Search

We present photometric and spectroscopic observations of SN2020xga and SN2022xgc, two hydrogen-poor superluminous supernovae (SLSNe-I) at $z = 0.4296$ and $z = 0.3103$ respectively, that show an additional set of broad Mg II absorption lines, blueshifted by a few thousand km s$^{-1}$ with respect to the host galaxy absorption system. Previous work interpreted this as due to resonance line scattering of the SLSN continuum by rapidly expanding CSM expelled shortly before the explosion. The peak rest-frame $g$-band magnitude of SN2020xga is $-22.30 \pm 0.04$ mag and of SN2022xgc is $-21.97 \pm 0.05$ mag, placing them among the brightest SLSNe-I. We use high-quality spectra from ultraviolet to near-infrared wavelengths to model the Mg II line profiles and infer the properties of the CSM shells. We find that the CSM shell of SN2020xga resides at $\sim 1.3 \times 10^{16} \rm cm$ moving with a maximum velocity of $4275~\rm km~s^{-1}$, and the shell of SN2022xgc is located at $\sim 0.8 \times 10^{16} \rm cm$ reaching up to $4400~\rm km~s^{-1}$. These shells were expelled $\sim 11$ and $\sim 5$ months before explosion for SN2020xga and SN2022xgc respectively, possibly as a result of Luminous Blue Variable-like eruptions or pulsational pair instability (PPI) mass loss. We also analyze optical photometric data and model the light curves considering powering from the magnetar spin-down mechanism. The results support very energetic magnetars, approaching the mass-shedding limit, powering these SNe with ejecta masses of $\sim 7-9 \rm~M_\odot$. The ejecta masses inferred from the magnetar modeling are not consistent with the PPI scenario pointing towards stars $> 50~\rm M_\odot$ He-core, hence alternative scenarios such as fallback accretion are discussed., Comment: 25 pages text, 8 pages appendix, 21 figures. Submitted to A&A

Near-sun sky twilight observations allow for the detection of asteroid interior to the orbit of Venus (Aylos), the Earth (Atiras), and comets. We present the results of observations with the Palomar 48-inch telescope (P48)/Zwicky Transient Facility (ZTF) camera in 30 s r-band exposures taken during evening astronomical twilight from 2019 Sep 20 to 2022 March 7 and during morning astronomical twilight sky from 2019 Sep 21 to 2022 Sep 29. More than 46,000 exposures were taken in evening and morning astronomical twilight within 31 to 66 degrees from the Sun with an r-band limiting magnitude between 18.1 and 20.9. The twilight pointings show a slight seasonal dependence in limiting magnitude and ability to point closer towards the Sun, with limiting magnitude slightly improving during summer. In total, the one Aylo, (594913) 'Ayl\'o'chaxnim, and 4 Atiras, 2020 OV1, 2021 BS1, 2021 PB2, and 2021 VR3, were discovered in evening and morning twilight observations. Additional twilight survey discoveries also include 6 long-period comets: C/2020 T2, C/2020 V2, C/2021 D2, C/2021 E3, C/2022 E3, and C/2022 P3, and two short-period comets: P/2021 N1 and P/2022 P2 using deep learning comet detection pipelines. The P48/ZTF twilight survey also recovered 11 known Atiras, one Aylo, three short-period comes, two long-period comets, and one interstellar object. Lastly, the Vera Rubin Observatory will conduct a twilight survey starting in its first year of operations and will cover the sky within 45 degrees of the Sun. Twilight surveys such as those by ZTF and future surveys will provide opportunities for discovering asteroids inside the orbits of Earth and Venus., Comment: 26 pages, 13 figures, 4 tables, accepted for publication in Icarus

Hydrogen-rich superluminous supernovae (SLSNe II) are rare. The exact mechanism producing their extreme light curve peaks is not understood. Analysis of single events and small samples suggest that CSM interaction is the main responsible for their features. However, other mechanisms can not be discarded. Large sample analysis can provide clarification. We aim to characterize the light curves of a sample of 107 SLSNe II to provide valuable information that can be used to validate theoretical models. We analyze the gri light curves of SLSNe II obtained through ZTF. We study peak absolute magnitudes and characteristic timescales. When possible we compute g-r colors, pseudo-bolometric light curves, and estimate lower limits for their total radiated energy. We also study the luminosity distribution of our sample and estimate the percentage of them that would be observable by the LSST. Finally, we compare our sample to other H-rich SNe and to H-poor SLSNe I. SLSNe II are heterogeneous. Their median peak absolute magnitude is -20.3 mag in optical bands. Their rise can take from two weeks to over three months, and their decline from twenty days to over a year. We found no significant correlations between peak magnitude and timescales. SLSNe II tend to show fainter peaks, longer declines and redder colors than SLSNe I. We present the largest sample of SLSNe II light curves to date, comprising of 107 events. Their diversity could be explained by considering different CSM morphologies. Although, theoretical analysis is needed to explore alternative scenarios. Other luminous transients, such as Active Galactic Nuclei, Tidal Disruption Events or SNe Ia-CSM, can easily become contaminants. Thus, good multi-wavelength light curve coverage becomes paramount. LSST could miss 30 percent of the ZTF events in the its footprint in gri bands. Redder bands become important to construct complete samples., Comment: 35 pages. 27 figures. 9 tables

Obtaining spectroscopic observations of the progenitors of core-collapse supernovae is often unfeasible due to an inherent lack of knowledge as to which stars will go supernova and when they will explode. In this letter, we present photometric and spectroscopic observations of the progenitor activity of SN 2023fyq in the preceding 150 days before the He-rich progenitor exploded as a Type Ibn supernova. The progenitor of SN 2023fyq shows an exponential rise in flux prior to core-collapse. Complex He I emission line features are observed, with a P-Cygni like profile, as well as an evolving broad base with velocities on the order of 10,000 km/s, possibly due to electron scattering. The luminosity and evolution of SN 2023fyq are consistent with a faint Type Ibn, reaching a peak r-band magnitude of 18.1 mag, although there is some uncertainty in the distance to the host, NGC 4388, located in the Virgo cluster. We present additional evidence of asymmetric He-rich material being present prior to the explosion of SN 2023fyq, as well as after, suggesting this material has survived the ejecta-CSM interaction. Broad [O I] and the Ca II triplet lines are observed at late phases, confirming that SN 2023fyq was a genuine supernova rather than a non-terminal interacting transient. SN 2023fyq provides insight into the final moments of a massive star's life, highlighting that the progenitor is likely highly unstable before core-collapse., Comment: 7 Pages, 5 Figures, accepted to A&A Letters

SN 2021adxl is a slowly evolving, luminous, Type IIn supernova with asymmetric emission line profiles, similar to the well-studied SN 2010jl. We present extensive optical, near-ultraviolet, and near-infrared photometry and spectroscopy covering ~1.5 years post discovery. SN 2021adxl occurred in an unusual environment, atop a vigorously star-forming region that is offset from its host galaxy core. The appearance of Ly-alpha, O II, as well as the compact core, would classify the host of SN 2021adxl as a Blueberry galaxy, analogous to the higher redshift Green Pea galaxies. Using several abundance indicators, we find a metallicity of the explosion environment of only 10% solar, the lowest reported metallicity for a Type IIn SN environment. SN 2021adxl reaches a peak magnitude of r ~ -20.2 mag and since discovery, SN 2021adxl has faded by only ~4 magnitudes in the r band with a cumulative radiated energy of ~1.5e50 erg over 18 months. SN 2021adxl shows strong signs of interaction with a complex circumstellar medium, seen by the detection of X-rays, revealed by the detection of coronal emission lines, and through multi-component hydrogen and helium profiles. In order to further understand this interaction, we model the H{\alpha} profile using a Monte-Carlo electron scattering code. The blueshifted high-velocity component is consistent with emission from a radially thin, spherical shell resulting in the broad emission components due to electron scattering. Using the velocity evolution of this emitting shell, we find that the SN ejecta collide with circumstellar material of at least 5 Msun, assuming a steady-state mass-loss rate of 4-6e-3 Msun per year for the first ~200 days of evolution. Continuing the observations of SN 2021adxl may reveal signatures of dust formation or an infrared excess, similar to that seen for SN 2010jl., Comment: 21 pages with 27 Figures. Accepted for publication to A&A. MC line scattering code can be found at https://github.com/Astro-Sean/escatter

Observing a supernova explosion shortly after it occurs can reveal important information about the physics of stellar explosions and the nature of the progenitor stars of supernovae (SNe). When a star with a well-defined edge explodes in vacuum, the first photons to escape from its surface appear as a brief shock-breakout flare. The duration of this flare can extend to at most a few hours even for nonspherical breakouts from supergiant stars, after which the explosion ejecta should expand and cool. Alternatively, for stars exploding within a distribution of sufficiently dense optically thick circumstellar material, the first photons escape from the material beyond the stellar edge, and the duration of the initial flare can extend to several days, during which the escaping emission indicates photospheric heating. The difficulty in detecting SN explosions promptly after the event has so far limited data regarding supergiant stellar explosions mostly to serendipitous observations that, owing to the lack of ultraviolet (UV) data, were unable to determine whether the early emission is heating or cooling, and hence the nature of the early explosion event. Here, we report observations of SN 2023ixf in the nearby galaxy M101, covering the early days of the event. Using UV spectroscopy from the Hubble Space Telescope (HST) as well as a comprehensive set of additional multiwavelength observations, we trace the photometric and spectroscopic evolution of the event and are able to temporally resolve the emergence and evolution of the SN emission.

Long-period comets are planetesimal remnants constraining the environment and volatiles of the protoplanetary disc. We report the discovery of hyperbolic long-period comet C/2022 E3 (ZTF), which has a perihelion $\sim$1.11 au, an eccentricity $\gtrsim$1 and an inclination $\sim$109$^{\circ}$, from images taken with the Palomar 48-inch telescope during morning twilight on 2022 Mar 2. Additionally, we report the characterization of C/2022 E3 (ZTF) from observations taken with the Palomar 200-inch, the Palomar 60-inch, and the NASA Infrared Telescope Facility in early 2023 February to 2023 March when the comet passed within $\sim$0.28 au of the Earth and reached a visible magnitude of $\sim$5. We measure g-r = 0.70$\pm$0.01, r-i = 0.20$\pm$0.01, i-z = 0.06$\pm$0.01, z-J = 0.90$\pm$0.01, J-H = 0.38$\pm$0.01 and H-K = 0.15$\pm$0.01 colours for the comet from observations. We measure the A(0$^\circ$)f$\rho$ (0.8~$\mu$m) in a 6500~km radius from the nucleus of 1483$\pm$40~cm, and CN, C$_3$, and C$_2$ production of 5.43$\pm0.11\times$10$^{25}$~mol/s, 2.01$\pm0.04\times$10$^{24}$, and 3.08$\pm0.5\times$10$^{25}$~mol/s, similar to other long period comets. We additionally observe the appearance of jet-like structures at a scale of $\sim$4,000 km in wide-field g-band images, which may be caused by the presence of CN gas in the near-nucleus coma., Comment: Accepted for publication in MNRAS:L, 9 pages, 6 figures, 2 tables

We report on our study of supernova (SN) 2022xxf based on observations obtained during the first four months of its evolution. The light curves (LCs) display two humps of similar maximum brightness separated by 75 days, unprecedented for a broad-lined (BL) Type Ic supernova (SN IcBL). SN 2022xxf is the most nearby SN IcBL to date (in NGC 3705, $z = 0.0037$, at a distance of about 20 Mpc). Optical and near-infrared photometry and spectroscopy are used to identify the energy source powering the LC. Nearly 50 epochs of high signal-to-noise-ratio spectroscopy were obtained within 130 days, comprising an unparalleled dataset for a SN IcBL, and one of the best-sampled SN datasets to date. The global spectral appearance and evolution of SN 2022xxf points to typical SN Ic/IcBL, with broad features (up to $\sim14000$ km s$^{-1}$) and a gradual transition from the photospheric to the nebular phase. However, narrow emission lines (corresponding to $\sim1000-2500$ km s$^{-1}$) are present in the spectra from the time of the second rise, suggesting slower-moving circumstellar material (CSM). These lines are subtle, in comparison to the typical strong narrow lines of CSM-interacting SNe, for example, Type IIn, Ibn, and Icn, but some are readily noticeable at late times such as in Mg I $\lambda$5170 and [O I] $\lambda$5577. Unusually, the near-infrared spectra show narrow line peaks in a number of features formed by ions of O and Mg. We infer the presence of CSM that is free of H and He. We propose that the radiative energy from the ejecta-CSM interaction is a plausible explanation for the second LC hump. This interaction scenario is supported by the color evolution, which progresses to the blue as the light curve evolves along the second hump, and the slow second rise and subsequent rapid LC drop. (Abstract abridged), Comment: Accepted version

We present and analyze observations of the Type Ib supernova (SN) 2019odp (a.k.a ZTF19abqwtfu) covering epochs within days of the explosion to the nebular phase at 360 d post-explosion. We discuss them in the context of recombination cooling emission for the early excess emission and consider progenitor models based on the nebular phase spectra. Our observations include photometric observations mainly in the optical and low to medium-resolution spectroscopic observations covering the complete observable time-range. We expand on existing methods to derive oxygen mass estimates from nebular phase spectroscopy. Our spectroscopic observations confirm the presence of He in the SN ejecta and we thus (re)classify it as a Type Ib supernova. From the pseudo-bolometric lightcurve we estimate a high ejecta mass $M_\text{ej} \sim 4 - 7~M_\odot$. The high ejecta mass, large nebular [O I]/[Ca II] line flux ratio ($1.2 - 1.9$) and an oxygen mass above $\gtrapprox 0.5\, M_\odot$ point towards a progenitor with pre-explosion mass higher than $18\,M_\odot$. The compact nature of the progenitor ($\lesssim 10\,R_\odot$) suggests a Wolf-Rayet (WR) star as progenitor., Comment: Accepted for publication in Astronomy & Astrophysics

Recently, the inner main belt asteroid (152830) Dinkinesh was identified as an additional fly-by target for the Lucy mission. The heliocentric orbit and approximate absolute magnitude of Dinkinesh are known, but little additional information was available prior to its selection as a target. In particular, the lack of color spectrophotometry or spectra made it impossible to assign a spectral type to Dinkinesh from which its albedo could be estimated. We set out to remedy this knowledge gap by obtaining visible wavelength spectra with the Keck telescope on 2022 November 23 and with Gemini-South on 2022 December 27. The spectra measured with the Keck I/Low Resolution Imaging Spectrometer (LRIS) and the Gemini South/Gemini Multi-Object Spectrograph South (GMOS-S) are most similar to the average spectrum of S- and Sq-type asteroids. The most diagnostic feature is the $\approx$15$\pm$1$\%$ silicate absorption feature at $\approx$0.9-1.0~micron. Small S- and Sq-type asteroids have moderately high albedos ranging from 0.17-0.35. Using this albedo range for Dinkinesh in combination with measured absolute magnitude, it is possible to derive an effective diameter and surface brightness for this body. The albedo, size and surface brightness are important inputs required for planning a successful encounter by the Lucy spacecraft., Comment: 7 pages, 1 figure. Accepted for publication in Icarus

Neptunian Trojans (NTs), trans-Neptunian objects in 1:1 mean-motion resonance with Neptune, are generally thought to have been captured from the original trans-Neptunian protoplanetary disk into co-orbital resonance with the ice giant during its outward migration. It is possible, therefore, that the colour distribution of NTs is a constraint on the location of any colour transition zones that may have been present in the disk. In support of this possible test, we obtained $g$, $r$, and $i$-band observations of 18 NTs, more than doubling the sample of NTs with known visible colours to 31 objects. Out of the combined sample, we found $\approx$4 objects with $g$-$i$ colours of $>$1.2 mags placing them in the very red (VR) category as typically defined. We find, without taking observational selection effects into account, that the NT $g$-$i$ colour distribution is statistically distinct from other trans-Neptunian dynamical classes. The optical colours of Jovian Trojans and NTs are shown to be less similar than previously claimed with additional VR NTs. The presence of VR objects among the NTs may suggest that the location of the red to VR colour transition zone in the protoplanetary disk was interior to 30-35 au., Comment: 8 pages, 3 figures, 3 tables, accepted for publication in MNRAS:Letters

If high-mass stars (>20-25 Msun) are the progenitors of stripped-envelope (SE) supernovae (SNe), their massive ejecta should lead to broad, long-duration lightcurves (LCs). Instead, literature samples of SE~SNe have reported relatively narrow LCs with ejecta masses between 1-4 Msun that favor progenitors <20-25 Msun. Working with the untargeted sample of (i)PTF SNe to better constrain their rates, we search for SE~SNe with broad LCs. Using a simple LC stretch compared to a template to measure broadness, we identified eight significantly broader Type~Ibc SNe after applying quantitative sample selection criteria. The LCs, colors, and spectra of these SNe are found to evolve more slowly relative to typical Type~Ibc SNe, proportional with the stretch. Bolometric LC modeling and their nebular spectra indicate high ejecta and nickel masses, assuming radioactive decay powering. Additionally, these objects are preferentially located in low-metallicity host galaxies with high star-formation rates, which may account for their massive progenitors, as well as their relative absence from the literature. Our study thus supports the link between broad LCs (as measured by stretch) and high-mass progenitor stars in SE~SNe with independent evidence from bolometric LC modeling, nebular spectra, host environment properties, and photometric evolution. In the first systematic search of its kind using an untargeted sample, we use the stretch distribution to identify a higher than previously appreciated fraction of SE~SNe with broad LCs (~13%). Correcting for Malmquist and LC duration observational biases, we conservatively estimate that a minimum of ~6% of SE~SNe are consistent with high-mass progenitors. This result has implications for the progenitor channels of SE~SNe, late stages of massive stellar evolution, oxygen fraction in the universe, and formation channels for stellar-mass black holes.(Abridged), Comment: 38 pages, 24 figures, 12 tables. Submitted to A&A

Near-Earth asteroid population models predict the existence of bodies located inside the orbit of Venus. Despite searches up to the end of 2019, none had been found. We report discovery and follow-up observations of (594913) 'Ayl\'o'chaxnim, an asteroid with an orbit entirely interior to Venus. (594913) 'Ayl\'o'chaxnim has an aphelion distance of ~0.65 au, is ~2 km in diameter and is red in colour. The detection of such a large asteroid inside the orbit of Venus is surprising given their rarity according to near-Earth asteroid population models. As the first officially numbered and named asteroid located entirely within the orbit of Venus, we propose that the class of interior to Venus asteroids be referred to as 'Ayl\'o'chaxnim asteroids., Comment: 7 pages, 8 figures, 1 table. Published in Monthly Notices of the Royal Astronomical Society: Letters (2022). arXiv admin note: text overlap with arXiv:2009.04125

With a rapidly rising number of transients detected in astronomy, classification methods based on machine learning are increasingly being employed. Their goals are typically to obtain a definitive classification of transients, and for good performance they usually require the presence of a large set of observations. However, well-designed, targeted models can reach their classification goals with fewer computing resources. This paper presents SNGuess, a model designed to find young extragalactic nearby transients with high purity. SNGuess works with a set of features that can be efficiently calculated from astronomical alert data. Some of these features are static and associated with the alert metadata, while others must be calculated from the photometric observations contained in the alert. Most of the features are simple enough to be obtained or to be calculated already at the early stages in the lifetime of a transient after its detection. We calculate these features for a set of labeled public alert data obtained over a time span of 15 months from the Zwicky Transient Facility (ZTF). The core model of SNGuess consists of an ensemble of decision trees, which are trained via gradient boosting. Approximately 88% of the candidates suggested by SNGuess from a set of alerts from ZTF spanning from April 2020 to August 2021 were found to be true relevant supernovae (SNe). For alerts with bright detections, this number ranges between 92% and 98%. Since April 2020, transients identified by SNGuess as potential young SNe in the ZTF alert stream are being published to the Transient Name Server (TNS) under the AMPEL_ZTF_NEW group identifier. SNGuess scores for any transient observed by ZTF can be accessed via a web service. The source code of SNGuess is publicly available., Comment: 14 pages, 10 figures, Astronomy & Astrophysics (A&A), Forthcoming article, source code https://github.com/nmiranda/SNGuess

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

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 ($<10$\,days) exist but are rare. We confirm previous findings that slowly rising SLSNe-I also tend to fade slowly. The rest-frame color and temperature evolution show large scatters, suggesting that the SLSN-I population may have diverse spectral energy distributions. The peak rest-frame color shows a moderate correlation with the peak absolute magnitude, i.e. brighter SLSNe-I tend to have bluer colors. With optical and ultraviolet photometry, we construct bolometric luminosity and derive a bolometric correction relation generally applicable for converting $g,r$-band photometry to bolometric luminosity for SLSNe-I., Comment: 38 pages, 25 figures, Accepted by APJ

Supernova (SN) siblings -- two or more SNe in the same parent galaxy -- are useful tools for exploring progenitor stellar populations as well as properties of the host galaxies such as distance, star formation rate, dust extinction, and metallicity. Since the average SN rate for a Milky Way-type galaxy is just one per century, a large imaging survey is required to discover an appreciable sample of SN siblings. From the wide-field Zwicky Transient Facility (ZTF) Bright Transient Survey (BTS; which aims for spectroscopic completeness for all transients which peak brighter than $r{<}$18.5 mag) we present 10 SN siblings in 5 parent galaxies. For each of these families we analyze the SN's location within the host and its underlying stellar population, finding agreement with expectations that SNe from more massive progenitors are found nearer to their host core and in regions of more active star formation. We also present an analysis of the relative rates of core collapse and thermonuclear SN siblings, finding a significantly lower ratio than past SN sibling samples due to the unbiased nature of the ZTF., Comment: 14 pages, 4 tables, 7 figures, accepted to MNRAS

The final explosive fate of massive stars, and the nature of the compact remnants they leave behind (black holes and neutron stars), are major open questions in astrophysics. Many massive stars are stripped of their outer hydrogen envelopes as they evolve. Such Wolf-Rayet (W-R) stars emit strong and rapidly expanding (v_wind>1000 km/s) winds indicating a high escape velocity from the stellar surface. A fraction of this population is also helium depleted, with spectra dominated by highly-ionized emission lines of carbon and oxygen (Types WC/WO). Evidence indicates that the most commonly-observed supernova (SN) explosions that lack hydrogen and helium (Types Ib/Ic) cannot result from massive WC/WO stars, leading some to suggest that most such stars collapse directly into black holes without a visible supernova explosions. Here, we present observations of supernova SN 2019hgp, discovered about a day after explosion. The short rise time and rapid decline place it among an emerging population of rapidly-evolving transients (RETs). Spectroscopy reveals a rich set of emission lines indicating that the explosion occurred within a nebula composed of carbon, oxygen, and neon. Narrow absorption features show that this material is expanding at relatively high velocities (>1500 km/s) requiring a compact progenitor. Our observations are consistent with an explosion of a massive WC/WO star, and suggest that massive W-R stars may be the progenitors of some rapidly evolving transients., Comment: Unedited author version, Nature in press

Stripped-envelope supernovae (SE SNe) of Type Ib and Type Ic are thought to result from explosions of massive stars having lost their outer envelopes. The favoured explosion mechanism is by core-collapse, with the shock later revived by neutrino heating. However, there is an upper limit to the amount of radioactive Nickel-56 that such models can accomplish. Recent literature point to a tension between the maximum luminosity from such simulations and observations. We use a well characterized sample of SE SNe from the Zwicky Transient Facility (ZTF) Bright Transient Survey (BTS) to collect a sample of spectroscopically classified normal Type Ibc SNe for which we use the ZTF light curves to determine the maximum luminosity. We cull the sample further based on data quality, light-curve shape, distance and colors. The methodology of the sample construction from this BTS sample can be used for many other future investigations. In total we use 129 Type Ib or Type Ic BTS SNe with an initial rough luminosity distribution peaked at Mr = -17.61 +- 0.72, and where 36% are apparently brighter than the theoretically predicted maximum brightness of Mr = -17.8. When we further cull this sample to ensure that the SNe are normal Type Ibc with good LC data within the Hubble flow, the sample of 94 objects has Mr = -17.64 +- 0.54. A main uncertainty in absolute magnitude determinations for SNe is the host galaxy extinction correction, but the reddened objects only get more luminous after corrections. If we simply exclude objects with red, unusual or uncertain colors, we are left with 14 objects at M = -17.90 +- 0.73, whereof a handful are most certainly brighter than the suggested theoretical limit. The main result of this study is thus that normal SNe Ibc do indeed reach luminosities above $10^{42.6}$ erg/s, apparently in conflict with existing explosion models., Comment: Submitted to A&A, this version includes revisions based on referee comments

We present SN 2020jfo, a Type IIP supernova in the nearby galaxy M61. Optical light curves from the Zwicky Transient Facility, complemented with data from Swift and near-IR photometry are presented. The 350-day duration bolometric light curve exhibits a relatively short (~ 65 days) plateau. This implies a moderate ejecta mass (~ 5 Msun). A series of spectroscopy is presented, including spectropolarimetric observations. The nebular spectra are dominated by Halpha but also reveal emission lines from oxygen and calcium. Comparisons to synthetic nebular spectra indicate an initial progenitor mass of about 12 Msun. Stable nickel is present in the nebular spectrum, with a super-solar Ni/Fe ratio. Several years of pre-discovery data are examined, but no signs of pre-cursor activity is found. Pre-explosion Hubble Space Telescope imaging reveals a probable progenitor star, detected only in the reddest band and is fainter than expected for stars in the 10 - 15 Msun range, in tension with the analysis of the LC and the nebular spectral modeling. We present two additional core-collapse SNe monitored by the ZTF, which also have nebular Halpha-dominated spectra. This illustrates how the absence or presence of interaction with circumstellar material affect both the LCs and in particular the nebular spectra. Type II SN 2020amv has a LC powered by CSM interaction, in particular after about 40 days when the LC is bumpy and slowly evolving. The late-time spectra show strong Halpha emission with a structure suggesting emission from a thin, dense shell. The evolution of the complex three-horn line profile is reminiscent of that observed for SN 1998S. SN 2020jfv has a poorly constrained early-time LC, but shows a transition from a hydrogen-poor Type IIb to a Type IIn, where the nebular spectrum after the light-curve rebrightening is dominated by Halpha, although with an intermediate line width., Comment: Paper on SN 2020jfo in M61, and on SNe 2020amv and 2020jfv. This is the version resubmitted to A&A after responding to first referee comments. 27 pages, 12 figures. Somewhat shortened abstract

We present observations and analysis of SN 2020cxd, a Low luminous (LL), long-lived Type IIP SN. This object was a clear outlier in the magnitude-limited SN sample recently presented by the ZTF Bright Transient Survey. We demonstrate that SN 2020cxd is an additional member of the group of LL SNe, and discuss the rarity of LL SNe in the context of the ZTF survey, and how further studies of these faintest members of the CC SN family might help understand the underlying initial mass function for stars that explode., Comment: 22 pages, 16 figures. This is the version resubmitted to A&A with replies to referee report

AM CVn systems are ultra-compact, helium-rich, accreting binaries with degenerate or semi-degenerate donors. We report the discovery of five new eclipsing AM CVn systems with orbital periods of 61.5, 55.5, 53.3, 37.4, and 35.4 minutes. These systems were discovered by searching for deep eclipses in the Zwicky Transient Facility (ZTF) lightcurves of white dwarfs selected using Gaia parallaxes. We obtained phase-resolved spectroscopy to confirm that all systems are AM CVn binaries, and we obtained high-speed photometry to confirm the eclipse and characterize the systems. The spectra of two long-period systems (61.5 and 53.3 minutes) show many emission and absorption lines, indicating the presence of N, O, Na, Mg, Si, and Ca, and also the K and Zn, elements which have never been detected in AM CVn systems before. By modelling the high-speed photometry, we measured the mass and radius of the donor star, potentially constraining the evolutionary channel that formed these AM CVn systems. We determined that the average mass of the accreting white dwarf is $\approx0.8$$\mathrm{M_{\odot}}$, and that the white dwarfs in long-period systems are hotter than predicted by recently updated theoretical models. The donors have a high entropy and are a factor of $\approx$ 2 more massive compared to zero-entropy donors at the same orbital period. The large donor radius is most consistent with He-star progenitors, although the observed spectral features seem to contradict this. The discovery of 5 new eclipsing AM~CVn systems is consistent with the known observed AM CVn space density and estimated ZTF recovery efficiency. Based on this estimate, we expect to find another 1--4 eclipsing AM CVn systems as ZTF continues to obtain data. This will further increase our understanding of the population, but will require high precision data to better characterize these 5 systems and any new discoveries., Comment: submitted to MNRAS

The Zwicky Transient Facility (ZTF) has been observing the entire northern sky since the start of 2018 down to a magnitude of 20.5 ($5 \sigma$ for 30s exposure) in $g$, $r$, and $i$ filters. Over the course of two years, ZTF has obtained light curves of more than a billion sources, each with 50-1000 epochs per light curve in $g$ and $r$, and fewer in $i$. To be able to use the information contained in the light curves of variable sources for new scientific discoveries, an efficient and flexible framework is needed to classify them. In this paper, we introduce the methods and infrastructure which will be used to classify all ZTF light curves. Our approach aims to be flexible and modular and allows the use of a dynamical classification scheme and labels, continuously evolving training sets, and the use of different machine learning classifier types and architectures. With this setup, we are able to continuously update and improve the classification of ZTF light curves as new data becomes available, training samples are updated, and new classes need to be incorporated.

We report on SRG/eROSITA, ZTF, ASAS-SN, Las Cumbres, NEOWISE-R, and Swift XRT/UVOT observations of the unique ongoing event AT 2019avd, located in the nucleus of a previously inactive galaxy at $z=0.029$. eROSITA first observed AT 2019avd on 2020-04-28 during its first all sky survey, when it was detected as an ultra-soft X-ray source ($kT\sim 85$ eV) that was $\gtrsim 90$ times brighter in the $0.2-2$ keV band than a previous 3$\sigma$ upper flux detection limit (with no archival X-ray detection at this position). The ZTF optical light curve in the $\sim 450$ days preceding the eROSITA detection is double peaked, and the eROSITA detection coincides with the rise of the second peak. Follow-up optical spectroscopy shows the emergence of a Bowen fluorescence feature and high-ionisation coronal lines ([\ion{Fe}{X}] 6375 {\AA}, [\ion{Fe}{XIV}] 5303 {\AA}), along with persistent broad Balmer emission lines (FWHM$\sim 1400$ km s$^{-1}$). Whilst the X-ray properties make AT 2019avd a promising tidal disruption event (TDE) candidate, the optical properties are atypical for optically selected TDEs. We discuss potential alternative origins that could explain the observed properties of AT 2019avd, such as a stellar binary TDE candidate, or a TDE involving a super massive black hole binary., Comment: A&A accepted 18/12/2020. 19 pages, 14 figures, 8 tables. Forthcoming article in A&A special issue: 'First science highlights from SRG/eROSITA'

AT2019wey (SRGA J043520.9+552226, SRGE J043523.3+552234) is a transient first reported by the ATLAS optical survey in 2019 December. It rose to prominence upon detection, three months later, by the Spektrum-Roentgen-Gamma (SRG) mission in its first all-sky survey. X-ray observations reported in Yao et al. suggest that AT2019wey is a Galactic low-mass X-ray binary (LMXB) with a black hole (BH) or neutron star (NS) accretor. Here we present ultraviolet, optical, near-infrared, and radio observations of this object. We show that the companion is a short-period (P < 16 hr) low-mass (< 1 Msun) star. We consider AT2019wey to be a candidate BH system since its locations on the L_radio--L_X and L_opt--L_X diagrams are closer to BH binaries than NS binaries. We demonstrate that from 2020 June to August, despite the more than 10 times brightening at radio and X-ray wavelengths, the optical luminosity of AT2019wey only increased by 1.3--1.4 times. We interpret the UV/optical emission before the brightening as thermal emission from a truncated disk in a hot accretion flow and the UV/optical emission after the brightening as reprocessing of the X-ray emission in the outer accretion disk. AT2019wey demonstrates that combining current wide-field optical surveys and SRG provides a way to discover the emerging population of short-period BH LMXB systems with faint X-ray outbursts., Comment: Accepted by ApJ

Type Ic supernovae represent the explosions of the most stripped massive stars, but their progenitors and explosion mechanisms remain unclear. Larger samples of observed supernovae can help characterize the population of these transients. We present an analysis of 44 spectroscopically normal Type Ic supernovae, with focus on the light curves. The photometric data were obtained over 7 years with the Palomar Transient Factory (PTF) and its continuation, the intermediate Palomar Transient Factory (iPTF). This is the first homogeneous and large sample of SNe Ic from an untargeted survey, and we aim to estimate explosion parameters for the sample. We present K-corrected Bgriz light curves of these SNe, obtained through photometry on template-subtracted images. We performed an analysis on the shape of the $r$-band light curves and confirmed the correlation between the rise parameter Delta m_{-10} and the decline parameter Delta m_{15}. Peak r-band absolute magnitudes have an average of -17.71 +- 0.85 mag. To derive the explosion epochs, we fit the r-band lightcurves to a template derived from a well-sampled light curve. We computed the bolometric light curves using r and g band data, g-r colors and bolometric corrections. Bolometric light curves and Fe II lambda 5169 velocities at peak were used to fit to the Arnett semianalytic model in order to estimate the ejecta mass M_{ej}, the explosion energy E_{K} and the mass of radioactive nickel (M(56) Ni) for each SN. Including 41 SNe, we find average values of =4.50 +-0.79 msun, =1.79 +- 0.29 x10^{51} erg, and = 0.19 +- 0.03 msun. The explosion-parameter distributions are comparable to those available in the literature, but our large sample also includes some transients with narrow and very broad light curves leading to more extreme ejecta masses values., Comment: Submitted to A&A

Near-Earth asteroids (NEAs) are organized into five main classes: Amor, Apollo, Aten, Atira and 'Ayl\'{o}'chaxnim. Asteroids belonging to the 'Ayl\'{o}'chaxnim class are located entirely within the orbit of Venus making them difficult to detect by ground-based observatories. The first-known asteroid of this class, (594913) 'Ayl\'{o}'chaxnim, was discovered by the Zwicky Transient Facility (ZTF) in 2020 January during a twilight search for asteroids at small solar elongations that ran between September 2019 and January 2020. Due to its large diameter of $\sim$2 km, the discovery of (594913) 'Ayl\'{o}'chaxnim is surprising because contemporary NEA population models predict a scarcity of asteroids of this size located inside the orbit of Venus. To compare the discovery of (594913) 'Ayl\'{o}'chaxnim by ZTF with the predictions of NEA population models, we estimated the ZTF survey completeness at detecting 'Ayl\'{o}'chaxnim asteroids and the number of 'Ayl\'{o}'chaxnim asteroids expected to have been discovered by simulating observations of synthetic 'Ayl\'{o}'chaxnim asteroids. We find that the 'Ayl\'{o}'chaxnim population completeness of the survey is $\sim$18$\%$ and there is only a 5$\%$ probability that a single 'Ayl\'{o}'chaxnim asteroid would have been discovered. Given the small chance for (594913) 'Ayl\'{o}'chaxnim to have been discovered, its presence is either a statistical fluke or it implies that asteroid population models may need to be revised., Comment: 9 pages, 2 figures. Accepted for publication in Icarus

We present SN 2019tsf (ZTF19ackjszs) and SN 2019oys (ZTF19abucwzt). These two stripped envelope Type Ib supernovae suddenly showed a (re-)brightening in their late light curves. We investigate this in the context of circumstellar material (CSM) interaction with previously ejected material, a phenomenon that is unusual among SE SNe. We analyse observational data, consisting of optical light curves and spectra. For SN 2019oys we also have detections in radio as well as limits from UV and X-rays. Both light curves show spectacular re-brightening after about 100 days. In the case of SN 2019tsf, the re-brightening is followed by a new period of decline, and the spectra never show signs of narrow emission lines that would indicate CSM interaction. On the contrary, SN 2019oys made a spectral makeover from a Type Ib to a spectrum clearly dominated by CSM interaction at the light curve brightening phase. Deep spectra reveal a plethora of narrow high ionization lines, including coronal lines, and the radio observations show strong emission. The rather similar light curve behaviour indicate CSM interaction as the powering source. For SN 2019oys the evidence for a phase where the ejecta hit H-rich material, likely ejected from the progenitor star, is conspicuous. We observe strong narrow lines of H and He, but also a plethora of high ionization lines, including coronal lines, revealing shock interaction. Spectral simulations of SN 2019oys show two distinct density components, one with density > 1e9/cm3, dominated by somewhat broader, low ionization lines of H I, He I, Na I and Ca II, and one with narrow, high ionization lines at a density about 1e6 /cm3. The former is strongly affected by electron scattering. The evidence for CSM interaction in SN 2019oys is corroborated by detections in radio. On the contrary, for SN 2019tsf, we find little evidence in the spectra for any CSM interaction., Comment: Resubmitted to A&A after first referee report

In this paper, we discuss the outcomes of the follow-up campaign of SN 2018ijp, discovered as part of the Zwicky Transient Facility survey for optical transients. Its first spectrum shows similarities to broad-lined Type Ic supernovae around maximum light, whereas later spectra display strong signatures of interaction between rapidly expanding ejecta and a dense H-rich circumstellar medium, coinciding with a second peak in the photometric evolution of the transient. This evolution, along with the results of modeling of the first light curve peak, suggests a scenario where a stripped star exploded within a dense circumstellar medium. The two main phases in the evolution of the transient could be interpreted as a first phase dominated by radioactive decays, and an later interaction-dominated phase where the ejecta collide with a pre-existing shell. We therefore discuss SN 2018jp within the context of a massive star depleted of its outer layers exploding within a dense H-rich circumstellar medium., Comment: Accepted for publication on Astronomy and Astrophysics. 11 pages, 10 figures, 1 table. Photometric table available at the CDS

Context: Type Ibn supernovae are a rare class of stripped envelope supernovae interacting with a helium-rich CSM. The majority of the SNe Ibn reported display a surprising homogeneity in their fast lightcurves and starforming hosts. Aims: We present the discovery and study of SN 2020bqj (ZTF20aalrqbu), a SN Ibn with a long-duration peak plateau lasting 40 days and hosted by a faint low-mass galaxy. We aim to explain its peculiar properties using an extensive data set. Methods: We compare the evolution of SN 2020bqj with SNe Ibn from the literature. We fit the bolometric and multi-band lightcurves with different powering mechanism models. Results: The risetime, peak magnitude and spectral features of SN 2020bqj are consistent with those of most SNe Ibn, but the SN is a clear outlier based on its bright, long-lasting peak plateau and low host mass. We show through modeling that the lightcurve can be powered predominantly by shock heating from the interaction of the SN ejecta and a dense CSM. The peculiar Type Ibn SN 2011hw is a close analog to SN 2020bqj, suggesting a similar progenitor and CSM scenario. In this scenario a very massive progenitor star in the transitional phase between a luminous blue variable and a compact Wolf-Rayet star undergoes core-collapse, embedded in a dense helium-rich CSM with an elevated opacity compared to normal SNe Ibn, due to the presence of residual hydrogen. This scenario is consistent with the observed properties of SN 2020bqj and the modeling results. Conclusions: SN 2020bqj is a compelling example of a transitional SN Ibn/IIn based on not only its spectral features, but also its lightcurve, host galaxy properties and the inferred progenitor properties. The strong similarity with SN 2011hw suggests this subclass may be the result of a progenitor in a stellar evolution phase that is distinct from those of progenitors of regular SNe Ibn., Comment: 22 pages, 14 figures, 5 tables. Accepted for publication in Astronomy & Astrophysics. Abstract abridged for arXiv submission

Helium is expected to be present in the ejecta of some hydrogen-poor superluminous supernovae (SLSN-I). However, so far only one event, PTF10hgi has been identified with He features in its photospheric spectra (Quimby et al. 2018). We present the discovery of a new He-rich SLSN-I, ZTF19aawfbtg (SN2019hge) at $z=0.0866$. This event has more than 10 optical spectra at phases from $-41$ to $+103$\,days relative to the peak, most of which match well with that of PTF10hgi. Confirmation comes from a near-IR spectrum taken at $+34$ days, revealing He I features with P-Cygni profiles at 1.083 and 2.058$\mu$m. Using the optical spectra of PTF10hgi and SN2019hge as templates, we examine 70 SLSN-I discovered by ZTF in the first two years of operation and found additional five SLSN-I with distinct He-features. The excitation of He\,I atoms in normal core collapse supernovae requires non-thermal radiation, as proposed by previous studies. These He-rich events can not be explained by traditional $^{56}$Ni mixing model because of their blue spectra, high peak luminosity and slow rising time scales. Magnetar models offer a possible solution since pulsar winds naturally generate high energy particles as sources of non-thermal excitation. An alternative model is ejecta interaction with H-poor CSM which may be supported by the observed light curve undulations. These six SLSN-Ib appear to have relatively low-peak luminosities (rest-frame $M_g = -20.06\pm0.16$ mag)., Comment: 12 pages, 6 figures, Accepted for publication in ApJL. Matched with the published version

We present observations of ZTF18abfcmjw (SN2019dge), a helium-rich supernova with a fast-evolving light curve indicating an extremely low ejecta mass ($\approx 0.3\,M_\odot$) and low kinetic energy ($\approx 1.2\times 10^{50}\,{\rm erg}$). Early-time (<4 d after explosion) photometry reveal evidence of shock cooling from an extended helium-rich envelope of $\sim0.1\,M_\odot$ located at $\sim 3\times 10^{12}\,{\rm cm}$ from the progenitor. Early-time He II line emission and subsequent spectra show signatures of interaction with helium-rich circumstellar material, which extends from $\gtrsim 5\times 10^{13}\,{\rm cm}$ to $\gtrsim 2\times 10^{16}\,{\rm cm}$. We interpret SN2019dge as a helium-rich supernova from an ultra-stripped progenitor, which originates from a close binary system consisting of a mass-losing helium star and a low-mass main sequence star or a compact object (i.e., a white dwarf, a neutron star, or a black hole). We infer that the local volumetric birth rate of 19dge-like ultra-stripped SNe is in the range of 1400--8200$\,{\rm Gpc^{-3}\, yr^{-1}}$ (i.e., 2--12% of core-collapse supernova rate). This can be compared to the observed coalescence rate of compact neutron star binaries that are not formed by dynamical capture., Comment: 29 pages, 23 figures, submitted to ApJ

Early observations of Type Ia supernovae (SNe$\,$Ia) provide essential clues for understanding the progenitor system that gave rise to the terminal thermonuclear explosion. We present exquisite observations of SN$\,$2019yvq, the second observed SN$\,$Ia, after iPTF$\,$14atg, to display an early flash of emission in the ultraviolet (UV) and optical. Our analysis finds that SN$\,$2019yvq was unusual, even when ignoring the initial flash, in that it was moderately underluminous for an SN$\,$Ia ($M_g \approx -18.5\,$mag at peak) yet featured very high absorption velocities ($v \approx 15,000\,\mathrm{km\,s}^{-1}$ for Si II $\lambda$6355 at peak). We find that many of the observational features of SN$\,$2019yvq, aside from the flash, can be explained if the explosive yield of radioactive $^{56}\mathrm{Ni}$ is relatively low (we measure $M_{^{56}\mathrm{Ni}} = 0.31 \pm 0.05\,M_\odot$) and it and other iron-group elements are concentrated in the innermost layers of the ejecta. To explain both the UV/optical flash and peak properties of SN$\,$2019yvq we consider four different models: interaction between the SN ejecta and a nondegenerate companion, extended clumps of $^{56}\mathrm{Ni}$ in the outer ejecta, a double-detonation explosion, and the violent merger of two white dwarfs. Each of these models has shortcomings when compared to the observations; it is clear additional tuning is required to better match SN$\,$2019yvq. In closing, we predict that the nebular spectra of SN$\,$2019yvq will feature either H or He emission, if the ejecta collided with a companion, strong [Ca II] emission, if it was a double detonation, or narrow [O I] emission, if it was due to a violent merger., Comment: 27 pages, 14 figures, accepted in ApJ

We present optical, radio, and X-ray observations of SN2020bvc (=ASASSN20bs; ZTF20aalxlis), a nearby ($z=0.0252$; $d$=114 Mpc) broad-lined (BL) Type Ic supernova (SN). Our observations show that SN2020bvc shares several properties in common with the Ic-BL SN2006aj, which was associated with the low-luminosity gamma-ray burst (LLGRB) 060218. First, the 10 GHz radio light curve is on the faint end of LLGRB-SNe ($L_\mathrm{radio} \approx 10^{37}$erg/s): we model our VLA observations (spanning 13-43 d) as synchrotron emission from a mildly relativistic ($v \gtrsim 0.3c$) forward shock. Second, with Swift and Chandra we detect X-ray emission ($L_X \approx 10^{41}$erg/s) that is not naturally explained as inverse Compton emission or as part of the same synchrotron spectrum as the radio emission. Third, high-cadence ($6\times$/night) data from the Zwicky Transient Facility (ZTF) shows a double-peaked optical light curve, the first peak from shock-cooling emission from extended low-mass material (mass $M<10^{-2} M_\odot$ at radius $R>10^{12}$cm) and the second peak from the radioactive decay of Ni-56. SN2020bvc is the first confirmed double-peaked Ic-BL SN discovered without a GRB trigger, and shows X-ray and radio emission similar to LLGRB-SNe: this is consistent with models in which the same mechanism produces both the LLGRB and the shock-cooling emission. For four of the five other nearby ($z\lesssim0.05$) Ic-BL SNe with ZTF high-cadence data, we rule out a first peak like that seen in SN2006aj and SN2020bvc, i.e. that lasts $\approx 1$d and reaches a peak luminosity $M \approx -18$. X-ray and radio follow-up observations of future such events will establish whether double-peaked optical light curves are indeed predictive of LLGRB-like X-ray and radio emission., Comment: Accepted to ApJ. 39 pages, 17 figures. Comments welcome

We present ZTF18abvkwla (the "Koala"), a fast blue optical transient discovered in the Zwicky Transient Facility (ZTF) One-Day Cadence (1DC) Survey. ZTF18abvkwla has a number of features in common with the groundbreaking transient AT2018cow: blue colors at peak ($g-r\approx-0.5$ mag), a short rise time from half-max of under two days, a decay time to half-max of only three days, a high optical luminosity ($M_{g,\mathrm{peak}}\approx-20.6$mag), a hot ($\gtrsim 40,000$K) featureless spectrum at peak light, and a luminous radio counterpart. At late times ($\Delta t>80$d) the radio luminosity of ZTF18abvkwla ($\nu L_\nu \gtrsim 10^{40}$erg/s at 10 GHz, observer-frame) is most similar to that of long-duration gamma-ray bursts (GRBs). The host galaxy is a dwarf starburst galaxy ($M\approx5\times10^{8}M_\odot$, $\mathrm{SFR}\approx7 M_\odot$/yr) that is moderately metal-enriched ($\log\mathrm{[O/H]} \approx 8.5$), similar to the hosts of GRBs and superluminous supernovae. As in AT2018cow, the radio and optical emission in ZTF18abvkwla likely arise from two separate components: the radio from fast-moving ejecta ($\Gamma \beta c >0.38c$) and the optical from shock-interaction with confined dense material ($<0.07M_\odot$ in $\sim 10^{15}$cm). Compiling transients in the literature with $t_\mathrm{rise} <5$d and $M_\mathrm{peak}<-20$mag, we find that a significant number are engine-powered, and suggest that the high peak optical luminosity is directly related to the presence of this engine. From 18 months of the 1DC survey, we find that transients in this rise-luminosity phase space are at least two to three orders of magnitude less common than CC SNe. Finally, we discuss strategies for identifying such events with future facilities like the Large Synoptic Survey Telescope, and prospects for detecting accompanying X-ray and radio emission., Comment: 27 pages, 11 figures. Resubmitted to ApJ on 13 April following comments by referee. Comments welcome!

While it is clear that Type Ia supernovae (SNe) are the result of thermonuclear explosions in C/O white dwarfs (WDs), a great deal remains uncertain about the binary companion that facilitates the explosive disruption of the WD. Here, we present a comprehensive analysis of a large, unique data set of 127 SNe$\,$Ia with exquisite coverage by the Zwicky Transient Facility (ZTF). High-cadence (six observations per night) ZTF observations allow us to measure the SN rise time and examine its initial evolution. We develop a Bayesian framework to model the early rise as a power law in time, which enables the inclusion of priors in our model. For a volume-limited subset of normal SNe$\,$Ia, we find that the mean power-law index is consistent with 2 in the $r_\mathrm{ZTF}$-band ($\alpha_r = 2.01\pm0.02$), as expected in the expanding fireball model. There are, however, individual SNe that are clearly inconsistent with $\alpha_r=2$. We estimate a mean rise time of 18.9$\,$d (with a range extending from $\sim$15 to 22$\,$d), though this is subject to the adopted prior. We identify an important, previously unknown, bias whereby the rise times for higher-redshift SNe within a flux-limited survey are systematically underestimated. This effect can be partially alleviated if the power-law index is fixed to $\alpha=2$, in which case we estimate a mean rise time of 21.7$\,$d (with a range from $\sim$18 to 23$\,$d). The sample includes a handful of rare and peculiar SNe$\,$Ia. Finally, we conclude with a discussion of lessons learned from the ZTF sample that can eventually be applied to observations from the Vera C. Rubin Observatory., Comment: 31 pages, 17 figures; ApJ accepted

Supernovae (SNe) Type Ibn are rapidly evolving and bright (M$_\text{R,peak}$ $\sim-19$) transients interacting with He-rich circumstellar material (CSM). SN 2018bcc, detected by the ZTF shortly after explosion, provides the best constraints on the shape of the rising light curve (LC) of a fast Type Ibn. Aims: We used the high-quality data set of SN 2018bcc to study observational signatures of the class. Additionally, the powering mechanism of SN 2018bcc offers insights into the debated progenitor connection of Type Ibn SNe. Methods: We compared well-constrained LC properties obtained from empirical models are compared with the literature. We fit the pseudo-bolometric LC with semi-analytical models powered by radioactive decay and CSM interaction. Finally, we modeled the line profiles and emissivity of the prominent He I lines, in order to study the formation of P-Cygni profiles and estimate CSM properties. Results: SN 2018bcc had a rise time to peak of $5.6^{+0.2}_{-0.1}$ days in the restframe with a rising shape power-law index close to 2, and seems to be a typical rapidly evolving Type Ibn SN. The spectrum lacked signatures of SN-like ejecta and was dominated by over 15 He emission features at 20 days past peak, alongside Ca and Mg, all with V$_{\text{FWHM}} \sim 2000~\text{km}~\text{s}^{-1}$. The luminous and rapidly evolving LC could be powered by CSM interaction but not by the decay of radioactive $^{56}$Ni. Modeling of the He I lines indicated a dense and optically thick CSM that can explain the P-Cygni profiles. Conclusions: Like other rapidly-evolving Type Ibn SNe, SN 2018bcc is a luminous transient with a rapid rise to peak powered by shock interaction inside a dense and He-rich CSM. Its spectra do not support the existence of two Type Ibn spectral classes. We also note the remarkable observational match to pulsational pair instability (PPI) SN models., Comment: Accepted for publication in the extragalactic astronomy section of A&A. 24 pages, 17 Figures. Data are made public via WiseRep

We present photometry and spectroscopy of four hydrogen-poor luminous supernovae discovered during the two-month science commissioning and early operations of the Zwicky Transient Facility (ZTF) survey. Three of these objects, SN2018bym (ZTF18aapgrxo), SN2018avk (ZTF18aaisyyp) and SN2018bgv (ZTF18aavrmcg) resemble typical SLSN-I spectroscopically, while SN2018don (ZTF18aajqcue) may be an object similar to SN2007bi experiencing considerable host galaxy reddening, or an intrinsically long-lived, luminous and red SN Ic. We analyze the light curves, spectra, and host galaxy properties of these four objects and put them in context of the population of SLSN-I. SN2018bgv stands out as the fastest-rising SLSN-I observed to date, with a rest-frame g-band rise time of just 10 days from explosion to peak -- if it is powered by magnetar spin-down, the implied ejecta mass is only ~1 M$_{\odot}$. SN2018don also displays unusual properties -- in addition to its red colors and comparatively massive host galaxy, the light curve undergoes some of the strongest light curve undulations post-peak seen in a SLSN-I, which we speculate may be due to interaction with circumstellar material. We discuss the promises and challenges of finding SLSNe in large-scale surveys like ZTF given the observed diversity in the population., Comment: Updated to match published version. Expanded discussion following referee comments; conclusions unchanged

Early-time observations of Type Ia supernovae (SNe Ia) are essential to constrain their progenitor properties. In this paper, we present high-quality light curves of 127 SNe Ia discovered by the Zwicky Transient Facility (ZTF) in 2018. We describe our method to perform forced point spread function (PSF) photometry, which can be applied to other types of extragalactic transients. With a planned cadence of six observations per night ($3g+3r$), all of the 127 SNe Ia are detected in both $g$ and $r$ band more than 10\,d (in the rest frame) prior to the epoch of $g$-band maximum light. The redshifts of these objects range from $z=0.0181$ to 0.165; the median redshift is 0.074. Among the 127 SNe, 50 are detected at least 14\,d prior to maximum light (in the rest frame), with a subset of 9 objects being detected more than 17\,d before $g$-band peak. This is the largest sample of young SNe Ia collected to date; it can be used to study the shape and color evolution of the rising light curves in unprecedented detail. We discuss six peculiar events in this sample, including one 02cx-like event ZTF18abclfee (SN\,2018crl), one Ia-CSM SN ZTF18aaykjei (SN\,2018cxk), and four objects with possible super-Chandrasekhar mass progenitors: ZTF18abhpgje (SN\,2018eul), ZTF18abdpvnd (SN\,2018dvf), ZTF18aawpcel (SN\,2018cir) and ZTF18abddmrf (SN\,2018dsx)., Comment: Accepted by ApJ

In this paper we report the results of the first $\sim$four years of spectroscopic and photometric monitoring of the Type IIn supernova SN 2015da (also known as PSN J13522411+3941286, or iPTF16tu). The supernova exploded in the nearby spiral galaxy NGC 5337 in a relatively highly extinguished environment. The transient showed prominent narrow Balmer lines in emission at all times and a slow rise to maximum in all bands. In addition, early observations performed by amateur astronomers give a very well-constrained explosion epoch. The observables are consistent with continuous interaction between the supernova ejecta and a dense and extended H-rich circumstellar medium. The presence of such an extended and dense medium is difficult to reconcile with standard stellar evolution models, since the metallicity at the position of SN 2015da seems to be slightly subsolar. Interaction is likely the mechanism powering the light curve, as confirmed by the analysis of the pseudo bolometric light curve, which gives a total radiated energy $\gtrsim10^{51}\,\rm{erg}$. Modeling the light curve in the context of a supernova shock breakout through a dense circumstellar medium allowed us to infer the mass of the prexisting gas to be $\simeq8\,\rm{M_{\odot}}$, with an extreme mass-loss rate for the progenitor star $\simeq0.6\,\rm{M_{\odot}}\,\rm{yr^{-1}}$, suggesting that most of the circumstellar gas was produced during multiple eruptive events. Near- and mid-infrared observations reveal a flux excess in these domains, similar to those observed in SN 2010jl and other interacting transients, likely due to preexisting radiatively heated dust surrounding the supernova. By modeling the infrared excess, we infer a mass $\gtrsim0.4\times10^{-3}\,\rm{M_{\odot}}$ for the dust., Comment: 23 pages (19+appendix), 15 figures, 11 tables (Tables A.1-A.4 at CDS only). Accepted for publication on Astronomy and Astrophysics

We present a sample of supernovae Type IIn (SNe IIn) from the untargeted, magnitude-limited surveys of the Palomar Transient Factory (PTF) and its successor, the intermediate PTF (iPTF). The SNe IIn found and followed by the PTF/iPTF were used to select a sample of 42 events with useful constraints on the rise times as well as with available post-peak photometry. The sample SNe were discovered in 2009-2016 and have at least one low-resolution classification spectrum, as well as photometry from the P48 and P60 telescopes at Palomar Observatory. We study the light-curve properties of these SNe IIn using spline fits (for the peak and the declining portion) and template matching (for the rising portion). We find that the typical rise times are divided into fast and slow risers at $20\pm6$ d and $50\pm11$ d, respectively. The decline rates are possibly divided into two clusters, but this division has weak statistical significance. We find no significant correlation between the peak luminosity of SNe IIn and their rise times, but the more luminous SNe IIn are generally found to be more long-lasting. Slowly rising SNe IIn are generally found to decline slowly. The SNe in our sample were hosted by galaxies of absolute magnitude $-22 \lesssim M_g \lesssim -13$ mag. The K-corrections at light-curve peak of the SNe IIn in our sample are found to be within 0.2 mag for the observer's frame $r$-band, for SNe at redshifts $z < 0.25$. By applying K-corrections and also including ostensibly "superluminous" SNe IIn, we find that the peak magnitudes are $M_{\rm peak}^{r} = -19.18\pm1.32$ mag. We conclude that the occurrence of conspicuous light-curve bumps in SNe IIn, such as in iPTF13z, are limited to $1.4^{+14.6}_{-1.0} \%$ of the SNe IIn. We also investigate a possible sub-type of SNe IIn with a fast rise to a $\gtrsim 50$ d plateau followed by a slow, linear decline., Comment: Matches journal version. Table 2 on CDS. Durations in Fig. 13 corrected, conclusions unchanged. Abstract abridged. 33 pages, 22 figures, 7 tables

Both multi-messenger astronomy and new high-throughput wide-field surveys require flexible tools for the selection and analysis of astrophysical transients. We here introduce the Alert Management, Photometry and Evaluation of Lightcurves (AMPEL) system, an analysis framework designed for high-throughput surveys and suited for streamed data. AMPEL combines the functionality of an alert broker with a generic framework capable of hosting user-contributed code, that encourages provenance and keeps track of the varying information states that a transient displays. The latter concept includes information gathered over time and data policies such as access or calibration levels. We describe a novel ongoing real-time multi-messenger analysis using AMPEL to combine IceCube neutrino data with the alert streams of the Zwicky Transient Facility (ZTF). We also reprocess the first four months of ZTF public alerts, and compare the yields of more than 200 different transient selection functions to quantify efficiencies for selecting Type Ia supernovae that were reported to the Transient Name Server (TNS). We highlight three channels suitable for (1) the collection of a complete sample of extragalactic transients, (2) immediate follow-up of nearby transients and (3) follow-up campaigns targeting young, extragalactic transients. We confirm ZTF completeness in that all TNS supernovae positioned on active CCD regions were detected. AMPEL can assist in filtering transients in real time, running alert reaction simulations, the reprocessing of full datasets as well as in the final scientific analysis of transient data. This text introduces how users can design their own channels for inclusion in the AMPEL live instance that parses the ZTF stream and the real-time submission of high quality extragalactic supernova candidates to the TNS., Comment: Updated to match version accepted for publication in A&A

We investigate ZTF18aalrxas, a double-peaked Type IIb core-collapse supernova (SN) discovered during science validation of the Zwicky Transient Facility (ZTF). ZTF18aalrxas was discovered while the optical emission was still rising towards the initial cooling peak (0.7 mag over 2 days). Our observations consist of multi-band (UV, optical) light-curves, and optical spectra spanning from $\approx0.7$ d to $\approx180$ d past the explosion. We use a Monte-Carlo based non-local thermodynamic equilibrium (NLTE) model, that simultanously reproduces both the $\rm ^{56}Ni$ powered bolometric light curve and our nebular spectrum. This model is used to constrain the synthesized radioactive nickel mass (0.17 $\mathrm{M}_{\odot}$) and the total ejecta mass (1.7 $\mathrm{M}_{\odot}$) of the SN. The cooling emission is modeled using semi-analytical extended envelope models to constrain the progenitor radius ($790-1050$ $\mathrm{R}_{\odot}$) at the time of explosion. Our nebular spectrum shows signs of interaction with a dense circumstellar medium (CSM), and this spetrum is modeled and analysed to constrain the amount of ejected oxygen ($0.3-0.5$ $\mathrm{M}_{\odot}$) and the total hydrogen mass ($\approx0.15$ $\mathrm{M}_{\odot}$) in the envelope of the progenitor. The oxygen mass of ZTF18aalrxas is consistent with a low ($12-13$ $\mathrm{M}_{\odot}$) Zero Age Main Sequence mass progenitor. The light curves and spectra of ZTF18aalrxas are not consistent with massive single star SN Type IIb progenitor models. The presence of an extended hydrogen envelope of low mass, the presence of a dense CSM, the derived ejecta mass, and the late-time oxygen emission can all be explained in a binary model scenario., Comment: 14 pages, 7 figures, submitted to ApJ

SN2010jl was a luminous Type IIn supernova (SN), detected in radio, optical, X-ray and hard X-rays. Here we report on its six year R- and g-band light curves obtained using the Palomar Transient Factory. The light curve was generated using a pipeline based on the proper image subtraction method and we discuss the algorithm performances. As noted before, the R-band light curve, up to about 300 days after maximum light is well described by a power-law decline with a power-law index of about -0.5. Between day 300 and day 2300 after maximum light, it is consistent with a power-law decline, with a power-law index of about -3.4. The longevity of the light curve suggests that the massive circum-stellar material around the progenitor was ejected on time scales of at least tens of years prior to the progenitor explosion., Comment: 6 pages, PASP in press

Current time domain facilities are discovering hundreds of new galactic and extra-galactic transients every week. Classifying the ever-increasing number of transients is challenging, yet crucial to further our understanding of their nature, discover new classes, or ensuring sample purity, for instance, for Supernova Ia cosmology. The Zwicky Transient Facility is one example of such a survey. In addition, it has a dedicated very-low resolution spectrograph, the SEDMachine, operating on the Palomar 60-inch telescope. This spectrograph's primary aim is object classification. In practice most, if not all, transients of interest brighter than ~19 mag are typed. This corresponds to approximately 10 to 15 targets a night. In this paper, we present a fully automated pipeline for the SEDMachine. This pipeline has been designed to be fast, robust, stable and extremely flexible. pysedm enables the fully automated spectral extraction of a targeted point source object in less than 5 minutes after the end of the exposure. The spectral color calibration is accurate at the few percent level. In the 19 weeks since pysedm entered production in early August of 2018, we have classified, among other objects, about 400 Type Ia supernovae and 140 Type II supernovae. We conclude that low resolution, fully automated spectrographs such as the `SEDMachine with pysedm' installed on 2-m class telescopes within the southern hemisphere could allow us to automatically and simultaneously type and obtain a redshift for most (if not all) bright transients detected by LSST within z<0.2, notably potentially all Type Ia Supernovae. In comparison to the current SEDM design, this would require higher spectral resolution (R~1000) and slightly improved throughput. With this perspective in mind, pysedm has been designed to easily be adaptable to any IFU-like spectrograph (see https://github.com/MickaelRigault/pysedm)., Comment: Submitted to Astronomy and Astrophysics