Examinando por Autor "Lundqvist, P."
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Ítem AT 2017gbl: A dust obscured TDE candidate in a luminous infrared galaxy(Oxford University Press, 2020-10) Kool, E.C.; Reynolds, T.M.; Mattila, S.; Kankare, E.; Perez-Torres, M.A.; Efstathiou, A.; Ryder, S.; Romero-Canizales, C.; Lu, W.; Heikkila, 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.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. © 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.Ítem Forbidden hugs in pandemic times II. The luminous red nova variety: AT 2020hat and AT 2020kog(EDP Sciences, 2021-03-01) Pastorello, A.; Valerin, G.; Fraser, M.; Elias-Rosa, N.; Valenti, S.; Reguitti, A.; Mazzali, P. A.; Amaro, R. C.; Andrews, J. E.; Dong, Y.; Jencson, J.; Lundquist, M.; Reichart, D. E.; Sand, D. J.; Wyatt, S.; Smartt, S. J.; Smith, K. W.; Srivastav, S.; Cai, Y.-Z.; Cappellaro, E.; Holmbo, S.; Fiore, A.; Jones, D.; Kankare, E.; Karamehmetoglu, E.; Lundqvist, P.; Morales-Garoffolo, A.; Reynolds, T. M.; Stritzinger, M. D.; Williams, S. C.; Chambers, K. C.; de Boer, T. J. L.; Huber, M. E.; Rest, A.; Wainscoat, R.We present the results of our monitoring campaigns of the luminous red novae (LRNe) AT 2020hat in NGC 5068 and AT 2020kog in NGC 6106. The two objects were imaged (and detected) before their discovery by routine survey operations. They show a general trend of slow luminosity rise, lasting at least a few months. The subsequent major LRN outbursts were extensively followed in photometry and spectroscopy. The light curves present an initial short-duration peak, followed by a redder plateau phase. AT 2020kog is a moderately luminous event peaking at ∼7 × 1040 erg s-1, while AT 2020hat is almost one order of magnitude fainter than AT 2020kog, although it is still more luminous than V838 Mon. In analogy with other LRNe, the spectra of AT 2020kog change significantly with time. They resemble those of type IIn supernovae at early phases, then they become similar to those of K-type stars during the plateau, and to M-type stars at very late phases. In contrast, AT 2020hat already shows a redder continuum at early epochs, and its spectrum shows the late appearance of molecular bands. A moderate-resolution spectrum of AT 2020hat taken at +37 d after maximum shows a forest of narrow P Cygni lines of metals with velocities of 180 km s-1, along with an Hα emission with a full-width at half-maximum velocity of 250 km s-1. For AT 2020hat, a robust constraint on its quiescent progenitor is provided by archival images of the Hubble Space Telescope. The progenitor is clearly detected as a mid-K type star, with an absolute magnitude of MF606W = -3.33 ± 0.09 mag and a colour of F606W - F814W = 1.14 ± 0.05 mag, which are inconsistent with the expectations from a massive star that could later produce a core-collapse supernova. Although quite peculiar, the two objects nicely match the progenitor versus light curve absolute magnitude correlations discussed in the literature.Ítem Forbidden hugs in pandemic times: I. Luminous red nova at 2019zhd, a new merger in M 31(EDP Sciences, 2021-02-01) Pastorello, A.; Fraser, M.; Valerin, G.; Reguitti, A.; Itagaki, K.; Ochner, P.; Williams, S.C.; Jones, D.; Munday, J.; Smartt, S.J.; Smith, K.W.; Srivastav S., S.; Elias-Rosa, N.; Kankare, E.; Karamehmetoglu, E.; Lundqvist, P.; Mazzali, P. A.; Munari, U.; Stritzinger, M. D.; Tomasella, L.; Anderson, J. P.; Chambers, K. C.; Rest, A.We present the follow-up campaign of the luminous red nova (LRN) AT 2019zhd, the third event of this class observed in M 31. The object was followed by several sky surveys for about five months before the outburst, during which it showed a slow luminosity rise. In this phase, the absolute magnitude ranged from Mr =-2.8 ± 0.2 mag to Mr =-5.6 ± 0.1 mag. Then, over a four to five day period, AT 2019zhd experienced a major brightening, reaching a peak of Mr =-9.61 ± 0.08 mag and an optical luminosity of 1.4 × 1039 erg s-1. After a fast decline, the light curve settled onto a short-duration plateau in the red bands. Although less pronounced, this feature is reminiscent of the second red maximum observed in other LRNe. This phase was followed by a rapid linear decline in all bands. At maximum, the spectra show a blue continuum with prominent Balmer emission lines. The post-maximum spectra show a much redder continuum, resembling that of an intermediate-type star. In this phase, Hα becomes very weak, Hβ is no longer detectable, and a forest of narrow absorption metal lines now dominate the spectrum. The latest spectra, obtained during the post-plateau decline, show a very red continuum (Teff ≈ 3000 K) with broad molecular bands of TiO, similar to those of M-type stars. The long-lasting, slow photometric rise observed before the peak resembles that of LRN V1309 Sco, which was interpreted as the signature of the common-envelope ejection. The subsequent outburst is likely due to the gas outflow following a stellar merging event. The inspection of archival HST images taken 22 years before the LRN discovery reveals a faint red source (MF555W = 0.21 ± 0.14 mag, with F555W-F814W = 2.96 ± 0.12 mag) at the position of AT 2019zhd, which is the most likely quiescent precursor. The source is consistent with expectations for a binary system including a predominant M5-type star.Ítem Forbidden hugs in pandemic times: III. Observations of the luminous red nova AT 2021biy in the nearby galaxy NGC 4631(EDP Sciences, 2022-11-01) Cai, Y.-Z.; Pastorello, A.; Fraser, M.; Wang, X.-F.; Filippenko, A.V.; Reguitti, A.; Patra, K.C.; Goranskij, V.P.; Barsukova, E.A.; Brink, T.G.; Elias-Rosa, N.; Stevance, H.F.; Zheng, W.; Yang, Y.; Atapin, K.E.; Benetti, S.; De Boer, T.J.L.; Bose, S.; Burke, J.; Byrne, R.; Cappellaro, E.; Chambers, K.C.; Chen, W.-L.; Emami, N.; Gao, H.; Hiramatsu, D.; Howell, D.A.; Huber, M.E.; Kankare, E.; Kelly, P.L.; Kotak, R.; Kravtsov, T.; Lander, V. Yu.; Li, Z.-T.; Lin, C.-C.; Lundqvist, P.; Magnier, E.A.; Malygin, E.A.; Maslennikova, N.A.; Matilainen, K.; Mazzali, P.A.; Mccully, C.; Mo, J.; Moran, S.; Newsome, M.; Oparin, D.V.; Padilla Gonzalez, E.; Reynolds, T.M.; Shatsky, N.I.; Smartt, S.J.; Smith, K.W.; Stritzinger, M.D.; Tatarnikov, A.M.; Terreran, G.; Uklein, R.I.; Valerin, G.; Vallely, P.J.; Vozyakova, O.V.; Wainscoat, R.; Yan, S.-Y.; Zhang, J.-J.; Zhang, T.-M.; Zheltoukhov, S.G.; Dastidar, R.; Fulton, M.; Galbany, L.; Gangopadhyay, A.; Ge, H.-W.; Gutiérrez, C.P.; Lin, H.; Misra, K.; Ou, Z.-W.; Salmaso, I.; Tartaglia, L.; Xiao, L.; Zhang, X.-H.We present an observational study of the luminous red nova (LRN) AT 2021biy in the nearby galaxy NGC 4631. The field of the object was routinely imaged during the pre-eruptive stage by synoptic surveys, but the transient was detected only at a few epochs from ∼231 days before maximum brightness. The LRN outburst was monitored with unprecedented cadence both photometrically and spectroscopically. AT 2021biy shows a short-duration blue peak, with a bolometric luminosity of ∼1.6×1041 erg s-1, followed by the longest plateau among LRNe to date, with a duration of 210 days. A late-time hump in the light curve was also observed, possibly produced by a shell-shell collision. AT 2021biy exhibits the typical spectral evolution of LRNe. Early-time spectra are characterised by a blue continuum and prominent H emission lines. Then, the continuum becomes redder, resembling that of a K-type star with a forest of metal absorption lines during the plateau phase. Finally, late-time spectra show a very red continuum (TBB ≈ 2050 K) with molecular features (e.g., TiO) resembling those of M-type stars. Spectropolarimetric analysis indicates that AT 2021biy has local dust properties similar to those of V838 Mon in the Milky Way Galaxy. Inspection of archival Hubble Space Telescope data taken on 2003 August 3 reveals a ∼20 M⊗ progenitor candidate with log (L/L⊗) = 5.0 dex and Teff 5900 K at solar metallicity. The above luminosity and colour match those of a luminous yellow supergiant. Most likely, this source is a close binary, with a 17-24 M⊗ primary component. © Y.-Z. Cai et al. 2022.Ítem Intermediate-luminosity red transients: Spectrophotometric properties and connection to electron-capture supernova explosions(EDP Sciences, 2021-10-01) Cai, Y.-Z.; Pastorello, A.; Fraser, M.; Botticella, M. T.; Elias-Rosa, N.; Wang, L.-Z.; Kotak, R.; Benetti, S.; Cappellaro, E.; Turatto, M.; Reguitti, A.; Mattila, S.; Smartt, S. J.; Ashall, C.; Benitez, S.; Chen, T.-W.; Harutyunyan, A.; Kankare, E.; Lundqvist, P.; Mazzali, P. A.; Morales-Garoffolo, A.; Ochner, P.; Pignata, G.; Prentice, S. J.; Reynolds, T. M.; Shu, X.-W.; Stritzinger, M. D.; Tartaglia, L.; Terreran, G.; Tomasella, L.; Valenti, S.; Valerin, G.; Wang, G.-J.; Wang, X.-F.; Borsato, L.; Callis, E.; Cannizzaro, G.; Chen, S.; Congiu, E.; Ergon, M.; Galbany, L.; Gal-Yam, A.; Gao, X.; Gromadzki, M.; Holmbo, S.; Huang, F.; Inserra, C.; Itagaki, K.; Kostrzewa-Rutkowska, Z.; Maguire, K.; Margheim, S.; Moran, S.; Onori, F.; Sagués Carracedo, A.; Smith, K. W.; Sollerman, J.; Somero, A.; Wang, B.; Young, D. R.We present the spectroscopic and photometric study of five intermediate-luminosity red transients (ILRTs), namely AT 2010dn, AT 2012jc, AT 2013la, AT 2013lb, and AT 2018aes. They share common observational properties and belong to a family of objects similar to the prototypical ILRT SN 2008S. These events have a rise time that is less than 15 days and absolute peak magnitudes of between-11.5 and-14.5 mag. Their pseudo-bolometric light curves peak in the range 0.5-9.0 × 1040 erg s-1 and their total radiated energies are on the order of (0.3-3) × 1047 erg. After maximum brightness, the light curves show a monotonic decline or a plateau, resembling those of faint supernovae IIL or IIP, respectively. At late phases, the light curves flatten, roughly following the slope of the 56Co decay. If the late-time power source is indeed radioactive decay, these transients produce 56Ni masses on the order of 10-4 to 10-3 M⊙. The spectral energy distribution of our ILRT sample, extending from the optical to the mid-infrared (MIR) domain, reveals a clear IR excess soon after explosion and non-negligible MIR emission at very late phases. The spectra show prominent H lines in emission with a typical velocity of a few hundred km s-1, along with Ca II features. In particular, the [Ca II] λ7291,7324 doublet is visible at all times, which is a characteristic feature for this family of transients. The identified progenitor of SN 2008S, which is luminous in archival Spitzer MIR images, suggests an intermediate-mass precursor star embedded in a dusty cocoon. We propose the explosion of a super-asymptotic giant branch star forming an electron-capture supernova as a plausible explanation for these events.Ítem PESSTO: Survey description and products from the first data release by the Public ESO Spectroscopic Survey of Transient Objects(EDP Sciences, 2015-07) Smartt, S.J.; Valenti, S.; Fraser, M.; Inserra, C.; Young, D.R.; Sullivan, M.; Pastorello, A.; Benetti, S.; Gal-Yam, A.; Knapic, C.; Molinaro, M.; Smareglia, R.; Smith, K.W.; Taubenberger, S.; Yaron, O.; Anderson, J.P.; Ashall, C.; Balland, C.; Baltay, C.; Barbarino, C.; Bauer, F.E.; Baumont, S.; Bersier, D.; Blagorodnova, N.; Bongard, S.; Botticella, M.T.; Bufano, F.; Bulla, M.; Cappellaro, E.; Campbell, H.; Cellier-Holzem, F.; Chen, T.-W.; Childress, M.J.; Clocchiatti, A.; Contreras, C.; Dall'Ora, M.; Danziger, J.; De Jaeger, T.; De Cia, A.; Della Valle, M.; Dennefeld, M.; Elias-Rosa, N.; Elman, N.; Feindt, U.; Fleury, M.; Gall, E.; Gonzalez-Gaitan, S.; Galbany, L.; Morales Garoffolo, A.; Greggio, L.; Guillou, L.L.; Hachinger, S.; Hadjiyska, E.; Hage, P.E.; Hillebrandt, W.; Hodgkin, S.; Hsiao, E.Y.; James, P.A.; Jerkstrand, A.; Kangas, T.; Kankare, E.; Kotak, R.; Kromer, M.; Kuncarayakti, H.; Leloudas, G.; Lundqvist, P.; Lyman, J.D.; Hook, I.M.; Maguire, K.; Manulis, I.; Margheim, S.J.; Mattila, S.; Maund, J.R.; Mazzali, P.A.; McCrum, M.; McKinnon, R.; Moreno-Raya, M.E.; Nicholl, M.; Nugent, P.; Pain, R.; Pignata, G.; Phillips, M.M.; Polshaw, J.; Pumo, M.; Rabinowitz, D.; Reilly, E.; Romero-Cañizales, C.; Scalzo, R.; Schmidt, B.; Schulze, S.; Sim, S.; Sollerman, J.; Taddia, F.; Tartaglia, L.; Terreran, G.; Tomasella, L.; Turatto, M.; Walker, E.; Walton, N.A.; Wyrzykowski, L.; Yuan, F.; Zampieri, L.Context. The Public European Southern Observatory Spectroscopic Survey of Transient Objects (PESSTO) began as a public spectroscopic survey in April 2012. PESSTO classifies transients from publicly available sources and wide-field surveys, and selects science targets for detailed spectroscopic and photometric follow-up. PESSTO runs for nine months of the year, January - April and August - December inclusive, and typically has allocations of 10 nights per month. Aims. We describe the data reduction strategy and data products that are publicly available through the ESO archive as the Spectroscopic Survey data release 1 (SSDR1). Methods. PESSTO uses the New Technology Telescope with the instruments EFOSC2 and SOFI to provide optical and NIR spectroscopy and imaging. We target supernovae and optical transients brighter than 20.5m for classification. Science targets are selected for follow-up based on the PESSTO science goal of extending knowledge of the extremes of the supernova population. We use standard EFOSC2 set-ups providing spectra with resolutions of 13-18 Å between 3345-9995 Å. A subset of the brighter science targets are selected for SOFI spectroscopy with the blue and red grisms (0.935-2.53 μm and resolutions 23-33 Å) and imaging with broadband JHKs filters. Results. This first data release (SSDR1) contains flux calibrated spectra from the first year (April 2012-2013). A total of 221 confirmed supernovae were classified, and we released calibrated optical spectra and classifications publicly within 24 h of the data being taken (via WISeREP). The data in SSDR1 replace those released spectra. They have more reliable and quantifiable flux calibrations, correction for telluric absorption, and are made available in standard ESO Phase 3 formats. We estimate the absolute accuracy of the flux calibrations for EFOSC2 across the whole survey in SSDR1 to be typically ∼15%, although a number of spectra will have less reliable absolute flux calibration because of weather and slit losses. Acquisition images for each spectrum are available which, in principle, can allow the user to refine the absolute flux calibration. The standard NIR reduction process does not produce high accuracy absolute spectrophotometry but synthetic photometry with accompanying JHKs imaging can improve this. Whenever possible, reduced SOFI images are provided to allow this. Conclusions. Future data releases will focus on improving the automated flux calibration of the data products. The rapid turnaround between discovery and classification and access to reliable pipeline processed data products has allowed early science papers in the first few months of the survey. © ESO, 2015.Ítem SN 2016gsd: An unusually luminous and linear Type II supernova with high velocities(Oxford University Press, 2020-04) Reynolds, T.M.; Fraser, M.; Mattila, S.; Ergon, M.; Dessart, L.; Lundqvist, P.; Dong, S.; Elias-Rosa, N.; Galbany, L.; Gutierrez, C.P.; Kangas, T.; Kankare, E.; Kotak, R.; Kuncarayakti, H.; Pastorello, A.; Rodriguez, O.; Smartt, S.J.; Stritzinger, M.; Tomasella, L.; Chen, P.; Harmanen, J.; Hosseinzadeh, G.; Howell, D.A.; Inserra, C.; Nicholl, M.; Nielsen, M.; Smith, K.; Somero, A.; Tronsgaard, R.; Young, D.R.We present observations of the unusually luminous Type II supernova (SN) 2016gsd. With a peak absolute magnitude of V = -19.95 ± 0.08, this object is one of the brightest Type II SNe, and lies in the gap of magnitudes between the majority of Type II SNe and the superluminous SNe. Its light curve shows little evidence of the expected drop from the optically thick phase to the radioactively powered tail. The velocities derived from the absorption in H α are also unusually high with the blue edge tracing the fastest moving gas initially at 20 000 km s-1, and then declining approximately linearly to 15 000 km s-1 over ∼100 d. The dwarf host galaxy of the SN indicates a low-metallicity progenitor which may also contribute to the weakness of the metal lines in its spectra. We examine SN 2016gsd with reference to similarly luminous, linear Type II SNe such as SNe 1979C and 1998S, and discuss the interpretation of its observational characteristics. We compare the observations with a model produced by the jekyll code and find that a massive star with a depleted and inflated hydrogen envelope struggles to reproduce the high luminosity and extreme linearity of SN 2016gsd. Instead, we suggest that the influence of interaction between the SN ejecta and circumstellar material can explain the majority of the observed properties of the SN. The high velocities and strong H α absorption present throughout the evolution of the SN may imply a circumstellar medium configured in an asymmetric geometry. © 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.Ítem SN 2017dio: A Type-Ic Supernova Exploding in a Hydrogen-rich Circumstellar Medium(Institute of Physics Publishing, 2018-02) Kuncarayakti, H.; Maeda, K.; Ashall, C.J.; Prentice, S.J.; Mattila, S.; Kankare, E.; Fransson, C.; Lundqvist, P.; Pastorello, A.; Leloudas, G.; Anderson, J.P.; Benetti, S.; Bersten, M.C.; Cappellaro, E.; Cartier, R.; Denneau, L.; Della Valle, M.; Elias-Rosa, N.; Folatelli, G.; Fraser, M.; Galbany, L.; Gall, C.; Gal-Yam, A.; Gutiérrez, C.P.; Hamanowicz, A.; Heinze, A.; Inserra, C.; Kangas, T.; Mazzali, P.; Melandri, A.; Pignata, G.; Rest, A.; Reynolds, T.; Roy, R.; Smartt, S.J.; Smith, K.W.; Sollerman, J.; Somero, A.; Stalder, B.; Stritzinger, M.; Taddia, F.; Tomasella, L.; Tonry, J.; Weiland, H.; Young, D.R.SN 2017dio shows both spectral characteristics of a type-Ic supernova (SN) and signs of a hydrogen-rich circumstellar medium (CSM). Prominent, narrow emission lines of H and He are superposed on the continuum. Subsequent evolution revealed that the SN ejecta are interacting with the CSM. The initial SN Ic identification was confirmed by removing the CSM interaction component from the spectrum and comparing with known SNe Ic and, reversely, adding a CSM interaction component to the spectra of known SNe Ic and comparing them to SN 2017dio. Excellent agreement was obtained with both procedures, reinforcing the SN Ic classification. The light curve constrains the pre-interaction SN Ic peak absolute magnitude to be around Mg = -17.6 mag. No evidence of significant extinction is found, ruling out a brighter luminosity required by an SN Ia classification. These pieces of evidence support the view that SN 2017dio is an SN Ic, and therefore the first firm case of an SN Ic with signatures of hydrogen-rich CSM in the early spectrum. The CSM is unlikely to have been shaped by steady-state stellar winds. The mass loss of the progenitor star must have been intense, M ∼ 0.02 ϵ Hα/0.01)-1(vwind/500 km s-1) (vshock 10,000 kms-1)-3Me yr-1, peaking at a few decades before the SN. Such a high mass-loss rate might have been experienced by the progenitor through eruptions or binary stripping.Ítem SN 2020acat: an energetic fast rising Type IIb supernova(Oxford University Press, 2022-07-01) Medler, K.; Mazzali, P.A.; Teffs, J.; Ashall, C.; Anderson, J.P.; Arcavi, I.; Benetti, S.; Bostroem, K.A.; Burke, J.; Cai, Y.-Z.; Charalampopoulos, P.; Elias Rosa, N.; Ergon, M.; Galbany, L.; Gromadzki, M.; Hiramatsu, D.; Howell, D.A.; Inserra, C.; Lundqvist, P.; McCully, C.; Müller Bravo, T.; Newsome, M.; Nicholl, M.; Gonzalez, E. Padilla; Paraskeva, E.; Pastorello, A.; Pellegrino, C.; Pessi, P.J.; Reguitti, A.; Reynolds, T.M.; Roy, R.; Terreran, G.; Tomasella, L.; Young, D.R.The ultraviolet (UV) and near-infrared (NIR) photometric and optical spectroscopic observations of SN 2020acat covering ∼250 d after explosion are presented here. Using the fast rising photometric observations, spanning from the UV to NIR wavelengths, a pseudo-bolometric light curve was constructed and compared to several other well-observed Type IIb supernovae (SNe IIb). SN 2020acat displayed a very short rise time reaching a peak luminosity of Log10(L) = 42.49 ± 0.17 erg s-1 in only ∼14.6 ± 0.3 d. From modelling of the pseudo-bolometric light curve, we estimated a total mass of 56Ni synthesized by SN 2020acat of MNi = 0.13 ± 0.03 M⊙, with an ejecta mass of Mej = 2.3 ± 0.4 M⊙ and a kinetic energy of Ek = 1.2 ± 0.3 × 1051 erg. The optical spectra of SN 2020acat display hydrogen signatures well into the transitional period (≳ 100 d), between the photospheric and the nebular phases. The spectra also display a strong feature around 4900 Å that cannot be solely accounted for by the presence of the Fe ii 5018 line. We suggest that the Fe ii feature was augmented by He i 5016 and possibly by the presence of N ii 5005. From both photometric and spectroscopic analysis, we inferred that the progenitor of SN 2020acat was an intermediate-mass compact star with an MZAMS of 15-20 M⊙. © 2022 The Author(s).Ítem SN 2021foa, a transitional event between a Type IIn (SN 2009ip-like) and a Type Ibn supernova(EDP Sciences, 2022-06-01) Reguitti, A.; Pastorello, A.; Pignata, G.; Fraser, M.; Stritzinger, M.D.; Brennan, S.J.; Cai, Y.-Z.; Elias-Rosa, N.; Fugazza, D.; Gutierrez, C.P.; Kankare, E.; Kotak, R.; Lundqvist, P.; Mazzali, P.A.; Moran, S.; Salmaso, I.; Tomasella, L.; Valerin, G.; Kuncarayakti, H.We present photometric and spectroscopic data of the unusual interacting supernova (SN) 2021foa. It rose to an absolute magnitude peak of Mr= 18 mag in 20 days. The initial light curve decline shows some luminosity fluctuations before a long-lasting flattening. A faint source (Mr∼ 14 mag) was detected in the weeks preceding the main event, showing a slowly rising luminosity trend. The r-band absolute light curve is very similar to those of SN 2009ip-like events, with a faint and shorter duration brightening ('Event A') followed by a much brighter peak ('Event B'). The early spectra of SN 2021foa show a blue continuum with narrow (∼400 km s1) H emission lines that, two weeks later, reveal a complex profile, with a narrow P Cygni on top of an intermediate-width (∼2700 km s1) component. At +12 days, metal lines in emission appear and Hea lines become very strong, with Hea λ5876 reaching half of the Hα luminosity, much higher than in previous SN 2009ip-like objects. We propose that SN 2021foa is a transitional event between the H-rich SN 2009ip-like SNe and the He-rich Type Ibn SNe. © A. Reguitti et al. 2022.Ítem SN 2021fxy: mid-ultraviolet flux suppression is a common feature of Type Ia supernovae(Oxford University Press, 2023-07-01) DerKacy, J.M.; Paugh, S.; Baron, E.; Brown, P.J.; Ashall, C.; Burns, C.R.; Hsiao, E.Y.; Kumar, S.; Lu, J.; Morrell, N.; Phillips, M.M.; Shahbandeh, M.; Shappee, B.J.; Stritzinger, M.D.; Tucker, M.A.; Yarbrough, Z.; Boutsia, K.; Hoeflich, P.; Wang, L.; Galbany, L.; Karamehmetoglu, E.; Krisciunas, K.; Mazzali, P.; Piro, A.L.; Suntzeff, N.B.; Fiore, A.; Gutiérrez, C.P.; Lundqvist, P.; Reguitti, A.We present ultraviolet (UV) to near-infrared (NIR) observations and analysis of the nearby Type Ia supernova SN 2021fxy. Our observations include UV photometry from Swift/UVOT, UV spectroscopy from HST/STIS, and high-cadence optical photometry with the Swope 1-m telescope capturing intranight rises during the early light curve. Early B − V colours show SN 2021fxy is the first 'shallow-silicon' (SS) SN Ia to follow a red-to-blue evolution, compared to other SS objects which show blue colours from the earliest observations. Comparisons to other spectroscopically normal SNe Ia with HST UV spectra reveal SN 2021fxy is one of several SNe Ia with flux suppression in the mid-UV. These SNe also show blueshifted mid-UV spectral features and strong high-velocity Ca II features. One possible origin of this mid-UV suppression is the increased effective opacity in the UV due to increased line blanketing from high velocity material, but differences in the explosion mechanism cannot be ruled out. Among SNe Ia with mid-UV suppression, SNe 2021fxy and 2017erp show substantial similarities in their optical properties despite belonging to different Branch subgroups, and UV flux differences of the same order as those found between SNe 2011fe and 2011by. Differential comparisons to multiple sets of synthetic SN Ia UV spectra reveal this UV flux difference likely originates from a luminosity difference between SNe 2021fxy and 2017erp, and not differing progenitor metallicities as suggested for SNe 2011by and 2011fe. These comparisons illustrate the complicated nature of UV spectral formation, and the need for more UV spectra to determine the physical source of SNe Ia UV diversity. © 2023 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.Ítem Supernova 2013fc in a circumnuclear ring of a luminous infrared galaxy: The big brother of SN 1998S(OXFORD UNIV PRESS, 2016-02) Kangas, T.; Mattila, S.; Kankare, E.; Lundqvist, P.; Väisänen, P.; Childress, M.; Pignata, G.; McCully, C.; Valenti, S.; Vinkó, J.; Pastorello, A.; Elias-Rosa, N.; Fraser, M.; Gal-Yam, A.; Kotak, R.; Kotilainen, J. K.; Smartt, S. J.; Galbany, L.; Harmanen, J.; Howell, D. A.; Inserra, C.; Marion, G. H.; Quimby, R. M.; Silverman, J. M.; Szalai, T.; Wheeler, J. C.; Ashall, C.; Benetti, S.; Romero-Cañizales, C.; Smith, K. W.; Sullivan, M.; Takáts, K.; Young, D. R.We present photometric and spectroscopic observations of SN 2013fc, a bright type II supernova (SN) in a circumnuclear star-forming ring in the luminous infrared galaxy ESO 154-G010, observed as part of the Public ESO Spectroscopic Survey of Transient Objects. SN 2013fc is both photometrically and spectroscopically similar to the well-studied type IIn SN 1998S and to the bright type II-L SN 1979C. It exhibits an initial linear decline, followed by a short plateau phase and a tail phase with a decline too fast for Co-56 decay with full. gamma-ray trapping. Initially, the spectrum was blue and featureless. Later on, a strong broad (similar to 8000 km s(-1)) H alpha emission profile became prominent. We apply a STARLIGHT stellar population model fit to the SN location (observed when the SN had faded) to estimate a high extinction of A(V) = 2.9 +/- 0.2 mag and an age of 10(+ 3) (- 2) Myr for the underlying cluster. We compare the SN to SNe 1998S and 1979C and discuss its possible progenitor star considering the similarities to these events. With a peak brightness of B = - 20.46 +/- 0.21 mag, SN 2013fc is 0.9 mag brighter than SN 1998S and of comparable brightness to SN 1979C. We suggest that SN 2013fc was consistent with a massive red supergiant (RSG) progenitor. Recent mass loss probably due to a strong RSG wind created the circumstellar matter illuminated through its interaction with the SN ejecta. We also observe a near- infrared excess, possibly due to newly condensed dust.