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Abstract We present a sample of 34 normal Type II supernovae (SNe II) detected with the Zwicky Transient Facility, with multiband UV light curves starting att≤ 4 days after explosion, and X-ray observations. We characterize the early UV-optical color, provide empirical host-extinction corrections, and show that thet> 2 day UV-optical colors and the blackbody evolution of the sample are consistent with shock cooling (SC) regardless of the presence of “flash ionization” features. We present a framework for fitting SC models that can reproduce the parameters of a set of multigroup simulations up to 20% in radius and velocity. Observations of 15 SNe II are well fit by models with breakout radii <10¹⁴cm. Eighteen SNe are typically more luminous, with observations att≥ 1 day that are better fit by a model with a large >10¹⁴cm breakout radius. However, these fits predict an early rise during the first day that is too slow. We suggest that these large-breakout events are explosions of stars with an inflated envelope or with confined circumstellar material (CSM). Using the X-ray data, we derive constraints on the extended (∼10¹⁵cm) CSM density independent of spectral modeling and find that most SN II progenitors lose $\dot{M}<{10}^{-4}{M}_{\odot }{\mathrm{yr}}^{-1}$up to a few years before explosion. We show that the overall observed breakout radius distribution is skewed to higher radii due to a luminosity bias. We argue that the ${66}_{-22}^{+11}\%$of red supergiants (RSGs) explode as SNe II with breakout radii consistent with the observed distribution of RSGs, with a tail extending to large radii, likely due to the presence of CSM. 

Abstract We present the discovery and analysis of SN 2022oqm, a Type Ic supernova (SN) detected <1 day after the explosion. The SN rises to a blue and short-lived (2 days) initial peak. Early-time spectral observations of SN 2022oqm show a hot (40,000 K) continuum with high ionization C and O absorption features at velocities of 4000 km s⁻¹, while its photospheric radius expands at 20,000 km s⁻¹, indicating a pre-existing distribution of expanding C/O material. After ∼2.5 days, both the spectrum and light curves evolve into those of a typical SN Ic, with line velocities of ∼10,000 km s⁻¹, in agreement with the evolution of the photospheric radius. The optical light curves reach a second peak att≈ 15 days. Byt= 60 days, the spectrum of SN 2022oqm becomes nearly nebular, displaying strong Caiiand [Caii] emission with no detectable [Oi], marking this event as Ca-rich. The early behavior can be explained by 10⁻³M_⊙of optically thin circumstellar material (CSM) surrounding either (1) a massive compact progenitor such as a Wolf–Rayet star, (2) a massive stripped progenitor with an extended envelope, or (3) a binary system with a white dwarf. We propose that the early-time light curve is powered by both the interaction of the ejecta with the optically thin CSM and shock cooling (in the massive star scenario). The observations can be explained by CSM that is optically thick to X-ray photons, is optically thick in the lines as seen in the spectra, and is optically thin to visible-light continuum photons that come either from downscattered X-rays or from the shock-heated ejecta. Calculations show that this scenario is self-consistent. 

Abstract We study a magnitude-limited sample of 36 broad-lined type Ic supernovae (SNe Ic-BL) from the Zwicky Transient Facility Bright Transient Survey (detected between 2018 March and 2021 August), which is the largest systematic study of SNe Ic-BL done in literature thus far. We present the light curves (LCs) for each of the SNe and analyze the shape of the LCs to derive empirical parameters, along with the explosion epochs for every event. The sample has an average absolute peak magnitude in therband of ${\overline{\mathit{M}}}_{\mathrm{r},\max }=-18.51\pm 0.15$mag. Using spectra obtained around peak light, we compute expansion velocities from the Feii5169 Å line for each event with high enough signal-to-noise ratio spectra, and find an average value of $\overline{v_{\mathrm{ph}}}=16,100\pm 1100$km s⁻¹. We also compute bolometric LCs, study the blackbody temperature and radii evolution over time, and derive the explosion properties of the SNe. The explosion properties of the sample have average values of ${\overline{\mathit{M}}}_{\mathrm{Ni}}={0.37}_{-0.06}^{+0.08}{\mathit{M}}_{\odot }$, ${\overline{\mathit{M}}}_{\mathrm{ej}}={2.45}_{-0.41}^{+0.47}{\mathit{M}}_{\odot }$, and ${\overline{\mathit{E}}}_{\mathrm{K}}=\left({4.02}_{-1.00}^{+1.37}\right)\times {10}^{51}$erg. Thirteen events have radio observations from the Very Large Array, with eight detections and five non-detections. We find that the populations that have radio detections and radio non-detections are indistinct from one another with respect to their optically inferred explosion properties, and there are no statistically significant correlations present between the events’ radio luminosities and optically inferred explosion properties. This provides evidence that the explosion properties derived from optical data alone cannot give inferences about the radio properties of SNe Ic-BL and likely their relativistic jet formation mechanisms. 

Abstract Luminous red novae (LRNe) are transients characterized by low luminosities and expansion velocities, and they are associated with mergers or common-envelope ejections in stellar binaries. Intermediate-luminosity red transients (ILRTs) are an observationally similar class with unknown origins, but they are generally believed to be either electron-capture supernovae in super-asymptotic giant branch stars or outbursts in dusty luminous blue variables (LBVs). In this paper, we present a systematic sample of eight LRNe and eight ILRTs detected as part of the Census of the Local Universe (CLU) experiment on the Zwicky Transient Facility (ZTF). The CLU experiment spectroscopically classifies ZTF transients associated with nearby (<150 Mpc) galaxies, achieving 80% completeness form_r< 20 mag. Using the ZTF-CLU sample, we derive the first systematic LRNe volumetric rate of ${7.8}_{-3.7}^{+6.5}\times {10}^{-5}$Mpc⁻³yr⁻¹in the luminosity range −16 ≤M_r≤ −11 mag. We find that, in this luminosity range, the LRN rate scales as $\mathit{dN}/\mathit{dL}\propto L^{-2.5\pm 0.3}$—significantly steeper than the previously derived scaling ofL^−1.4±0.3for lower-luminosity LRNe (M_V≥ −10 mag). The steeper power law for LRNe at high luminosities is consistent with the massive merger rates predicted by binary population synthesis models. We find that the rates of the brightest LRNe (M_r≤ −13 mag) are consistent with a significant fraction of them being progenitors of double compact objects that merge within a Hubble time. For ILRTs, we derive a volumetric rate of ${2.6}_{-1.4}^{+1.8}\times {10}^{-6}$Mpc⁻³yr⁻¹forM_r≤ −13.5 mag, which scales as $\mathit{dN}/\mathit{dL}\propto L^{-2.5\pm 0.5}$. This rate is ∼1%–5% of the local core-collapse supernova rate and is consistent with theoretical ECSN rate estimates. 

Abstract Among the supernovae (SNe) that show strong interaction with a circumstellar medium (CSM), there is a rare subclass of Type Ia supernovae, SNe Ia-CSM, which show strong narrow hydrogen emission lines much like SNe IIn but on top of a diluted Type Ia spectrum. The only previous systematic study of this class identified 16 SNe Ia-CSM, eight historic and eight from the Palomar Transient Factory (PTF). Now using the successor survey to PTF, the Zwicky Transient Facility (ZTF), we have classified 12 additional SNe Ia-CSM through the systematic Bright Transient Survey (BTS). Consistent with previous studies, we find these SNe to have slowly evolving optical light curves with peak absolute magnitudes between −19.1 and −21, spectra having weak Hβand large Balmer decrements of ∼7. Out of the 10 SNe from our sample observed by NEOWISE, nine have 3σdetections, with some SNe showing a reduction in the red wing of Hα, indicative of newly formed dust. We do not find our SN Ia-CSM sample to have a significantly different distribution of equivalent widths of Heiλ5876 than SNe IIn as observed in Silverman et al. The hosts tend to be late-type galaxies with recent star formation. We derive a rate estimate of ${29}_{-21}^{+27}$Gpc⁻³yr⁻¹for SNe Ia-CSM, which is ∼0.02%–0.2% of the SN Ia rate. We also identify six ambiguous SNe IIn/Ia-CSM in the BTS sample and including them gives an upper limit rate of 0.07%–0.8%. This work nearly doubles the sample of well-studied Ia-CSM objects in Silverman et al., increasing the total number to 28. 

Abstract We present a search for extragalactic fast blue optical transients (FBOTs) during Phase I of the Zwicky Transient Facility (ZTF). We identify 38 candidates with durations above half-maximum light 1 day <t_1/2< 12 days, of which 28 have blue (g−r≲ −0.2 mag) colors at peak light. Of the 38 transients (28 FBOTs), 19 (13) can be spectroscopically classified as core-collapse supernovae (SNe): 11 (8) H- or He-rich (Type II/IIb/Ib) SNe, 6 (4) interacting (Type IIn/Ibn) SNe, and 2 (1) H&He-poor (Type Ic/Ic-BL) SNe. Two FBOTs (published previously) had predominantly featureless spectra and luminous radio emission: AT2018lug (The Koala) and AT2020xnd (The Camel). Seven (five) did not have a definitive classification: AT 2020bdh showed tentative broad Hαin emission, and AT 2020bot showed unidentified broad features and was 10 kpc offset from the center of an early-type galaxy. Ten (eight) have no spectroscopic observations or redshift measurements. We present multiwavelength (radio, millimeter, and/or X-ray) observations for five FBOTs (three Type Ibn, one Type IIn/Ibn, one Type IIb). Additionally, we search radio-survey (VLA and ASKAP) data to set limits on the presence of radio emission for 24 of the transients. All X-ray and radio observations resulted in nondetections; we rule out AT2018cow-like X-ray and radio behavior for five FBOTs and more luminous emission (such as that seen in the Camel) for four additional FBOTs. We conclude that exotic transients similar to AT2018cow, the Koala, and the Camel represent a rare subset of FBOTs and use ZTF’s SN classification experiments to measure the rate to be at most 0.1% of the local core-collapse SN rate. 

We present 42 rapidly evolving (time spent above half-maximum brightness t1/2<12d) extragalactic transients from Phase I of the Zwicky Transient Facility (ZTF), of which 22 have spectroscopic classifications. This is one of the largest systematically selected samples of day-timescale transients, and the first with spectroscopic classifications. Most can be classified as core-collapse supernovae (SNe), and we identify several predominant subtypes: (1) subluminous Type IIb or Type Ib SNe; (2) luminous Type Ibn or hybrid IIn/Ibn SNe; and (3) radio-loud, short-duration luminous events similar to AT2018cow. We conclude that rates quoted in the literature for rapidly evolving extragalactic transients are dominated by the subluminous events (mostly Type IIb SNe). From our spectroscopic classifications and radio, X-ray, and millimeter-band upper limits, we are motivated to consider the AT2018cow-like objects a distinct class, and use ZTF's systematic classification experiments to calculate that their rate does not exceed 0.1% of the local core-collapse SN rate, in agreement with previous work. By contrast, most other events are simply the extreme of a continuum of established SN types extending to ordinary timescales. The light curves of our objects are very similar to those of unclassified events in the literature, illustrating how spectroscopically classified samples of low-redshift objects in shallow surveys like ZTF can be used to photometrically classify larger numbers of events at higher redshift.