Type Ia Supernova Rate Research Articles

Constraining the Initial Mass Function via Stellar Transients

The stellar initial mass function (IMF) represents a fundamental quantity in astrophysics and cosmology describing the mass distribution of stars from low mass all the way up to massive and very massive stars. It is intimately linked to a wide variety of topics, including stellar and binary evolution, galaxy evolution, chemical enrichment, and cosmological reionization. Nonetheless, the IMF still remains highly uncertain. In this work, we aim to determine the IMF with a novel approach based on the observed rates of transients of stellar origin. We parametrize the IMF with a simple but flexible Larson shape, and insert it into a parametric model for the cosmic UV luminosity density, local stellar mass density, type Ia supernova (SN Ia), core-collapse supernova (CCSN), and long gamma-ray burst (LGRB) rates as a function of redshift. We constrain our free parameters by matching the model predictions to a set of empirical determinations for the corresponding quantities via a Bayesian Markov Chain Monte Carlo method. Remarkably, we are able to provide an independent IMF determination with a characteristic mass mc=0.10−0.08+0.24M⊙ and high-mass slope ξ=−2.53−0.27+0.24 that are in accordance with the widely used IMF parameterizations (e.g., Salpeter, Kroupa, Chabrier). Moreover, the adoption of an up-to-date recipe for the cosmic metallicity evolution allows us to constrain the maximum metallicity of LGRB progenitors to Zmax=0.12−0.05+0.29Z⊙. We also find which progenitor fraction actually leads to SN Ia or LGRB emission (e.g., due to binary interaction or jet-launching conditions), put constraints on the CCSN and LGRB progenitor mass ranges, and test the IMF universality. These results show the potential of this kind of approach for studying the IMF, its putative evolution with the galactic environment and cosmic history, and the properties of SN Ia, CCSN, and LGRB progenitors, especially considering the wealth of data incoming in the future.

The Scale of Stellar Yields: Implications of the Measured Mean Iron Yield of Core Collapse Supernovae

The scale of α-element yields is difficult to predict from theory because of uncertainties in massive star evolution, supernova physics, and black hole formation, and it is difficult to constrain empirically because the impact of higher yields can be compensated by greater metal loss in galactic winds. We use a recent measurement of the mean iron yield of core collapse supernovae (CCSN) by Rodriguez et al., y¯Fecc=0.058±0.007M⊙ , to infer the scale of α-element yields by assuming that the plateau of [α/Fe] abundance ratios observed in low-metallicity stars represents the yield ratio of CCSN. For a plateau at [α/Fe]cc = 0.45, we find that the population-averaged yields of O and Mg are about equal to the solar abundance of these elements, logyOcc/ZO,⊙=logyMgcc/ZMg,⊙=−0.01±0.1 , where yXcc is the mass of element X produced by massive stars per unit mass of star formation. The inferred O and Fe yields agree with predictions of the Sukhbold et al. CCSN models assuming their Z9.6+N20 neutrino-driven engine, a scenario in which many progenitors with M < 40M ⊙ implode to black holes rather than exploding. The yields are lower than assumed in many models of the galaxy mass–metallicity relation, reducing the level of outflows needed to match observed abundances. Our one-zone chemical evolution models with η=Ṁout/Ṁ*≈0.6 evolve to solar metallicity at late times. By further requiring that models reach [α/Fe] ≈ 0 at late times, we infer a Hubble-time integrated Type Ia supernova rate of 1.1×10−3M⊙−1 , compatible with estimates from supernova surveys.

Cosmic Type Ia supernova rate and constraints on supernova Ia progenitors

Type Ia supernovae play a key role in the evolution of galaxies by polluting the interstellar medium with a fraction of iron peak elements larger than that released in the core-collapse supernova events. Their light curve, moreover, is widely used in cosmological studies as it constitutes a reliable distance indicator on extragalactic scales. Among the mechanisms proposed to explain the Type Ia supernovae (SNe), the single- and double-degenerate channels are thought to be the dominant ones, which implies a different distribution of time delays between the progenitor formation and the explosion. In this paper, we aim to determine the dominant mechanism by comparing a compilation of Type Ia SN rates with those computed from various cosmic star-formation histories coupled with different delay-time distribution functions. We also evaluate the relative contributions of both channels. By using a least-squares fitting procedure, we modeled the observations of Type Ia SN rates assuming different combinations of three recent cosmic star-formation rates and seven delay-time distributions. The goodness of these fits are statistically quantified by the $ test. For two of the three cosmic star-formation rates, the single degenerate scenario provides the most accurate explanation for the observations, while a combination of 34&lt;!PCT!&gt; single-degenerate- and 66&lt;!PCT!&gt; double-degenerate delay-time distributions is more plausible for the remaining tested cosmic star-formation rates. Though dependent on the assumed cosmic star-formation rate, we find arguments in favor of the single-degenerate model. From the theoretic point of view, at least sim 34&lt;!PCT!&gt; of the Type Ia SN must have been produced through the single-degenerate channel to account for the observations. The wide, double-degenerate mechanism slightly under-predicts the observations at redshift $z 1$, unless the cosmic SFR flattens in that regime. On the contrary, although the purely close double-degenerate scenario can be ruled out, we cannot rule out a mixed scenario with single- and double-degenerate progenitors.

Binaries drive high Type Ia supernova rates in dwarf galaxies

ABSTRACT The scaling of the specific Type Ia supernova (SN Ia) rate with host galaxy stellar mass $\dot{\text{N}}_\text{Ia} / \text{M}_\star \sim \text{M}_\star ^{-0.3}$ as measured in ASAS-SN and DES strongly suggests that the number of SNe Ia produced by a stellar population depends inversely on its metallicity. We estimate the strength of the required metallicity dependence by combining the average star formation histories (SFHs) of galaxies as a function of their stellar mass with the mass–metallicity relation (MZR) for galaxies and common parametrizations for the SN Ia delay-time distribution. The differences in SFHs can account for only ∼30 per cent of the increase in the specific SN Ia rate between stellar masses of M⋆ = 1010 and 107.2 M⊙. We find that an additional metallicity dependence of approximately ∼Z−0.5 is required to explain the observed scaling. This scaling matches the metallicity dependence of the close binary fraction observed in APOGEE, suggesting that the enhanced SN Ia rate in low-mass galaxies can be explained by a combination of their more extended SFHs and a higher binary fraction due to their lower metallicities. Due to the shape of the MZR, only galaxies below M⋆ ≈ 3 × 109 M⊙ are significantly affected by the metallicity-dependent SN Ia rates. The $\dot{\text{N}}_\text{Ia} / \text{M}_\star \sim \text{M}_\star ^{-0.3}$ scaling becomes shallower with increasing redshift, dropping by factor of ∼2 at 107.2 M⊙ between z = 0 and 1 with our ∼Z−0.5 scaling. With metallicity-independent rates, this decrease is a factor of ∼3. We discuss the implications of metallicity-dependent SN Ia rates for one-zone models of galactic chemical evolution.

Exploring metallicity-dependent rates of Type Ia supernovae and their impact on galaxy formation

ABSTRACT Type Ia supernovae are critical for feedback and elemental enrichment in galaxies. Recent surveys like the All-Sky Automated Survey for Supernova (ASAS-SN) and the Dark Energy Survey (DES) find that the specific supernova Ia rate at z ∼ 0 may be ≲20–50× higher in lower mass galaxies than at Milky Way-mass. Independently, observations show that the close-binary fraction of solar-type Milky Way stars is higher at lower metallicity. Motivated by these observations, we use the FIRE-2 cosmological zoom-in simulations to explore the impact of metallicity-dependent rate models on galaxies of $M_* \sim 10^7\!-\!10^{11}\, \rm {M}_{\odot }$. First, we benchmark our simulated star formation histories against observations, and show that the assumed stellar mass functions play a major role in determining the degree of tension between observations and metallicity-independent rate models, potentially causing ASAS-SN and DES observations to agree more than might appear. Models in which the supernova Ia rate increases with decreasing metallicity ($\propto Z^{-0.5 \,\, \rm {to} \,\, -1}$) provide significantly better agreement with observations. Encouragingly, these rate increases (≳10× in low-mass galaxies) do not significantly impact galaxy masses and morphologies, which remain largely unaffected except for our most extreme models. We explore implications for both [Fe/H] and [$\alpha /\rm {Fe}$] enrichment; metallicity-dependent rate models can improve agreement with the observed stellar mass–metallicity relations in low-mass galaxies. Our results demonstrate that a range of metallicity-dependent rate models are viable for galaxy formation and motivate future work.

A Statistical View of the Stable and Unstable Roche Lobe Overflow of a Tertiary Star onto the Inner Binary in Triple Systems

Abstract In compact stellar triple systems, an evolved tertiary star can overflow its Roche lobe around the inner binary. Subsequently, the tertiary star can transfer mass to the inner binary in a stable manner, or Roche lobe overflow (RLOF) can be unstable and lead to common-envelope (CE) evolution. In the latter case, the inner binary enters the extended envelope of the tertiary star and spirals in toward the donor’s core, potentially leading to mergers or ejections. Although studied in detail for individual systems, a comprehensive statistical view on the various outcomes of triple RLOF is lacking. Here, we carry out 105 population synthesis simulations of tight triples, self-consistently taking into account stellar evolution, binary interactions, and gravitational dynamics. Also included are prescriptions for the long-term evolution of stable triple mass transfer, and triple CE evolution. Although simple and ignoring hydrodynamic effects, these prescriptions allow for a qualitative statistical study. We find that triple RLOF occurs in ∼0.06% of all triple systems. Of these 0.06%, ∼64% of cases lead to stable mass transfer, and ∼36% to triple CE evolution. Triple CE is most often (∼76%) followed by one or multiple mergers in short succession, most likely an inner binary merger of two main-sequence stars. Other outcomes of triple CE are a binary+single system (∼23%, most of which do not involve exchange interactions), and a stable triple (∼1%). We also estimate the rate of type Ia supernovae involving white dwarf mergers following triple RLOF, but find only a negligible contribution.

White Dwarf Subsystems in Core-Collapsed Globular Clusters

Abstract Numerical and observational evidence suggests that massive white dwarfs dominate the innermost regions of core-collapsed globular clusters by both number and total mass. Using NGC 6397 as a test case, we constrain the features of white dwarf populations in core-collapsed clusters, both at present day and throughout their lifetimes. The dynamics of these white dwarf subsystems have a number of astrophysical implications. We demonstrate that the collapse of globular cluster cores is ultimately halted by the dynamical burning of white dwarf binaries. We predict that core-collapsed clusters in the local universe yield a white dwarf merger rate of  ( 10 ) Gpc − 3 yr − 1 , roughly 0.1%–1% of the observed Type Ia supernova rate. We show that prior to merger, inspiraling white dwarf binaries will be observable as gravitational-wave sources at millihertz and decihertz frequencies. Over 90% of these mergers have a total mass greater than the Chandrasekhar limit. We argue that the merger/collision remnants, if not destroyed completely in an explosive transient, may be observed in core-collapsed clusters either as young neutron stars/pulsars/magnetars (in the event of accretion-induced collapse) or as young massive white dwarfs offset from the standard white dwarf cooling sequence. Finally, we show that collisions between white dwarfs and main-sequence stars, which may be detectable as bright transients, occur at a rate of  ( 100 ) Gpc − 3 yr − 1 in the local universe. We find that these collisions lead to depletion of blue straggler stars and main-sequence star binaries in the centers of core-collapsed clusters.

Thermonuclear explosion of a massive hybrid HeCO white dwarf triggered by a He detonation on a companion

ABSTRACT Normal type Ia supernovae (SNe) are thought to arise from the thermonuclear explosion of massive (&amp;gt;0.8 M⊙) carbon–oxygen white dwarfs (WDs), although the exact mechanism is debated. In some models, helium accretion on to a carbon–oxygen (CO) WD from a companion was suggested to dynamically trigger a detonation of the accreted helium shell. The helium detonation then produces a shock that after converging on itself close to the core of the CO WD, triggers a secondary carbon detonation, and gives rise to an energetic explosion. However, most studies of such scenarios have been done in one or two dimensions, and/or did not consider self-consistent models for the accretion and the He donor. Here, we make use of detailed 3D simulation to study the interaction of a He-rich hybrid $0.69\, \mathrm{M_\odot }$ HeCO WD with a more massive $0.8\, \mathrm{M_\odot }$ CO WD. We find that accretion from the hybrid WD on to the CO WD gives rise to a helium detonation. However, the helium detonation does not trigger a carbon detonation in the CO WD. Instead, the helium detonation burns through the accretion stream to also burn the helium shell of the donor hybrid HeCO WD. The detonation of its massive helium shell then compresses its CO core, and triggers its detonation and full destruction. The explosion gives rise to a faint, likely highly reddened transient, potentially observable by the Vera Rubin survey, and the high-velocity ($\sim \! 1000\, \mathrm{km s^{-1}}$) ejection of the heated surviving CO WD companion. Pending on uncertainties in stellar evolution, we estimate the rate of such transient to be up to $\sim \! 10{{\ \rm per\ cent}}$ of the rate of type Ia SNe.

The Zwicky Transient Facility Bright Transient Survey. II. A Public Statistical Sample for Exploring Supernova Demographics*

Abstract We present a public catalog of transients from the Zwicky Transient Facility (ZTF) Bright Transient Survey, a magnitude-limited (m &lt; 19 mag in either the g or r filter) survey for extragalactic transients in the ZTF public stream. We introduce cuts on survey coverage, sky visibility around peak light, and other properties unconnected to the nature of the transient, and show that the resulting statistical sample is spectroscopically 97% complete at &lt;18 mag, 93% complete at &lt;18.5 mag, and 75% complete at &lt;19 mag. We summarize the fundamental properties of this population, identifying distinct duration–luminosity correlations in a variety of supernova (SN) classes and associating the majority of fast optical transients with well-established spectroscopic SN types (primarily SN Ibn and II/IIb). We measure the Type Ia SN and core-collapse (CC) SN rates and luminosity functions, which show good consistency with recent work. About 7% of CC SNe explode in very low-luminosity galaxies (M i &gt; −16 mag), 10% in red-sequence galaxies, and 1% in massive ellipticals. We find no significant difference in the luminosity or color distributions between the host galaxies of SNe Type II and SNe Type Ib/c, suggesting that line-driven wind stripping does not play a major role in the loss of the hydrogen envelope from their progenitors. Future large-scale classification efforts with ZTF and other wide-area surveys will provide high-quality measurements of the rates, properties, and environments of all known types of optical transients and limits on the existence of theoretically predicted but as yet unobserved explosions.

The supernova remnant population of the Small Magellanic Cloud

Aims.We present a comprehensive study on the supernova remnant (SNR) population of the Small Magellanic Cloud (SMC). We measured multiwavelength properties of the SMC SNRs and compare them to those of the Large Magellanic Cloud (LMC) population.Methods.This study combines the large dataset ofXMM-Newtonobservations of the SMC, archival and recent radio continuum observations, an optical line emission survey, and new optical spectroscopic observations. We were therefore able to build a complete and clean sample of 19 confirmed and four candidate SNRs. The homogeneous X-ray spectral analysis allowed us to search for SN ejecta and Fe K line emission, and to measure interstellar medium abundances. We estimated the ratio of core-collapse to type Ia supernova rates of the SMC based on the X-ray properties and the local stellar environment of each SNR.Results.After the removal of unconfirmed or misclassified objects, and the addition of two newly confirmed SNRs based on multi-wavelength features, we present a final list of 21 confirmed SNRs and two candidates. While no Fe K line is detected even for the brightest and youngest SNR, we find X-ray evidence of SN ejecta in 11 SNRs. We estimate a fraction of 0.62–0.92 core-collapse supernova for every supernova (90% confidence interval), higher than in the LMC. The difference can be ascribed to the absence of the enhanced star-formation episode in the SMC, which occurred in the LMC 0.5–1.5 Gyr ago. The hot-gas abundances of O, Ne, Mg, and Fe are 0.1–0.2 times solar. Their ratios, with respect to SMC stellar abundances, reflect the effects of dust depletion and partial dust destruction in SNR shocks. We find evidence that the ambient medium probed by SMC SNRs is less disturbed and less dense on average than in the LMC, consistent with the different morphologies of the two galaxies.

Common envelope to explosion delay time of Type Ia supernovae

ABSTRACT I study the rate of Type Ia supernovae (SNe Ia) within about a million years after the assumed common envelope evolution (CEE) that forms the progenitors of these SNe Ia, and find that the population of SNe Ia with short CEE to explosion delay (CEED) time is ≈few × 0.1 of all SNe Ia. I also claim for an expression for the rate of these SNe Ia that occur at short times after the CEE ($t_{\rm CEED} \lesssim 10^6 {~\rm yr}$), which is different from that of the delay time distribution (DTD) billions of years after star formation. This tentatively hints that the physical processes that determine the short CEED time distribution (CEEDTD) are different (at least to some extent) from those that determine the DTD at billions of years. To reach these conclusions I examine SNe Ia that interact with a circumstellar matter (CSM) within months after explosion, so-called SNe Ia-CSM, and the rate of SNe Ia that on a time-scale of tens to hundreds of years interact with a CSM that might have been a planetary nebula, so-called SNe Ia inside a planetary nebula (SNIPs). I assume that the CSM in these populations results from a CEE, and hence this study is relevant mainly to the core-degenerate (CD) scenario, the double-degenerate (DD) scenario, the double-detonation (DDet) scenario with white dwarf companions, and to the CEE-wind channel of the single-degenerate (SD) scenario.

The Impact of White Dwarf Natal Kicks and Stellar Flybys on the Rates of Type Ia Supernovae in Triple-star Systems

Abstract SNe Ia could arise from mergers of carbon–oxygen white dwarfs (WDs) triggered by Lidov–Kozai (LK) oscillations in hierarchical triple-star systems. However, predicted merger rates are several orders of magnitude lower than the observed SNe Ia rate. The low predicted rates can be attributed in part to the fact that many potential WD-merger progenitor systems, with high mutual orbital inclination, merge or interact before the WD stage. Recently, evidence was found for the existence of natal kicks imparted on WDs with a typical magnitude of 0.75 km s−1. In triples, kicks change the mutual inclination and in general increase the outer orbit eccentricity, bringing the triple into an active LK regime at late stages and avoiding the issue of pre-WD merger or interaction. Stars passing by the triple can result in similar effects. However, both processes can also disrupt the triple. In this paper, we quantitatively investigate the impact of WD kicks and flybys on the rate of WD mergers using detailed simulations. We find that WD kicks and flybys combine to increase the predicted WD merger rates by a factor of ∼2.5, resulting in a time-integrated rate of ≈1.1 × 10−4 M ⊙ −1. Despite the significant boost, the predicted rates are still more than one order of magnitude below the observed rate of ∼10−3 M ⊙ −1. However, many systematic uncertainties still remain in our calculations, in particular the potential contributions from tighter triples, dynamically unstable systems, unbound systems due to WD kicks, and quadruple systems.

Correlation of the rate of Type Ia supernovae with the parent galaxy properties: Light and shadows

Context. The identification of the progenitors of Type Ia supernovae (SNIa) is extremely important in several astrophysical contexts, ranging from stellar evolution in close binary systems to evaluating cosmological parameters. Determining the distribution of the delay times (DTD) of SNIa progenitors can shed light on their nature. The DTD can be constrained by analysing the correlation between the SNIa rate and those properties of the parent galaxy which trace the average age of their stellar populations. Aims. We investigate the diagnostic capabilities of this correlation by examining its systematics with the various parameters at play: simple stellar population models, the adopted description for the star formation history (SFH) in galaxies, and the way in which the masses of the galaxies are evaluated. Methods. We computed models for the diagnostic correlations for a variety of input ingredients and for a few astrophysically motivated DTD laws appropriate for a wide range of possibilities for the SNIa progenitors. The models are compared to the results of three independent observational surveys. Results. The scaling of the SNIa rate with the properties of the parent galaxy is sensitive to all input ingredients mentioned above. This is a severe limitation on the possibility to discriminate alternative DTDs. In addition, current surveys show some discrepancies for the reddest and bluest galaxies, likely because of limited statistics and the inhomogeneity of the observations. For galaxies with intermediate colours the rates are in agreement, leading to a robust determination of the productivity of SNIa from stellar populations of ≃0.8 events per 1000 M⊙. Conclusions. Large stastistics of SNIa events along with accurate measurements of the SFH in the galaxies are required to derive firm constraints on the DTD. The LSST will achieve these results by providing a homogeneous, unbiased, and vast database on both SNIa and galaxies.

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

Abstract 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 ≤ 0.09 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 realizations 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 $r_\mathrm{ v}=2.43\pm 0.29\, \text{(stat)}_{-0.19}^{+0.33}\text{(sys)}\times 10^{-5}\, \rm{SNe\,yr}^{-1}\, \text{Mpc}^{-3}\, h_{70}^{3}$. This represents the most precise local measurement of the SN Ia rate. We fit a simple SN Ia delay-time distribution model, ∝ t−β, to our PTF rate measurement combined with a literature sample of rate measurements from surveys at higher redshifts. We find β ∼ 1, consistent with a progenitor channel governed by the gravitational inspiral of binary white dwarfs.

The relative specific Type Ia supernovae rate from three years of ASAS-SN

We analyze the 476 SN Ia host galaxies from the All-Sky Automated Survey for Supernova (ASAS-SN) Bright Supernova Catalogs to determine the observed relative Type Ia supernova (SN) rates as a function of luminosity and host galaxy properties. We find that the luminosity distribution of the SNe Ia in our sample is reasonably well described by a Schechter function with a faint-end slope $\alpha \approx 1.5$ and a knee $M_{\star} \approx -18.0$. Our specific SN Ia rates are consistent with previous results but extend to far lower host galaxy masses. We find an overall rate that scales as $(M_{\star}/10^{10} M_{\odot})^{\alpha}$ with $\alpha \approx -0.5$. This shows that the specific SN Ia rate continues rising towards lower masses even in galaxies as small as $\log(M_{\star} / M_{\odot}) \lesssim 7.0$, where it is enhanced by a factor of $\sim10-20$ relative to host galaxies with stellar masses $\sim10^{10}M_{\odot}$. We find no strong dependence of the specific SN Ia rate on the star formation activity of the host galaxies, but additional observations are required to improve the constraints on the star formation rates.

The demographics of neutron star – white dwarf mergers

Context. The mergers of neutron stars (NSs) and white dwarfs (WDs) could give rise to explosive transients, potentially observable with current and future transient surveys. However, the expected properties and distribution of such events is not well understood. Aims. Here we characterise the rates of such events, their delay-time distributions, their progenitors, and the distribution of their properties. Methods. We use binary population synthesis models and consider a wide range of initial conditions and physical processes. In particular we consider different common-envelope evolution models and different NS natal kick distributions. We provide detailed predictions arising from each of the models considered. Results. We find that the majority of NS–WD mergers are born in systems in which mass-transfer played an important role, and the WD formed before the NS. For the majority of the mergers the WDs have a carbon-oxygen composition (60−80%) and most of the rest are with oxygen-neon WDs. The time-integrated rates of NS–WD mergers are in the range of 3−15% of the type Ia supernovae (SNe) rate. Their delay-time distribution is very similar to that of type Ia SNe, but is slightly biased towards earlier times. They typically explode in young 100 Myr &lt; τ &lt; 1 Gyr environments, but have a tail distribution extending to long, gigayear-timescales. Models including significant kicks give rise to relatively wide offset distribution extending to hundreds of kiloparsecs. Conclusions. The demographic and physical properties of NS–WD mergers suggest they are likely to be peculiar type Ic-like SNe, mostly exploding in late-type galaxies. Their overall properties could be related to a class of recently observed rapidly evolving SNe, while they are less likely to be related to the class of Ca-rich SNe.

Reconciling volumetric and individual galaxy type Ia supernova rates

Significant observational effort has been devoted to determining volumetric type Ia supernova rates at high redshifts, leading to clues about the nature of Ia supernova progenitors and constraints on the iron production in the universe. A complementary approach is to investigate type Ia supernova rates in individual, more nearby, galaxies. The popular A+B model for the specific supernova rate, while reliable for a wide range of galaxy properties, diverges for large specific star formation rates. Applying it outside its range of validity could lead to the prediction of excessive type Ia supernova rates. Moreover, the A+B model it is not directly derived from a delay time distribution. We here introduce a new model which is explicitly motivated by a simple delay time distribution composed of a prompt and a delayed component. The model is in remarkably good agreement with current observational constraints. It yields a prompt fraction of $f_{p}= 0.11^{+0.10}_{-0.06}$ in agreement with results based on volumetric rates of type Ia supernovae at high redshift (Rodney et al. 2014). The model is tested against realistic star formation rates from the Illustris-1 simulation and is found to be self consistent in the asymptotic limits. An analytic function that encapsulates the features of the new model is shown to be in excellent agreement with the data. In terms of goodness of fit, the new model is strongly preferred over the A+B model. At $\log{({\rm sSFR})} \gtrsim -9$ there are no constraints from observations. Observations in this regime will further constrain the delay time distribution of type Ia supernovae at short delay times.

The rate of Type-Ia supernovae in galaxy clusters and the delay-time distribution out to redshift 1.75

The observed delay-time distribution (DTD) of Type-Ia supernovae (SNe Ia) is a valuable probe of SN Ia progenitors and physics, and of the role of SNe Ia in cosmic metal enrichment. The SN Ia rate in galaxy clusters as a function of cluster redshift is an almost-direct measure of the DTD, but current estimates have been limited out to a mean redshift z=1.1, corresponding to time delays, after cluster star-formation, of over 3.2 Gyr. We analyze data from a Hubble Space Telescope monitoring project of 12 galaxy clusters at z=1.13-1.75, where we discover 29 SNe, and present their multi-band light curves. Based on the SN photometry and the apparent host galaxies, we assess cluster membership and SN type, finding 11 cases that are likely SNe Ia in cluster galaxies and 4 more cases which are possible but not certain cluster SNe Ia. We conduct simulations to estimate the SN detection efficiency, the experiment's completeness, and the photometric errors, and perform photometry of the cluster galaxies to derive the cluster stellar masses. Separating the cluster sample into high-z and low-z bins, we obtain rest-frame SN Ia rates per unit formed stellar mass of $2.2 ^{+2.6}_{-1.3}\times 10^{-13}{\rm yr}^{-1}{\rm M}_\odot^{-1}$ at a mean redshift z=1.25, and $3.5^{+6.6}_{-2.8} \times 10^{-13}{\rm yr}^{-1}{\rm M}_\odot^{-1}$ at z=1.58. Combining our results with previous cluster SN Ia rates, we fit the DTD, now down to delays of 1.5 Gyr, with a power-law dependence, $t^\alpha$, with $\alpha=-1.30^{+0.23}_{-0.16}$. We confirm previous indications for a Hubble-time-integrated SN Ia production efficiency that is several times higher in galaxy clusters than in the field, perhaps caused by a peculiar stellar initial mass function in clusters, or by a higher incidence of binaries that will evolve into SNe Ia.

The Volumetric Rate of Calcium-rich Transients in the Local Universe

Abstract 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: 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 ∼0.05 . 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 that calcium-rich transients prefer large physical offsets from their host galaxies.

On the rates of Type Ia supernovae originating from white dwarf collisions in quadruple star systems

We consider the evolution of stellar hierarchical quadruple systems in the 2+2 (two binaries orbiting each other's barycentre) and 3+1 (triple orbited by a fourth star) configurations. In our simulations, we take into account the effects of secular dynamical evolution, stellar evolution, tidal evolution and encounters with passing stars. We focus on type Ia supernovae (SNe Ia) driven by collisions of carbon-oxygen (CO) white dwarfs (WDs). Such collisions can arise from several channels: (1) collisions due to extremely high eccentricities induced by secular evolution, (2) collisions following a dynamical instability of the system, and (3) collisions driven by semisecular evolution. The systems considered here have initially wide inner orbits, with initial semilatus recti larger than 12 AU, implying no interaction if the orbits were isolated. However, taking into account dynamical evolution, we find that $\approx 0.4$ ($\approx 0.6$) of 2+2 (3+1) systems interact. In particular, Roche Lobe overflow can be triggered possibly in highly eccentric orbits, dynamical instability can ensue due to mass-loss-driven orbital expansion or secular evolution, or a semisecular regime can be entered. We compute the delay-time distributions (DTDs) of collision-induced SNe Ia, and find that they are flatter compared to the observed DTD. Moreover, our combined SNe Ia rates are $(3.7\pm0.7) \times 10^{-6} \,\mathrm{M}_\odot^{-1}$ and $(1.3\pm0.2) \times 10^{-6} \,\mathrm{M}_\odot^{-1}$ for 2+2 and 3+1 systems, respectively, three orders of magnitude lower compared to the observed rate, of order $10^{-3} \, \mathrm{M}_\odot^{-1}$. The low rates can be ascribed to interactions before the stars evolve to CO WDs. However, our results are lower limits given that we considered a subset of quadruple systems.