The Zwicky Transient Facility Census of the Local Universe survey yielded a sample of 330 Type IIP supernovae (SNe) with well-constrained peak luminosities. In paper I, we measured their luminosity function and volumetric rate. Here (paper II), we present the largest systematic study of lightcurve properties for Type IIP SNe from a volume-limited survey, analyzing a selected subset of 129 events, including 16 low-luminosity Type IIP (LLIIP) SNe with Mr,peak >= -16 mag. We find that plateau slope correlates with peak brightness, with many LLIIP SNe showing positive slopes-suggesting smaller progenitor radii and distinct density profiles compared to brighter Type IIP SNe. The plateau duration shows only a weak dependence on peak brightness, likely suggesting binary interaction. One SN exhibits a plateau-to-tail drop of >3.5 mag, consistent with an electron-capture or failed SN with very low or zero nickel mass. We derive explosion and progenitor parameters of the entire Type IIP SN sample using semi-analytical and radiation-hydrodynamical models. Based on radiation-hydrodynamical model fitting, LLIIP SNe are characterized by low nickel masses (0.001-0.025 M-circle dot), low explosion energies (0.1-0.28 & times; 10(51 )erg), low ejecta masses ( 8.1(-1.7)(+0.8) M-circle dot), and ZAMS masses below 11 M-circle dot. In comparison, the full Type IIP SN sample spans a wider range with nickel masses (0.001-0.222 M-circle dot), explosion energies (0.10-4.43 & times; 10(51 )erg), ejecta masses (5.4-24.8 M-circle dot), and ZAMS masses (9.3-16.7 M-circle dot). We find strong correlations between peak brightness, explosion energy, and nickel mass that extend to the low-luminosity end. We conclude that LLIIP SNe represent the faint, low-energy end of the Type IIP population and originate from the lowest-mass core-collapse progenitors.

We present optical/UV photometric and spectroscopic observations, as well as X-ray and radio follow-up, of the extraordinary event AT2019cmw. With a peak bolometric luminosity of similar to 10(45.6) erg s(-1), it is one of the most luminous thermal transients ever discovered. Extensive spectroscopic follow-up post-peak showed only a featureless continuum throughout its evolution. This, combined with its nuclear location, blue colour at peak and lack of prior evidence of an AGN in its host lead us to interpret this event as a 'featureless' tidal disruption event (TDE). It displays photometric evolution atypical of most TDEs, cooling from similar to 30 to similar to 10kK in the first similar to 300 d post-peak, with potential implications for future photometric selection of candidate TDEs. No X-ray or radio emission is detected, placing constraints on the presence of on-axis jetted emission or a visible inner-accretion disc. Modelling the optical light curve with existing theoretical prescriptions, we find that AT2019cmw may be the result of the disruption of a star in the tens of solar masses by a supermassive black hole (SMBH). Combined with a lack of detectable star formation in its host galaxy, it could imply the existence of a localized region of star formation around the SMBH. This could provide a new window to probe nuclear star formation and the shape of the initial mass function (IMF) in close proximity to SMBHs out to relatively high redshifts.

We present the searches conducted with the Zwicky Transient Facility (ZTF) in response to S250206dm, a bona fide event with an online false alarm rate of one in 25 yr, detected by the International Gravitational Wave Network. Although the event is significant, the nature of the compact objects involved remains unclear, with at least one likely neutron star. ZTF covered 68% of the last refined Bilby localization region, though we did not identify any likely optical counterpart. We describe the ZTF strategy, potential candidates, and the observations that helped rule out candidates, including sources circulated by other collaborations. Similar to Ahumada et al., we perform a frequentist analysis, using simsurvey, as well as Bayesian analysis, using nimbus, to quantify the efficiency of our searches. We find that, given the nominal up-to-date distance to this event of 373 +/- 104 Mpc, our efficiencies are above 10% for KNe brighter than -17.5 absolute magnitude. Assuming the optical counterpart known as kilonova (KN) lies within the ZTF footprint, our limits constrain the brightest end of the KN parameter space. Through dedicated radiative transfer simulations of KNe from binary neutron star (BNS) and black hole-neutron star mergers, we exclude parts of the BNS KN parameter space. Up to 35% of the models with high wind ejecta mass (Mwind approximate to 0.13 M circle dot) are ruled out when viewed face-on ( cos theta obs=1.0 ). Finally, we present a joint analysis using the combined coverage from ZTF and the Gravitational Wave Multimessenger Dark Energy Camera Survey. The joint observations cover 73% of the Bilby localization region, and the combined efficiency has a stronger impact on rising and slowly fading models, allowing us to rule out 55% of the high-mass KN models viewed face-on.

Modern time-domain surveys like the Zwicky Transient Facility (ZTF) and the Legacy Survey of Space and Time (LSST) generate hundreds of thousands to millions of alerts, demanding automatic, unified classification of transients and variable stars for efficient follow-up. We present Applying multimodal learning to Classify transient Detections Early (AppleCiDEr), a novel framework that integrates four key data modalities (photometry, image cutouts, metadata, and spectra) to overcome limitations of single-modality classification approaches. Our architecture introduces (i) two transformer encoders for photometry, (ii) a multimodal convolutional neural network (CNN) with domain-specialized metadata towers and Mixture-of-Experts fusion for combining metadata and images, and (iii) a CNN for spectra classification. Training on similar to 30,000 real ZTF alerts, AppleCiDEr achieves high accuracy, allowing early identification and suggesting follow-up for rare transient spectra. The system provides the first unified framework for transients classification using real observational data, with seamless integration into brokering pipelines, demonstrating readiness for the LSST era.

The Zwicky Transient Facility Data Release 2 (ZTF DR2) includes a total of 3628 Type Ia supernovae (SNe Ia), providing the largest and most complete sample of spectroscopically confirmed SNe Ia at low redshift to date. In this paper, we present a photometric and spectroscopic analysis of 124 subluminous SNe Ia, the largest sample of spectroscopically classified subluminous Type Ia supernova observed with a single instrument, comprising 87 91bg-like, 12 86G-like, 18 04gs-like, and 7 02es-like events. We complement the published DR2 SALT2 light-curve parameters with new parameters obtained using template-based fits from SNOOPY. We measured the expansion velocities and pseudo-equivalent widths (pEW) of key spectral features using SPEXTRACTOR. Next, the spectral averages were constructed for each subluminous subtype, binned by phase. We also analyzed the host galaxy environments, both global and local, in terms of g − z color, stellar mass, and directional light radius (dDLR). We found that all subluminous SNe Ia (except the 02es-like subtype) are intrinsically red. This is made evident when we separate the extrinsic color components from intrinsic ones. Since SALT2 has not been trained on subluminous SNe Ia, it compensates for their redder colors by inflating the c parameter, thereby extending the luminosity-width relation to negative values of x1. As expected, all subluminous SNe Ia fall within the cool region of the Branch et al. (2006, PASP, 118, 560) diagram, with the exception of 02es-like events, which display lower Si IIλ5972 pEW values. All subluminous subtypes tend to occur in more massive, redder host galaxies and in the reddest local environments within their stellar mass bins. Notably, 91bg- and 86G-like SNe Ia explode at significantly larger normalized galactocentric distances. Finally, we identified the pEW of the blended Ti II+Si II+Mg II absorption feature at 4300 Å, along with sBV, as robust and sufficient indicators for subclassifying subluminous SNe Ia.

In recent years, a class of stripped-envelope supernovae (SESNe) has emerged that show two distinct peaks in their light curves, where the first peak cannot be attributed to shock cooling emission. Such peculiar supernovae are often studied individually, explained by invoking some combination of powering mechanisms. However, they have seldom been discussed in the broader context of double-peaked SESNe. In this paper, we attempt to form a picture of the landscape of double-peaked SESNe and their powering mechanisms by adding two more objects-SN 2021uvy and SN 2022hgk. SN 2021uvy is a broad and luminous SN Ib with an unusually long rise of the first peak and constant color evolution with rising photospheric temperature during the second peak. Although its first peak is similar to that of SN 2019stc, their second peaks differ in properties, making it unique among double-peaked objects. SN 2022hgk shows striking photometric similarity to SN 2019cad and spectroscopic similarity to SN 2005bf, both of which have been suggested to be powered by a double-nickel distribution in their ejecta. We analyze their light curves and colors, compare them with a sample of other double-peaked published supernovae for which we have additional data, and analyze the light curve parameters of the sample. We observe a correlation (p-value similar to 0.025) between the peak absolute magnitudes of the first and second peaks. The sample shows variety in the photometric and spectroscopic properties, and thus no single definitive powering mechanism applies to the whole sample. However, sub-groups of similarity exist that can be explained by mechanisms like the double-nickel distribution, magnetar central engine, interaction, and fallback accretion. We also map out the duration between the peaks (Delta t21) versus the difference between peak absolute magnitudes (Delta M21) as a phase-space that could potentially delineate the most promising powering mechanisms for the double-peaked SESNe.

We present new rotational period estimates for 216 Jupiter Trojans using photometric data from the Zwicky Transient Facility (ZTF), including 80 Trojans with previously unknown periods. Our analysis reveals rotation periods ranging from 4.6 hours to 447.8 hours. These results support the existence of a spin barrier for Trojans larger than 10 km, with periods clustering between 4 and 4.8 hours. This spin barrier is roughly twice as long as that observed for main-belt asteroids, suggesting that Jupiter Trojans have significantly lower bulk densities, likely due to a higher fraction of ices and volatile materials in their composition. We identify three new Trojans with reliable rotation periods near the spin barrier, doubling the number of known Trojans in this critical period range. Using these results, we estimate a mean density of approximately 0.52 g/cm^3 for rubble-pile Trojans. Our findings support the growing evidence that many Trojans are rubble-pile bodies with distinct physical properties compared to main-belt asteroids. Looking forward, we anticipate that data from the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) will provide rotational period estimates for several hundred thousand Trojans, down to objects as small as 1 km, enabling a more detailed investigation of their rotational properties and internal structure.

In this work, we use the Jansky Very Large Array Sky Survey to compile the first sample of six radio-selected tidal disruption events (TDEs) with transient optical counterparts. While we still lack the statistics to do detailed population studies of radio-selected TDEs, we use these events to suggest trends in host galaxy and optical light-curve properties that may correlate with the presence of radio emission and hence can inform optically selected TDE radio follow-up campaigns. We find tentative trends that radio-selected TDEs tend to have faint and cool optical flares, as well as host galaxies with low supermassive black hole masses, although larger samples are required to establish these trends as statistically significant. Our radio-selected TDEs also tend to have more energetic, larger radio-emitting regions than radio-detected, optically selected TDEs. We consider possible explanations for these trends, including by invoking super-Eddington accretion and enhanced circumnuclear media. Finally, we constrain the radio-emitting TDE rate to be ≳10 Gpc ^−3 yr ^−1 .

We present volume-limited samples of cataclysmic variables (CVs) and AM CVn binaries jointly selected from SRG/eROSITA eRASS1 and Gaia DR3 using an X-ray + optical color-color diagram (the "X-ray Main Sequence"). This tool identifies all CV subtypes, including magnetic and low-accretion rate systems, in contrast to most previous surveys. We find 23 CVs, 3 of which are AM CVns, out to 150 pc in the Western Galactic Hemisphere. Our 150 pc sample is spectroscopically verified and complete down to LX = 1.3 x 1029 erg s-1 in the 0.2-2.3 keV band, and we also present CV candidates out to 300 pc and 1000 pc. We discovered two previously unknown systems in our 150 pc sample: the third nearest AM CVn and a magnetic period bouncer. We find the mean LX of CVs to be < LX > approximate to 4.6 x 1030 erg s-1, in contrast to previous surveys which yielded < LX > similar to 1031-1032 erg s-1. We construct X-ray luminosity functions that, for the first time, flatten out at LX similar to 1030 erg s-1. We infer average number, mass, and luminosity densities of rho N,CV = (3.7 +/- 0.7) x 10-6pc-3, rho M=(5.0 +/- 1.0)x10-5M circle dot-1 , and rho LX=(2.3 +/- 0.4)x1026ergs-1M circle dot-1 , respectively, in the solar neighborhood. Our uniform selection method also allows us to place meaningful estimates on the space density of AM CVns, rho N,AM CVn = (5.5 +/- 3.7) x 10-7 pc-3. Magnetic CVs and period bouncers make up 35% and 25% of our sample, respectively. This work, through a novel discovery technique, shows that the observed number densities of CVs and AM CVns, as well as the fraction of period bouncers, are still in tension with population synthesis estimates.

We present the luminosity function and volumetric rate of a sample of Type IIP supernovae (SNe) from the Zwicky Transient Facility Census of the Local Universe survey (CLU). This is the largest sample of Type IIP SNe from a systematic volume-limited survey to-date. The final sample includes 330 Type IIP SNe and 36 low-luminosity Type II (LLIIP) SNe with M r ,peak > −16 mag, which triples the literature sample of LLIIP SNe. The fraction of LLIIP SNe is 1 9 − 4 + 3 % of the total CLU Type IIP SNe population ( 8 − 2 + 1 % of all core-collapse SNe). This implies that while LLIIP SNe likely represent the fate of core-collapse SNe of 8–12 M ⊙ progenitors, they alone cannot account for the fate of all massive stars in this mass range. To derive an absolute rate, we estimate the ZTF pipeline efficiency as a function of the apparent magnitude and the local surface brightness. We derive a volumetric rate of ( 3 . 9 − 0.4 + 0.4 ) × 1 0 4 Gpc − 3 yr − 1 for Type IIP SNe and ( 7 . 3 − 0.6 + 0.6 ) × 1 0 3 Gpc − 3 yr − 1 for LLIIP SNe. Now that the rate of LLIIP SNe is robustly derived, the unresolved discrepancy between core-collapse SN rates and star formation rates cannot be explained by LLIIP SNe alone.

We present multiwavelength analysis of ZTF23abelseb (AT 2023sva), an optically discovered fast-fading (Delta m(r)=2.2 mag in Delta t=0.74 d), luminous (M-r similar to-30.0 mag), and red (g-r=0.50 mag) transient at z=2.28 with accompanying luminous radio emission. AT 2023sva does not possess a gamma-ray burst (GRB) counterpart to an isotropic equivalent energy limit of E-gamma,(iso)<1.6x10(52) erg, determined through searching gamma-ray satellite archives between the last non-detection and first detection, making it the sixth example of an optically discovered afterglow with a redshift measurement and no detected GRB counterpart. We analyse AT 2023sva's optical, radio, and X-ray observations to characterize the source. From radio analyses, we find the clear presence of strong interstellar scintillation (ISS) 72 d after the initial explosion, allowing us to place constraints on the source's angular size and bulk Lorentz factor. When comparing the source sizes derived from ISS of orphan events to those of the classical GRB population, we find orphan events have statistically smaller source sizes. We also utilize Bayesian techniques to model the multiwavelength afterglow. Within this framework, we find evidence that AT 2023sva possesses a shallow power-law structured jet viewed slightly off-axis (theta(v)=0.07 +/- 0.02) just outside of the jet's core opening angle (theta(c)=0.06 +/- 0.02). We determine this is likely the reason for the lack of a detected GRB counterpart, but also investigate other scenarios. AT 2023sva's evidence for possessing a structured jet stresses the importance of broadening orphan afterglow search strategies to a diverse range of GRB jet angular energy profiles, to maximize the return of future optical surveys.

Tidal disruption events (TDEs) that are spatially offset from the nuclei of their host galaxies offer a new probe of massive black hole (MBH) wanderers, binaries, triples, and recoiling MBHs. Here we present AT2024tvd, the first off-nuclear TDE identified through optical sky surveys. High-resolution imaging with the Hubble Space Telescope shows that AT2024tvd is 0 . ″ 914 ± 0 . ″ 010 offset from the apparent center of its host galaxy, corresponding to a projected distance of 0.808 ± 0.009 kpc at z = 0.045. Chandra and Very Large Array observations support the same conclusion for the TDE’s X-ray and radio emission. AT2024tvd exhibits typical properties of nuclear TDEs, including a persistent hot UV/optical component that peaks at L bb ∼ 6 × 10 43 erg s −1 , broad hydrogen lines in its optical spectra, and delayed brightening of luminous ( L X,peak ∼ 3 × 10 43 erg s −1 ), highly variable soft X-ray emission. The MBH mass of AT2024tvd is 10 6±1 M ⊙ , at least 10 times lower than its host galaxy’s central black hole mass (≳10 8 M ⊙ ). The MBH in AT2024tvd has two possible origins: a wandering MBH from the lower-mass galaxy in a minor merger during the dynamical friction phase or a recoiling MBH ejected by triple interactions. Combining AT2024tvd with two previously known off-nuclear TDEs discovered in X-rays (3XMM J2150 and EP240222a), which likely involve intermediate-mass black holes in satellite galaxies, we find that the parent galaxies of all three events are very massive (∼10 10.9 M ⊙ ). This result aligns with expectations from cosmological simulations that the number of offset MBHs scales linearly with the host halo mass.

While it is generally accepted that Type Ia supernovae (SNe Ia) are the terminal explosions of white dwarfs (WDs), the nature of their progenitor systems and the mechanisms that lead up to these explosions remain widely debated. In rare cases, the SN ejecta interact with circumstellar material (CSM) that had previously been ejected from the progenitor system. The longer the delay between the creation of the CSM and the SN explosion, the greater the distance between the SN explosion site and the CSM and the later the onset of the interaction. The unknown distance between the CSM and SN explosion site makes it impossible to predict when the interaction will start. If the time between the SN explosion and the onset of the CSM interaction is of the order of several months to years, the SN has generally faded and it is no longer actively followed up on. This makes it even more difficult to detect the interaction while it is happening. In this work, we report on a real-time monitoring programme running between 13 November 2023 and 9 July 2024. It monitored 6914 SNe Ia for signs of late-time rebrightening using the Zwicky Transient Facility (ZTF). Flagged candidates were rapidly followed up on with photometry and spectroscopy to confirm the late-time excess and its position. We report the discovery of a similar to 50 day rebrightening event in SN 2020qxz around 1200 rest-frame days after the peak of its light curve. SN 2020qxz exhibited signs of an early CSM interaction, but had faded from view over two years before its reappearance. Initial follow-up spectroscopy revealed the presence of four emission lines, while later follow-up spectroscopy showed that these had faded shortly after the end of the ZTF-detected rebrightening event. Our best match for these emission lines are H beta (blueshifted by similar to 5900 km s(-1)) and Ca II lambda 8542, N I-lambda 8567, and K I-lambda lambda 8763,I- 8767 (all blueshifted by 5100 km s(-1); although we note that the line identifications are uncertain). This shows that catching and following up on late-time interactions as they occur can offer new clues on the nature of the progenitor systems that produce these SNe by putting constraints on the possible type of donor star. The only way to do this systematically is to use large sky surveys such as ZTF and the upcoming Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) to monitor a large sample of objects for the rare events that reappear long after the object has faded from view.

The nature of Type Ia supernova (SN Ia) progenitor systems and the mechanisms that lead up to their explosions are still widely debated. In rare cases the SN ejecta interact with circumstellar material (CSM) that was ejected from the progenitor system prior to the SN. The unknown distance between the CSM and SN explosion site makes it impossible to predict when the interaction will start. If the time between the SN and start of CSM interaction is of the order of months to years the SN has generally faded and is not actively followed up anymore, making it even more difficult to detect the interaction while it happens. Here we report on a real-time monitoring program which ran between 13-11-2023 and 09-07-2024, monitoring 6914 SNe Ia for signs of late-time rebrightening using the Zwicky Transient Facility (ZTF). Flagged candidates were rapidly followed up with photometry and spectroscopy to confirm the late-time excess and its position. We report the discovery of a ∼50 day rebrightening event in SN 2020qxz around 1200 days after the peak of its light curve. SN 2020qxz had signs of early CSM interaction but faded from view over 2 years before its reappearance. Follow-up spectroscopy revealed 4 emission lines that faded shortly after the end of the ZTF detected rebrightening. Our best match for these emission lines are Hβ (blue shifted by ∼5900 km s^-1) and CaII_λ8542, NI_λ8567, and KI_λλ8763, 8767, all blue shifted by 5100 km s^-1 (although we note that these identifications are uncertain). This shows that catching and following up on late-time interactions as they occur can give new clues about the nature of the progenitor systems that produce these SNe by putting constraints on the possible type of donor star, and the only way to do this systematically is to use large sky surveys such as ZTF to monitor a large sample of objects.

Astrophysical high-energy (TeV-PeV) neutrinos were first discovered in 2013, but their origin remains largely unknown. Here we present SN 2023uqf, a supernova found in coincidence with high-energy neutrino IC231004A, as part of a systematic optical follow-up program with the Zwicky Transient Facility. SN 2023uqf had a luminous and rapidly-evolving lightcurve, and spectroscopic observations indicated that the source was a Type Ibn supernova. Spectroscopic signatures confirm ongoing interaction between the supernova ejecta and a dense circumstellar medium, as expected for high-energy neutrino production in a core-collapse supernova. Given the rare nature of Type Ibn supernovae, SN 2023uqf is unlikely to have been discovered by chance over the course of our program (p=0.3

White dwarfs (WDs) are the most abundant compact objects, and recent surveys have suggested that over a third of WDs in accreting binaries host a strong (B greater than or similar to 1 MG) magnetic field. However, the origin and evolution of WD magnetism remain under debate. Two WD pulsars, AR Sco and J191213.72-441045.1 (J1912), have been found, which are non-accreting binaries hosting rapidly spinning (1.97 minutes and 5.30 minutes, respectively) magnetic WDs. The WD in AR Sco is slowing down on a P/P-center dot approximate to 5.6 x 10(6) yr timescale. It is believed they will eventually become polars, accreting systems in which a magnetic WD (B approximate to 10-240 MG) accretes from a Roche lobe-filling donor spinning in sync with the orbit (greater than or similar to 78 minutes). Here, we present multiwavelength data and analysis of Gaia22ayj, which outbursted in 2022 March. We find that Gaia22ayj is a magnetic accreting WD that is rapidly spinning down (P/P-center dot = 6.1(-0.2)(+0.3 )x 10(6) yr) like WD pulsars, but shows clear evidence of accretion, like polars. Strong linear polarization (40%) is detected in Gaia22ayj; such high levels have only been seen in the WD pulsar AR Sco and demonstrate the WD is magnetic. High speed photometry reveals a 9.36 minutes period accompanying a high amplitude (similar to 2 mag) modulation. We associate this with a WD spin or spin-orbit beat period, not an orbital period as was previously suggested. Fast (60 s) optical spectroscopy reveals a broad "hump," reminiscent of cyclotron emission in polars, between 4000 and 8000 & Aring;. We find an X-ray luminosity of L-X = 2.7(-0.8)(+6.2 )x 10(32)ergs(-1) in the 0.3-8 keV energy range, while two very large array radio campaigns resulted in a non-detection with a F-r < 15.8 mu Jy 3 sigma upper limit. The shared properties of both WD pulsars and polars suggest that Gaia22ayj is a missing link between the two classes of magnetic WD binaries.

The Taurid Complex is a large interplanetary system that contains comet 2P/Encke, several meteoroid streams, and possibly a number of near-Earth asteroids. The size and nature of the system have led to the speculation that it was formed through a large-scale cometary breakup. Numerical investigations have suggested that planetary dynamics can create a resonant region with a large number of objects concentrated in a small segment of the orbit, known as the Taurid swarm, which approaches the Earth in certain years and provides favorable conditions for studying the Taurid Complex. Recent meteor observations confirmed the existence of the swarm for millimeter- to meter-sized objects. Here we present a dedicated telescopic search for potentially hazardous asteroids and other macroscopic objects in the Taurid swarm using the Zwicky Transient Facility survey. We determine from our nondetection that there are no more than 9–14 H ≤ 24 (equivalent to a diameter of D ≳ 100 m) objects in the swarm, suggesting that the Encke–Taurid progenitor was ∼10 km in size. A progenitor of such a size is compatible with the prediction of state-of-the-art solar system dynamical models, which expects ∼0.1 D > 10 km objects on Encke-like orbits at any given time.

Stars are initially powered by the fusion of hydrogen to helium. These ashes serve as fuel in a series of stages1-3, transforming massive stars into a structure of shells. These are composed of natal hydrogen on the outside and consecutively heavier compositions inside, predicted to be dominated by He, C/O, O/Ne/Mg and O/Si/S (refs. 4,5). Silicon and sulfur are fused into iron, leading to the collapse of the core and either a supernova explosion or the formation of a black hole6-9. Stripped stars, in which the outer hydrogen layer has been removed and the internal He-rich or even the C/O layer below it is exposed10, provide evidence for this shell structure and the cosmic element production mechanism it reflects. The supernova types that arise from stripped stars embedded in shells of circumstellar material (CSM) confirm this scenario11-15. However, direct evidence for the most interior shells, which are responsible for producing elements heavier than oxygen, is lacking. Here we report the discovery of the supernova (SN) 2021yfj resulting from a star stripped to its O/Si/S-rich layer. We directly observe a thick, massive Si/S-rich shell, expelled by the progenitor shortly before the supernova explosion. Exposing such an inner stellar layer is theoretically challenging and probably requires a rarely observed mass-loss mechanism. This rare supernova event reveals advanced stages of stellar evolution, forming heavier elements, including silicon, sulfur and argon, than those detected on the surface of any known class of massive stars.

Microlensing has a unique advantage for detecting dark objects in the Milky Way, such as free floating planets, neutron stars, and stellar-mass black holes. Most microlensing surveys focus towards the Galactic bulge, where higher stellar density leads to a higher event rate. However, microlensing events in the Galactic plane are closer, and take place over longer timescales. This enables a better measurement of the microlensing parallax, which serves as an independent constraint on the mass of the dark lens. In this work, we systematically searched for microlensing events in Zwicky Transient Facility (ZTF) Data Release 17 from 2018--2023 in the Galactic plane region $|b| < 20^\circ$. We find 124 high-confidence microlensing events and 54 possible events. In the event selection, we use the efficient \texttt{EventFinder} algorithm to detect microlensing signals, which could be used for large datasets such as future ZTF data releases or data from the Rubin Observatory Legacy Survey of Space and Time (LSST). With detection efficiencies of ZTF fields from catalog-level simulations, we calculate the mean Einstein timescale to be $\langle t_\mathrm{E}\rangle = 51.7 \pm 3.3$ days, smaller than previous results of the Galactic plane to within 1.5-$\sigma$. We calculate optical depths and event rates, which we interpret with caution due to the use of visual inspection in creating our final sample. With two years of additional ZTF data in DR17, we have more than doubled the amount of microlensing events (60) found in the three-year DR5 search and found events with longer Einstein timescales than before.

We report observations of the optical counterpart of the long gamma-ray burst (LGRB) GRB 230812B, and its associated supernova (SN) SN 2023pel. The proximity ($z = 0.36$) and high energy ($E_{\gamma, \rm{iso}} \sim 10^{53}$ erg) make it an important event to study as a probe of the connection between massive star core-collapse and relativistic jet formation. With a phenomenological power-law model for the optical afterglow, we find a late-time flattening consistent with the presence of an associated SN. SN 2023pel has an absolute peak $r$-band magnitude of $M_r = -19.46 \pm 0.18$ mag (about as bright as SN 1998bw) and evolves on quicker timescales. Using a radioactive heating model, we derive a nickel mass powering the SN of $M_{\rm{Ni}} = 0.38 \pm 0.01$ $\rm{M_\odot}$, and a peak bolometric luminosity of $L_{\rm{bol}} \sim 1.3 \times 10^{43}$ $\rm{erg}$ $\rm{s^{-1}}$. We confirm SN 2023pel's classification as a broad-lined Type Ic SN with a spectrum taken 15.5 days after its peak in $r$ band, and derive a photospheric expansion velocity of $v_{\rm{ph}} = 11,300 \pm 1,600$ $\rm{km}$ $\rm{s^{-1}}$ at that phase. Extrapolating this velocity to the time of maximum light, we derive the ejecta mass $M_{\rm{ej}} = 1.0 \pm 0.6$ $\rm{M_\odot}$ and kinetic energy $E_{\rm{KE}} = 1.3^{+3.3}_{-1.2} \times10^{51}$ $\rm{erg}$. We find that GRB 230812B/SN 2023pel has SN properties that are mostly consistent with the overall GRB-SN population. The lack of correlations found in the GRB-SN population between SN brightness and $E_{\gamma, \rm{iso}}$ for their associated GRBs, across a broad range of 7 orders of magnitude, provides further evidence that the central engine powering the relativistic ejecta is not coupled to the SN powering mechanism in GRB-SN systems.