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We present photometric and spectroscopic observations of the Type IIn supernova SN 2019zrk (also known as ZTF20aacbyec). The SN shows a $\gtrsim$ 100 day precursor, with a slow rise, followed by a rapid rise to M $\sim -19.2$ in the $r$ and $g$ bands. The post-peak light-curve decline is well fit with an exponential decay with a timescale of $\sim 39$ days, but it shows prominent undulations, with an amplitude of $\sim 1$ mag. Both the light curve and spectra are dominated by an interaction with a dense circumstellar medium (CSM), probably from previous mass ejections. The spectra evolve from a scattering-dominated Type IIn spectrum to a spectrum with strong P-Cygni absorptions. The expansion velocity is high, $\sim 16,000$ km s$^{-1}$, even in the last spectra. The last spectrum $\sim 110$ days after the main eruption reveals no evidence for advanced nucleosynthesis. From analysis of the spectra and light curves, we estimate the mass-loss rate to be $\sim 4 \times 10^{-2}$ M$_\odot$ yr$^{-1}$ for a CSM velocity of 100 km s$^{-1}$, and a CSM mass of $\gtrsim 1$ M$_\odot$. We find strong similarities for both the precursor, general light curve, and spectral evolution with SN 2009ip and similar SNe, although SN 2019zrk displays a brighter peak magnitude. Different scenarios for the nature of the 09ip-class of SNe, based on pulsational pair instability eruptions, wave heating, and mergers, are discussed. }, Comment: 18 pages, 12 figures. Astronomy & Astrophysics, in press

Spectroscopic detection of narrow emission lines traces the presence of circumstellar mass distributions around massive stars exploding as core-collapse supernovae. Transient emission lines disappearing shortly after the supernova explosion suggest that the material spatial extent is compact and implies an increased mass loss shortly prior to explosion. Here, we present a systematic survey for such transient emission lines (Flash Spectroscopy) among Type II supernovae detected in the first year of the Zwicky Transient Facility survey. We find that at least six out of ten events for which a spectrum was obtained within two days of the estimated explosion time show evidence for such transient flash lines. Our measured flash event fraction (>30% at 95% confidence level) indicates that elevated mass loss is a common process occurring in massive stars that are about to explode as supernovae.

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 $M10^{12}$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., Accepted to ApJ. 39 pages, 17 figures. Comments welcome

We present a survey of the early evolution of 12 Type IIn supernovae (SNe IIn) in the Ultra-Violet (UV) and visible light. We use this survey to constrain the geometry of the circumstellar material (CSM) surrounding SN IIn explosions, which may shed light on their progenitor diversity. In order to distinguish between aspherical and spherical circumstellar material (CSM), we estimate the blackbody radius temporal evolution of the SNe IIn of our sample, following the method introduced by Soumagnac et al. We find that higher luminosity objects tend to show evidence for aspherical CSM. Depending on whether this correlation is due to physical reasons or to some selection bias, we derive a lower limit between 35% and 66% on the fraction of SNe IIn showing evidence for aspherical CSM. This result suggests that asphericity of the CSM surrounding SNe IIn is common - consistent with data from resolved images of stars undergoing considerable mass loss. It should be taken into account for more realistic modelling of these events., Comment: Submitted to ApJ. Comments are welcome

Author(s): Strotjohann, NL; Ofek, EO; Gal-Yam, A; Bruch, R; Schulze, S; Shaviv, N; Sollerman, J; Filippenko, AV; Yaron, O; Fremling, C; Nordin, J; Kool, EC; Perley, DA; Ho, AYQ; Yang, Y; Yao, Y; Soumagnac, MT; Graham, ML; Barbarino, C; Tartaglia, L; De, K; Goldstein, DA; Cook, DO; Brink, TG; Taggart, K; Yan, L; Lunnan, R; Kasliwal, M; Kulkarni, SR; Nugent, PE; Masci, FJ; Rosnet, P; Adams, SM; Andreoni, I; Bagdasaryan, A; Bellm, EC; Burdge, K; Duev, DA; Dugas, A; Frederick, S; Goldwasser, S; Hankins, M; Irani, I; Karambelkar, V; Kupfer, T; Liang, J; Neill, JD; Porter, M; Riddle, RL; Sharma, Y; Short, P; Taddia, F; Tzanidakis, A; Van Roestel, J; Walters, R; Zhuang, Z | Abstract: Interaction-powered supernovae (SNe) explode within an optically thick circumstellar medium (CSM) that could be ejected during eruptive events. To identify and characterize such pre-explosion outbursts, we produce forcedphotometry light curves for 196 interacting SNe, mostly of Type IIn, detected by the Zwicky Transient Facility between early 2018 and 2020 June. Extensive tests demonstrate that we only expect a few false detections among the 70,000 analyzed pre-explosion images after applying quality cuts and bias corrections. We detect precursor eruptions prior to 18 Type IIn SNe and prior to the Type Ibn SN 2019uo. Precursors become brighter and more frequent in the last months before the SN and month-long outbursts brighter than magnitude -13 occur prior to 25% (5-69%, 95% confidence range) of all Type IIn SNe within the final three months before the explosion. With radiative energies of up to 1049erg, precursors could eject ~1M⊙of material. Nevertheless, SNe with detected precursors are not significantly more luminous than other SNe IIn, and the characteristic narrow hydrogen lines in their spectra typically originate from earlier, undetected mass-loss events. The long precursor durations require ongoing energy injection, and they could, for example, be powered by interaction or by a continuum-driven wind. Instabilities during the neon- and oxygen-burning phases are predicted to launch precursors in the final years to months before the explosion; however, the brightest precursor is 100 times more energetic than anticipated.

Author(s): Schulze, S; Yaron, O; Sollerman, J; Leloudas, G; Gal, A; Wright, AH; Lunnan, R; Gal-Yam, A; Ofek, EO; Perley, DA; Filippenko, AV; Kasliwal, MM; Kulkarni, SR; Neill, JD; Nugent, PE; Quimby, RM; Sullivan, M; Strotjohann, NL; Arcavi, I; Ben-Ami, S; Bianco, F; Bloom, JS; De, K; Fraser, M; Fremling, CU; Horesh, A; Johansson, J; Kelly, PL; Kneževic, N; Kneževic, S; Maguire, K; Nyholm, A; Papadogiannakis, S; Petrushevska, T; Rubin, A; Yan, L; Yang, Y; Adams, SM; Bufano, F; Clubb, KI; Foley, RJ; Green, Y; Harmanen, J; Ho, AYQ; Hook, IM; Hosseinzadeh, G; Howell, DA; Kong, AKH; Kotak, R; Matheson, T; McCully, C; Milisavljevic, D; Pan, YC; Poznanski, D; Shivvers, I; Van Velzen, S; Verbeek, KK | Abstract: Several thousand core-collapse supernovae (CCSNe) of different flavors have been discovered so far. However, identifying their progenitors has remained an outstanding open question in astrophysics. Studies of SN host galaxies have proven to be powerful in providing constraints on the progenitor populations. In this paper, we present all CCSNe detected between 2009 and 2017 by the Palomar Transient Factory. This sample includes 888 SNe of 12 distinct classes out to redshift z ≈ 1. We present the photometric properties of their host galaxies from the far-ultraviolet to the mid-infrared and model the host-galaxy spectral energy distributions to derive physical properties. The galaxy mass function of Type Ic, Ib, IIb, II, and IIn SNe ranges from 105 to 1011.5 M o˙, probing the entire mass range of star-forming galaxies down to the least-massive star-forming galaxies known. Moreover, the galaxy mass distributions are consistent with models of star-formation-weighted mass functions. Regular CCSNe are hence direct tracers of star formation. Small but notable differences exist between some of the SN classes. Type Ib/c SNe prefer galaxies with slightly higher masses (i.e., higher metallicities) and star formation rates than Type IIb and II SNe. These differences are less pronounced than previously thought. H-poor superluminous supernovae (SLSNe) and SNe Ic-BL are scarce in galaxies above 1010 M o˙. Their progenitors require environments with metallicities of l 0.4 and l 1 solar, respectively. In addition, the hosts of H-poor SLSNe are dominated by a younger stellar population than all other classes of CCSNe. Our findings corroborate the notion that low metallicity and young age play an important role in the formation of SLSN progenitors.

Motivated by the identification of the blazar TXS 0506+056 as the first promising high-energy neutrino counterpart candidate, we search for additional neutrino blazars candidates among the Fermi-LAT detected blazars. We investigate the multi-wavelength behavior from radio to GeV gamma rays of blazars found to be in spatial coincidence with single high-energy neutrinos and lower-energy neutrino flare candidates. In addition, we compare the average gamma-ray emission of the potential neutrino-emitting sources to the entire sample of gamma-ray blazars. We find that neutrino-emitting blazar candidates are statistically compatible with both hypothesis of a linear correlation and of no correlation between neutrino and gamma-ray energy flux., accepted for publication by ApJ

We describe a consequence of the Eddington bias which occurs when a single astrophysical neutrino event is used to infer the neutrino flux of the source. A trial factor is introduced by the potentially large number of similar sources that remain undetected; if this factor is not accounted for the luminosity of the observed source can be overestimated by several orders of magnitude. Based on the resulting unrealistically high neutrino fluxes, associations between high-energy neutrinos and potential counterparts or emission scenarios were rejected in the past. Correcting for the bias might justify a reevaluation of these cases.

The progenitors of some supernovae (SNe) exhibit outbursts with super-Eddington luminosities prior to their final explosions. This behavior is common among Type IIn SNe, but the driving mechanisms of these precursors are not yet well understood. SNHunt 275 was announced as a possible new SN during May 2015. Here we report on pre-explosion observations of the location of this event by the Palomar Transient Factory (PTF) and report the detection of a precursor about 500 days prior to the 2015 May activity (PTF 13efv). The observed velocities in the 2015 transient and its 2013 precursor absorption spectra are low (1000-2000 km/s), so it is not clear yet if the recent activity indeed marks the final disruption of the progenitor. Regardless of the nature of this event, we use the PTF photometric and spectral observations, as well as Swift-UVOT observations, to constrain the efficiency of the radiated energy relative to the total kinetic energy of the precursor. We find that, using an order-of-magnitude estimate and under the assumption of spherical symmetry, the ratio of the radiated energy to the kinetic energy is in the range of 0.04 to 3400., ApJ in press, 10 pages

The progenitor stars of several Type IIb supernovae (SNe) show indications for extended hydrogen envelopes. These envelopes might be the outcome of luminous energetic pre-explosion events, so-called precursor eruptions. We use the Palomar Transient Factory (PTF) pre-explosion observations of a sample of 27 nearby Type IIb SNe to look for such precursors during the final years prior to the SN explosion. No precursors are found when combining the observations in 15-day bins, and we calculate the absolute-magnitude-dependent upper limit on the precursor rate. At the 90% confidence level, Type IIb SNe have on average $, 16 pages, 10 figures

We present a public catalog of transients from the Zwicky Transient Facility (ZTF) Bright Transient Survey (BTS), a magnitude-limited (m -16 mag), 10% in red-sequence galaxies, and 1% in massive ellipticals. We find no significant difference in the luminosity or color distributions between the host galaxies of Type II and Type Ib/c supernovae, suggesting that line-driven wind stripping does not play a major role in the loss of the hydrogen envelope from their progenitors. Future large-scale classification efforts with ZTF and other wide-area surveys will provide high-quality measurements of the rates, properties, and environments of all known types of optical transients and limits on the existence of theoretically predicted but as of yet unobserved explosions., Accepted to ApJ. Live BTS statistics are available online at https://sites.astro.caltech.edu/ztf/bts/bts.php and an interactive catalog of our sample is available at https://sites.astro.caltech.edu/ztf/bts/explorer.php

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

We present observations of SN 2020faa. This Type II supernova displays a luminous light curve that started to rebrighten from an initial decline. We investigate this in relation to the famous supernova iPTF14hls, which received a lot of attention and multiple interpretations in the literature, however whose nature and source of energy still remains unknown. We demonstrate the great similarity between SN 2020faa and iPTF14hls during the first 6 months, and use this comparison both to forecast the evolution of SN 2020faa and to reflect on the less well observed early evolution of iPTF14hls. We present and analyse our observational data, consisting mainly of optical light curves from the Zwicky Transient Facility in the gri bands as well as a sequence of optical spectra. We construct colour curves, a bolometric light curve, compare ejecta-velocity and Black-body radius evolutions for the two supernovae, as well as for more typical Type II supernovae. The light curves show a great similarity with those of iPTF14hls over the first 6 months, in luminosity, timescale and colours. Also the spectral evolution of SN 2020faa is that of a Type II supernova, although it probes earlier epochs than those available for iPTF14hls. The similar light curve behaviour is suggestive of SN 2020faa being a new iPTF14hls. We present these observations now to advocate follow-up observations, since most of the more striking evolution of supernova iPTF14hls came later, with light curve undulations and a spectacular longevity. On the other hand, for SN 2020faa we have better constraints on the explosion epoch than we had for iPTF14hls, and we have been able to spectroscopically monitor it from earlier phases than was done for the more famous sibling., Comment: 14 pages, 12 figures, submitted to A&A