Supernova siblings and their parent galaxies in the Zwicky Transient Facility Bright Transient Survey

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 (which aims for spectroscopic completeness for all transients which peak brighter than r < 18.5 mag) we present 10 SN siblings in five parent galaxies. For each of these families, we analyse 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

Helium-rich Superluminous Supernovae from the Zwicky Transient Facility

Helium is expected to be present in the massive ejecta of some hydrogen-poor superluminous supernovae (SLSN-I). However, until now only one event has been identified with He features in its photospheric spectra (PTF10hgi). 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 μm. Using the optical spectra of PTF10hgi and SN2019hge as templates, we examined 70 other SLSNe-I discovered by Zwicky Transient Facility in the first two years of operation and found five additional SLSNe-I with distinct He-features. The excitation of He i atoms in normal core-collapse supernovae requires nonthermal radiation, as proposed by previous studies. These He-rich events cannot be explained by the traditional 56Ni mixing model because of their blue spectra, high peak luminosities, and long rise timescales. Magnetar models offer a possible solution since pulsar winds naturally generate high-energy particles, potential sources of nonthermal excitation. An alternative model is the interaction between the ejecta and dense H-poor circumstellar material, which may be supported by observed undulations in the light curves. These six SLSNe-Ib have relatively low-peak luminosities (rest frame Mg = −20.06 ± 0.16)

Initial Characterization of Active Transitioning Centaur, P/2019 LD2 (ATLAS), Using Hubble, Spitzer, ZTF, Keck, Apache Point Observatory, and GROWTH Visible and Infrared Imaging and Spectroscopy

We present visible and mid-infrared imagery and photometry of temporary Jovian co-orbital comet P/2019 LD2 taken with Hubble Space Telescope/Wide Field Camera 3 (HST/WFC3), Spitzer Space Telescope/Infrared Array Camera (Spitzer/IRAC), and the GROWTH telescope network, visible spectroscopy from Keck/Low-Resolution Imaging Spectrometer (LRIS), and archival Zwicky Transient Facility observations taken between 2019 April and 2020 August. Our observations indicate that the nucleus of LD2 has a radius between 0.2 and 1.8 km assuming a 0.08 albedo and a coma dominated by ∼100 μm-scale dust ejected at ∼1 m s−1 speeds with a ∼1′ jet pointing in the southwest direction. LD2 experienced a total dust mass loss of ∼108 kg at a loss rate of ∼6 kg s−1 with Afρ/cross section varying between ∼85 cm/125 km2 and ∼200 cm/310 km2 from 2019 April 9 to 2019 November 8. If the increase in Afρ/cross section remained constant, it implies LD2's activity began ∼2018 November when within 4.8 au of the Sun, implying the onset of H2O sublimation. We measure CO/CO2 gas production of ≲1027 mol s−1/≲1026 mol s−1 from our 4.5 μm Spitzer observations; g–r = 0.59 ± 0.03, r–i = 0.18 ± 0.05, and i–z = 0.01 ± 0.07 from GROWTH observations; and H2O gas production of ≲80 kg s−1 scaling from our estimated C2 production of ${Q}_{{C}_{2}}\lesssim 7.5\times {10}^{24}$ mol s−1 from Keck/LRIS spectroscopy. We determine that the long-term orbit of LD2 is similar to Jupiter-family comets having close encounters with Jupiter within ∼0.5 Hill radius in the last ∼3 y and within 0.8 Hill radius in ∼9 y. Additionally, 78.8% of our orbital clones are ejected from the solar system within 1 × 106 yr, having a dynamical half-life of 3.4 × 105 yr

Time-series and Phase-curve Photometry of the Episodically Active Asteroid (6478) Gault in a Quiescent State Using APO, GROWTH, P200, and ZTF

We observed the episodically active asteroid (6478) Gault in 2020 with multiple telescopes in Asia and North America and found that it is no longer active after its recent outbursts at the end of 2018 and the start of 2019. The inactivity during this apparition allowed us to measure the absolute magnitude of Gault of Hr = 14.63 ± 0.02, Gr = 0.21 ± 0.02 from our secular phase-curve observations. In addition, we were able to constrain Gault's rotation period using time-series photometric lightcurves taken over 17 hr on multiple days in 2020 August, September, and October. The photometric lightcurves have a repeating ≲0.05 mag feature suggesting that (6478) Gault has a rotation period of ∼2.5 hr and may have a semispherical or top-like shape, much like the near-Earth asteroids Ryugu and Bennu. The rotation period of ∼2.5 hr is near the expected critical rotation period for an asteroid with the physical properties of (6478) Gault, suggesting that its activity observed over multiple epochs is due to surface mass shedding from its fast rotation spin-up by the Yarkovsky–O'Keefe–Radzievskii–Paddack effect

Role of amorphous and aggregate phases on field-induced exciton dissociation in a conjugated polymer

We have applied electric field assisted pump-probe spectroscopy in order to unravel the interplay of amorphous and aggregate phases on the polaron-pair photogeneration process in a conjugated porphyrin polymer. We find that excitons photogenerated in both phases are precursors for polaron pairs with different yields. Kinetic modeling indicates a substantially larger barrier for exciton dissociation in aggregates compared to amorphous areas. The majority of polaron pairs are however formed in aggregate phases due to efficient energy transfer from the amorphous phase. Based on the change in the Stark shift associated with the photogenerated polaron density, we provide a picture of the motion of polaron pairs under the external electric field. © 2013 American Physical Society

Interaction of genetic and exposure factors in the prevalence of berylliosis

Prevalence of berylliosis, a lung disorder driven by the activation of beryllium-specific T cells, is associated with a major histocompatibility complex (MHC) class II marker (HLA-DPB1Glu69) and with the type of industrial exposure. We evaluated the interaction between marker and exposure in a beryllium-exposed population in which the prevalence of berylliosis was associated with machining beryllium. The presence of the marker was associated with higher prevalence (HLA-DPB1Glu69-positive machinists 25%; HLA-DPB1Glu69-negative machinists 3.2%, P = 0.05) and predicted berylliosis independent of machining history (odds ratios 11.8 and 10.1). The study shows that in berylliosis the carrier status of a genetic susceptibility factor adds to the effect of process-related risk factors

Photoinduced on-chain charge-separation and ultrafast recombination in a sugar-coated insulated molecular wire

Transient absorption three-beam pump-push-probe experiments demonstrate that cyclodextrin-encapsulation of conjugated polymer chains prevents interchain effects, such as energy migration and charge hopping. In the unencapsulated polymer, transient population of high-lying singlet states leads to interchain ionization, generating long-lived charge-separated species. Supramolecular encapsulation prevents this process; with high-lying singlets undergoing on-chain ionization, followed by very rapid charge recombination. Threading is an efficient way to control charge recombination and to obtain a material suitable for photonic applications, where the push effect can be implemented for all-optical ultrafast switching. © 2009 The American Physical Society