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1.
  • Ahumada, Tomas, et al. (author)
  • In Search of Short Gamma-Ray Burst Optical Counterparts with the Zwicky Transient Facility
  • 2022
  • In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 932:1
  • Journal article (peer-reviewed)abstract
    • The Fermi Gamma-ray Burst Monitor (GBM) triggers on-board in response to ∼40 short gamma-ray bursts (SGRBs) per year; however, their large localization regions have made the search for optical counterparts a challenging endeavour. We have developed and executed an extensive program with the wide field of view of the Zwicky Transient Facility (ZTF) camera, mounted on the Palomar 48 inch Oschin telescope (P48), to perform target-of-opportunity (ToO) observations on 10 Fermi-GBM SGRBs during 2018 and 2020–2021. Bridging the large sky areas with small field-of-view optical telescopes in order to track the evolution of potential candidates, we look for the elusive SGRB afterglows and kilonovae (KNe) associated with these high-energy events. No counterpart has yet been found, even though more than 10 ground-based telescopes, part of the Global Relay of Observatories Watching Transients Happen (GROWTH) network, have taken part in these efforts. The candidate selection procedure and the follow-up strategy have shown that ZTF is an efficient instrument for searching for poorly localized SGRBs, retrieving a reasonable number of candidates to follow up and showing promising capabilities as the community approaches the multi-messenger era. Based on the median limiting magnitude of ZTF, our searches would have been able to retrieve a GW170817-like event up to ∼200 Mpc and SGRB afterglows to z = 0.16 or 0.4, depending on the assumed underlying energy model. Future ToOs will expand the horizon to z = 0.2 and 0.7, respectively.
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2.
  • Andreoni, Igor, et al. (author)
  • Constraining the Kilonova Rate with Zwicky Transient Facility Searches Independent of Gravitational Wave and Short Gamma-Ray Burst Triggers
  • 2020
  • In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 904:2
  • Journal article (peer-reviewed)abstract
    • The first binary neutron star merger, GW170817, was accompanied by a radioactivity-powered optical/infrared transient called a kilonova. To date, no compelling kilonova has been found in all-sky optical surveys, independently of short gamma-ray burst and gravitational-wave triggers. In this work, we searched the first 23 months of the Zwicky Transient Facility (ZTF) data stream for candidate kilonovae in the form of rapidly evolving transients. We combined ZTF alert queries with forced point-spread-function photometry and nightly flux stacking to increase our sensitivity to faint and fast transients. Automatic queries yielded >11,200 candidates, 24 of which passed quality checks and selection criteria based on a grid of kilonova models tailored for both binary neutron star and neutron star-black hole mergers. None of the candidates in our sample was deemed a possible kilonova after thorough vetting. The sources that passed our selection criteria are dominated by Galactic cataclysmic variables. We identified two fast transients at high Galactic latitude, one of which is the confirmed afterglow of long-duration GRB.190106A, the other is a possible cosmological afterglow. Using a survey simulation code, we constrained the kilonova rate for a range of models including top-hat, linearly decaying light curves, and synthetic light curves obtained with radiative transfer simulations. For prototypical GW170817-like kilonovae, we constrain the rate to be R < 1775 Gpc(-3) yr(-1) (95% confidence). By assuming a population of kilonovae with the same geometry and composition of GW170817 observed under a uniform viewing angle distribution, we obtained a constraint on the rate of R.<.4029 Gpc(-3) yr(-1).
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3.
  • Andreoni, Igor, et al. (author)
  • Fast-transient Searches in Real Time with ZTFReST : Identification of Three Optically Discovered Gamma-Ray Burst Afterglows and New Constraints on the Kilonova Rate
  • 2021
  • In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 918:2
  • Journal article (peer-reviewed)abstract
    • The most common way to discover extragalactic fast transients, which fade within a few nights in the optical, is via follow-up of gamma-ray burst and gravitational-wave triggers. However, wide-field surveys have the potential to identify rapidly fading transients independently of such external triggers. The volumetric survey speed of the Zwicky Transient Facility (ZTF) makes it sensitive to objects as faint and fast fading as kilonovae, the optical counterparts to binary neutron star mergers, out to almost 200 Mpc. We introduce an open-source software infrastructure, the ZTF REaltime Search and Triggering, ZTFReST, designed to identify kilonovae and fast transients in ZTF data. Using the ZTF alert stream combined with forced point-spread-function photometry, we have implemented automated candidate ranking based on their photometric evolution and fitting to kilonova models. Automated triggering, with a human in the loop for monitoring, of follow-up systems has also been implemented. In 13 months of science validation, we found several extragalactic fast transients independently of any external trigger, including two supernovae with post-shock cooling emission, two known afterglows with an associated gamma-ray burst (ZTF20abbiixp, ZTF20abwysqy), two known afterglows without any known gamma-ray counterpart (ZTF20aajnksq, ZTF21aaeyldq), and three new fast-declining sources (ZTF20abtxwfx, ZTF20acozryr, ZTF21aagwbjr) that are likely associated with GRB200817A, GRB201103B, and GRB210204A. However, we have not found any objects that appear to be kilonovae. We constrain the rate of GW170817-like kilonovae to R < 900 Gpc(-3) yr(-1) (95% confidence). A framework such as ZTFReST could become a prime tool for kilonova and fast-transient discovery with the Vera Rubin Observatory.
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4.
  • Arcavi, Iair, et al. (author)
  • Energetic eruptions leading to a peculiar hydrogen-rich explosion of a massive star
  • 2017
  • In: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 551:7679, s. 210-213
  • Journal article (peer-reviewed)abstract
    • Every supernova so far observed has been considered to be the terminal explosion of a star. Moreover, all supernovae with absorption lines in their spectra show those lines decreasing in velocity over time, as the ejecta expand and thin, revealing slower-moving material that was previously hidden. In addition, every supernova that exhibits the absorption lines of hydrogen has one main light-curve peak, or a plateau in luminosity, lasting approximately 100 days before declining(1). Here we report observations of iPTF14hls, an event that has spectra identical to a hydrogen-rich core-collapse supernova, but characteristics that differ extensively from those of known supernovae. The light curve has at least five peaks and remains bright for more than 600 days; the absorption lines show little to no decrease in velocity; and the radius of the line-forming region is more than an order of magnitude bigger than the radius of the photosphere derived from the continuum emission. These characteristics are consistent with a shell of several tens of solar masses ejected by the progenitor star at supernova-level energies a few hundred days before a terminal explosion. Another possible eruption was recorded at the same position in 1954. Multiple energetic pre-supernova eruptions are expected to occur in stars of 95 to 130 solar masses, which experience the pulsational pair instability(2-5). That model, however, does not account for the continued presence of hydrogen, or the energetics observed here. Another mechanism for the violent ejection of mass in massive stars may be required.
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5.
  • Bellm, Eric C., et al. (author)
  • The Zwicky Transient Facility : System Overview, Performance, and First Results
  • 2019
  • In: Publications of the Astronomical Society of the Pacific. - : IOP Publishing. - 0004-6280 .- 1538-3873. ; 131:995
  • Journal article (peer-reviewed)abstract
    • The Zwicky Transient Facility (ZTF) is a new optical time-domain survey that uses the Palomar 48 inch Schmidt telescope. A custom-built wide-field camera provides a 47 deg(2) field of view and 8 s readout time, yielding more than an order of magnitude improvement in survey speed relative to its predecessor survey, the Palomar Transient Factory. We describe the design and implementation of the camera and observing system. The ZTF data system at the Infrared Processing and Analysis Center provides near-real-time reduction to identify moving and varying objects. We outline the analysis pipelines, data products, and associated archive. Finally, we present on-sky performance analysis and first scientific results from commissioning and the early survey. ZTF's public alert stream will serve as a useful precursor for that of the Large Synoptic Survey Telescope.
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6.
  • Bulla, Mattia, et al. (author)
  • ZTF Early Observations of Type Ia Supernovae. III. Early-time Colors As a Test for Explosion Models and Multiple Populations
  • 2020
  • In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 902:1
  • Journal article (peer-reviewed)abstract
    • Colors of Type Ia supernovae (SNe Ia) in the first few days after explosion provide a potential discriminant between different models. In this paper, we present g - r colors of 65 SNe Ia discovered within 5 days from first light by the Zwicky Transient Facility in 2018, a sample that is about three times larger than that in the literature. We find that g - r colors are intrinsically rather homogeneous at early phases, with about half of the dispersion attributable to photometric uncertainties (0.18 mag). Colors are nearly constant starting from 6 days after first light (g-r similar to -0.15 mag), while the time evolution at earlier epochs is characterized by a continuous range of slopes, from events rapidly transitioning from redder to bluer colors (slope of similar to-0.25 mag day(-1)) to events with a flatter evolution. The continuum in the slope distribution is in good agreement both with models requiring some amount of Ni-56 mixed in the outermost regions of the ejecta and with double-detonation models having thin helium layers (M-He = 0.01 M-circle dot) and varying carbon-oxygen core masses. At the same time, six events show evidence for a distinctive red bump signature predicted by double-detonation models with larger helium masses. We finally identify a significant correlation between the early-timeg - rslopes and supernova brightness, with brighter events associated to flatter color evolution (p-value = 0.006). The distribution of slopes, however, is consistent with being drawn from a single population, with no evidence for two components as claimed in the literature based on B - V colors.
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7.
  • Corsi, Alessandra, et al. (author)
  • A Search for Relativistic Ejecta in a Sample of ZTF Broad-lined Type Ic Supernovae
  • 2023
  • In: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 953:2
  • Journal article (peer-reviewed)abstract
    • The dividing line between gamma-ray bursts (GRBs) and ordinary stripped-envelope core-collapse supernovae (SNe) is yet to be fully understood. Observationally mapping the variety of ejecta outcomes (ultrarelativistic, mildly relativistic, or nonrelativistic) in SNe of Type Ic with broad lines (Ic-BL) can provide a key test to stellar explosion models. However, this requires large samples of the rare SN Ic-BL events with follow-up observations in the radio, where fast ejecta can be probed largely free of geometry and viewing angle effects. Here, we present the results of a radio (and X-ray) follow-up campaign of 16 SNe Ic-BL detected by the Zwicky Transient Facility (ZTF). Our radio campaign resulted in four counterpart detections and 12 deep upper limits. None of the events in our sample is as relativistic as SN 1998bw and we constrain the fraction of SN 1998bw-like explosions to <19% (3σ Gaussian equivalent), a factor of ≈2 smaller than previously established. We exclude relativistic ejecta with radio luminosity densities in between ≈5 × 1027 erg s−1 Hz−1 and ≈1029 erg s−1 Hz−1 at t ≳ 20 days since explosion for ≈60% of the events in our sample. This shows that SNe Ic-BL similar to the GRB-associated SNe 1998bw, 2003lw, and 2010bh, or to the relativistic SNe 2009bb and iPTF17cw, are rare. Our results also exclude an association of the SNe Ic-BL in our sample with largely off-axis GRBs with energies E ≳ 1050 erg. The parameter space of SN 2006aj-like events (faint and fast-peaking radio emission) is, on the other hand, left largely unconstrained, and systematically exploring it represents a promising line of future research.
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8.
  • Coughlin, Michael W., et al. (author)
  • 2900 Square Degree Search for the Optical Counterpart of Short Gamma-Ray Burst GRB 180523B with the Zwicky Transient Facility
  • 2019
  • In: Publications of the Astronomical Society of the Pacific. - : IOP Publishing. - 0004-6280 .- 1538-3873. ; 131:998
  • Journal article (peer-reviewed)abstract
    • There is significant interest in the models for production of short gamma-ray bursts (GRBs). Until now, the number of known short GRBs with multi-wavelength afterglows has been small. While the Fermi GRB Monitor detects many GRBs relative to the Neil Gehrels Swift Observatory, the large localization regions makes the search for counterparts difficult. With the Zwicky Transient Facility (ZTF) recently achieving first light, it is now fruitful to use its combination of depth (m(AB) similar to 20.6), field of view (approximate to 47 square degrees), and survey cadence (every similar to 3 days) to perform Target of Opportunity observations. We demonstrate this capability on GRB 180523B, which was recently announced by the Fermi GRB Monitor as a short GRB. ZTF imaged approximate to 2900 square degrees of the localization region, resulting in the coverage of 61.6% of the enclosed probability over two nights to a depth of m(AB) similar to 20.5. We characterized 14 previously unidentified transients, and none were found to be consistent with a short GRB counterpart. This search with the ZTF shows it is an efficient camera for searching for coarsely localized short GRB and gravitational-wave counterparts, allowing for a sensitive search with minimal interruption to its nominal cadence.
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9.
  • Das, Kaustav K., et al. (author)
  • Probing the Low-mass End of Core-collapse Supernovae Using a Sample of Strongly-stripped Calcium-rich Type IIb Supernovae from the Zwicky Transient Facility
  • 2023
  • In: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 959:1
  • Journal article (peer-reviewed)abstract
    • The fate of stars in the zero-age main-sequence (ZAMS) range ≈8–12 M⊙ is unclear. They could evolve to form white dwarfs or explode as electron-capture supernovae (SNe) or iron core-collapse SNe (CCSNe). Even though the initial mass function indicates that this mass range should account for over 40% of all CCSN progenitors, few have been observationally confirmed, likely due to the faintness and rapid evolution of some of these transients. In this paper, we present a sample of nine Ca-rich/O-poor Type IIb SNe detected by the Zwicky Transient Facility with progenitors likely in this mass range. These sources have a [Ca ii] λλ7291, 7324/[O i] λλ6300, 6364 flux ratio of ≳2 in their nebular spectra. Comparing the measured [O i] luminosity (≲1039 erg s−1) and derived oxygen mass (≈0.01 M⊙) with theoretical models, we infer that the progenitor ZAMS mass for these explosions is less than 12 M⊙. The ejecta properties (Mej ≲ 1 M⊙ and Ekin ∼ 1050 erg) are also consistent. The low ejecta mass of these sources indicates a class of strongly-stripped SNe that is a transition between the regular stripped-envelope SNe and ultra-stripped SNe. The progenitor could be stripped by a main-sequence companion and result in the formation of a neutron star−main sequence binary. Such binaries have been suggested to be progenitors of neutron star−white dwarf systems that could merge within a Hubble time and be detectable with LISA.
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10.
  • De, Kishalay, et al. (author)
  • The Zwicky Transient Facility Census of the Local Universe. I. Systematic Search for Calcium-rich Gap Transients Reveals Three Related Spectroscopic Subclasses
  • 2020
  • In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 905:1
  • Journal article (peer-reviewed)abstract
    • Using the Zwicky Transient Facility alert stream, we are conducting a large spectroscopic campaign to construct a complete, volume-limited sample of transients brighter than 20 mag, and coincident within 100 '' of galaxies in the Census of the Local Universe catalog. We describe the experiment design and spectroscopic completeness from the first 16 months of operations, which have classified 754 supernovae. We present results from a systematic search for calcium-rich gap transients in the sample of 22 low-luminosity (peak absolute magnitude M > -17), hydrogen-poor events found in the experiment. We report the detection of eight new events, and constrain their volumetric rate to greater than or similar to 15% +/- 5% of the SN Ia rate. Combining this sample with 10 previously known events, we find a likely continuum of spectroscopic properties ranging from events with SN Ia-like features (Ca-Ia objects) to those with SN Ib/c-like features (Ca-Ib/c objects) at peak light. Within the Ca-Ib/c events, we find two populations distinguished by their red (g - r approximate to 1.5 mag) or green (g - r approximate to 0.5 mag) colors at the r-band peak, wherein redder events show strong line blanketing features and slower light curves (similar to Ca-Ia objects), weaker He lines, and lower [Ca II]/[O I] in the nebular phase. We find that all together the spectroscopic continuum, volumetric rates, and striking old environments are consistent with the explosive burning of He shells on low-mass white dwarfs. We suggest that Ca-Ia and red Ca-Ib/c objects arise from the double detonation of He shells, while green Ca-Ib/c objects are consistent with low-efficiency burning scenarios like detonations in low-density shells or deflagrations.
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11.
  • Dhawan, Suhail, et al. (author)
  • A Uniform Type Ia Supernova Distance Ladder with the Zwicky Transient Facility : Absolute Calibration Based on the Tip of the Red Giant Branch Method
  • 2022
  • In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 934:2
  • Journal article (peer-reviewed)abstract
    • The current Cepheid-calibrated distance ladder measurement of H0 is reported to be in tension with the values inferred from the cosmic microwave background (CMB), assuming standard cosmology. However, some tip of the red giant branch (TRGB) estimates report H0 in better agreement with the CMB. Hence, it is critical to reduce systematic uncertainties in local measurements to understand the Hubble tension. In this paper, we propose a uniform distance ladder between the second and third rungs, combining Type Ia supernovae (SNe Ia) observed by the Zwicky Transient Facility (ZTF) with a TRGB calibration of their absolute luminosity. A large, volume-limited sample of both calibrator and Hubble flow SNe Ia from the same survey minimizes two of the largest sources of systematics: host-galaxy bias and nonuniform photometric calibration. We present results from a pilot study using the existing TRGB distance to the host galaxy of ZTF SN Ia SN 2021rhu (aka ZTF21abiuvdk) in NGC7814. Combining the ZTF calibrator with a volume-limited sample from the first data release of ZTF Hubble flow SNe Ia, we infer H0 = 76.94 ± 6.4 km s−1 Mpc−1, an 8.3% measurement. The error budget is dominated by the single object calibrating the SN Ia luminosity in this pilot study. However, the ZTF sample includes already five other SNe Ia within ∼20 Mpc for which TRGB distances can be obtained with the Hubble Space Telescope. Finally, we present the prospects of building this distance ladder out to 80 Mpc with James Webb Space Telescope observations of more than 100 ZTF SNe Ia.
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12.
  • Frederick, Sara, et al. (author)
  • A New Class of Changing-look LINERs
  • 2019
  • In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 883:1
  • Journal article (peer-reviewed)abstract
    • We report the discovery of six active galactic nuclei (AGNs) caught turning on during the first nine months of the Zwicky Transient Facility (ZTF) survey. The host galaxies were classified as low-ionization nuclear emissionline region galaxies (LINERs) by weak narrow forbidden line emission in their archival SDSS spectra, and detected by ZTF as nuclear transients. In five of the cases, we found via follow-up spectroscopy that they had transformed into broad-line AGNs, reminiscent of the changing-look LINER iPTF16bco. In one case, ZTF18aajupnt/ AT2018dyk, follow-up Hubble Space Telescope ultraviolet and ground-based optical spectra revealed the transformation into a narrow-line Seyfert 1 with strong [Fe VII, X, XIV] and He II lambda 4686 coronal lines. Swift monitoring observations of this source reveal bright UV emission that tracks the optical flare, accompanied by a luminous soft X-ray flare that peaks similar to 60 days later. Spitzer follow-up observations also detect a luminous midinfrared flare, implying a large covering fraction of dust. Archival light curves of the entire sample from CRTS, ATLAS, and ASAS-SN constrain the onset of the optical nuclear flaring from a prolonged quiescent state. Here we present the systematic selection and follow-up of this new class of changing-look LINERs, compare their properties to previously reported changing-look Seyfert galaxies, and conclude that they are a unique class of transients well-suited to test the uncertain physical processes associated with the LINER accretion state.
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13.
  • Ho, Anna Y. Q., et al. (author)
  • Cosmological Fast Optical Transients with the Zwicky Transient Facility : A Search for Dirty Fireballs
  • 2022
  • In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 938:1
  • Journal article (peer-reviewed)abstract
    • Dirty fireballs are a hypothesized class of relativistic massive-star explosions with an initial Lorentz factor Γinit below the Γinit ∼ 100 required to produce a long-duration gamma-ray burst (LGRB), but which could still produce optical emission resembling LGRB afterglows. Here we present the results of a search for on-axis optical afterglows using the Zwicky Transient Facility (ZTF). Our search yielded seven optical transients that resemble on-axis LGRB afterglows in terms of their red colors (g − r > 0 mag), faint host galaxies (r > 23 mag), rapid fading (dr/dt > 1 mag day−1), and in some cases X-ray and radio emission. Spectroscopy of the transient emission within a few days of discovery established cosmological distances (redshift z = 0.876 to 2.9) for six of the seven events, tripling the number of afterglows with redshift measurements discovered by optical surveys without a γ-ray trigger. A likely associated LGRB (GRB 200524A, GRB 210204A, GRB 210212B, and GRB 210610B) was identified for four events (ZTF 20abbiixp/AT 2020kym, ZTF 21aagwbjr/AT 2021buv, ZTF 21aakruew/AT 2021cwd, and ZTF 21abfmpwn/AT 2021qbd) post facto, while three (ZTF 20aajnksq/AT 2020blt, ZTF 21aaeyldq/AT 2021any, and ZTF 21aayokph/AT 2021lfa) had no detected LGRB counterpart. The simplest explanation for the three "orphan" events is that they were regular LGRBs missed by high-energy satellites owing to detector sensitivity and duty cycle, although it is possible that they were intrinsically subluminous in γ-rays or viewed slightly off-axis. We rule out a scenario in which dirty fireballs have a similar energy per solid angle to LGRBs and are an order of magnitude more common. In addition, we set the first direct constraint on the ratio of the opening angles of the material producing γ-rays and the material producing early optical afterglow emission, finding that they must be comparable.
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14.
  • Ho, Anna Y. Q., et al. (author)
  • iPTF Archival Search for Fast Optical Transients
  • 2018
  • In: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 854:1
  • Journal article (peer-reviewed)abstract
    • There has been speculation about a class of relativistic explosions with an initial Lorentz factor Gamma(init) smaller than that of classical gamma-ray bursts (GRBs). These dirty fireballs would lack prompt GRB emission but could be pursued via their optical afterglow, appearing as transients that fade overnight. Here we report a search for such transients (that fade by 5-sigma in magnitude overnight) in four years of archival photometric data from the intermediate Palomar Transient Factory (iPTF). Our search criteria yielded 50 candidates. Of these, two were afterglows to GRBs that had been found in dedicated follow-up observations to triggers from the Fermi GRB Monitor. Another (iPTF14yb) was a GRB afterglow discovered serendipitously. Eight were spurious artifacts of reference image subtraction, and one was an asteroid. The remaining 38 candidates have red stellar counterparts in external catalogs. The photometric and spectroscopic properties of the counterparts identify these transients as strong flares from M dwarfs of spectral type M3-M7 at distances of d approximate to 0.15-2.1 kpc; three counterparts were already spectroscopically classified as late-type M stars. With iPTF14yb as the only confirmed relativistic outflow discovered independently of a high-energy trigger, we constrain the all-sky rate of transients that peak at m = 18 and fade by Delta m = 2 mag in Delta t = 3 hr to be 680 yr(-1), with a 68% confidence interval of 119-2236 yr(-1). This implies that the rate of visible dirty fireballs is at most comparable to that of the known population of long-duration GRBs.
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15.
  • Ho, Anna Y. Q., et al. (author)
  • SN 2020bvc : A Broad-line Type Ic Supernova with a Double-peaked Optical Light Curve and a Luminous X-Ray and Radio Counterpart
  • 2020
  • In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 902:1
  • Journal article (peer-reviewed)abstract
    • We present optical, radio, and X-ray observations of SN 2020bvc (=ASASSN-20bs, ZTF 20aalxlis), a nearby (z = 0.0252; d.=.114Mpc) broad-line (BL) Type Ic supernova (SN) and the first double-peaked Ic-BL discovered without a gamma-ray burst (GRB) trigger. Our observations show that SN 2020bvc shares several properties in common with the Ic-BL SN 2006aj, which was associated with the low-luminosity gamma-ray burst (LLGRB) 060218. First, the 10 GHz radio luminosity (L-radio approximate to 10(37) erg s(-1)) is brighter than ordinary core-collapse SNe but fainter than LLGRB SNe such as SN 1998bw (associated with LLGRB 980425). We model our VLA observations (spanning 13-43 days) as synchrotron emission from a mildly relativistic (v greater than or similar to 0.3c) forward shock. Second, with Swift and Chandra, we detect X-ray emission (L-X approximate to 10(41) erg s(-1)) that is not naturally explained as inverse Compton emission or part of the same synchrotron spectrum as the radio emission. Third, high-cadence (6x night(-1)) data from the Zwicky Transient Facility (ZTF) show a double-peaked optical light curve, the first peak from shock cooling of extended low-mass material (mass M-e < 10(-2) M-circle dot at radius R-e > 10(12) cm) and the second peak from the radioactive decay of 56Ni. SN 2020bvc is the first double-peaked Ic-BL SN discovered without a GRB trigger, so it is noteworthy that it shows X-ray and radio emission similar to LLGRB SNe. For four of the five other nearby (z less than or similar to 0.05) Ic-BL SNe with ZTF high-cadence data, we rule out a first peak like that seen in SN 2006aj and SN 2020bvc, i.e., that lasts approximate to 1 day.and reaches a peak luminosity M approximate to -18. Follow-up X-ray and radio observations of Ic-BL SNe with well-sampled early optical light curves will establish whether double-peaked optical light curves are indeed predictive of LLGRB-like X-ray and radio emission.
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16.
  • Ho, Anna Y. Q., et al. (author)
  • The Broad-lined Ic Supernova ZTF18aaqjovh (SN 2018bvw) : An Optically Discovered Engine-driven Supernova Candidate with Luminous Radio Emission
  • 2020
  • In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 893:2
  • Journal article (peer-reviewed)abstract
    • We present ZTF18aaqjovh (SN 2018bvw), a high-velocity (broad-lined) stripped-envelope (Type Ic) supernova (Ic-BL SN) discovered in the Zwicky Transient Facility one-day cadence survey. ZTF18aaqjovh shares a number of features in common with engine-driven explosions: the photospheric velocity and the shape of the optical light curve are very similar to those of the Type.Ic-BL SN 1998bw, which was associated with a low-luminosity gamma-ray burst (LLGRB) and had relativistic ejecta. However, the radio luminosity of ZTF18aaqjovh is almost two orders of magnitude fainter than that of SN 1998bw at the same velocity phase, and the shock velocity is at most mildly relativistic (v.=.0.06-0.4c). A search of high-energy catalogs reveals no compelling gamma-ray burst (GRB) counterpart to ZTF18aaqjovh, and the limit on the prompt GRB luminosity of g >> ' L 1.6 10 erg s, iso 48 1 excludes a classical GRB but not an LLGRB. Altogether, ZTF18aaqjovh represents another transition event between engine-driven SNe associated with GRBs and ordinary Ic-BL SNe.
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17.
  • Ho, Anna Y. Q., et al. (author)
  • ZTF20aajnksq (AT 2020blt) : A Fast Optical Transient at z ≈ 2.9 with No Detected Gamma-Ray Burst Counterpart
  • 2020
  • In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 905:2
  • Journal article (peer-reviewed)abstract
    • We present ZTF20aajnksq (AT 2020blt), a fast-fading (Delta r = 2.3 mag in Delta t = 1.3 days) red (g - r 0.6 mag) and luminous (M-1626 A = -25.9 mag) optical transient at z = 2.9 discovered by the Zwicky Transient Facility (ZTF). AT 2020blt shares several features in common with afterglows to long-duration gamma-ray bursts (GRBs): (1) an optical light curve well-described by a broken power law with a break at t(j) = 1 d (observer frame); (2) a luminous (L0.3-10 KeV = 10(46) erg s(-1)) X-ray counterpart; and (3) luminous (L-10 GHz = 4 x 10(31) erg s(-1) Hz(-1)) radio emission. However, no GRB was detected in the 0.74 days between the last ZTF nondetection (r > 21.36 mag) and the first ZTF detection (r = 19.60 mag), with an upper limit on the isotropic-equivalent gamma-ray energy release of E-gamma,E-iso < 7 x 10(52) erg. AT 2020blt is thus the third afterglow-like transient discovered without a detected GRB counterpart (after PTF11agg and ZTF19abvizsw) and the second (after ZTF19abvizsw) with a redshift measurement. We conclude that the properties of AT 2020blt are consistent with a classical (initial Lorentz factor Gamma(0) greater than or similar to 100) on-axis GRB that was missed by high-energy satellites. Furthermore, by estimating the rate of transients with light curves similar to that of AT 2020blt in ZTF high-cadence data, we agree with previous results that there is no evidence for an afterglow-like phenomenon that is significantly more common than classical GRBs, such as dirty fireballs. We conclude by discussing the status and future of fast-transient searches in wide-field high-cadence optical surveys.
  •  
18.
  • Horesh, Assaf, et al. (author)
  • A Non-equipartition Shock Wave Traveling in a Dense Circumstellar Environment around SN 2020oi
  • 2020
  • In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 903:2
  • Journal article (peer-reviewed)abstract
    • We report the discovery and panchromatic follow-up observations of the young Type Ic supernova (SN Ic) SN 2020oi in M100, a grand-design spiral galaxy at a mere distance of 14 Mpc. We followed up with observations at radio, X-ray, and optical wavelengths from only a few days to several months after explosion. The optical behavior of the supernova is similar to those of other normal SNe Ic. The event was not detected in the X-ray band but our radio observations revealed a bright mJy source (L-nu approximate to 1.2 x 10(27) erg s(-1) Hz(-1)). Given the relatively small number of stripped envelope SNe for which radio emission is detectable, we used this opportunity to perform a detailed analysis of the comprehensive radio data set we obtained. The radio-emitting electrons initially experience a phase of inverse Compton cooling, which leads to steepening of the spectral index of the radio emission. Our analysis of the cooling frequency points to a large deviation from equipartition at the level of epsilon(e)/epsilon(B) greater than or similar to 200, similar to a few other cases of stripped envelope SNe. Our modeling of the radio data suggests that the shock wave driven by the SN ejecta into the circumstellar matter (CSM) is moving at similar to 3 x 10(4) km s(-1). Assuming a constant mass loss from the stellar progenitor, we find that the mass-loss rate is (M)over dot approximate to 1.4 x 10(-4) M-circle dot yr(-1) for an assumed wind velocity of 1000 km s(-1). The temporal evolution of the radio emission suggests a radial CSM density structure steeper than the standard r(-2).
  •  
19.
  • Hosseinzadeh, Griffin, et al. (author)
  • Type Ibn Supernovae Show Photometric Homogeneity and Spectral Diversity at Maximum Light
  • 2017
  • In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 836:2
  • Journal article (peer-reviewed)abstract
    • Type Ibn supernovae (SNe) are a small yet intriguing class of explosions whose spectra are characterized by low-velocity helium emission lines with little to no evidence for hydrogen. The prevailing theory has been that these are the core-collapse explosions of very massive stars embedded in helium-rich circumstellar material (CSM). We report optical observations of six new SNe Ibn: PTF11rfh, PTF12ldy, iPTF14aki, iPTF15ul, SN 2015G, and iPTF15akq. This brings the sample size of such objects in the literature to 22. We also report new data, including a near-infrared spectrum, on the Type Ibn SN 2015U. In order to characterize the class as a whole, we analyze the photometric and spectroscopic properties of the full Type Ibn sample. We find that, despite the expectation that CSM interaction would generate a heterogeneous set of light curves, as seen in SNe IIn, most Type Ibn light curves are quite similar in shape, declining at rates around 0.1 mag day(-1) during the first month after maximum light, with a few significant exceptions. Early spectra of SNe Ibn come in at least two varieties, one that shows narrow P Cygni lines and another dominated by broader emission lines, both around maximum light, which may be an indication of differences in the state of the progenitor system at the time of explosion. Alternatively, the spectral diversity could arise from viewing-angle effects or merely from a lack of early spectroscopic coverage. Together, the relative light curve homogeneity and narrow spectral features suggest that the CSM consists of a spatially confined shell of helium surrounded by a less dense extended wind.
  •  
20.
  • Hung, T., et al. (author)
  • Sifting for Sapphires : Systematic Selection of Tidal Disruption Events in iPTF
  • 2018
  • In: Astrophysical Journal Supplement Series. - : American Astronomical Society. - 0067-0049 .- 1538-4365. ; 238:2
  • Journal article (peer-reviewed)abstract
    • We present results from a systematic selection of tidal disruption events (TDEs) in a wide-area (4800 deg(2)), g+ R band, Intermediate Palomar Transient Factory experiment. Our selection targets typical optically selected TDEs: bright (> 60% flux increase) and blue transients residing in the centers of red galaxies. Using photometric selection criteria to down-select from a total of 493 nuclear transients to a sample of 26 sources, we then use follow-up UV imaging with the Neil Gehrels Swift Telescope, ground-based optical spectroscopy, and light curve fitting to classify them as 14 Type Ia supernovae (SNe Ia), 9 highly variable active galactic nuclei (AGNs), 2 confirmed TDEs, and 1 potential core-collapse supernova. We find it possible to filter AGNs by employing a more stringent transient color cut (g - r < -0.2 mag); further, UV imaging is the best discriminator for filtering SNe, since SNe Ia can appear as blue, optically, as TDEs in their early phases. However, when UV-optical color is unavailable, higher-precision astrometry can also effectively reduce SNe contamination in the optical. Our most stringent optical photometric selection criteria yields a 4.5: 1 contamination rate, allowing for a manageable number of TDE candidates for complete spectroscopic follow-up and real-time classification in the Zwicky Transient Facility era. We measure a TDE per galaxy rate of 1.7(-1.3)(+2.9) 10(-4) gal yr(-1) (90% CL in Poisson statistics). This does not account for TDEs outside our selection criteria, and thus may not reflect the total TDE population, which is yet to be fully mapped.
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21.
  • Irani, Ido, et al. (author)
  • SN 2022oqm-A Ca-rich Explosion of a Compact Progenitor Embedded in C/O Circumstellar Material
  • 2024
  • In: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 962:2
  • Journal article (peer-reviewed)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 at t ≈ 15 days. By t = 60 days, the spectrum of SN 2022oqm becomes nearly nebular, displaying strong Ca ii and [Ca ii] emission with no detectable [O i], 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.
  •  
22.
  • Karambelkar, Viraj R., et al. (author)
  • Faintest of Them All : ZTF 21aaoryiz/SN 2021fcg-Discovery of an Extremely Low Luminosity Type Iax Supernova
  • 2021
  • In: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 921:1
  • Journal article (peer-reviewed)abstract
    • We present the discovery of ZTF 21aaoryiz/SN 2021fcg-an extremely low luminosity Type Tax supernova. SN 2021fcg was discovered by the Zwicky Transient Facility in the star-forming galaxy IC0512 at a distance of approximate to 27 Mpc. It reached a peak absolute magnitude of M-r = -12.66 +/- 0.20 mag, making it the least luminous thermonuclear supernova discovered to date. The E(B - V) contribution from the underlying host galaxy is unconstrained. However, even if it were as large as 0.5 mag, the peak absolute magnitude would be M-r = -13.78 +/- 0.20 mag-still consistent with being the lowest-luminosity SN. Optical spectra of SN 2021fcg taken at 37 and 65 days post-maximum show strong [Ca II], Ca II, and Na I D emission and several weak [Fe II] emission lines. The [Ca II] emission in the two spectra has extremely low velocities of approximate to 1300 and 1000 km s(-1), respectively. The spectra very closely resemble those of the very low luminosity Type Tax supernovae SN 2008 ha, SN 2010ae, and SN 2019gsc taken at similar phases. The peak bolometric luminosity of SN 2021fcg is approximate to 2.5(-0.3)(+1.5) x 10(40) erg s(-1), which is a factor of 3 lower than that for SN 2008 ha. The bolometric lightcurve of SN 2021fcg is consistent with a very low ejected nickel mass (M-Ni approximate to 0.8(-0.5)(+0.4) x 10(-3) M-circle dot). The low luminosity and nickel mass of SN 2021fcg pose a challenge to the picture that low-luminosity SNe Tax originate from deflagrations of near-M-ch hybrid carbon-oxygen-neon white dwarfs. Instead, the merger of a carbon-oxygen and oxygen-neon white dwarf is a promising model to explain SN 2021fcg.
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23.
  • Karambelkar, Viraj R., et al. (author)
  • Volumetric Rates of Luminous Red Novae and Intermediate-luminosity Red Transients with the Zwicky Transient Facility
  • 2023
  • In: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 948:2
  • Journal article (peer-reviewed)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 for m ( r ) < 20 mag. Using the ZTF-CLU sample, we derive the first systematic LRNe volumetric rate of 7.8-3.7+6.5x10-5 M ( r ) <= -11 mag. We find that, in this luminosity range, the LRN rate scales as dN/dL proportional to L-2.5 +/- 0.3 L (-1.4 +/- 0.3) for 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+1.8x10-6 M ( r ) <= -13.5 mag, which scales as dN/dL proportional to L-2.5 +/- 0.5
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24.
  • Kasliwal, Mansi M., et al. (author)
  • Kilonova Luminosity Function Constraints Based on Zwicky Transient Facility Searches for 13 Neutron Star Merger Triggers during O3
  • 2020
  • In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 905:2
  • Journal article (peer-reviewed)abstract
    • We present a systematic search for optical counterparts to 13 gravitational wave (GW) triggers involving at least one neutron star during LIGO/Virgo's third observing run (O3). We searched binary neutron star (BNS) and neutron star black hole (NSBH) merger localizations with the Zwicky Transient Facility (ZTF) and undertook follow-up with the Global Relay of Observatories Watching Transients Happen (GROWTH) collaboration. The GW triggers had a median localization area of 4480 deg(2), a median distance of 267 Mpc, and false-alarm rates ranging from 1.5 to 10(-25) yr(-1). The ZTF coverage in the g and r bands had a median enclosed probability of 39%, median depth of 20.8 mag, and median time lag between merger and the start of observations of 1.5 hr. The O3 follow-up by the GROWTH team comprised 340 UltraViolet/Optical/InfraRed (UVOIR) photometric points, 64 OIR spectra, and three radio images using 17 different telescopes. We find no promising kilonovae (radioactivity-powered counterparts), and we show how to convert the upper limits to constrain the underlying kilonova luminosity function. Initially, we assume that all GW triggers are bona fide astrophysical events regardless of false-alarm rate and that kilonovae accompanying BNS and NSBH mergers are drawn from a common population; later, we relax these assumptions. Assuming that all kilonovae are at least as luminous as the discovery magnitude of GW170817 (-16.1 mag), we calculate that our joint probability of detecting zero kilonovae is only 4.2%. If we assume that all kilonovae are brighter than -16.6 mag (the extrapolated peak magnitude of GW170817) and fade at a rate of 1 mag day(-1) (similar to GW170817), the joint probability of zero detections is 7%. If we separate the NSBH and BNS populations based on the online classifications, the joint probability of zero detections, assuming all kilonovae are brighter than -16.6 mag, is 9.7% for NSBH and 7.9% for BNS mergers. Moreover, no more than <57% (<89%) of putative kilonovae could be brighter than -16.6 mag assuming flat evolution (fading by 1 mag day(-1)) at the 90% confidence level. If we further take into account the online terrestrial probability for each GW trigger, we find that no more than <68% of putative kilonovae could be brighter than -16.6 mag. Comparing to model grids, we find that some kilonovae must have M-ej M, X-lan > 10(-4), or > 30 degrees to be consistent with our limits. We look forward to searches in the fourth GW observing run; even 17 neutron star mergers with only 50% coverage to a depth of -16 mag would constrain the maximum fraction of bright kilonovae to <25%.
  •  
25.
  • Kupfer, Thomas, et al. (author)
  • Year 1 of the ZTF high-cadence Galactic plane survey : strategy, goals, and early results on new single-mode hot subdwarf B-star pulsatos
  • 2021
  • In: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 505:1, s. 1254-1267
  • Journal article (peer-reviewed)abstract
    • We present the goals, strategy, and first results of the high-cadence Galactic plane survey using the Zwicky Transient Facility (ZTF). The goal of the survey is to unveil the Galactic population of short-period variable stars, including short-period binaries, and stellar pulsators with periods less than a few hours. Between 2018 June and 2019 January, we observed 64 ZTF fields resulting in 2990 deg2 of high stellar density in the ZTF-r band along the Galactic plane. Each field was observed continuously for 1.5 to 6 h with a cadence of 40 sec. Most fields have between 200 and 400 observations obtained over 2–3  continuous nights. As part of this survey, we extract a total of ≈230 million individual objects with at least 80 epochs obtained during the high-cadence Galactic plane survey reaching an average depth of ZTF–r ≈ 20.5 mag. For four selected fields with 2–10 million individual objects per field, we calculate different variability statistics and find that ≈1–2  per cent of the objects are astrophysically variable over the observed period. We present a progress report on recent discoveries, including a new class of compact pulsators, the first members of a new class of Roche lobe filling hot subdwarf binaries as well as new ultracompact double white dwarfs and flaring stars. Finally, we present a sample of 12 new single-mode hot subdwarf B-star pulsators with pulsation amplitudes between ZTF–r = 20–76 mmag and pulsation periods between P = 5.8–16 min with a strong cluster of systems with periods ≈6 min. All of the data have now been released in either ZTF Data Release 3 or Data Release 4.
  •  
26.
  • Mohite, Siddharth R., et al. (author)
  • Inferring Kilonova Population Properties with a Hierarchical Bayesian Framework. I. Nondetection Methodology and Single-event Analyses
  • 2022
  • In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 925:1
  • Journal article (peer-reviewed)abstract
    • We present nimbus: a hierarchical Bayesian framework to infer the intrinsic luminosity parameters of kilonovae (KNe) associated with gravitational-wave (GW) events, based purely on nondetections. This framework makes use of GW 3D distance information and electromagnetic upper limits from multiple surveys for multiple events and self-consistently accounts for the finite sky coverage and probability of astrophysical origin. The framework is agnostic to the brightness evolution assumed and can account for multiple electromagnetic passbands simultaneously. Our analyses highlight the importance of accounting for model selection effects, especially in the context of nondetections. We show our methodology using a simple, two-parameter linear brightness model, taking the follow-up of GW190425 with the Zwicky Transient Facility as a single-event test case for two different prior choices of model parameters: (i) uniform/uninformative priors and (ii) astrophysical priors based on surrogate models of Monte Carlo radiative-transfer simulations of KNe. We present results under the assumption that the KN is within the searched region to demonstrate functionality and the importance of prior choice. Our results show consistency with simsurvey-an astronomical survey simulation tool used previously in the literature to constrain the population of KNe. While our results based on uniform priors strongly constrain the parameter space, those based on astrophysical priors are largely uninformative, highlighting the need for deeper constraints. Future studies with multiple events having electromagnetic follow-up from multiple surveys should make it possible to constrain the KN population further.
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27.
  • Nicholl, Matt, et al. (author)
  • An extremely energetic supernova from a very massive star in a dense medium
  • 2020
  • In: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; 4, s. 893-899
  • Journal article (peer-reviewed)abstract
    • The interaction of a supernova with a circumstellar medium (CSM) can dramatically increase the emitted luminosity by converting kinetic energy to thermal energy. In 'superluminous' supernovae of type IIn-named for narrow hydrogen lines(1) in their spectra-the integrated emission can reach(2-6) similar to 10(51) erg, attainable by thermalizing most of the kinetic energy of a conventional supernova. A few transients in the centres of active galaxies have shown similar spectra and even larger energies(7,8), but are difficult to distinguish from accretion onto the supermassive black hole. Here we present a new event, SN2016aps, offset from the centre of a low-mass galaxy, that radiated greater than or similar to 5 x 10(51) erg, necessitating a hyper-energetic supernova explosion. We find a total (supernova ejecta + CSM) mass likely exceeding 50-100 M-circle dot, with energy greater than or similar to 10(52) erg, consistent with some models of pair-instability supernovae or pulsational pair-instability supernovae-theoretically predicted thermonuclear explosions from helium cores >50 M-circle dot. Independent of the explosion mechanism, this event demonstrates the existence of extremely energetic stellar explosions, detectable at very high redshifts, and provides insight into dense CSM formation in the most massive stars.
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28.
  • Nyholm, Anders, 1985-, et al. (author)
  • Type IIn supernova light-curve properties measured from an untargeted survey sample
  • 2020
  • In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 637
  • Journal article (peer-reviewed)abstract
    • The evolution of a Type IIn supernova (SN IIn) is governed by the interaction between the SN ejecta and a hydrogen-rich circumstellar medium. The SNe IIn thus allow us to probe the late-time mass-loss history of their progenitor stars. We present a sample of SNe IIn from the untargeted, magnitude-limited surveys of the Palomar Transient Factory (PTF) and its successor, the intermediate PTF (iPTF). To date, statistics on SN IIn optical light-curve properties have generally been based on small (≲ 10 SNe) samples from targeted SN surveys. The SNe IIn found and followed by the PTF/iPTF were used to select a sample of 42 events with useful constraints on the rise times as well as with available post-peak photometry. The sample SNe were discovered in 2009-2016 and have at least one low-resolution classification spectrum, as well as photometry from the P48 and P60 telescopes at Palomar Observatory. We study the light-curve properties of these SNe IIn using spline fits (for the peak and the declining portion) and template matching (for the rising portion). We study the peak-magnitude distribution, rise times, decline rates, colour evolution, host galaxies, and K-corrections of the SNe in our sample. We find that the typical rise times are divided into fast and slow risers at 20±6 d and 50±11 d, respectively. The decline rates are possibly divided into two clusters (with slopes 0.013 ± 0.006 mag d^-1 and 0.040±0.010 mag d^-1), but this division has weak statistical significance. We find no significant correlation between the peak luminosity of SNe IIn and their rise times, but the more luminous SNe IIn are generally found to be more long-lasting. Slowly rising SNe IIn are generally found to decline slowly. The SNe in our sample were hosted by galaxies of absolute magnitude -22 ≲ M_g ≲ -13 mag. The K-corrections at light-curve peak of the SNe IIn in our sample are found to be within 0.2 mag for the observer's frame r-band, for SNe at redshifts z < 0.25. By applying K-corrections and also including ostensibly "superluminous" SNe IIn, we find that the peak magnitudes are M_peak^r = -19.18±1.32 mag. We conclude that the occurrence of conspicuous light-curve bumps in SNe IIn, such as in iPTF13z, are limited to 1.4+14.6−1.0 % of the SNe IIn. We also investigate a possible sub-type of SNe IIn with a fast rise to a ≳ 50 d plateau followed by a slow, linear decline.
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29.
  • Ofek, Eran O., et al. (author)
  • INTERACTION-POWERED SUPERNOVAE : RISE-TIME VERSUS PEAK-LUMINOSITY CORRELATION AND THE SHOCK-BREAKOUT VELOCITY
  • 2014
  • In: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 788:2, s. 154-
  • Journal article (peer-reviewed)abstract
    • Interaction of supernova (SN) ejecta with the optically thick circumstellar medium (CSM) of a progenitor star can result in a bright, long-lived shock-breakout event. Candidates for such SNe include Type IIn and superluminous SNe. If some of these SNe are powered by interaction, then there should be a specific relation between their peak luminosity, bolometric light-curve rise time, and shock-breakout velocity. Given that the shock velocity during shock breakout is not measured, we expect a correlation, with a significant spread, between the rise time and the peak luminosity of these SNe. Here, we present a sample of 15 SNe IIn for which we have good constraints on their rise time and peak luminosity from observations obtained using the Palomar Transient Factory. We report on a possible correlation between the R-band rise time and peak luminosity of these SNe, with a false-alarm probability of 3%. Assuming that these SNe are powered by interaction, combining these observables and theory allows us to deduce lower limits on the shock-breakout velocity. The lower limits on the shock velocity we find are consistent with what is expected for SNe (i.e., similar to 10(4) km s(-1)). This supports the suggestion that the early-time light curves of SNe IIn are caused by shock breakout in a dense CSM. We note that such a correlation can arise from other physical mechanisms. Performing such a test on other classes of SNe ( e. g., superluminous SNe) can be used to rule out the interaction model for a class of events.
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30.
  • Perley, Daniel A., et al. (author)
  • Real-time discovery of AT2020xnd : a fast, luminous ultraviolet transient with minimal radioactive ejecta
  • 2021
  • In: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 508:4, s. 5138-5147
  • Journal article (peer-reviewed)abstract
    • The many unusual properties of the enigmatic AT2018cow suggested that at least some subset of the empirical class of fast blue optical transients (FBOTs) represents a genuinely new astrophysical phenomenon. Unfortunately, the intrinsic rarity and fleeting nature of these events have made it difficult to identify additional examples early enough to acquire the observations necessary to constrain theoretical models. We present here the Zwicky Transient Facility discovery of AT2020xnd (ZTF20acigmel, the 'Camel') at z = 0.243, the first unambiguous AT2018cow analogue to be found and confirmed in real time. AT2018cow and AT2020xnd share all key observational properties: a fast optical rise, sustained high photospheric temperature, absence of a second peak attributable to ejection of a radioactively heated stellar envelope, extremely luminous radio, millimetre, and X-ray emission, and a dwarf-galaxy host. This supports the argument that AT2018cow-like events represent a distinct phenomenon from slower-evolving radio-quiet supernovae, likely requiring a different progenitor or a different central engine. The sample properties of the four known members of this class to date disfavour tidal disruption models but are consistent with the alternative model of an accretion powered jet following the direct collapse of a massive star to a black hole. Contextual filtering of alert streams combined with rapid photometric verification using multiband imaging provides an efficient way to identify future members of this class, even at high redshift.
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31.
  • Purdum, Josiah N., et al. (author)
  • Time-series and Phase-curve Photometry of the Episodically Active Asteroid (6478) Gault in a Quiescent State Using APO, GROWTH, P200, and ZTF
  • 2021
  • In: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 911:2
  • Journal article (peer-reviewed)abstract
    • 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 H ( r ) = 14.63 +/- 0.02, G ( r ) = 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 less than or similar to 0.05 mag feature suggesting that (6478) Gault has a rotation period of similar to 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 similar to 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.
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32.
  • Reusch, Simeon, et al. (author)
  • Candidate Tidal Disruption Event AT2019fdr Coincident with a High-Energy Neutrino
  • 2022
  • In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 128:22
  • Journal article (peer-reviewed)abstract
    • The origins of the high-energy cosmic neutrino flux remain largely unknown. Recently, one high-energy neutrino was associated with a tidal disruption event (TDE). Here we present AT2019fdr, an exceptionally luminous TDE candidate, coincident with another high-energy neutrino. Our observations, including a bright dust echo and soft late-time x-ray emission, further support a TDE origin of this flare. The probability of finding two such bright events by chance is just 0.034%. We evaluate several models for neutrino production and show that AT2019fdr is capable of producing the observed high-energy neutrino, reinforcing the case for TDEs as neutrino sources.
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33.
  • Silverman, Jeffrey M., et al. (author)
  • SN 2000cx and SN 2013bh : extremely rare, nearly twin Type Ia supernovae
  • 2013
  • In: Monthly notices of the Royal Astronomical Society. - : Oxford University Press. - 0035-8711 .- 1365-2966. ; 436:2, s. 1225-1237
  • Journal article (peer-reviewed)abstract
    • The Type Ia supernova (SN Ia) SN 2000cx was one of the most peculiar transients ever discovered, with a rise to maximum brightness typical of a SN Ia, but a slower decline and a higher photospheric temperature. 13 yr later SN 2013bh (also known as iPTF13abc), a near identical twin, was discovered and we obtained optical and near-infrared photometry and low-resolution optical spectroscopy from discovery until about 1 month past r-band maximum brightness. The spectra of both objects show iron-group elements [Co ii, Ni ii, Fe ii, Fe iii and high-velocity features (HVFs) of Ti ii], intermediate-mass elements (Si ii, Si iii and S ii) and separate normal velocity features (similar to 12 000 km s(-1)) and HVFs (similar to 24 000 km s(-1)) of Ca ii. Persistent absorption from Fe iii and Si iii, along with the colour evolution, implies high blackbody temperatures for SNe 2013bh and 2000cx (similar to 12 000 K). Both objects lack narrow Na i D absorption and exploded in the outskirts of their hosts, indicating that the SN environments were relatively free of interstellar or circumstellar material and may imply that the progenitors came from a relatively old and low-metallicity stellar population. Models of SN 2000cx, seemingly applicable to SN 2013bh, imply the production of up to similar to 1 M-circle dot of Ni-56 and (4.3-5.5) x 10(-3) M-circle dot of fast-moving Ca ejecta.
  •  
34.
  • Soumagnac, Maayane T., et al. (author)
  • Early Ultraviolet Observations of Type IIn Supernovae Constrain the Asphericity of Their Circumstellar Material
  • 2020
  • In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 899:1
  • Journal article (peer-reviewed)abstract
    • We present a survey of the early evolution of 12 Type IIn supernovae (SNe IIn) at ultraviolet and visible light wavelengths. 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 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% for 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 modeling of these events.
  •  
35.
  • Soumagnac, Maayane T., et al. (author)
  • SN 2018fif : The Explosion of a Large Red Supergiant Discovered in Its Infancy by the Zwicky Transient Facility
  • 2020
  • In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 902:1
  • Journal article (peer-reviewed)abstract
    • High-cadence transient surveys are able to capture supernovae closer to their first light than ever before. Applying analytical models to such early emission, we can constrain the progenitor stars' properties. In this paper, we present observations of SN 2018fif (ZTF 18abokyfk). The supernova was discovered close to first light and monitored by the Zwicky Transient Facility (ZTF) and the Neil Gehrels Swift Observatory. Early spectroscopic observations suggest that the progenitor of SN 2018fif was surrounded by relatively small amounts of circumstellar material compared to all previous cases. This particularity, coupled with the high-cadence multiple-band coverage, makes it a good candidate to investigate using shock-cooling models. We employ the SOPRANOS code, an implementation of the model by Sapir & Waxman and its extension to early times by Morag et al. Compared with previous implementations, SOPRANOS has the advantage of including a careful account of the limited temporal validity domain of the shock-cooling model as well as allowing usage of the entirety of the early UV data. We find that the progenitor of SN 2018fif was a large red supergiant with a radius of R = 744.0(-128.0)(+183.0) R-circle dot and an ejected mass of M-ej = 9.3(-5.8)(+0.4) M-circle dot. Our model also gives information on the explosion epoch, the progenitor's inner structure, the shock velocity, and the extinction. The distribution of radii is double-peaked, with smaller radii corresponding to lower values of the extinction, earlier recombination times, and a better match to the early UV data. If these correlations persist in future objects, denser spectroscopic monitoring constraining the time of recombination, as well as accurate UV observations (e.g., with ULTRASAT), will help break the extinction/radius degeneracy and independently determine both.
  •  
36.
  • Stein, Robert, et al. (author)
  • A tidal disruption event coincident with a high-energy neutrino
  • 2021
  • In: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; :5, s. 510-518
  • Journal article (peer-reviewed)abstract
    • Cosmic neutrinos provide a unique window into the otherwise hidden mechanism of particle acceleration in astrophysical objects. The IceCube Collaboration recently reported the likely association of one high-energy neutrino with a flare from the relativistic jet of an active galaxy pointed towards the Earth. However a combined analysis of many similar active galaxies revealed no excess from the broader population, leaving the vast majority of the cosmic neutrino flux unexplained. Here we present the likely association of a radio-emitting tidal disruption event, AT2019dsg, with a second high-energy neutrino. AT2019dsg was identified as part of our systematic search for optical counterparts to high-energy neutrinos with the Zwicky Transient Facility. The probability of finding any coincident radio-emitting tidal disruption event by chance is 0.5%, while the probability of finding one as bright in bolometric energy flux as AT2019dsg is 0.2%. Our electromagnetic observations can be explained through a multizone model, with radio analysis revealing a central engine, embedded in a UV photosphere, that powers an extended synchrotron-emitting outflow. This provides an ideal site for petaelectronvolt neutrino production. Assuming that the association is genuine, our observations suggest that tidal disruption events with mildly relativistic outflows contribute to the cosmic neutrino flux. The tidal disruption event AT2019dsg is probably associated with a high-energy neutrino, suggesting that such events can contribute to the cosmic neutrino flux. The electromagnetic emission is explained in terms of a central engine, a photosphere and an extended synchrotron-emitting outflow.
  •  
37.
  • Stein, Robert, et al. (author)
  • tdescore : An Accurate Photometric Classifier for Tidal Disruption Events
  • 2024
  • In: Astrophysical Journal Letters. - 2041-8205 .- 2041-8213. ; 965:2
  • Journal article (peer-reviewed)abstract
    • Optical surveys have become increasingly adept at identifying candidate tidal disruption events (TDEs) in large numbers, but classifying these generally requires extensive spectroscopic resources. Here we present tdescore, a simple binary photometric classifier that is trained using a systematic census of ∼3000 nuclear transients from the Zwicky Transient Facility (ZTF). The sample is highly imbalanced, with TDEs representing ∼2% of the total. tdescore is nonetheless able to reject non-TDEs with 99.6% accuracy, yielding a sample of probable TDEs with recall of 77.5% for a precision of 80.2%. tdescore is thus substantially better than any available TDE photometric classifier scheme in the literature, with performance not far from spectroscopy as a method for classifying ZTF nuclear transients, despite relying solely on ZTF data and multiwavelength catalog cross matching. In a novel extension, we use "Shapley additive explanations" to provide a human-readable justification for each individual tdescore classification, enabling users to understand and form opinions about the underlying classifier reasoning. tdescore can serve as a model for photometric identification of TDEs with time-domain surveys, such as the upcoming Rubin observatory.
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38.
  • Strotjohann, Nora L., et al. (author)
  • SEARCH FOR PRECURSOR ERUPTIONS AMONG TYPE IIB SUPERNOVAE
  • 2015
  • In: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 811:2
  • Journal article (peer-reviewed)abstract
    • The progenitor stars of several Type IIb supernovae (SNe) show indications of 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 SNe IIb 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, SNe IIb have on average <0.86 precursors as bright as an absolute R-band magnitude of -14 in the final 3.5 years before the explosion and <0.56 events over the final year. In contrast, precursors among SNe IIn have a greater than or similar to 5 times higher rate. The kinetic energy required to unbind a low-mass stellar envelope is comparable to the radiated energy of a few-weeks-long precursor that would be detectable for the closest SNe in our sample. Therefore, mass ejections, if they are common in such SNe, are radiatively inefficient or have durations longer than months. Indeed, when using 60-day bins, a faint precursor candidate is detected prior to SN 2012cs (similar to 2% false-alarm probability). We also report the detection of the progenitor of SN 2011dh that does not show detectable variability over the final two years before the explosion. The suggested progenitor of SN 2012P is still present, and hence is likely a compact star cluster or an unrelated object.
  •  
39.
  • van Velzen, Sjoert, et al. (author)
  • Establishing accretion flares from supermassive black holes as a source of high-energy neutrinos
  • 2024
  • In: Monthly notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 529:3, s. 2559-2576
  • Journal article (peer-reviewed)abstract
    • The origin of cosmic high-energy neutrinos remains largely unexplained. For high-energy neutrino alerts from IceCube, a coincidence with time-variable emission has been seen for three different types of accreting black holes: (1) a gamma-ray flare from a blazar (TXS 0506+056), (2) an optical transient following a stellar tidal disruption event (TDE; AT2019dsg), and (3) an optical outburst from an active galactic nucleus (AGN; AT2019fdr). For the latter two sources, infrared follow-up observations revealed a powerful reverberation signal due to dust heated by the flare. This discovery motivates a systematic study of neutrino emission from all supermassive black hole with similar dust echoes. Because dust reprocessing is agnostic to the origin of the outburst, our work unifies TDEs and high-amplitude flares from AGN into a population that we dub accretion flares. Besides the two known events, we uncover a third flare that is coincident with a PeV-scale neutrino (AT2019aalc). Based solely on the optical and infrared properties, we estimate a significance of 3.6σ for this association of high-energy neutrinos with three accretion flares. Our results imply that at least ∼10 per cent of the IceCube high-energy neutrino alerts could be due to accretion flares. This is surprising because the sum of the fluence of these flares is at least three orders of magnitude lower compared to the total fluence of normal AGN. It thus appears that the efficiency of high-energy neutrino production in accretion flares is increased compared to non-flaring AGN. We speculate that this can be explained by the high Eddington ratio of the flares.
  •  
40.
  • van Velzen, Sjoert, et al. (author)
  • Seventeen Tidal Disruption Events from the First Half of ZTF Survey Observations : Entering a New Era of Population Studies
  • 2021
  • In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 908:1
  • Journal article (peer-reviewed)abstract
    • While tidal disruption events (TDEs) have long been heralded as laboratories for the study of quiescent black holes, the small number of known TDEs and uncertainties in their emission mechanism have hindered progress toward this promise. Here we present 17 new TDEs that have been detected recently by the Zwicky Transient Facility along with Swift UV and X-ray follow-up observations. Our homogeneous analysis of the optical/UV light curves, including 22 previously known TDEs from the literature, reveals a clean separation of light-curve properties with spectroscopic class. The TDEs with Bowen fluorescence features in their optical spectra have smaller blackbody radii, lower optical luminosities, and higher disruption rates compared to the rest of the sample. The small subset of TDEs that show only helium emission lines in their spectra have the longest rise times, the highest luminosities, and the lowest rates. A high detection rate of Bowen lines in TDEs with small photometric radii could be explained by the high density that is required for this fluorescence mechanism. The stellar debris can provide a source for this dense material. Diffusion of photons through this debris may explain why the rise and fade timescale of the TDEs in our sample are not correlated. We also report, for the first time, the detection of soft X-ray flares from a TDE on similar to day timescales. Based on the fact that the X-ray flares peak at a luminosity similar to the optical/UV blackbody luminosity, we attribute them to brief glimpses through a reprocessing layer that otherwise obscures the inner accretion flow.
  •  
41.
  • van Velzen, Sjoert, et al. (author)
  • The First Tidal Disruption Flare in ZTF : From Photometric Selection to Multi-wavelength Characterization
  • 2019
  • In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 872:2
  • Journal article (peer-reviewed)abstract
    • We present Zwicky Transient Facility (ZTF) observations of the tidal disruption flare AT2018zr/PS18kh reported by Holoien et al. and detected during ZTF commissioning. The ZTF light curve of the tidal disruption event (TDE) samples the rise-to-peak exceptionally well, with 50. days of g- and r-band detections before the time of maximum light. We also present our multi-wavelength follow-up observations, including the detection of a thermal (kT approximate to 100 eV) X-ray source that is two orders of magnitude fainter than the contemporaneous optical/UV blackbody luminosity, and a stringent upper limit to the radio emission. We use observations of 128 known active galactic nuclei (AGNs) to assess the quality of the ZTF astrometry, finding a median host-flare distance of 0.'' 2 for genuine nuclear flares. Using ZTF observations of variability from known AGNs and supernovae we show how these sources can be separated from TDEs. A combination of light-curve shape, color, and location in the host galaxy can be used to select a clean TDE sample from multi-band optical surveys such as ZTF or the Large Synoptic Survey Telescope.
  •  
42.
  • Vreeswijk, Paul M., et al. (author)
  • ON THE EARLY-TIME EXCESS EMISSION IN HYDROGEN-POOR SUPERLUMINOUS SUPERNOVAE
  • 2017
  • In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 835:1
  • Journal article (peer-reviewed)abstract
    • We present the light curves of the hydrogen-poor superluminous supernovae (SLSNe I) PTF 12dam and iPTF 13dcc, discovered by the (intermediate) Palomar Transient Factory. Both show excess emission at early times and a slowly declining light curve at late times. The early bump in PTF 12dam is very similar in duration (similar to 10 days) and brightness relative to the main peak (2-3 mag fainter) compared to that observed in other SLSNe I. In contrast, the long-duration (>30 days) early excess emission in iPTF 13dcc, whose brightness competes with that of the main peak, appears to be of a different nature. We construct bolometric light curves for both targets, and fit a variety of light-curve models to both the early bump and main peak in an attempt to understand the nature of these explosions. Even though the slope of the late-time decline in the light curves of both SLSNe is suggestively close to that expected from the radioactive decay of Ni-56 and Co-56, the amount of nickel required to power the full light curves is too large considering the estimated ejecta mass. The magnetar model including an increasing escape fraction provides a reasonable description of the PTF 12dam observations. However, neither the basic nor the double-peaked magnetar model is capable of reproducing the light curve of iPTF 13dcc. A model combining a shock breakout in an extended envelope with late-time magnetar energy injection provides a reasonable fit to the iPTF 13dcc observations. Finally, we find that the light curves of both PTF 12dam and iPTF 13dcc can be adequately fit with the model involving interaction with the circumstellar medium.
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43.
  • Vreeswijk, Paul M., et al. (author)
  • THE HYDROGEN-POOR SUPERLUMINOUS SUPERNOVA iPTF 13ajg AND ITS HOST GALAXY IN ABSORPTION AND EMISSION
  • 2014
  • In: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 797:1, s. 24-
  • Journal article (peer-reviewed)abstract
    • We present imaging and spectroscopy of a hydrogen-poor superluminous supernova (SLSN) discovered by the intermediate Palomar Transient Factory, iPTF 13ajg. At a redshift of z = 0.7403, derived from narrow absorption lines, iPTF 13ajg peaked at an absolute magnitude of M-u,M-AB = -22.5, one of the most luminous supernovae to date. The observed bolometric peak luminosity of iPTF 13ajg is 3.2 x 10(44) erg s(-1), while the estimated total radiated energy is 1.3 x 10(51) erg. We detect narrow absorption lines of Mg I, Mg II, and Fe II, associated with the cold interstellar medium in the host galaxy, at two different epochs with X-shooter at the Very Large Telescope. From Voigt profile fitting, we derive the column densities log N(Mg I) = 11.94 +/- 0.06, log N(Mg II) = 14.7 +/- 0.3, and log N(Fe II) = 14.25 +/- 0.10. These column densities, as well as the Mg I and Mg II equivalent widths of a sample of hydrogen-poor SLSNe taken from the literature, are at the low end of those derived for gamma-ray bursts (GRBs) whose progenitors are also thought to be massive stars. This suggests that the environments of hydrogen-poor SLSNe and GRBs are different. From the nondetection of Fe II fine-structure absorption lines, we derive a lower limit on the distance between the supernova and the narrow-line absorbing gas of 50 pc. The neutral gas responsible for the absorption in iPTF 13ajg exhibits a single narrow component with a low velocity width, Delta V = 76 km s(-1), indicating a low-mass host galaxy. No host galaxy emission lines are detected, leading to an upper limit on the unobscured star formation rate (SFR) of SFR[O II] < 0.07 M-circle dot yr(-1). Late-time imaging shows the iPTF 13ajg host galaxy to be faint, with g(AB) approximate to 27.0 and R-AB >= 26.0 mag, corresponding to M-B,M-Vega greater than or similar to -17.7 mag.
  •  
44.
  • White, Christopher J., et al. (author)
  • SLOW-SPEED SUPERNOVAE FROM THE PALOMAR TRANSIENT FACTORY : TWO CHANNELS
  • 2015
  • In: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 799:1
  • Journal article (peer-reviewed)abstract
    • Since the discovery of the unusual prototype SN 2002cx, the eponymous class of Type I (hydrogen-poor) supernovae with low ejecta speeds has grown to include approximately two dozen members identified from several heterogeneous surveys, in some cases ambiguously. Here we present the results of a systematic study of 1077 Type I supernovae discovered by the Palomar Transient Factory, leading to nine new members of this peculiar class. Moreover, we find there are two distinct subclasses based on their spectroscopic, photometric, and host galaxy properties: SN 2002cx-like supernovae tend to be in later-type or more irregular hosts, have more varied and generally dimmer luminosities, have longer rise times, and lack a Ti II trough when compared to SN 2002es-like supernovae. None of our objects show helium, and we counter a previous claim of two such events. We also find that the occurrence rate of these transients relative to Type Ia supernovae is 5.6(-3.8)(+22) % (90% confidence), lower compared to earlier estimates. Combining our objects with the literature sample, we propose that these subclasses have two distinct physical origins.
  •  
45.
  • Yao, Yuhan, et al. (author)
  • SN2019dge : A Helium-rich Ultra-stripped Envelope Supernova
  • 2020
  • In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 900:1
  • Journal article (peer-reviewed)abstract
    • We present observations of ZTF18abfcmjw (SN2019dge), a helium-rich supernova with a fast-evolving light curve indicating an extremely low ejecta mass (approximate to 0.33M(circle dot)) and low kinetic energy (approximate to 1.3 x 10(50)erg). Early-time (<4 days after explosion) photometry reveals evidence of shock cooling from an extended helium-rich envelope of similar to 0.1 M-circle dot located similar to 1.2 x 10(13) cm from the progenitor. Early-time He II line emission and subsequent spectra show signatures of interaction with helium-rich circumstellar material, which extends from greater than or similar to 5 x 10(13)cm to greater than or similar to 2 x 10(16)cm. We interpret SN2019dge as a helium-rich supernova from an ultra-stripped progenitor, which originates from a close binary system consisting of a mass-losing helium star and a low-mass main-sequence star or a compact object (i.e., a white dwarf, a neutron star, or a black hole). We infer that the local volumetric birth rate of 19dge-like ultra-stripped SNe is in the range of 1400-8200 Gpc(-3)yr(-1) (i.e., 2%-12% of core-collapse supernova rate). This can be compared to the observed coalescence rate of compact neutron star binaries that are not formed by dynamical capture.
  •  
46.
  • Yao, Yuhan, et al. (author)
  • ZTF Early Observations of Type Ia Supernovae. I. Properties of the 2018 Sample
  • 2019
  • In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 886:2
  • Journal article (peer-reviewed)abstract
    • Early-time observations of Type Ia supernovae (SNe Ia) are essential to constrain the properties of their progenitors. In this paper, we present high-quality light curves of 127 SNe Ia discovered by the Zwicky Transient Facility (ZTF) in 2018. We describe our method to perform forced point-spread function photometry, which can be applied to other types of extragalactic transients. With a planned cadence of six observations per night (three g + three r), all of the 127 SNe Ia are detected in both g and r bands more than 10 days (in the rest frame) prior to the epoch of g-band maximum light. The redshifts of these objects range from z = 0.0181 to 0.165; the median redshift is 0.074. Among the 127 SNe, 50 are detected at least 14 days prior to maximum light (in the rest frame), with a subset of nine objects being detected more than 17 days before g-band peak. This is the largest sample of young SNe Ia collected to date; it can be used to study the shape and color evolution of the rising light curves in unprecedented detail. We discuss six peculiar events in this sample: one 02cx-like event ZTF18abclfee (SN 2018crl), one Ia-CSM SN ZTF18aaykjei (SN 2018cxk), and four objects with possible super-Chandrasekhar mass progenitors: ZTF18abhpgje (SN 2018eul), ZTF18abdpvnd (SN 2018dvf), ZTF18aawpcel (SN 2018cir), and ZTF18abddmrf (SN 2018dsx).
  •  
47.
  • Ye, Quanzhi, et al. (author)
  • Toward Efficient Detection of Small Near-Earth Asteroids Using the Zwicky Transient Facility (ZTF)
  • 2019
  • In: Publications of the Astronomical Society of the Pacific. - : IOP Publishing. - 0004-6280 .- 1538-3873. ; 131:1001
  • Journal article (peer-reviewed)abstract
    • We describe ZStreak, a semi-real-time pipeline specialized in detecting small, fast-moving, near-Earth asteroids (NEAs), which is currently operating on the data from the newly commissioned Zwicky Transient Facility (ZTF) survey. Based on a prototype originally developed by Waszczak et al. (2017) for the Palomar Transient Factory (PTF), the predecessor of ZTF, ZStreak features an improved machine-learning model that can cope with the 10x data rate increment between PTF and ZTF. Since its first discovery on 2018 February 5 (2018 CL), ZTF/ZStreak has discovered 45 confirmed new NEAs over a total of 232 observable nights until 2018 December 31. Most of the discoveries are small NEAs, with diameters less than similar to 100. m. By analyzing the discovery circumstances, we find that objects having the first to last detection time interval under 2. hr are at risk of being lost. We will further improve real-time follow-up capabilities, and work on suppressing false positives using deep learning.
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