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Kasliwal M.M.,California Institute of Technology | Kasliwal M.M.,Carnegie Institution for Science | Kulkarni S.R.,California Institute of Technology | Gal-Yam A.,Weizmann Institute of Science | And 28 more authors.
Astrophysical Journal | Year: 2012

From the first two seasons of the Palomar Transient Factory, we identify three peculiar transients (PTF09dav, PTF10iuv, and PTF11bij) with five distinguishing characteristics: peak luminosity in the gap between novae and supernovae (MR ≈ -15.5 to -16.5mag), rapid photometric evolution (t rise 12-15days), large photospheric velocities (6000-11,000km s-1), early spectroscopic evolution into nebular phase (1-3months), and peculiar nebular spectra dominated by calcium. We also culled the extensive decade-long Lick Observatory Supernova Search database and identified an additional member of this group, SN2007ke. Our choice of photometric and spectroscopic properties was motivated by SN2005E (Perets et al.). To our surprise, as in the case of SN2005E, all four members of this group are also clearly offset from the bulk of their host galaxy. Given the well-sampled early- and late-time light curves, we derive ejecta masses in the range of 0.4-0.7M ⊙. Spectroscopically, we find that there may be a diversity in the photospheric phase, but the commonality is in the unusual nebular spectra. Our extensive follow-up observations rule out standard thermonuclear and standard core-collapse explosions for this class of "calcium-rich gap" transients. If the progenitor is a white dwarf, we are likely seeing a detonation of the white dwarf core and perhaps even shock-front interaction with a previously ejected nova shell. If the progenitor is a massive star, a nonstandard channel specific to a low-metallicity environment needs to be invoked (e.g., ejecta fallback leading to black hole formation). Detection (or the lack thereof) of a faint underlying host (dwarf galaxy and cluster) will provide a crucial and decisive diagnostic to choose between these alternatives. © 2012. The American Astronomical Society. All rights reserved. Source

White C.J.,Princeton University | Kasliwal M.M.,Carnegie Institution for Science | Nugent P.E.,Lawrence Berkeley National Laboratory | Nugent P.E.,University of California at Berkeley | And 26 more authors.
Astrophysical Journal | Year: 2015

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 (90% confidence), lower compared to earlier estimates. Combining our objects with the literature sample, we propose that these subclasses have two distinct physical origins. © 2015. The American Astronomical Society. All rights reserved. Source

Gomez H.L.,University of Cardiff | Vlahakis C.,Leiden University | Stretch C.M.,University of Cardiff | Dunne L.,University of Nottingham | And 5 more authors.
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2010

Previous submillimetre (submm) observations detected 0.7 M. of cool dust emission around the luminous blue variable (LBV) star η Carinae. These observations were hindered by the low declination of η Carinae and contamination from free-free emission originating from the stellar wind. Here, we present deep submm observations with LABOCA at 870 μm, taken shortly after a maximum in the 5.5-year radio cycle. We find a significant difference in the submm flux measured here compared with the previous measurement: the first indication of variability at submm wavelengths. A comparison of the submm structures with ionized emission features suggests the 870 μm is dominated by emission from the ionized wind and not thermal emission from dust. We estimate 0.4 ±0.1 M. of dust surrounding η Carinae. The spatial distribution of the submm emission limits the mass loss to within the last thousand years, and is associated with mass ejected during the great eruptions and the pre-outburst LBV wind phase; we estimate that η Carinae has ejected >40 M. of gas within this time-scale. © 2009 RAS. Source

Chen T.-W.,Queens University of Belfast | Smartt S.J.,Queens University of Belfast | Bresolin F.,Institute for Astronomy | Pastorello A.,National institute for astrophysics | And 6 more authors.
Astrophysical Journal Letters | Year: 2013

Super-luminous supernovae have a tendency to occur in faint host galaxies which are likely to have low mass and low metallicity. While these extremely luminous explosions have been observed from z = 0.1 to 1.55, the closest explosions allow more detailed investigations of their host galaxies. We present a detailed analysis of the host galaxy of SN 2010gx (z = 0.23), one of the best studied super-luminous type Ic supernovae. The host is a dwarf galaxy (M g = -17.42 ± 0.17) with a high specific star formation rate. It has a remarkably low metallicity of 12 + log (O/H) = 7.5 ± 0.1 dex as determined from the detection of the [O III] λ4363 line. This is the first reliable metallicity determination of a super-luminous stripped-envelope supernova host. We collected deep multi-epoch imaging with Gemini + GMOS between 240 and 560 days after explosion to search for any sign of radioactive 56Ni, which might provide further insights on the explosion mechanism and the progenitor's nature. We reach griz magnitudes of m AB ∼ 26, but do not detect SN 2010gx at these epochs. The limit implies that any 56Ni production was similar to or below that of SN 1998bw (a luminous type Ic SN that produced around 0.4 M⊙ of 56Ni). The low volumetric rates of these supernovae (∼10-4 of the core-collapse population) could be qualitatively matched if the explosion mechanism requires a combination of low-metallicity (below 0.2 Z ⊙), high progenitor mass (>60M) and high rotation rate (fastest 10% of rotators). © 2013. The American Astronomical Society. All rights reserved. Source

Price-Whelan A.M.,Columbia University | Agueros M.A.,Columbia University | Fournier A.P.,University of California at Santa Barbara | Fournier A.P.,Las Cumbres Observatory Global Telescope Network Inc. | And 7 more authors.
Astrophysical Journal | Year: 2014

Many photometric time-domain surveys are driven by specific goals, such as searches for supernovae or transiting exoplanets, which set the cadence with which fields are re-imaged. In the case of the Palomar Transient Factory (PTF), several sub-surveys are conducted in parallel, leading to non-uniform sampling over its ∼20,000 deg2 footprint. While the median 7.26 deg 2 PTF field has been imaged ∼40 times in the R band, ∼2300 deg2 have been observed >100 times. We use PTF data to study the trade off between searching for microlensing events in a survey whose footprint is much larger than that of typical microlensing searches, but with far-from-optimal time sampling. To examine the probability that microlensing events can be recovered in these data, we test statistics used on uniformly sampled data to identify variables and transients. We find that the von Neumann ratio performs best for identifying simulated microlensing events in our data. We develop a selection method using this statistic and apply it to data from fields with >10 R-band observations, 1.1 × 109 light curves, uncovering three candidate microlensing events. We lack simultaneous, multi-color photometry to confirm these as microlensing events. However, their number is consistent with predictions for the event rate in the PTF footprint over the survey's three years of operations, as estimated from near-field microlensing models. This work can help constrain all-sky event rate predictions and tests microlensing signal recovery in large data sets, which will be useful to future time-domain surveys, such as that planned with the Large Synoptic Survey Telescope. © 2014. The American Astronomical Society. All rights reserved. Source

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