. D.; Parker, S.; Reynolds, T.; Fraser, M.; Pastorello, A.; Cappellaro, E.; Mazzali, P. A.; Ochner, P.; Tomasella, L.; Turatto, M.; Kotilainen, J.; Kuncarayakti, H.; Pérez-Torres, M. A.; Randriamanakoto, Z.; Romero-Cañizales, C.; Berton, M.; Cartier, R.; Chen, T. W.; Galbany, L.; Gromadzki, M.; Inserra, C.; Maguire, K.; Moran, S.; Müller-Bravo, T. E.; Nicholl, M.; Reguitti, A.; Young, D. R.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The fraction of core-collapse supernovae (CCSNe) occurring in the central regions of galaxies is not well constrained at present. This is partly because large-scale transient surveys operate at optical wavelengths, making it challenging to detect transient sources that occur in regions susceptible to high extinction factors. Here we present the discovery and follow-up observations of two CCSNe that occurred in the luminous infrared galaxy (LIRG) NGC 3256. The first, SN 2018ec, was discovered using the ESO HAWK-I/GRAAL adaptive optics seeing enhancer, and was classified as a Type Ic with a host galaxy extinction of AV = 2.1-0.1+0.3 mag. The second, AT 2018cux, was discovered during the course of follow-up observations of SN 2018ec, and is consistent with a subluminous Type IIP classification with an AV = 2.1 ± 0.4 mag of host extinction. A third CCSN, PSN J10275082-4354034 in NGC 3256, was previously reported in 2014, and we recovered the source in late-time archival Hubble Space Telescope imaging. Based on template light curve fitting, we favour a Type IIn classification for it with modest host galaxy extinction of AV = 0.3-0.3+0.4 mag. We also extend our study with follow-up data of the recent Type IIb SN 2019lqo and Type Ib SN 2020fkb that occurred in the LIRG system Arp 299 with host extinctions of AV = 2.1-0.3+0.1 and AV = 0.4-0.2+0.1 mag, respectively. Motivated by the above, we inspected, for the first time, a sample of 29 CCSNe located within a projected distance of 2.5 kpc from the host galaxy nuclei in a sample of 16 LIRGs. We find, if star formation within these galaxies is modelled assuming a global starburst episode and normal IMF, that there is evidence of a correlation between the starburst age and the CCSN subtype. We infer that the two subgroups of 14 H-poor (Type IIb/Ib/Ic/Ibn) and 15 H-rich (Type II/IIn) CCSNe have different underlying progenitor age distributions, with the H-poor progenitors being younger at 3σ significance. However, we note that the currently available sample sizes of CCSNe and host LIRGs are small, and the statistical comparisons between subgroups do not take into account possible systematic or model errors related to the estimated starburst ages.
  • The enigmatic double-peaked stripped-envelope SN 2023aew
    (2024-09-01) Kangas, T.; Kuncarayakti, H.; Nagao, T.; Kotak, R.; Kankare, E.; Fraser, M.; Stevance, H.; Mattila, S.; Maeda, K.; Stritzinger, M.; Lundqvist, P.; Elias-Rosa, N.; Ferrari, L.; Folatelli, G.; Frohmaier, C.; Galbany, L.; Kawabata, M.; Koutsiona, E.; Müller-Bravo, T. E.; Piscarreta, L.; Pursiainen, M.; Singh, A.; Taguchi, K.; Teja, R. S.; Valerin, G.; Pastorello, A.; Benetti, S.; Cai, Y. Z.; Charalampopoulos, P.; Gutiérrez, C. P.; Kravtsov, T.; Reguitti, A.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We present optical and near-infrared photometry and spectroscopy of SN 2023aew and our findings on its remarkable properties. This event, initially resembling a Type IIb supernova (SN), rebrightens dramatically ~90 d after the first peak, at which time its spectrum transforms into that of a SN Ic. The slowly evolving spectrum specifically resembles a post-peak SN Ic with relatively low line velocities even during the second rise. The second peak, reached 119 d after the first peak, is both more luminous (Mr = -18.75±0.04 mag) and much broader than those of typical SNe Ic. Blackbody fits to SN 2023aew indicate that the photosphere shrinks almost throughout its observed evolution, and the second peak is caused by an increasing temperature. Bumps in the light curve after the second peak suggest interaction with circumstellar matter (CSM) or possibly accretion. We consider several scenarios for producing the unprecedented behavior of SN 2023aew. Two separate SNe, either unrelated or from the same binary system, require either an incredible coincidence or extreme fine-tuning. A pre-SN eruption followed by a SN requires an extremely powerful, SN-like eruption (consistent with ~1051 erg) and is also disfavored. We therefore consider only the first peak a true stellar explosion. The observed evolution is difficult to reproduce if the second peak is dominated by interaction with a distant CSM shell. A delayed internal heating mechanism is more likely, but emerging embedded interaction with a CSM disk should be accompanied by CSM lines in the spectrum, which are not observed, and is difficult to hide long enough. A magnetar central engine requires a delayed onset to explain the long time between the peaks. Delayed fallback accretion onto a black hole may present the most promising scenario, but we cannot definitively establish the power source.
  • Evidence for rapid disc formation and reprocessing in the X-ray bright tidal disruption event candidate AT 2018fyk
    (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.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We 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.
  • The evolution of luminous red nova at 2017jfs in NGC4470?
    (2019-01-01) Pastorello, A.; Chen, T. W.; Cai, Y. Z.; Morales-Garoffolo, A.; Cano, Z.; Mason, E.; Barsukova, E. A.; Benetti, S.; Berton, M.; Bose, S.; Bufano, F.; Callis, E.; Cannizzaro, G.; Cartier, R.; Chen, Ping; Dong, Subo; Dyrbye, S.; Elias-Rosa, N.; Flörs, A.; Fraser, M.; Geier, S.; Goranskij, V. P.; Kann, D. A.; Kuncarayakti, H.; Onori, F.; Reguitti, A.; Reynolds, T.; Losada, I. R.; Sagués Carracedo, A.; Schweyer, T.; Smartt, S. J.; Tatarnikov, A. M.; Valeev, A. F.; Vogl, C.; Wevers, T.; De Ugarte Postigo, A.; Izzo, L.; Inserra, C.; Kankare, E.; Maguire, K.; Smith, K. W.; Stalder, B.; Tartaglia, L.; Thöne, C. C.; Valerin, G.; Young, D. R.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We present the results of our photometric and spectroscopic follow-up of the intermediate-luminosity optical transient AT 2017jfs. At peak, the object reaches an absolute magnitude of Mg = -15:46 ± 0:15 mag and a bolometric luminosity of 5:5 × 1041 erg s-1. Its light curve has the doublepeak shape typical of luminous red novae (LRNe), with a narrow first peak bright in the blue bands, while the second peak is longer-lasting and more luminous in the red and near-infrared (NIR) bands. During the first peak, the spectrum shows a blue continuum with narrow emission lines of H and Fe II. During the second peak, the spectrum becomes cooler, resembling that of a K-type star, and the emission lines are replaced by a forest of narrow lines in absorption. About 5 months later, while the optical light curves are characterized by a fast linear decline, the NIR ones show a moderate rebrightening, observed until the transient disappears in solar conjunction. At these late epochs, the spectrum becomes reminiscent of that of M-type stars, with prominent molecular absorption bands. The late-time properties suggest the formation of some dust in the expanding common envelope or an IR echo from foreground pre-existing dust. We propose that the object is a common-envelope transient, possibly the outcome of a merging event in a massive binary, similar to NGC4490-2011OT1.
  • Luminous red novae : Stellar mergers or giant eruptions?
    (2019-09-24) Pastorello, A.; Mason, E.; Taubenberger, S.; Fraser, M.; Cortini, G.; Tomasella, L.; Botticella, M. T.; Elias-Rosa, N.; Kotak, R.; Smartt, S. J.; Benetti, S.; Cappellaro, E.; Turatto, M.; Tartaglia, L.; Djorgovski, S. G.; Drake, A. J.; Berton, M.; Briganti, F.; Brimacombe, J.; Bufano, F.; Cai, Y-Z; Chen, S.; Christensen, E. J.; Ciabattari, F.; Congiu, E.; Dimai, A.; Inserra, C.; Kankare, E.; Magill, L.; Maguire, K.; Martinelli, F.; Morales-Garoffolo, A.; Ochner, P.; Pignata, G.; Reguitti, A.; Sollerman, J.; Spiro, S.; Terreran, G.; Wright, D. E.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We present extensive datasets for a class of intermediate-luminosity optical transients known as luminous red novae. They show double-peaked light curves, with an initial rapid luminosity rise to a blue peak (at -13 to -15 mag), which is followed by a longer-duration red peak that sometimes is attenuated, resembling a plateau. The progenitors of three of them (NGC 4490-2011OT1, M 101-2015OT1, and SNhunt248), likely relatively massive blue to yellow stars, were also observed in a pre-eruptive stage when their luminosity was slowly increasing. Early spectra obtained during the first peak show a blue continuum with superposed prominent narrow Balmer lines, with P Cygni profiles. Lines of Fe II are also clearly observed, mostly in emission. During the second peak, the spectral continuum becomes much redder, H alpha is barely detected, and a forest of narrow metal lines is observed in absorption. Very late-time spectra (similar to 6 months after blue peak) show an extremely red spectral continuum, peaking in the infrared (IR) domain. H alpha is detected in pure emission at such late phases, along with broad absorption bands due to molecular overtones (such as TiO, VO). We discuss a few alternative scenarios for luminous red novae. Although major instabilities of single massive stars cannot be definitely ruled out, we favour a common envelope ejection in a close binary system, with possibly a final coalescence of the two stars. The similarity between luminous red novae and the outburst observed a few months before the explosion of the Type IIn SN 2011ht is also discussed.
  • MAGIC long-term study of the distant TeV blazar PKS 1424+240 in a multiwavelength context
    (2014) Aleksic, J.; Ansoldi, S.; Antonelli, L.A.; Antoranz, P.; Babic, A.; Bangale, P.; Barres de Almeida, U.; Barrio, J.A.; Becerra González, J.; Bednarek, W.; Berger, K.; Bernardini, E.; Biland, A.; Blanch, O.; Bock, R.K.; Bonnefoy, S.; Bonnoli, G.; Borracci, F.; Bretz, T.; Carmona, E.; Carosi, A.; Carreto Fidalgo, D.; Colin, P.; Colombo, E.; Contreras, J.L.; Cortina, Juan; Covino, S.; Da Vela, P.; Dazzi, F.; De Angelis, A.; De Caneva, G.; De Lotto, B.; Delgado Mendez, C.; Doert, M.; Domínguez, A.; Dominis Prester, D.; Dorner, D.; Doro, M.; Einecke, S.; Eisenacher, D.; Elsaesser, D.; Farina, E.; Ferenc, D.; Fonseca, M.V.; Font, L.; Frantzen, K.; Fruck, C.; García López, R.J.; Garczarczyk, M.; Garrido Terrats, D.; Gaug, M.; Giavitto, G.; Godinovic, N.; González Muñoz, A.; Gozzini, S.R.; Hadasch, D.; Hayashida, M.; Herrero, A.; Hildebrand, D.; Hose, J.; Hrupec, D.; Idec, W.; Kadenius, V.; Kellermann, H.; Kodani, K.; Konno, Y.; Krause, J.; Kubo, H.; Kushida, J.; La Barbera, A.; Lelas, D.; Lewandowska, N.; Lindfors, E.; Lombardi, S.; López, M.; López-Coto, R.; López-Oramas, A.; Lorenz, E.; Lozano, I.; Makariev, M.; Mallot, K.; Maneva, G.; Mankuzhiyil, N.; Mannheim, K.; Maraschi, L.; Marcote, B.; Mariotti, M.; Martínez, M.; Mazin, D.; Menzel, U.; Meucci, M.; Miranda, J.M.; Mirzoyan, R.; Moralejo, A.; Munar-Adrover, P.; Nakajima, D.; Niedzwiecki, A.; Nilsson, K.; Nishijima, K.; Nowak, N.; Orito, R.; Overkemping, A.; Paiano, S.; Palatiello, M.; Paneque, D.; Paoletti, R.; Paredes, J.M.; Paredes-Fortuny, X.; Partini, S.; Persic, M.; Prada, F.; Prada Moroni, P.G.; Prandini, E.; Preziuso, S.; Puljak, I.; Reinthal, R.; Rhode, W.; Ribó, M.; Rico, J.; Rodriguez Garcia, J.; Rügamer, S.; Saggion, A.; Saito, T.; Saito, K.; Salvati, M.; Satalecka, K.; Scalzotto, V.; Scapin, V.; Schultz, C.; Schweizer, T.; Shore, S.N.; Sillanpää, A.; Sitarek, J.; Snidaric, I.; Sobczynska, D.; Spanier, F.; Stamatescu, V.; Stamerra, A.; Steinbring, T.; Storz, J.; Sun, S.; Suric, T.; Takalo, L.; Takami, H.; Tavecchio, F.; Temnikov, P.; Terzic, T.; Tescaro, D.; Teshima, M.; Thaele, J.; Tibolla, O.; Torres, D.F.; Toyama, T.; Treves, A.; Uellenbeck, M.; Vogler, P.; Wagner, R.M.; Zandanel, F.; Zanin, R.; Cutini, S.; Gasparrini, D.; Furniss, A.; Hovatta, T.; Kankare, E.; Kotilainen, J.; Lister, M.; Lähteenmäki, A.; Max-Moerbeck, W.; Pavlidou, V.; Readhead, A.; Richards, J.; Kangas, Tuomas
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • Photometry and spectroscopy of the Type Icn supernova 2021ckj: The diverse properties of the ejecta and circumstellar matter of Type Icn supernovae
    (2023-05-01) Nagao, T.; Kuncarayakti, H.; Maeda, K.; Moore, Thomas J. T.; Pastorello, A.; Mattila, S.; Uno, K.; Smartt, S. J.; Sim, S. A.; Ferrari, L.; Tomasella, L.; Anderson, J. P.; Chen, T. W.; Galbany, L.; Gao, H.; Gromadzki, M.; Gutiérrez, C. P.; Inserra, C.; Kankare, E.; Magnier, E. A.; Müller-Bravo, T. E.; Reguitti, A.; Young, D. R.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We present photometric and spectroscopic observations of the Type Icn supernova (SN) 2021ckj. This rare type of SNe is characterized by a rapid evolution and high peak luminosity as well as narrow lines of highly ionized carbon at early phases, implying an interaction with hydrogen- and helium-poor circumstellar matter (CSM). SN 2021ckj reached a peak brightness of ~-20 mag in the optical bands, with a rise time and a time above half maximum of ~4 and ~10 days, respectively, in the g and cyan bands. These features are reminiscent of those of other Type Icn SNe (SNe 2019hgp, 2021csp, and 2019jc), with the photometric properties of SN 2021ckj being almost identical to those of SN 2021csp. Spectral modeling of SN 2021ckj reveals that its composition is dominated by oxygen, carbon, and iron group elements, and the photospheric velocity at peak is ~10000 km s-1. Modeling the spectral time series of SN 2021ckj suggests aspherical SN ejecta. From the light curve (LC) modeling applied to SNe 2021ckj, 2019hgp, and 2021csp, we find that the ejecta and CSM properties of Type Icn SNe are diverse. SNe 2021ckj and 2021csp likely have two ejecta components (an aspherical high-energy component and a spherical standard-energy component) with a roughly spherical CSM, while SN 2019hgp can be explained by a spherical ejecta-CSM interaction alone. The ejecta of SNe 2021ckj and 2021csp have larger energy per ejecta mass than the ejecta of SN 2019hgp. The density distribution of the CSM is similar in these three SNe, and is comparable to those of Type Ibn SNe. This may imply that the mass-loss mechanism is common between Type Icn (and also Type Ibn) SNe. The CSM masses of SN 2021ckj and SN 2021csp are higher than that of SN 2019hgp, although all these values are within those seen in Type Ibn SNe. The early spectrum of SN 2021ckj shows narrow emission lines from C II and C III, without a clear absorption component, in contrast with that observed in SN 2021csp. The similarity of the emission components of these lines implies that the emitting regions of SNe 2021ckj and 2021csp have similar ionization states, and thus suggests that they have similar properties as the ejecta and CSM, which is also inferred from the LC modeling. Taking the difference in the strength of the absorption features into account, this heterogeneity may be attributed to viewing angle effects in otherwise common aspherical ejecta. In particular, in this scenario SN 2021ckj is observed from the polar direction, while SN 2021csp is seen from an off-axis direction. This is also supported by the fact that the late-time spectra of SNe 2021ckj and 2021csp show similar features but with different line velocities.
  • 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.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We 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.
  • SN 2017gci: A nearby Type i Superluminous Supernova with a bumpy tail
    (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.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We 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.
  • SN 2017gmr: An Energetic Type II-P Supernova with Asymmetries
    (2019-11-01) Andrews, Jennifer E.; Sand, D. J.; Valenti, S.; Smith, Nathan; Dastidar, Raya; Sahu, D. K.; Misra, Kuntal; Singh, Avinash; Hiramatsu, D.; Brown, P. J.; Hosseinzadeh, G.; Wyatt, S.; Vinko, J.; Anupama, G. C.; Arcavi, I.; Ashall, Chris; Benetti, S.; Berton, Marco; Bostroem, K. A.; Bulla, M.; Burke, J.; Chen, S.; Chomiuk, L.; Cikota, A.; Congiu, E.; Cseh, B.; Davis, Scott; Elias-Rosa, N.; Faran, T.; Fraser, Morgan; Galbany, L.; Gall, C.; Gal-Yam, A.; Gangopadhyay, Anjasha; Gromadzki, M.; Haislip, J.; Howell, D. A.; Hsiao, E. Y.; Inserra, C.; Kankare, E.; Kuncarayakti, H.; Kouprianov, V.; Kumar, Brajesh; Li, Xue; Lin, Han; Maguire, K.; Mazzali, P.; McCully, C.; Milne, P.; Mo, Jun; Morrell, N.; Nicholl, M.; Ochner, P.; Olivares, F.; Pastorello, A.; Patat, F.; Phillips, M.; Pignata, G.; Prentice, S.; Reguitti, A.; Reichart, D. E.; Rodríguez; Rui, Liming; Sanwal, Pankaj; Sárneczky, K.; Shahbandeh, M.; Singh, Mridweeka; Smartt, S.; Strader, J.; Stritzinger, M. D.; Szakáts, R.; Tartaglia, L.; Wang, Huijuan; Wang, Lingzhi; Wang, Xiaofeng; Wheeler, J. C.; Xiang, Danfeng; Yaron, O.; Young, D. R.; Zhang, Junbo
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We present high-cadence UV, optical, and near-infrared data on the luminous Type II-P supernova SN 2017gmr from hours after discovery through the first 180 days. SN 2017gmr does not show signs of narrow, high-ionization emission lines in the early optical spectra, yet the optical light-curve evolution suggests that an extra energy source from circumstellar medium (CSM) interaction must be present for at least 2 days after explosion. Modeling of the early light curve indicates a ∼500 R o progenitor radius, consistent with a rather compact red supergiant, and late-time luminosities indicate that up to 0.130 ± 0.026 M o of 56Ni are present, if the light curve is solely powered by radioactive decay, although the 56Ni mass may be lower if CSM interaction contributes to the post-plateau luminosity. Prominent multipeaked emission lines of Hα and [O i] emerge after day 154, as a result of either an asymmetric explosion or asymmetries in the CSM. The lack of narrow lines within the first 2 days of explosion in the likely presence of CSM interaction may be an example of close, dense, asymmetric CSM that is quickly enveloped by the spherical supernova ejecta.