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We present observations from X-ray to mid-infrared wavelengths of the most energetic non-quasar transient ever observed, AT2021lwx. Our data show a single optical brightening by a factor $>100$ to a luminosity of $7\times10^{45}$ erg s$^{-1}$, and a total radiated energy of $1.5\times10^{53}$ erg, both greater than any known optical transient. The decline is smooth and exponential and the ultra-violet - optical spectral energy distribution resembles a black body with temperature $1.2\times10^4$ K. Tentative X-ray detections indicate a secondary mode of emission, while a delayed mid-infrared flare points to the presence of dust surrounding the transient. The spectra are similar to recently discovered optical flares in known active galactic nuclei but lack some characteristic features. The lack of emission for the previous seven years is inconsistent with the short-term, stochastic variability observed in quasars, while the extreme luminosity and long timescale of the transient disfavour the disruption of a single solar-mass star. The luminosity could be generated by the disruption of a much more massive star, but the likelihood of such an event occurring is small. A plausible scenario is the accretion of a giant molecular cloud by a dormant black hole of $10^8 - 10^9$ solar masses. AT2021lwx thus represents an extreme extension of the known scenarios of black hole accretion., 11 pages, 5 figures, Accepted for publication in MNRAS

We present an in-depth study of the late-time near-infrared plateau in Type Ia supernovae (SNe Ia), which occurs between 70-500 d. We double the existing sample of SNe Ia observed during the late-time near-infrared plateau with new observations taken with the Hubble Space Telescope, Gemini, New Technology Telescope, the 3.5m Calar Alto Telescope, and the Nordic Optical Telescope. Our sample consists of 24 nearby SNe Ia at redshift < 0.025. We are able to confirm that no plateau exists in the Ks band for most normal SNe Ia. SNe Ia with broader optical light curves at peak tend to have a higher average brightness on the plateau in J and H, most likely due to a shallower decline in the preceding 100 d. SNe Ia that are more luminous at peak also show a steeper decline during the plateau phase in H. We compare our data to state-of-the-art radiative transfer models of nebular SNe Ia in the near-infrared. We find good agreement with the sub-Mch model that has reduced non-thermal ionisation rates, but no physical justification for reducing these rates has yet been proposed. An analysis of the spectral evolution during the plateau demonstrates that the ratio of [Fe II] to [Fe III] contribution in a near-infrared filter determines the light curve evolution in said filter. We find that overluminous SNe decline slower during the plateau than expected from the trend seen for normal SNe Ia, 17 pages, 8 figures, Accepted for publication in MNRAS

We present photometric and spectroscopic observations of the Type Icn supernova (SN) 2021ckj. 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. 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 the diversity 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 of the ejecta and CSM, which is inferred also from the LC modeling. Taking into account the difference in the strength of the absorption features, this heterogeneity may be attributed to viewing angle effects in otherwise common aspherical ejecta., Comment: 13 pages, 5 figures, accepted for publication in A&A

Spectroscopically, tidal disruption events (TDEs) are characterized by broad (∼104 km s−1) emission lines and show a large diversity as well as different line profiles. After carefully and consistently performing a series of data reduction tasks including host galaxy light subtraction, we present here the first detailed, spectroscopic population study of 16 optical and UV TDEs. We study a number of emission lines prominent among TDEs including Hydrogen, Helium, and Bowen lines and we quantify their evolution with time in terms of line luminosities, velocity widths, and velocity offsets. We report a time lag between the peaks of the optical light curves and the peak luminosity of Hα spanning between ∼7 and 45 days. If interpreted as light echoes, these lags correspond to distances of ∼2 − 12 × 1016 cm, which are one to two orders of magnitudes larger than the estimated blackbody radii (RBB) of the same TDEs and we discuss the possible origin of this surprisingly large discrepancy. We also report time lags for the peak luminosity of the He I 5876 Å line, which are smaller than the ones of Hα for H TDEs and similar or larger for N III Bowen TDEs. We report that N III Bowen TDEs have lower Hα velocity widths compared to the rest of the TDEs in our sample and we also find that a strong X-ray to optical ratio might imply weakening of the line widths. Furthermore, we study the evolution of line luminosities and ratios with respect to their radii (RBB) and temperatures (TBB). We find a linear relationship between Hα luminosity and the RBB (Lline ∝ RBB) and potentially an inverse power-law relation with TBB (Lline ∝ TBB−β), leading to weaker Hα emission for TBB ≥ 25 000 K. The He II/He I ratio becomes large at the same temperatures, possibly pointing to an ionization effect. The He II/Hα ratio becomes larger as the photospheric radius recedes, implying a stratified photosphere where Helium lies deeper than Hydrogen. We suggest that the large diversity of the spectroscopic features seen in TDEs along with their X-ray properties can potentially be attributed to viewing angle effects., We thank Tom Holoien for providing us with the spectra of AT2018zr. P.C., G.L., D.B.M. and M.P. are supported by a research grant (19054) from VILLUM FONDEN. IA is a CIFAR Azrieli Global Scholar in the Gravity and the Extreme Universe Program and acknowledges support from that program, from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement number 852097), from the Israel Science Foundation (grant number 2752/19), from the United States – Israel Binational Science Foundation (BSF), and from the Israeli Council for Higher Education Alon Fellowship. M.N. is supported by a Royal Astronomical Society Research Fellowship and by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 948381). T.-W.C. acknowledges the EU Funding under Marie Skłodowska-Curie grant H2020-MSCA-IF-2018-842471. L.G. acknowledges financial support from the Spanish Ministry of Science, Innovation and Universities (MICIU) under the 2019 Ramón y Cajal program RYC2019-027683 and from the Spanish MICIU project PID2020-115253GA-I00. M.G. is supported by the EU Horizon 2020 research and innovation programme under grant agreement No 101004719. T.M.B. was funded by the CONICYT PFCHA/DOCTORADOBECAS CHILE/2017-72180113. This work is based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, as part of PESSTO/ePESSTO/ePESSTO+ (the extended Public ESO Spectroscopic Survey for Transient Objects Survey). PESSTO/ePESSTO/ePESSTO+ observations were obtained under ESO program IDs 188.D-3003, 191.D-0935, 199.D-0143, 1103.D-0328. This work is based on observations made with the Nordic Optical Telescope, owned in collaboration by the University of Turku and Aarhus University, and operated jointly by Aarhus University, the University of Turku and the University of Oslo, representing Denmark, Finland and Norway, the University of Iceland and Stockholm University at the Observatorio del Roque de los Muchachos, La Palma, Spain, of the Instituto de Astrofisica de Canarias.

Thanks to the advent of large-scale optical surveys, a diverse set of flares from the nuclear regions of galaxies has recently been discovered. These include the disruption of stars by supermassive black holes at the centers of galaxies - nuclear transients known as tidal disruption events (TDEs). Active galactic nuclei (AGN) can show extreme changes in the brightness and emission line intensities, often referred to as changing-look AGN (CLAGN). Given the physical and observational similarities, the interpretation and distinction of nuclear transients as CLAGN or TDEs remains difficult. One of the obstacles of making progress in the field is the lack of well-sampled data of long-lived nuclear outbursts in AGN. Here, we study PS16dtm, a nuclear transient in a Narrow Line Seyfert 1 (NLSy1) galaxy, which has been proposed to be a TDE candidate. Our aim is to study the spectroscopic and photometric properties of PS16dtm, in order to better understand the outbursts originating in NLSy1 galaxies. Our extensive multiwavelength follow-up that spans around 2000 days includes photometry and spectroscopy in the UV/optical, as well as mid-infrared (MIR) and X-ray observations. Furthermore, we improved an existing semiempirical model in order to reproduce the spectra and study the evolution of the spectral lines. The UV/optical light curve shows a double peak at $\sim50$ and $\sim100$ days after the first detection, and it declines and flattens afterward, reaching preoutburst levels after 2000 days of monitoring. The MIR light curve rises almost simultaneously with the optical, but unlike the UV/optical which is approaching the preoutburst levels in the last epochs of our observations, the MIR emission is still rising at the time of writing. The optical spectra show broad Balmer features and the strongest broad Fe II emission ever detected in a nuclear transient. [abridged], Accepted for publication in A&A, 19 pages and 18 figures

S. J. Brennan et al., We present the bolometric light curve, identification and analysis of the progenitor candidate, and preliminary modelling of AT 2016jbu (Gaia16cfr). We find a progenitor consistent with a ∼ 22–25 M⊙ yellow hypergiant surrounded by a dusty circumstellar shell, in agreement with what has been previously reported. We see evidence for significant photometric variability in the progenitor, as well as strong Hα emission consistent with pre-existing circumstellar material. The age of the environment, as well as the resolved stellar population surrounding AT 2016jbu, supports a progenitor age of >10 Myr, consistent with a progenitor mass of ∼22 M⊙. A joint analysis of the velocity evolution of AT 2016jbu and the photospheric radius inferred from the bolometric light curve shows the transient is consistent with two successive outbursts/explosions. The first outburst ejected material with velocity ∼650 km s−1, while the second, more energetic event ejected material at ∼4500 km s−1. Whether the latter is the core collapse of the progenitor remains uncertain. We place a limit on the ejected 56Ni mass of, SJB acknowledges support from Science Foundation Ireland and the Royal Society (RS-EA/3471). MF is supported by a Royal Society–Science Foundation Ireland University Research Fellowship. TMB was funded by CONICYT PFCHA/DOCTORADOBECAS CHILE/2017-72180113 and acknowledges financial support from the Spanish Ministerio de Ciencia e Innovación (MCIN), the Agencia Estatal de Investigación (AEI) 10.13039/501100011033 under the PID2020-115253GA-I00 HOSTFLOWS project, and Centro Superior de Investigaciones Científicas (CSIC) under the PIE project 20215AT016. KM is funded by the EU H2020 ERC grant no. 758638. TWC acknowledges EU Funding under Marie Skłodowska–Curie grant H2020-MSCA-IF-2018-842471, and thanks Thomas Krühler for GROND data reduction. MN is supported by a Royal Astronomical Society Research Fellowship. BJS is supported by NSF grants AST-1908952, AST-1920392, AST-1911074, and NASA award 80NSSC19K1717. MS is supported by generous grants from Villum FONDEN (13261,28021) and by a project grant (8021-00170B) from the Independent Research Fund Denmark. LH acknowledges support for Watcher from Science Foundation Ireland grant 07/RFP/PHYF295. Time-domain research by DJS is supported by NSF grants AST-1821987, 1813466, and 1908972, and by the Heising–Simons Foundation under grant #2020-1864. NER acknowledges support from MIUR, PRIN 2017 (grant 20179ZF5KS). Support for JLP is provided in part by ANID through the Fondecyt regular grant 1191038 and through the Millennium Science Initiative grant ICN12_009, awarded to The Millennium Institute of Astrophysics, MAS. LG acknowledges financial support from the Spanish Ministry of Science, Innovation and Universities (MICIU) under the 2019 Ramón y Cajal program RYC2019-027683 and from the Spanish MICIU project PID2020-115253GA-I00. DAH and DH are supported by AST-1911151, AST19-11225, and NASA Swift grant 80NSSC19K1639. GP acknowledges support by the Ministry of Economy, Development, and Tourism’s Millennium Science Initiative through grant IC120009, awarded to The Millennium Institute of Astrophysics, MAS. LT acknowledges support from MIUR (PRIN 2017 grant 20179ZF5KS). Support for TW-SH was provided by NASA through the NASA Hubble Fellowship grant HST-HF2-51458.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. HK was funded by the Academy of Finland projects 324504 and 328898. This research made use of ASTROPY,8 a community-developed core PYTHON package for Astronomy (Astropy Collaboration 2013; Price-Whelan et al. 2018). This research made use of data provided by Astrometry.net.9 Parts of this research were supported by the Australian Research Council Centre of Excellence for All Sky Astrophysics in Three Dimensions (ASTRO 3D), through project number CE170100013. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. We acknowledge the Telescope Access Program (TAP) funded by the NAOC, CAS, and the Special Fund for Astronomy from the Ministry of Finance. This work was partially supported by Polish NCN grants: Harmonia No. 2018/30/M/ST9/00311 and Daina No. 2017/27/L/ST9/03221. This work made use of v2.2.1 of the Binary Population and Spectral Synthesis (BPASS) models as described in Eldridge et al. (2017) and Stanway & Eldridge (2018). This research is based on observations made with the NASA/ESA Hubble Space Telescope obtained from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program 15645. Observations were also obtained from the Hubble Legacy Archive, which is a collaboration between the Space Telescope Science Institute (STScI/NASA), the Space Telescope European Coordinating Facility (ST-ECF/ESAC/ESA), and the Canadian Astronomy Data Centre (CADC/NRC/CSA). This research has made use of the SVO Filter Profile Service10 supported from the Spanish MINECO through grant AYA2017-84089.

SN\,2020qlb (ZTF20abobpcb) is a hydrogen-poor superluminous supernova (SLSN-I) that is among the most luminous (maximum M$_{g} = -22.25$ mag) and that has one of the longest rise times (77 days from explosion to maximum). We estimate the total radiated energy to be $>2.1\times10^{51}$ erg. SN\,2020qlb has a well-sampled light curve that exhibits clear near and post peak undulations, a phenomenon seen in other SLSNe, whose physical origin is still unknown. We discuss the potential power source of this immense explosion as well as the mechanisms behind its observed light curve undulations. We analyze photospheric spectra and compare them to other SLSNe-I. We constructed the bolometric light curve using photometry from a large data set of observations from the Zwicky Transient Facility (ZTF), Liverpool Telescope (LT), and Neil Gehrels Swift Observatory and compare it with radioactive, circumstellar interaction and magnetar models. Model residuals and light curve polynomial fit residuals are analyzed to estimate the undulation timescale and amplitude. We also determine host galaxy properties based on imaging and spectroscopy data, including a detection of the [O III]$\lambda$4363, auroral line, allowing for a direct metallicity measurement. We rule out the Arnett $^{56}$Ni decay model for SN\,2020qlb's light curve due to unphysical parameter results. Our most favored power source is the magnetic dipole spin-down energy deposition of a magnetar. Two to three near peak oscillations, intriguingly similar to those of SN\,2015bn, were found in the magnetar model residuals with a timescale of $32\pm6$ days and an amplitude of 6$\%$ of peak luminosity. We rule out centrally located undulation sources due to timescale considerations; and we favor the result of ejecta interactions with circumstellar material (CSM) density fluctuations as the source of the undulations., Comment: 22 pages, 25 figures, submitted to A&A

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 $\pm$ 2 days, ATLAS $o$ band) and high luminosity (peaking at $-$20.78 $\pm$ 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 days. 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 >$\sim$+800 days., Accepted to A&A

During the Zwicky Transient Facility (ZTF) Phase-I operation, 78 hydrogen-poor superluminous supernovae (SLSNe-I) were discovered in less than three years, making up the largest sample from a single survey. This paper (Paper I) presents the data, including the optical/ultraviolet light curves and classification spectra, while Paper II in this series will focus on the detailed analysis of the light curves and modeling. Our photometry is primarily taken by the ZTF in the $g,r,i$ bands, and with additional data from other ground-based facilities and Swift. The events of our sample cover a redshift range of $z = 0.06 - 0.67$, with a median and $1\sigma$ error (16\% and 84\% percentiles) $z_{\rm med} = 0.265^{+0.143}_{-0.135}$. The peak luminosity covers $-22.8\,{\rm mag} \leq M_{g,\rm peak} \leq -19.8$\,mag, with a median value of $-21.48^{+1.13}_{-0.61}$\,mag. Their light curves evolve slowly with the mean rest-frame rise time of $t_{\rm rise} = 41.9\pm17.8$\,days. The luminosity and time scale distributions suggest that low luminosity SLSNe-I with peak luminosity $\sim -20$\,mag or extremely fast rising events ($, Comment: 38 pages, 25 figures, Accepted by APJ

Brennan, S. J. et al (ASTROPY Collaboration), We present the results from a high-cadence, multiwavelength observation campaign of AT 2016jbu (aka Gaia16cfr), an interacting transient. This data set complements the current literature by adding higher cadence as well as extended coverage of the light-curve evolution and late-time spectroscopic evolution. Photometric coverage reveals that AT 2016jbu underwent significant photometric variability followed by two luminous events, the latter of which reached an absolute magnitude of MV ∼-18.5 mag. This is similar to the transient SN 2009ip whose nature is still debated. Spectra are dominated by narrow emission lines and show a blue continuum during the peak of the second event. AT 2016jbu shows signatures of a complex, non-homogeneous circumstellar material (CSM). We see slowly evolving asymmetric hydrogen line profiles, with velocities of 500 km s-1 seen in narrow emission features from a slow-moving CSM, and up to 10 000 km s-1 seen in broad absorption from some high-velocity material. Late-time spectra (∼+1 yr) show a lack of forbidden emission lines expected from a core-collapse supernova and are dominated by strong emission from H, He i, and Ca ii. Strong asymmetric emission features, a bumpy light curve, and continually evolving spectra suggest an inhibit nebular phase. We compare the evolution of H α among SN 2009ip-like transients and find possible evidence for orientation angle effects. The light-curve evolution of AT 2016jbu suggests similar, but not identical, circumstellar environments to other SN 2009ip-like transients., SJB acknowledges support from Science Foundation Ireland and the Royal Society (RS-EA/3471). MF is supported by a Royal Society - Science Foundation Ireland University Research Fellowship. TMB was funded by the CONICYT PFCHA / DOCTORADOBECAS CHILE/2017-72180113 and acknowledges their financial support from the Spanish Ministerio de Ciencia e Innovación (MCIN), the Agencia Estatal de Investigación (AEI) 10.13039/501100011033 under the PID2020-115253GA-I00 HOSTFLOWS project, and from Centro Superior de Investigaciones Científicas (CSIC) under the PIE project 20215AT016. KM is funded by the EU H2020 ERC grant no. 758638. TWC acknowledges the EU Funding under Marie Skłodowska-Curie grant H2020-MSCA-IF-2018-842471, and thanks to Thomas Krühler for GROND data reduction. MN is supported by a Royal Astronomical Society Research Fellowship. BJS is supported by NSF grants AST-1908952, AST-1920392, AST-1911074, and NASA award 80NSSC19K1717. MS is supported by generous grants from Villum FONDEN (13261, 28021) and by a project grant (8021-00170B) from the Independent Research Fund Denmark. LH acknowledges support for Watcher from Science Foundation Ireland grant 07/RFP/PHYF295. Time domain research by DJS is supported by NSF grants AST-1821987, 1813466, and 1908972, and by the Heising-Simons Foundation under grant #2020-1864. NER acknowledges support from MIUR, PRIN 2017 (grant 20179ZF5KS). LG acknowledges financial support from the Spanish Ministry of Science, Innovation and Universities (MICIU) under the 2019 Ramón y Cajal program RYC2019-027683 and from the Spanish MICIU project PID2020-115253GA-I00. Support for TW-SH was provided by NASA through the NASA Hubble Fellowship grant HST-HF2-51458.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. Support for JLP is provided in part by ANID through the Fondecyt regular grant 1191038 and through the Millennium Science Initiative grant ICN12_009, awarded to The Millennium Institute of Astrophysics, MAS. DAH and DH are supported by AST-1911151, AST19-11225, and NASA Swift grant 80NSSC19K1639. GP acknowledge support by the Ministry of Economy, Development, and Tourism’s Millennium Science Initiative through grant IC120009, awarded to The Millennium Institute of Astrophysics, MAS. LT acknowledges support from MIUR (PRIN 2017 grant 20179ZF5KS). HK was funded by the Academy of Finland projects 324504 and 328898.

[Abridged] We classify AT 2020zso as a TDE based on the blackbody evolution inferred from UV/optical photometric observations, and spectral line content and evolution. We identify transient, double-peaked Bowen (N III), He I, He II and Halpha emission lines. We model medium resolution optical spectroscopy of the He II (after careful deblending of the N III contribution) and Halpha lines during the rise, peak and early decline of the light curve using relativistic, elliptical accretion disk models. We find that the spectral evolution before peak can be explained by optical depth effects consistent with an outflowing, optically thick Eddington envelope. Around peak the envelope reaches its maximum extent (approximately 10^15 or 3000-6000 gravitational radii for an inferred black hole mass of 5-10 10^5) and becomes optically thin. The Halpha and He II emission lines at and after peak can be reproduced with a highly inclined (i=85+-5 degrees), highly elliptical (e=0.97+-0.01) and relatively compact (Rin = several 100 Rg and Rout = several 1000 Rg ) accretion disk. Overall, the line profiles suggest a highly elliptical geometry for the new accretion flow, consistent with theoretical expectations of newly formed TDE disks. We quantitatively confirm, for the first time, the high inclination nature of a Bowen (and X-ray dim) TDE, consistent with the unification picture of TDEs where the inclination largely determines the observational appearance. Rapid line profile variations rule out the binary SMBH hypothesis as the origin of the eccentricity; these results thus provide a direct link between a TDE in an AGN and the eccentric accretion disk. We illustrate for the first time how optical spectroscopy can be used to constrain the black hole spin, through (the lack of) disk precession signatures (changes in inferred inclination) - and rule out high black hole spin values (a < 0.8)., 20 pages, 15 figures and 5 tables. Accepted for publication in A&A. The spectra will be made publicly available through WISErep

We present a spectroscopic analysis of the most nearby Type I superluminous supernova (SLSN-I), SN 2018bsz. The photometric evolution of SN 2018bsz has several surprising features, including an unusual pre-peak plateau and evidence for rapid formation of dust greater than or similar to 200 d post-peak. We show here that the spectroscopic and polarimetric properties of SN 2018bsz are also unique. While its spectroscopic evolution closely resembles SLSNe-I, with early O II absorption and C II P Cygni profiles followed by Ca, Mg, Fe, and other O features, a multi-component H alpha profile appearing at similar to 30 d post-maximum is the most atypical. The H alpha is at first characterised by two emission components, one at similar to+3000 km s(-1) and a second at similar to - 7500 km s(-1), with a third, near-zero-velocity component appearing after a delay. The blue and central components can be described by Gaussian profiles of intermediate width (FWHM similar to 2000-6000 km s(-1)), but the red component is significantly broader (FWHM greater than or similar to 10000 km s(-1)) and Lorentzian. The blue H alpha component evolves towards a lower-velocity offset before abruptly fading at similar to + 100 d post-maximum brightness, concurrently with a light curve break. Multi-component profiles are observed in other hydrogen lines, including Pa beta, and in lines of Ca II and He I. Spectropolarimetry obtained before (10.2 d) and after (38.4 d) the appearance of the H lines shows a large shift on the Stokes Q - U plane consistent with SN 2018bsz undergoing radical changes in its projected geometry. Assuming the supernova is almost unpolarised at 10.2 d, the continuum polarisation at 38.4 d reaches P similar to 1.8%, implying an aspherical configuration. We propose that the observed evolution of SN 2018bsz can be explained by highly aspherical, possibly disk-like, circumstellar material (CSM) with several emitting regions. After the supernova explosion, the CSM is quickly overtaken by the ejecta, but as the photosphere starts to recede, the different CSM regions re-emerge, producing the peculiar line profiles. Based on the first appearance of H alpha, we can constrain the distance of the CSM to be less than similar to 6.5 x 10(15) cm (430 AU), or even lower (less than or similar to 87 AU) if the pre-peak plateau is related to an eruption that created the CSM. The presence of CSM has been inferred previously for other SLSNe-I, both directly and indirectly. However, it is not clear whether the rare properties of SN 2018bsz can be generalised for SLSNe-I, for example in the context of pulsational pair instability, or whether they are the result of an uncommon evolutionary path, possibly involving a binary companion., European Organisation for Astronomical Research in the Southern Hemisphere under ESO programme 2101.D-5023, Villum Fonden 19054, Science Foundation Ireland, European Commission, Royal Society of London, European Commission RS-EA/3471, Swedish Research Council, European Commission 2020-03330, National Agency for Research and Development (ANID)/Scholarship Program/Doctorado Nacional 2021 - 21211203, European Commission H2020-MSCA-IF-2018-842471, Ministry of Science and Innovation, Spain (MICINN), Agencia Estatal de Investigacion (AEI), European Social Fund (ESF) "Investing in your future" under the 2019 Ramon y Cajal program RYC2019-027683-I, Centro Superior de Investigaciones Cientificas (CSIC) 20215AT016, program Unidad de Excelencia Maria de Maeztu CEX2020-001058-M, EU Horizon 2020 research and innovation programme 101004719, European Research Council (ERC), European Commission 948381, Alan Turing Institute, GRAWITA/PRIN-MIUR project: "The new frontier of the Multi-Messenger Astrophysics: follow-up of electromagnetic transient counterparts of gravitational wave sources", HORIZON2020: AHEAD2020 871158 1103.D-0328 PID2020-115253GA-I00 HOSTFLOWS Swedish Research Council, European Research Council (ERC) European Commission 948381, HORIZON2020: AHEAD2020 871158 1103.D-0328 PID2020-115253GA-I00 HOSTFLOWS

We thank the anonymous referee for the very useful comments, which contributed to improve the manuscript. AF is partially supported by the PRIN-INAF 2017 with the project Towards the SKA and CTA era: discovery, localisation, and physics of transients sources (P.I. M. Giroletti). These observations made use of the LCO network. DAH, CP, DH, and JB are supported by NSF Grant AST1911225 and NASA Grant 80NSSC19k1639. TMB was funded by the CONICYT PFCHA/DOCTORADOBECAS CHILE/201772180113. MG is supported by the Polish NCN MAESTRO grant 2014/14/A/ST9/00121. TWC acknowledges the funding provided by the Alexander von Humboldt Foundation and the EU Funding under Marie Sklodowska-Curie grant agreement No 842471, and Thomas Kruhler for reducing X-Shooter spectrum. LG was funded by the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 839090. This work has been partially supported by the Spanish grant PGC2018-095317-B-C21 within the European Funds for Regional Development (FEDER). CPG acknowledges support from EU/FP7ERC grant no. [615929]. GL was supported by a research grant (19054) from VILLUM FONDEN. MN is supported by a Royal Astronomical Society Research Fellowship. RL is supported by a Marie Sklodowska-Curie Individual Fellowship within the Horizon 2020 European Union (EU) Framework Programme for Research and Innovation (H2020-MSCA-IF-2017-794467). GT acknowledges partial support by the National Science Foundation under Award No. AST-1909796. Research by SV is supported by NSF grants AST-1813176 and AST-2008108. Some of the observations reported here were obtained at the MMT Observatory, a joint facility of the University of Arizona and the Smithsonian Institution under program 2018A-UAO-G16 (PI Terreran). Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration under program NW440 (PI Fong). The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. W. M. Keck Observatory and MMT Observatory accesswas supported by Northwestern University and the Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA). Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programmes 199.D-0143, 0100.D-0751(B), 0101.D-0199(B), 099.A-9025(A), 0100.A-9099(A)099.A-9099 and 0100.A-9099. This work makes use of observations from the LCO network. Part of the funding for GROND (both hardware as well as personnel) was generously granted from the Leibniz-Prize to Prof. G. Hasinger (DFG grant HA 1850/28-1). The Pan-STARRS1 Surveys (PS1) have been made possible through contributions of the Institute for Astronomy, the University of Hawaii, the Pan-STARRS Project Office, the Max-Planck Society and its participating institutes, the Max Planck Institute for Astronomy, Heidelberg, and the Max Planck Institute for Extraterrestrial Physics, Garching, The Johns Hopkins University, Durham University, the University of Edinburgh, Queen's University Belfast, the Harvard-Smithsonian Center for Astrophysics, the Las Cumbres Observatory Global Telescope Network Incorporated, the National Central University of Taiwan, the Space Telescope Science Institute, the National Aeronautics and Space Administration Grants No.s NNX08AR22G, NNX12AR65G, and NNX14AM74G, the National Science Foundation under Grant No. AST-1238877, the University of Maryland, Eotvos Lorand University (ELTE), the Los Alamos National Laboratory and the Gordon and Betty Moore foundation. TheATLAS surveys are funded through NASA grants NNX12AR55G. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium).Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This research made use of TARDIS, a community-developed software package for spectral synthesis in supernovae (Kerzendorf & Sim 2014). The development of TARDIS received support from the Google Summer of Code initiative and from ESA's Summer of Code in Space program. TARDIS makes extensive use of Astropy and PyNE., This article has been accepted for publication in MNRAS published by Oxford University Press on behalf of the Royal Astronomical Society, 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., PRIN-INAF 2017, National Science Foundation (NSF) AST1911225 AST-1813176 AST-2008108, CONICYT PFCHA/DOCTORADOBECAS CHILE/2017 72180113, Polish NCN MAESTRO 2014/14/A/ST9/00121, Alexander von Humboldt Foundation, European Commission 842471, European Commission 839090, European Commission PGC2018-095317-B-C21, VILLUM FONDEN 19054, Royal Astronomical Society Research Fellowship, Marie Sklodowska-Curie Individual Fellowship within the Horizon 2020 European Union (EU) Framework Programme for Research and Innovation H2020-MSCA-IF-2017-794467, National Science Foundation (NSF) AST-1909796 AST-1238877, University of Arizona 2018A-UAO-G16, Smithsonian Institution 2018A-UAO-G16, National Aeronautics & Space Administration (NASA) NW440 NNX08AR22G NNX12AR65G NNX14AM74G, W.M. Keck Foundation, Northwestern University, Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), European Organisation for Astronomical Research in the Southern Hemisphere 199.D-0143 0100.D-0751(B) 0101.D-0199(B) 099.A-9025(A) 0100.A-9099(A)099.A-9099 0100.A-9099, German Research Foundation (DFG), European Commission HA 1850/28-1, National Aeronautics & Space Administration (NASA) NNX12AR55G 80NSSC19k1639, Google Summer of Code initiative, ESA's Summer of Code in Space program, European Commission 615929

SN 2018hti was a very nearby (z = 0.0614) superluminous supernova with an exceedingly bright absolute magnitude of −21.7 mag in r band at maximum. The densely sampled pre-maximum light curves of SN 2018hti show a slow luminosity evolution and constrain the rise time to ∼50 rest-frame d. We fitted synthetic light curves to the photometry to infer the physical parameters of the explosion of SN 2018hti for both the magnetar and the CSM-interaction scenarios. We conclude that one of two mechanisms could be powering the luminosity of SN 2018hti; interaction with ∼10 M⊙ of circumstellar material or a magnetar with a magnetic field of Bp∼ 1.3 × 1013 G, and initial period of Pspin∼ 1.8 ms. From the nebular spectrum modelling we infer that SN 2018hti likely results from the explosion of a ∼40M⊙ progenitor star., MG is supported by the EU Horizon 2020 research and innovation programme under grant agreement No 101004719. MS acknowledges the Infrared Telescope Facility, which is operated by the University of Hawaii under contract 80HQTR19D0030 with the National Aeronautics and Space Administration. NER acknowledges support from MIUR, PRIN 2017 (grant 20179ZF5KS). TMB was funded by the CONICYT PFCHA / DOCTORADOBECAS CHILE/2017-72180113. AJ acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Program (ERC Starting Grant. AR acknowledges support from ANID BECAS/DOCTORADO NACIONAL 21202412. Y-Z Cai is funded by China Postdoctoral Science Foundation (grant no. 2021M691821). T-WC acknowledges the EU Funding under Marie Skłodowska-Curie grant H2020-MSCA-IF-2018-842471. KM is funded by the EU H2020 ERC grant no. 758638. GP is supported by ANID - Millennium Science Initiative - ICN12_009. We thank the staff at the different observatories for performing the observations. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, as part of ePESSTO+ (the advanced Public ESO Spectroscopic Survey for Transient Objects). ePESSTO+ observations were obtained under ESO program id 199.D-0143 (PI: Inserra). Based on observations made with the Gran Telescopio Canarias (GTC), installed in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, in the island of La Palma. This work uses observations from the Las Cumbres Observatory network. The LCO team is supported by NSF grants AST-1911225 and AST-1911151.

KM, MRM, and SJP are supported by H2020 ERC grant no. 758638. LG acknowledges financial support from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement no. 839090, and from the Spanish Ministry of Science, Innovation and Universities (MICIU) under the 2019 Ramon y Cajal programme RYC2019-027683. TMB ´ was funded by the CONICYT PFCHA / DOCTORADOBECAS CHILE/2017-72180113. MG is supported by the EU Horizon 2020 research and innovation programme under grant agreement no. 101004719. SGG acknowledges support by FCT under Project CRISP PTDC/FIS-AST-31546/2017. MN is supported by a Royal Astronomical Society Research Fellowship and H2020 ERC grant no. 948381. T-WC acknowledges the EU Funding under Marie Skłodowska-Curie grant H2020-MSCA-IF-2018-842471. The LT is operated on the island of La Palma by Liverpool John Moores University in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias with financial support from the UK Science and Technology Facilities Council. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, as part of ePESSTO+ (the advanced Public ESO Spectroscopic Survey for Transient Objects Survey). ePESSTO+ observations were obtained under ESO programme ID 1103.D-0328 (PI: Inserra). The WHT is operated on the island of La Palma by the Isaac Newton Group of Telescopes in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrof´ısica de Canarias. SJP thanks GPL for many insightful discussions at the bar over the last few years., The division between stripped-envelope supernovae (SE-SNe) and superluminous supernovae (SLSNe) is not well-defined in either photometric or spectroscopic space. While a sharp luminosity threshold has been suggested, there remains an increasing number of transitional objects that reach this threshold without the spectroscopic signatures common to SLSNe. In this work, we present data and analysis on four SNe transitional between SE-SNe and SLSNe; the He-poor SNe 2019dwa and 2019cri, and the He-rich SNe 2019hge and 2019unb. Each object displays long-lived and variable photometric evolution with luminosities around the SLSN threshold of Mr < -19.8 mag. Spectroscopically however, these objects are similar to SE-SNe, with line velocities lower than either SE-SNe and SLSNe, and thus represent an interesting case of rare transitional events., H2020 ERC grant no. 758638, European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement no. 839090, Spanish Ministry of Science, Innovation and Universities (MICIU) under the 2019 Ramon y Cajal programme RYC2019-027683, CONICYT PFCHA / DOCTORADOBECAS CHILE/2017-72180113, EU Horizon 2020 research and innovation programme under grant agreement no. 101004719, FCT under Project CRISP PTDC/FIS-AST-31546/2017, Royal Astronomical Society Research Fellowship, H2020 ERC grant no. 948381, UK Science and Technology Facilities Council, ESO programme ID 1103.D-0328 (PI: Inserra)

Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.--Full list of authors: Ackley, K.; Amati, L.; Barbieri, C.; Bauer, F. E.; Benetti, S.; Bernardini, M. G.; Bhirombhakdi, K.; Botticella, M. T.; Branchesi, M.; Brocato, E.; Bruun, S. H.; Bulla, M.; Campana, S.; Cappellaro, E.; Castro-Tirado, A. J.; Chambers, K. C.; Chaty, S.; Chen, T. -W.; Ciolfi, R.; Coleiro, A.; Copperwheat, C. M.; Covino, S.; Cutter, R.; D'Ammando, F.; D'Avanzo, P.; De Cesare, G.; D'Elia, V.; Della Valle, M.; Denneau, L.; De Pasquale, M.; Dhillon, V. S.; Dyer, M. J.; Elias-Rosa, N.; Evans, P. A.; Eyles-Ferris, R. A. J.; Fiore, A.; Fraser, M.; Fruchter, A. S.; Fynbo, J. P. U.; Galbany, L.; Gall, C.; Galloway, D. K.; Getman, F. I.; Ghirlanda, G.; Gillanders, J. H.; Gomboc, A.; Gompertz, B. P.; González-Fernández, C.; González-Gaitán, S.; Grado, A.; Greco, G.; Gromadzki, M.; Groot, P. J.; Gutiérrez, C. P.; Heikkilä, T.; Heintz, K. E.; Hjorth, J.; Hu, Y. -D.; Huber, M. E.; Inserra, C.; Izzo, L.; Japelj, J.; Jerkstrand, A.; Jin, Z. P.; Jonker, P. G.; Kankare, E.; Kann, D. A.; Kennedy, M.; Kim, S.; Klose, S.; Kool, E. C.; Kotak, R.; Kuncarayakti, H.; Lamb, G. P.; Leloudas, G.; Levan, A. J.; Longo, F.; Lowe, T. B.; Lyman, J. D.; Magnier, E.; Maguire, K.; Maiorano, E.; Mandel, I.; Mapelli, M.; Mattila, S.; McBrien, O. R.; Melandri, A.; Michałowski, M. J.; Milvang-Jensen, B.; Moran, S.; Nicastro, L.; Nicholl, M.; Nicuesa Guelbenzu, A.; Nuttal, L.; Oates, S. R.; O'Brien, P. T.; Onori, F.; Palazzi, E.; Patricelli, B.; Perego, A.; Torres, M. A. P.; Perley, D. A.; Pian, E.; Pignata, G.; Piranomonte, S.; Poshyachinda, S.; Possenti, A.; Pumo, M. L.; Quirola-Vásquez, J.; Ragosta, F.; Ramsay, G.; Rau, A.; Rest, A.; Reynolds, T. M.; Rosetti, S. S.; Rossi, A.; Rosswog, S.; Sabha, N. B.; Sagués Carracedo, A.; Salafia, O. S.; Salmon, L.; Salvaterra, R.; Savaglio, S.; Sbordone, L.; Schady, P.; Schipani, P.; Schultz, A. S. B.; Schweyer, T.; Smartt, S. J.; Smith, K. W.; Smith, M.; Sollerman, J.; Srivastav, S.; Stanway, E. R.; Starling, R. L. C.; Steeghs, D.; Stratta, G.; Stubbs, C. W.; Tanvir, N. R.; Testa, V.; Thrane, E.; Tonry, J. L.; Turatto, M.; Ulaczyk, K.; van der Horst, A. J.; Vergani, S. D.; Walton, N. A.; Watson, D.; Wiersema, K.; Wiik, K.; Wyrzykowski, Ł.; Yang, S.; Yi, S. -X.; Young, D. R., Context. Gravitational wave (GW) astronomy has rapidly reached maturity, becoming a fundamental observing window for modern astrophysics. The coalescences of a few tens of black hole (BH) binaries have been detected, while the number of events possibly including a neutron star (NS) is still limited to a few. On 2019 August 14, the LIGO and Virgo interferometers detected a high-significance event labelled S190814bv. A preliminary analysis of the GW data suggests that the event was likely due to the merger of a compact binary system formed by a BH and a NS. Aims. In this paper, we present our extensive search campaign aimed at uncovering the potential optical and near infrared electromagnetic counterpart of S190814bv. We found no convincing electromagnetic counterpart in our data. We therefore use our non-detection to place limits on the properties of the putative outflows that could have been produced by the binary during and after the merger. Methods. Thanks to the three-detector observation of S190814bv, and given the characteristics of the signal, the LIGO and Virgo Collaborations delivered a relatively narrow localisation in low latency - a 50% (90%) credible area of 5 deg2 (23 deg2) - despite the relatively large distance of 267 ± 52 Mpc. ElectromagNetic counterparts of GRAvitational wave sources at the VEry Large Telescope collaboration members carried out an intensive multi-epoch, multi-instrument observational campaign to identify the possible optical and near infrared counterpart of the event. In addition, the ATLAS, GOTO, GRAWITA-VST, Pan-STARRS, and VINROUGE projects also carried out a search on this event. In this paper, we describe the combined observational campaign of these groups. Results. Our observations allow us to place limits on the presence of any counterpart and discuss the implications for the kilonova (KN), which was possibly generated by this NS-BH merger, and for the strategy of future searches. The typical depth of our wide-field observations, which cover most of the projected sky localisation probability (up to 99.8%, depending on the night and filter considered), is r ∼ 22 (resp. K ∼ 21) in the optical (resp. near infrared). We reach deeper limits in a subset of our galaxy-targeted observations, which cover a total ∼50% of the galaxy-mass-weighted localisation probability. Altogether, our observations allow us to exclude a KN with large ejecta mass M 0.1 M- to a high (> 90%) confidence, and we can exclude much smaller masses in a sub-sample of our observations. This disfavours the tidal disruption of the neutron star during the merger. Conclusions. Despite the sensitive instruments involved in the campaign, given the distance of S190814bv, we could not reach sufficiently deep limits to constrain a KN comparable in luminosity to AT 2017gfo on a large fraction of the localisation probability. This suggests that future (likely common) events at a few hundred megaparsecs will be detected only by large facilities with both a high sensitivity and large field of view. Galaxy-targeted observations can reach the needed depth over a relevant portion of the localisation probability with a smaller investment of resources, but the number of galaxies to be targeted in order to get a fairly complete coverage is large, even in the case of a localisation as good as that of this event. © K. Ackley et al. 2020., Based on observations collected at the European Southern Observatory under ESO programmes 1102.D-0353(E), 1102.D0353(F), 1102.D-0353(Q), 1102.D-0353(G), 0103.D-0070(A), 0103.D-0070(B), 0103.D-0703(A), 0103.D-0722(A), 0103.A-9099(A), 198.D-2010(D) and 60.A9285(A). ATLAS is primarily funded through NEO NASA grants NN12AR55G, 80NSSC18K0284, and 80NSSC18K1575. The ATLAS science products have been made possible through the contributions of the University of Hawaii IfA, the Queen's University Belfast, the Space Telescope Science Institute, and the South African Astronomical Observatory. PanSTARRS is primarily funded through NEO NASA grants NASA Grants NNX08AR22G, NNX14AM74G. The PanSTARRS science products for LIGO-Virgo follow-up are made possible through the contributions of the University of Hawaii IfA and the Queen's University Belfast. The Gravitational-wave Optical Transient Observer (GOTO) project acknowledges the support of the Monash-Warwick Alliance; Warwick University; Monash University; She ffield University; Leicester University; Armagh Observatory & Planetarium; the National Astronomical Research Institute of Thailand (NARIT); University of Portsmouth; Turku University and the Instituto de Astrofisica de Canarias (IAC). Part of the funding for GROND was generously granted from the Leibniz-Prize to Prof. G. Hasinger (DFG grant HA 1850/28-1). The Liverpool Telescope is operated on the island of La Palma by Liverpool John Moores University in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias with financial support from the UK Science and Technology Facilities Council. The WHT and its override programme are operated on the island of La Palma by the Isaac Newton Group of Telescopes in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias; part of these data were taken under program (19A)N3. FEB thanks CONICYT Basal AFB-170002 and Chile's Ministry of Economy fund IC120009. MGB, PDA and AM acknowledge support from ASI grant I/004/11/3. MBr, EC, AP and SPi acknowledge support from MIUR (PRIN 2017 grant 20179ZF5KS). EB, EM and MT acknowledge funding from GRAWITA. SHB is indebted to the Danish National Research Foundation (DNRF132) for support. SCa acknowledges support from grant MAE0065741. EC acknowledges the support of the H2020 OPTICON programme 730890. TWC acknowledges the Humboldt Foundation and Marie Sklodowska-Curie grant 842471. MDP thanks Istanbul University for support. PAE acknowledges UKSA support. RAJEF is supported by an STFC studentship. MF is supported by a Royal Society -SFI University Research Fellowship. LG was funded by the EU H2020 programme under MSCA grant no. 839090. CG, JH and LI were supported by a research grant from VILLUM FONDEN (project 16599). CG and LI were supported by a research grant from VILLUM FONDEN (25501). GGh acknowledges the PRIN MIUR "Figaro" for financial support. AGo acknowledges financial support from the Slovenian Research Agency (grants P1-0031, I0-0033, and J1-8136). BPG, AJL and JDL acknowledge support from ERC grant 725246 (TEDE, PI Levan). SGG acknowledges support by FCT Fundacao para a Ciencia e Tecnologia and by Project PTDC/FIS-AST-31546. GGr acknowledges the ESCAPE H2020 project no. 824064. MG is supported by the Polish NCN MAESTRO grant 2014/14/A/ST9/00121. PJG acknowledges support from NOVA and from the South African NRF SARChI grant 111692. CPG and MS acknowledge support from EU/FP7-ERC grant no. 615929. KEH acknowledges support by a Project Grant from The Icelandic Research Fund. YDH acknowledges support from the China Scholarships Council. JJ acknowledges support from NOVA and NWO-FAPESP grant for instrumentation. AJ acknowledges funding from the European Research Council (ERC). ZPJ was supported by the Foundation for Distinguished Young Scholars of Jiangsu Province (no. BK20180050). PGJ acknowledges funding from the ERC under Consolidator Grant agreement no. 647208. DAK acknowledges Spanish research project RTI2018-098104-J-I00 (GRBPhot). SKl acknowledges support by DFG grant Kl 766/16-3. ECK acknowledges support from the GREAT research environment. GPL acknowledges support from STFC via grant ST/N000757/1. GL was supported by a research grant (19054) from VILLUM FONDEN. KM acknowledges support from the ERC (grant no. 758638). IM is partially supported by OzGrav (ARC project CE17010000). MMacknowledges support from ERC through ERC-2017-CoG no. 770017. MJM acknowledges the National Science Centre, Poland, grant 2018/30/E/ST9/00208. BMJ and DW are supported by Independent Research Fund Denmark grant DFF-7014-00017. MN is supported by a Royal Astronomical Society Research Fellowship. ANG acknowledges support by grant DFG Kl 766/16-3. PTOB acknowledges funding from STFC. SRO gratefully acknowledges the support of the Leverhulme Trust. FO acknowledges the support of the H2020 Hemera program, grant no. 730970. MAPT was supported by grants RYC-2015-17854 and AYA201783216-P. EP aknowledges financial support from INAF. GP is supported by the Millennium Science Initiative through grant IC120009. MLP is partially supported by a "Linea 2" project of the Catania University. JQV acknowledges support from CONICYT folio 21180886. TMR acknowledges the support of the Vilho, Yrjo and Kalle Vaisala Foundation. ARo acknowledges support from Premiale LBT 2013. SR is supported by VR grants 2016-03657_3 and the research environment grant GREAT, Dnr. 2016-06012, and the Swedish National Space board, Dnr. 107/16. OSS acknowledges the Italian Ministry of Research (MIUR) grant 1.05.06.13. LSa acknowledges the Irish Research Council Scholarship no. GOIPG/2017/1525. SJS acknowledges support from STFC Grant ST/P000312/1. ERS and DS acknowledge funding from UK STFC CG ST/P000495/1. RLCS acknowledges funding from STFC. DS acknowledges support from STFC via grant ST/T007184/1. SDV acknowledges the support of the CNES. LWsupported by Polish NCN DAINA 2017/27/L/ST9/03221. The Cosmic DAWN center is funded by the Danish National Research Foundation.

We present high-cadence, comprehensive data on the nearby ($D\simeq33\,\rm{Mpc}$) Type II SN 2017ahn, discovered within $\sim$1 day of explosion, from the very early phases after explosion to the nebular phase. The observables of SN 2017ahn show a significant evolution over the $\simeq470\,\rm{d}$ of our follow-up campaign, first showing prominent, narrow Balmer lines and other high-ionization features purely in emission (i.e. flash spectroscopy features), which progressively fade and lead to a spectroscopic evolution similar to that of more canonical Type II supernovae. Over the same period, the decline of the light curves in all bands is fast, resembling the photometric evolution of linearly declining H-rich core-collapse supernovae. The modeling of the light curves and early flash spectra suggest a complex circumstellar medium surrounding the progenitor star at the time of explosion, with a first dense shell produced during the very late stages of its evolution being swept up by the rapidly expanding ejecta within the first $\sim6\,\rm{d}$ of the supernova evolution, while signatures of interaction are observed also at later phases. Hydrodynamical models support the scenario in which linearly declining Type II supernovae are predicted to arise from massive yellow super/hyper giants depleted of most of their hydrogen layers., 26 pages (21+Appendices), 19 figures, 4 tables, accepted for publication on ApJ

This paper describes the rapidly evolving and unusual supernova LSQ13ddu, discovered by the La Silla-QUEST survey. LSQ13ddu displayed a rapid rise of just 4.8$\pm$0.9 d to reach a peak brightness of $-$19.70$\pm$0.02 mag in the $\mathit{LSQgr}$ band. Early spectra of LSQ13ddu showed the presence of weak and narrow He I features arising from interaction with circumstellar material (CSM). These interaction signatures weakened quickly, with broad features consistent with those seen in stripped-envelope SNe becoming dominant around two weeks after maximum. The narrow He I velocities are consistent with the wind velocities of luminous blue variables but its spectra lack the typically seen hydrogen features. The fast and bright early light curve is inconsistent with radioactive $^{56}$Ni powering but can be explained through a combination of CSM interaction and an underlying $^{56}$Ni decay component that dominates the later time behaviour of LSQ13ddu. Based on the strength of the underlying broad features, LSQ13ddu appears deficient in He compared to standard SNe Ib., Comment: 22 pages, 20 figures; accepted for publication in MNRAS

This work presents the observations and analysis of ATLAS19dqr/SN 2019bkc, an extraordinary rapidly evolving transient event located in an isolated environment, tens of kiloparsecs from any likely host. Its light curves rise to maximum light in $5-6$ d and then display a decline of $\Delta m_{15} \sim5$ mag. With such a pronounced decay, it has one of the most rapidly evolving light curves known for a stellar explosion. The early spectra show similarities to normal and `ultra-stripped' type Ic SNe, but the early nebular phase spectra, which were reached just over two weeks after explosion, display prominent calcium lines, marking SN 2019bkc as a Ca-rich transient. The Ca emission lines at this phase show an unprecedented and unexplained blueshift of 10,000 -- 12,000 km/s. Modelling of the light curve and the early spectra suggests that the transient had a low ejecta mass of $0.2 - 0.4$ M$_\odot$ and a low kinetic energy of $ (2-4)\times 10^{50}$ erg, giving a specific kinetic energy $\sim1$ [$10^{51}$ erg]/M$_\odot$. The origin of this event cannot be unambiguously defined. While the abundance distribution used to model the spectra marginally favours a progenitor of white dwarf origin through the tentative identification of \ArII, the specific kinetic energy, which is defined by the explosion mechanism, is found to be more similar to an ultra-stripped core-collapse events. SN 2019bkc adds to the diverse range of physical properties shown by Ca-rich events., Comment: Accepted for publication in Astronomy & Astrophysics. Minor changes to section 4.3, some minor discussion added regarding opacities and line identification

We present DES16C3cje, a low-luminosity, long-lived type II supernova (SN II) at redshift 0.0618, detected by the Dark Energy Survey (DES). DES16C3cje is a unique SN. The spectra are characterized by extremely narrow photospheric lines corresponding to very low expansion velocities of . 1500 km s−1 , and the light curve shows an initial peak that fades after 50 days before slowly rebrightening over a further 100 days to reach an absolute brightness of M푟 ∼ −15.5 mag. The decline rate of the late-time light curve is then slower than that expected from the powering by radioactive decay of 56Co, but is comparable to that expected from accretion power. Comparing the bolometric light curve with hydrodynamical models, we find that DES16C3cje can be explained by either i) a low explosion energy (0.11 foe) and relatively large 56Ni production of 0.075 M from a ∼ 15 M red supergiant progenitor typical of other SNe II, or ii) a relatively compact ∼ 40 M star, explosion energy of 1 foe, and 0.08 M of 56Ni. Both scenarios require additional energy input to explain the late-time light curve, which is consistent with fallback accretion at a rate of ∼ 0.5 × 10−8 M s−1., EU/FP7-ERC grant 615929, European Union (EU) 839090, Alexander von Humboldt Foundation, Science Foundation Ireland, Polish NCN MAESTRO 2014/14/A/ST9/00121, Royal Astronomical Society Research Fellowship, European Organisation for Astronomical Research in the Southern Hemisphere, Chile 299.D-5040(A) 299.D-5040(B) 0100.D-0461(A) 194.C-0207(I), PESSTO, (the Public ESO Spectroscopic Survey for Transient Objects Survey) ESO program 197.D1075 199.D-0143, Programme NOAO GS-2016B-Q-9, United States Department of Energy (DOE), National Science Foundation (NSF), Spanish Government, Science & Technology Facilities Council (STFC), Higher Education Funding Council for England, National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign, Kavli Institute of Cosmological Physics at the University of Chicago, Ohio State University, Mitchell Institute for Fundamental Physics and Astronomy at Texas AM University, Ciencia Tecnologia e Inovacao (FINEP), Fundacao Carlos Chagas Filho de Amparo a Pesquisa do Estado do Rio de Janeiro, National Council for Scientific and Technological Development (CNPq), Ministerio da Ciencia, Tecnologia e Inovacao, German Research Foundation (DFG), Collaborating Institutions in the Dark Energy Survey, United States Department of Energy (DOE) University of Chicago, University of California at Santa Cruz, University of Cambridge, Centro de Investigaciones Energeticas, Medioambientales y Tecnologicas-Madrid, University of Chicago, University College London, DES-Brazil Consortium, University of Edinburgh, ETH Zurich, University of Illinois at Urbana-Champaign, Institut de Ciencies de l'Espai (IEEC/CSIC), Institut de Fisica d'Altes Energies, Ludwig-Maximilians Universitat Munchen and the associated Excellence Cluster Universe, University of Michigan System, National Science Foundation (NSF) NSF - Directorate for Mathematical & Physical Sciences (MPS), University of Nottingham, University of Pennsylvania, University of Portsmouth, Stanford University United States Department of Energy (DOE), Stanford University, University of Sussex, Texas AM University, OzDES Membership Consortium, German Research Foundation (DFG) HA 1850/28-1, European Union (EU) PGC2018-095317-B-C21, National Science Foundation (NSF) AST-1138766 AST-1536171, MINECO AYA2015-71825 ESP2015-66861 FPA2015-68048 SEV-2016-0588 SEV2016-0597 MDM-2015-0509, ERDF funds from the European Union, CERCA program of the Generalitat de Catalunya, European Research Council under the European Union's Seventh Framework Program (FP7/2007-2013), European Research Council (ERC) 240672 291329 306478, National Council for Scientific and Technological Development (CNPq) 465376/2014-2, National Energy Research Scientific Computing Center (NERSC), a U.S. Department of Energy Office of Science User Facility DE-AC02-05CH11231, United States Department of Energy (DOE) DE-AC02-07CH11359

On 17th August 2017 a strong source of gravitational waves was detected by the LIGO-Virgo collaboration. The signal lasted for 60 seconds, and the event was followed just 2 seconds later by a short burst of gamma-rays that was detected by Fermi and INTEGRAL. The gravitational-wave and gamma-ray source had consistent sky positions to within about 30 square degrees. Within 10 hours of the gravitational-wave source event, a fast fading optical and near-infrared counterpart was discovered, which was subsequently followed-up and studied intensively for several weeks and months by numerous facilities. This talk presented the results from our optical and near-infrared imaging and spectroscopic follow-up campaign of this unprecedented discovery, which was the first electromagnetic counterpart of a gravitational-wave source, the first identification of a neutron star–neutron star merger, and the first direct evidence of the source of r-process elements. It focussed on the results of the GROND and ePESSTO teams, showing that this remarkable transient truly opened up the era of multi-messenger astronomy.

High-speed milling is a machining method with a low cutting depth, high feed rate, high cutting speed and high spindle speed. It also has the advantages of small thermal deformation, low cutting force resistance, and low tool wear. In this experiment, the cutting of S45C medium carbon steel was tested. This study used four factors in Taguchi’s experimental design regulations, and each factor used three level configurations. An L9 (34) orthogonal table was used to configure the factors and levels. In this study, experiments were conducted on CNC machine tools to explore the difference in the surface roughness of a work piece after cutting with different cutting parameters. It was found that high-speed cutting could indeed obtain quite excellent surfaces. After the experiment, the Taguchi method was analyzed and the results were obtained under different cutting parameters. The experiment is to use milling parameters as variables to analyze the surface roughness, and then the results were analyzed to derive the relationship between the milling parameters and surface roughness. When the feed per edge of the end mill was larger and the number of spindle revolutions was slower, the surface roughness value was larger. The process parameter combination with the best surface quality was 0.1 mm/tooth per edge and a cutting speed of 550 m/min. The best surface roughness of the work piece could be obtained under the combination of a cutting depth of 0.2 mm and a spindle speed 6500 rpm.

Schistosomiasis is an inflammatory disease that occurs when schistosome species eggs are deposited in the liver, resulting in fibrosis and portal hypertension. Schistosomes can interact with host inflammasomes to elicit host immune responses, leading to mitochondrial damage, generation of high levels of reactive oxygen species (ROS) and activation of apoptosis during inflammation. This study aims to examine whether ROS and NF-κB (p65) expression elicited other types of inflammasome activation in Schistosoma mansoni-infected mouse livers. We examine the relationship between inflammasome activation, mitochondrial damage and ROS production in mouse livers infected with S. mansoni. We demonstrate a significant release of ROS and superoxides and increased NF-κB (p65) in S. mansoni-infected mouse livers. Moreover, activation of the NLRP3 and AIM2 inflammasomes was triggered by S. mansoni infection. Stimulation of HuH-7 hepatocellular carcinoma cells with soluble egg antigen induced activation of the AIM2 inflammasome pathway. In this study, we demonstrate that S. mansoni infection promotes both NLRP3 and AIM2 inflammasome activation.