The volumetric rate of normal type Ia supernovae in the local universe discovered by the Palomar Transient Factory

We present the volumetric rate of normal type Ia supernovae (SNe Ia) discovered by the Palomar Transient Factory (PTF). Using strict data-quality cuts, and considering only periods when the PTF maintained a regular cadence, PTF discovered 90 SNe Ia at $z\le0.09$ in a well-controlled sample over three years of operation (2010-2012). We use this to calculate the volumetric rate of SN Ia events by comparing this sample to simulations of hundreds of millions of SN Ia light curves produced in statistically representative realisations of the PTF survey. This quantifies the recovery efficiency of each PTF SN Ia event, and thus the relative weighting of each event. From this, the volumetric SN Ia rate was found to be $r_v=2.43\pm0.29\,\text{(stat)}_{-0.19}^{+0.33}\text{(sys)}\times10^{-5}\,\text{SNe yr}^{-1}\,\text{Mpc}^{-3}\, h_{70}^{3}$. This represents the most precise local measurement of the SN Ia rate. We fit a simple SN Ia delay-time distribution model, $\propto\mathrm{t}^{-\beta}$, to our PTF rate measurement combined with a literature sample of rate measurements from surveys at higher-redshifts. We find $\beta{\sim}1$, consistent with a progenitor channel governed by the gravitational in-spiral of binary white dwarfs.Comment: 14 pages, 8 figure

Searching for late-time interaction signatures in Type Ia supernovae from the Zwicky Transient Facility

The nature of the progenitor systems and explosion mechanisms that give rise to Type Ia supernovae (SNe Ia) are still debated. The interaction signature of circumstellar material (CSM) being swept up by expanding ejecta can constrain the type of system from which it was ejected. Most previous studies have focused on finding CSM ejected shortly before the SN Ia explosion still residing close to the explosion site, resulting in short delay times until the interaction starts. We use a sample of 3627 SNe Ia from the Zwicky Transient Facility discovered between 2018 and 2020 and search for interaction signatures over 100 days after peak brightness. By binning the late-time light curve data to push the detection limit as deep as possible, we identify potential late-time rebrightening in 3 SNe Ia (SN 2018grt, SN 2019dlf, SN 2020tfc). The late-time detections occur between 550 and 1450 d after peak brightness, have mean absolute $r$-band magnitudes of -16.4 to -16.8 mag and last up to a few hundred days, significantly brighter than the late-time CSM interaction discovered in the prototype SN 2015cp. The late-time detections all occur within 0.8 kpc of the host nucleus and are not easily explained by nuclear activity, another transient at a similar sky position, or data quality issues. This suggests environment or specific progenitor characteristics playing a role in producing potential CSM signatures in these SNe Ia. By simulating the ZTF survey we estimate that <0.5 per cent of normal SNe Ia display late-time strong H $\alpha$-dominated CSM interaction. This is equivalent to an absolute rate of $8_{-4}^{+20}$ to $54_{-26}^{+91}$ Gpc$^{-3}$ yr$^{-1}$ assuming a constant SN Ia rate of $2.4\times10^{-5}$ Mpc$^{-3}$ yr$^{-1}$ for $z \leq 0.1$. Weaker interaction signatures, more similar to the strength seen in SN 2015cp, could be more common but are difficult to constrain with our survey depth.Comment: 24 pages, 13 figures, 6 tables, A&A accepte

The effect of environment on type Ia supernovae in the dark energy survey three-year cosmological sample

Analyses of type Ia supernovae (SNe Ia) have found puzzling correlations between their standardised luminosities and host galaxy properties: SNe Ia in high-mass, passive hosts appear brighter than those in lower-mass, star-forming hosts. We examine the host galaxies of SNe Ia in the Dark Energy Survey three-year spectroscopically-confirmed cosmological sample, obtaining photometry in a series of ‘local’ apertures centred on the SN, and for the global host galaxy. We study the differences in these host galaxy properties, such as stellar mass and rest-frame U − R colours, and their correlations with SN Ia parameters including Hubble residuals. We find all Hubble residual steps to be >3σ in significance, both for splitting at the traditional environmental property sample median and for the step of maximum significance. For stellar mass, we find a maximal local step of 0.098 ± 0.018 mag; ∼0.03 mag greater than the largest global stellar mass step in our sample (0.070 ± 0.017 mag). When splitting at the sample median, differences between local and global U − R steps are small, both ∼0.08 mag, but are more significant than the global stellar mass step (0.057 ± 0.017 mag). We split the data into sub-samples based on SN Ia light curve parameters: stretch (x1) and colour (c), finding that redder objects (c > 0) have larger Hubble residual steps, for both stellar mass and U − R, for both local and global measurements, of ∼0.14 mag. Additionally, the bluer (star-forming) local environments host a more homogeneous SN Ia sample, with local U − R r.m.s. scatter as low as 0.084 ± 0.017 mag for blue (c < 0) SNe Ia in locally blue U − R environments

The rate of cosmic thermonuclear Explosions in the Local Universe

This thesis investigates the volumetric rates of thermonuclear supernovae (SNe) in the Palomar Transient Factory (PTF). SN rates are a measure of how frequently stellar explosions occur as a function of cosmological volumes, or host galaxy properties. SNe are powerful cosmological probes; understanding their rates offers insight into the progenitors to the explosion and the astrophysics of galactic chemical evolution.The Palomar Transient Factory was an automated optical sky survey designed for transient discovery. It spectroscopically confirmed ~1900 SNe during the period of 2009-2012. PTF operated with a 3-5 day cadence, and scanned more than 8,000 square degrees of the sky. I quantified the performance of PTF through large scale simulations of transient events. Firstly, ~7 x 106 fake transient events were inserted into real observational images. These 'fakes' were designed to test the real-time transient discovery pipeline. The images were treated identically to a new PTF observation, where the fakes were either recovered or not.Multidimensional grids were created to describe how a transient would be recovered as a function of the fake's brightness and observing conditions. I found that bright fakes (mR &lt; 18.5) were recovered with ~97% efficiency. PTF was 50% complete at mR = 20.3. The recovery efficiency was also strongly dependent on: the limiting magnitude, the image quality, the sky background, and the immediate environment brightness.The second stage of quantifying the performance of PTF was transient specific. Hundreds of millions of SNe Ia light curves were simulated on an artificial night sky. The simulations shared the statistical properties of the single epoch efficiencies. Through a Monte-Carlo simulation of the SNe Ia populations, I derived recovery efficiencies as a function of SNe Ia light curve parameters.A sample of 90 SNe Ia (z ≤ 0.09), were compared to the simulation recovery efficiencies. This provided the probability of the SNe passing rigorous quality cuts, and was used as a weighting factor. The weighted objects were summed and the volumetric SNe Ia rate was found to be 2.43 (+0.29 0.29 stat) (+0.33 0.19 sys) ×10-5 SNe Ia yr-1 Mpc-3 h370.I fit a simple delay-time model,  Ψ = Ψ1t-β, to the data and found β ~ 1.I applied the same methodology to a newly discovered class of SN: Ca-rich SNe. Their volumetric rate was found to be 1.62(±1.07) × 10-5 SNe yr-1 Mpc-3 h370. Furthermore, I used model nucleosynthetic yields for Ca-Rich, SNe Ia and CCSNe models and found that a Ca-rich rate ~ 30 - 50% of the SNe Ia rate would explain the observed Ca/Fe intra-cluster medium abundances

Real-Time Recovery Efficiencies and Performance of the Palomar Transient Factory&#39;s Transient Discovery Pipeline: Fakes Catalog

This CSV file is a complete catalog of all the source stars and fake events in the observational data used in the analysis of PTF&#39;s real-time efficiency. From this the final efficiency grids can be reconstructed. The accompanying README file describes the columns. This catalogue supports the publication Frohmaier et al, (2017) &quot;Real-Time Recovery Efficiencies and Performance of the Palomar Transient Factory&#39;s Transient Discovery Pipeline&rdquo;, Astrophysical Journal. </span

Real-time recovery efficiencies and performance of the Palomar Transient Factory's transient discovery pipeline

We present the transient source detection efficiencies of the Palomar Transient Factory (PTF), parameterizing the number of transients that PTF found, versus the number of similar transients that occurred over the same period in the survey search area but that were missed. PTF was an optical sky survey carried out with the Palomar 48-inch telescope over 2009-2012, observing more than 8000 square degrees of sky with cadences of between 1 and 5 days, locating around 50,000 non-moving transient sources, and spectroscopically confirming around 1900 supernovae. We assess the effectiveness with which PTF detected transient sources, by inserting ~7 million artificial point sources into real PTF data. We then study the efficiency with which the PTF real-time pipeline recovered these sources as a function of the source magnitude, host galaxy surface brightness, and various observing conditions (using proxies for seeing, sky brightness, and transparency). The product of this study is a multi-dimensional recovery efficiency grid appropriate for the range of observing conditions that PTF experienced, and that can then be used for studies of the rates, environments, and luminosity functions of different transient types using detailed Monte Carlo simulations. We illustrate the technique using the observationally well-understood class of type Ia supernovae

The volumetric rate of calcium-rich transients in the local universe

We present a measurement of the volumetric rate of ‘calcium-rich’ optical transients in the local universe, using a sample of three events from the Palomar Transient Factory (PTF). This measurement builds on a detailed study of the PTF transient detection efficiencies, and uses a Monte Carlo simulation of the PTF survey. We measure the volumetric rate of calcium-rich transients to be higher than previous estimates: 1.21+1.13−0.39×10−5 events yr−1 Mpc−3. This is equivalent to 33-94% of the local volumetric type Ia supernova rate. This calcium-rich transient rate is sufficient to reproduce the observed calcium abundances in galaxy clusters, assuming an asymptotic calcium yield per calcium-rich event of ~0.05M⊙. We also study the PTF detection efficiency of these transients as a function of position within their candidate host galaxies. We confirm as a real physical effect previous results that suggest calcium-rich transients prefer large physical offsets from their host galaxies

The detection efficiency of Type Ia supernovae from the Zwicky Transient Facility: limits on the intrinsic rate of early flux excesses

Samples of young Type Ia supernovae have shown ‘early excess’ emission in a few cases. Similar excesses are predicted by some explosion and progenitor scenarios and hence can provide important clues regarding the origin of thermonuclear supernovae. They are, however, only predicted to last up to the first few days following explosion. It is therefore unclear whether such scenarios are intrinsically rare or whether the relatively small sample size simply reflects the difficulty in obtaining sufficiently early detections. To that end, we perform toy simulations covering a range of survey depths and cadences, and investigate the efficiency with which young Type Ia supernovae are recovered. As input for our simulations, we use models that broadly cover the range of predicted luminosities. Based on our simulations, we find that in a typical 3 d cadence survey, only ∼10 per cent of Type Ia supernovae would be detected early enough to rule out the presence of an excess. A 2 d cadence, however, should see this increase to ∼15 per cent. We find comparable results from more detailed simulations of the Zwicky Transient Facility surveys. Using the recovery efficiencies from these detailed simulations, we investigate the number of young Type Ia supernovae expected to be discovered assuming some fraction of the population comes from scenarios producing an excess at early times. Comparing the results of our simulations to observations, we find that the intrinsic fraction of Type Ia supernovae with early flux excesses is ∼28+13−11 per cent⁠

A machine learning algorithm to predict a culprit lesion after out of hospital cardiac arrest

Background: we aimed to develop a machine learning algorithm to predict the presence of a culprit lesion in patients with out-of-hospital cardiac arrest (OHCA). Methods: we used the King's Out-of-Hospital Cardiac Arrest Registry, a retrospective cohort of 398 patients admitted to King's College Hospital between May 2012 and December 2017. The primary outcome was the presence of a culprit coronary artery lesion, for which a gradient boosting model was optimized to predict. The algorithm was then validated in two independent European cohorts comprising 568 patients. Results: a culprit lesion was observed in 209/309 (67.4%) patients receiving early coronary angiography in the development, and 199/293 (67.9%) in the Ljubljana and 102/132 (61.1%) in the Bristol validation cohorts, respectively. The algorithm, which is presented as a web application, incorporates nine variables including age, a localizing feature on electrocardiogram (ECG) (≥2 mm of ST change in contiguous leads), regional wall motion abnormality, history of vascular disease and initial shockable rhythm. This model had an area under the curve (AUC) of 0.89 in the development and 0.83/0.81 in the validation cohorts with good calibration and outperforms the current gold standard-ECG alone (AUC: 0.69/0.67/0/67). Conclusions: a novel simple machine learning-derived algorithm can be applied to patients with OHCA, to predict a culprit coronary artery disease lesion with high accuracy.</p