RINGO3 polarimetry of very young ZTF supernovae

The early phases of the observed evolution of the supernovae (SNe) are expected to be dominated by the shock breakout and ‘flash’ ionization of the surrounding circumstellar medium. This material arises from the last stages of the evolution of the progenitor, such that photometry and spectroscopy of SNe at early times can place vital constraints on the latest and fastest evolutionary phases leading up to stellar death. These signatures are erased by the expansion of the ejecta within ∼5 d after explosion. Here we present the earliest constraints, to date, on the polarization of 10 transients discovered by the Zwicky Transient Facility (ZTF), between 2018 June and 2019 August. Rapid polarimetric follow-up was conducted using the Liverpool Telescope RINGO3 instrument, including three SNe observed within 0.65 (assuming an oblate spheroidal configuration). We also present polarimetric observations of the Type I Superluminous SN 2018bsz and Type II SN 2018hna, observed around and after maximum light

RINGO3 polarimetry of very young ZTF supernovae

The early phases of the observed evolution of the supernovae (SNe) are expected to be dominated by the shock breakout and ‘flash’ ionization of the surrounding circumstellar medium. This material arises from the last stages of the evolution of the progenitor, such that photometry and spectroscopy of SNe at early times can place vital constraints on the latest and fastest evolutionary phases leading up to stellar death. These signatures are erased by the expansion of the ejecta within ∼5 d after explosion. Here we present the earliest constraints, to date, on the polarization of 10 transients discovered by the Zwicky Transient Facility (ZTF), between 2018 June and 2019 August. Rapid polarimetric follow-up was conducted using the Liverpool Telescope RINGO3 instrument, including three SNe observed within 0.65 (assuming an oblate spheroidal configuration). We also present polarimetric observations of the Type I Superluminous SN 2018bsz and Type II SN 2018hna, observed around and after maximum light

SN2020cpg: an energetic link between Type IIb and Ib supernovae

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

SN 2020cpg: an energetic link between Type IIb and Ib supernovae

S.J. Prentice is supported by H2020 ERC grant no. 758638. J.J. Teffs is funded by the consolidated STFC grant no. R27610. This paper is based in part on observations collected at the European Southern Observatory (ESO) under ESO programme 1103.D-0328(J). T.W. Chen acknowledges the European Union Funding under Marie Sklodowska-Curie grant no. H2020-MSCA-IF-2018-842471. L. Galbanywas funded by the European Union'sHorizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant no. 839090. This work has been partially supported by the Spanish grant no. PGC2018-095317-B-C21 within the European Funds for Regional Development (FEDER). M. Gromadzki is supported by the Polish National Science Center (NCN) MAESTRO grant no. 2014/14/A/ST9/00121. T. M uller-Bravo was funded by the CONICYT PFCHA/DOCTORADOBECAS CHILE/2017-72180113. M. Nicholl is supported by a Royal Astronomical Society Research Fellowship. Thiswork makes use of observations obtained by the Las Cumbres Observatory global telescope network. The LCO team is supported by NSF grant nos AST-1911225 and AST-1911151. Based in part on observations made with the Liverpool Telescope operated on the island of La Palma by Liverpool John Moores University in the Spanish Observatorio del Roque de los Muchachos of the Institutode Astrofisica de Canarias with financial support from the UK Science and Technology Facilities Council. The data presented here were obtained in part with ALFOSC, which is provided by the Instituto de As-trofisica de Andalucia (IAA) under a joint agreement with the University of Copenhagen and NOTSA, with observation having been made with the Nordic Optical Telescope, operated at the Observatorio del Roque de los Muchachos, La Palma, Spain, of the Instituto de Astrofisica de Canarias. This work has made use of data from the Asteroid Terrestrial-impact Last Alert System (ATLAS) project. ATLAS is primarily funded to search for near earth asteroids through NASA grant nos NN12AR55G, 80NSSC18K0284, and 80NSSC18K1575; by-products of the NEO search include images and catalogues from the survey area. The ATLAS science products have been made possible through the contributions of the University of Hawaii Institute for Astronomy, the Queen's University Belfast, and the Space Telescope Science Institute. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, as part of ePESSTO+(the advanced Public ESO Spectroscopic Survey for Transient Objects Survey). ePESSTO + observations were obtained under ESO programme ID 1103.D-0328 (PI: Inserra). LCO data have been obtained via OPTICON proposals (IDs: SUPA2020B-002 SUPA2020A-001 OPTICON 20A/015 and OPTICON 20B/003). The OPTICON project has received funding from the European Union's Horizon 2020 research and innovation programme under grant no. 730890.Stripped-envelope supernovae (SE-SNe) show a wide variety of photometric and spectroscopic properties. This is due to the different potential formation channels and the stripping mechanism that allows for a large diversity within the progenitors outer envelope compositions. Here, the photometric and spectroscopic observations of SN 2020cpg covering ∼130 d from the explosion date are presented. SN 2020cpg (z = 0.037) is a bright SE-SNe with the B-band peaking at MB = −17.75 ± 0.39 mag and a maximum pseudo-bolometric luminosity of Lmax = 6.03 ± 0.01 × 1042 erg s−1. Spectroscopically, SN2020cpg displays a weak high- and low-velocity H α feature during the photospheric phase of its evolution, suggesting that it contained a detached hydrogen envelope prior to explosion. From comparisons with spectral models, the mass of hydrogen within the outer envelope was constrained to be ∼0.1 M . From the pseudo-bolometric light curve of SN 2020cpg a 56Ni mass of MNi ∼ 0.27 ± 0.08M was determined using an Arnett-like model. The ejecta mass and kinetic energy of SN 2020cpg were determined using an alternative method that compares the light curve of SN 2020cpg and several modelled SE-SNe, resulting in an ejecta mass of Mejc ∼ 5.5 ± 2.0 M and a kinetic energy of EK ∼ 9.0 ± 3.0 × 1051 erg. The ejected mass indicates a progenitor mass of 18−25 M . The use of the comparative light curve method provides an alternative process to the commonly used Arnett-like model to determine the physical properties of SE-SNe.H2020 ERC 758638UK Research & Innovation (UKRI)Science & Technology Facilities Council (STFC) R27610European Southern Observatory (ESO) 1103.D-0328(J)European Commission H2020-MSCA-IF-2018-842471 839090 730890 PGC2018-095317-B-C21Polish National Science Center (NCN) MAESTRO 2014/14/A/ST9/00121CONICYT PFCHA/DOCTORADOBECAS CHILE/2017-72180113Royal Astronomical Society Research FellowshipNational Science Foundation (NSF) AST-1911225 AST-1911151UK Research & Innovation (UKRI)Science & Technology Facilities Council (STFC)National Aeronautics & Space Administration (NASA) NN12AR55G 80NSSC18K0284 80NSSC18K1575ESO programme 1103.D-032

Accuracy of environmental tracers and consequence for determining the Type Ia Supernovae magnitude step

International audienceType Ia Supernovae (SNe Ia) are standardizable candles that allow us to measure the recent expansion rate of the Universe. Due to uncertainties in progenitor physics, potential astrophysical dependencies may bias cosmological measurements if not properly accounted for. The dependency of the intrinsic luminosity of SNe Ia with their host-galaxy environment is often used to standardize SNe Ia luminosity and is commonly parameterized as a step function. This functional form implicitly assumes two-populations of SNe Ia. In the literature, multiple environmental indicators have been considered, finding different, sometimes incompatible, step function amplitudes. We compare these indicators in the context of a two-populations model, based on their ability to distinguish the two populations. We show that local H$\alpha$-based specific star formation rate (lsSFR) and global stellar mass are better tracers than, for instance, host galaxy morphology. We show that tracer accuracy can explain the discrepancy between the observed SNe Ia step amplitudes found in the literature. Using lsSFR or global mass to distinguish the two populations can explain all other observations, though lsSFR is favoured. As lsSFR is strongly connected to age, our results favour a prompt and delayed population model. In any case, there exists two populations that differ in standardized magnitude by at least $0.121\pm0.010\,\mathrm{mag}$