SN2020cpg: an energetic link between Type IIb and Ib supernovae

Stripped-envelope supernovae (SE-SNe) show a wide variety of photometric and spectroscopic properties. This is due to the different potential formation channels and the stripping mechanism that allows for a large diversity within the progenitors outer envelope compositions. Here, the photometric and spectroscopic observations of SN 2020cpg covering ~130 d from the explosion date are presented. SN 2020cpg (z = 0.037) is a bright SE-SNe with the B-band peaking at MB = -17.75 ± 0.39 mag and a maximum pseudo-bolometric luminosity of Lmax = 6.03 ± 0.01 × 1042 erg s-1. Spectroscopically, SN 2020cpg displays a weak high- and low-velocity H α feature during the photospheric phase of its evolution, suggesting that it contained a detached hydrogen envelope prior to explosion. From comparisons with spectral models, the mass of hydrogen within the outer envelope was constrained to be ~0.1 M⊙. From the pseudo-bolometric light curve of SN 2020cpg a 56Ni mass of MNi ~0.27 ± 0.08 M⊙ was determined using an Arnett-like model. The ejecta mass and kinetic energy of SN 2020cpg were determined using an alternative method that compares the light curve of SN 2020cpg and several modelled SE-SNe, resulting in an ejecta mass of Mejc ~5.5 ± 2.0 M⊙ and a kinetic energy of EK ~9.0 ± 3.0 × 1051 erg. The ejected mass indicates a progenitor mass of 18-25 M⊙. The use of the comparative light curve method provides an alternative process to the commonly used Arnett-like model to determine the physical properties of SE-SNe

The low-luminosity Type II SN2016aqf: a well-monitored spectral evolution of the Ni/Fe abundance ratio

Low-luminosity Type II supernovae (LL SNe II) make up the low explosion energy end of core-collapse SNe, but their study and physical understanding remain limited. We present SN 2016aqf, an LL SN II with extensive spectral and photometric coverage. We measure a V-band peak magnitude of -14.58 mag, a plateau duration of similar to 100 d, and an inferred Ni-56 mass of 0.008 +/- 0.002 M-circle dot. The peak bolometric luminosity, L-bol approximate to 10(41.4) erg s(-1), and its spectral evolution are typical of other SNe in the class. Using our late-time spectra, we measure the [O I] lambda lambda 6300, 6364 lines, which we compare against SN II spectral synthesis models to constrain the progenitor zero-age main-sequence mass. We find this to be 12 +/- 3 M-circle dot. Our extensive late-time spectral coverage of the [Fe II] lambda 7155 and [Ni II] lambda 7378 lines permits a measurement of the Ni/Fe abundance ratio, a parameter sensitive to the inner progenitor structure and explosion mechanism dynamics. We measure a constant abundance ratio evolution of 0.081(-0.010)(+0.009) and argue that the best epochs to measure the ratio are at similar to 200-300 d after explosion. We place this measurement in the context of a large sample of SNe II and compare against various physical, light-curve, and spectral parameters, in search of trends that might allow indirect ways of constraining this ratio. We do not find correlations predicted by theoretical models; however, this may be the result of the exact choice of parameters and explosion mechanism in the models, the simplicity of them, and/or primordial contamination in the measured abundance ratio

PS15cey and PS17cke: prospective candidates from the Pan-STARRS Search for kilonovae

Time domain astronomy was revolutionized with the discovery of the first kilonova, AT2017gfo, in August 2017, which was associated with the gravitational wave signal GW170817. Since this event, numerous wide-field surveys have been optimizing search strategies to maximize their efficiency of detecting these fast and faint transients. With the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS), we have been conducting a volume-limited survey for intrinsically faint and fast-fading events to a distance of D similar or equal to 200 Mpc. Two promising candidates have been identified from this archival search, with sparse data - PS15cey and PS17cke. Here, we present more detailed analysis and discussion of their nature. We observe that PS15cey was a luminous, fast-declining transient at 320 Mpc. Models of BH-NS mergers with a very stiff equation of state could possibly reproduce the luminosity and decline but the physical parameters are extreme. A more likely scenario is that this was an AT2018kzr-like merger event. PS17cke was a faint and fast-declining event at 15 Mpc. We explore several explosion scenarios of this transient including models of it as a NS-NS and BH-NS merger, the outburst of a massive luminous star, and compare it against other known fast-fading transients. Although there is uncertainty in the explosion scenario due to difficulty in measuring the explosion epoch, we find PS17cke to be a plausible kilonova candidate from the model comparisons

Accretion disc cooling and narrow absorption lines in the tidal disruption event AT2019dsg

We present the results of a large multiwavelength follow-up campaign of the tidal disruption event (TDE) AT2019dsg, focusing on low to high resolution optical spectroscopy, X-ray, and radio observations. The galaxy hosts a super massive black hole of mass (5.4 ± 3.2) ×106M⊙  and careful analysis finds no evidence for the presence of an active galactic nucleus, instead the TDE host galaxy shows narrow optical emission lines that likely arise from star formation activity. The transient is luminous in the X-rays, radio, UV, and optical. The X-ray emission becomes undetected after ∼100 d, and the radio luminosity density starts to decay at frequencies above 5.4 GHz by ∼160 d. Optical emission line signatures of the TDE are present up to ∼200 d after the light-curve peak. The medium to high resolution spectra show traces of absorption lines that we propose originate in the self-gravitating debris streams. At late times, after ∼200 d, narrow Fe lines appear in the spectra. The TDE was previously classified as N-strong, but after careful subtraction of the host galaxy's stellar contribution, we find no evidence for these N lines in the TDE spectrum, even though O Bowen lines are detected. The observed properties of the X-ray emission are fully consistent with the detection of the inner regions of a cooling accretion disc. The optical and radio properties are consistent with this central engine seen at a low inclination (i.e. seen from the poles).</p

Transitional events in the spectrophotometric regime between stripped envelope and superluminous supernovae

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 M-r < -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

An elliptical accretion disk following the tidal disruption event AT 2020zso

Aims. The modelling of spectroscopic observations of tidal disruption events (TDEs) to date suggests that the newly formed accretion disks are mostly quasi-circular. In this work we study the transient event AT 2020zso, hosted by an active galactic nucleus (AGN; as inferred from narrow emission line diagnostics), with the aim of characterising the properties of its newly formed accretion flow.Methods. 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 H alpha emission lines. We model medium-resolution optical spectroscopy of the He II (after careful de-blending of the N III contribution) and H alpha lines during the rise, peak, and early decline of the light curve using relativistic, elliptical accretion disk models.Results. We find that the spectral evolution before the peak can be explained by optical depth effects consistent with an outflowing, optically thick Eddington envelope. Around the peak, the envelope reaches its maximum extent (approximately 10(15) cm, or similar to 3000-6000 gravitational radii for an inferred black hole mass of 5-10 x 10(5) M-circle dot) and becomes optically thin. The H alpha and He II emission lines at and after the peak can be reproduced with a highly inclined (i  = 85 +/- 5 degrees), highly elliptical (e  = 0.97 +/- 0.01), and relatively compact (R-in = several 100 R-g and R-out = several 1000 R-g) accretion disk.Conclusions. 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 supermassive black hole 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). We constrain the disk alignment timescale to > 15 days in AT2020zso, which rules out high black hole spin values (a  < 0.8) for M-BH  similar to  10(6) M-circle dot and disk viscosity alpha  greater than or similar to  0.1.</p

TRY plant trait database - enhanced coverage and open access

Plant traits-the morphological, anatomical, physiological, biochemical and phenological characteristics of plants-determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait-based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits-almost complete coverage for 'plant growth form'. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait-environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives

SN 2018gjx reveals that some SNe Ibn are SNe IIb exploding in dense circumstellar material

We present the data and analysis of SN 2018gjx, an unusual low-luminosity transient with three distinct spectroscopic phases. Phase I shows a hot blue spectrum with signatures of ionized circumstellar material (CSM), Phase II has the appearance of broad SN features, consistent with those seen in a Type IIb supernova at maximum light, and Phase III is that of a supernova interacting with helium-rich CSM, similar to a Type Ibn supernova. This event provides an apparently rare opportunity to view the inner workings of an interacting supernova. The observed properties can be explained by the explosion of a star in an aspherical CSM. The initial light is emitted from an extended CSM (similar to 4000 R-circle dot), which ionizes the exterior unshocked material. Some days after, the SN photosphere envelops this region, leading to the appearance of a SN IIb. Over time, the photosphere recedes in velocity space, revealing interaction between the supernova ejecta and the CSM that partially obscures the supernova nebular phase. Modelling of the initial spectrum reveals a surface composition consistent with compact H-deficient Wolf-Rayet and Luminous Blue Variable (LBV) stars. Such configurations may not be unusual, with SNe IIb being known to have signs of interaction so at least some SNe IIb and SNe Ibn may be the same phenomena viewed from different angles, or possibly with differing CSM configurations

SN 2017gci: a nearby Type I Superluminous Supernova with a bumpy tail

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