Modern wide-field, optical time-domain surveys must solve a basic optimization problem: maximize the number of transient discoveries or minimize the follow-up needed for the new discoveries. Here, we ...describe the Color Me Intrigued experiment, the first from the intermediate Palomar Transient Factory (iPTF) to search for transients simultaneously in the $g_\mathrm{PTF}$- and $R_\mathrm{PTF}$-bands. During the course of this experiment we discovered iPTF$\,$16fnm, a new member of the 02cx-like subclass of type Ia supernovae (SNe). iPTF$\,$16fnm peaked at $M_{g_\mathrm{PTF}} = -15.09 \pm 0.17 \; \mathrm{mag}$, making it the second least-luminous known type Ia SN. iPTF 16fnm exhibits all the hallmarks of the 02cx-like class: (i) low luminosity at peak, (ii) low ejecta velocities, and (iii) a non-nebular spectra several months after peak. Spectroscopically, iPTF$\,$16fnm exhibits a striking resemblence to 2 other low-luminosity 02cx-like SNe: SNe 2007qd and 2010ae. iPTF$\,$16fnm and SN 2005hk decline at nearly the same rate, despite a 3 mag difference in brightness at peak. When considering the full subclass of 02cx-like SNe, we do not find evidence for a tight correlation between peak luminosity and decline rate in either the $g'$ or $r'$ band. We further examine the $g' - r'$ evolution of 02cx-like SNe and find that their unique color evolution can be used to separate them from 91bg-like and normal type Ia SNe. This selection function will be especially important in the spectroscopically incomplete Zwicky Transient Facility/Large Synoptic Survey Telescope era. We measure the relative rate of 02cx-like SNe to normal SNe Ia and find $r_{N_{02cx}/N_{Ia}} = 25^{+75}_{-18.5}\%$. Finally, we close by recommending that LSST periodically evaluate, and possibly update, its observing cadence to maximize transient science.
Aims. We present a ground-based, near-infrared search for lensed supernovae behind the massive cluster Abell 1689 at z= 0.18, which is one of the most powerful gravitational telescopes that nature ...provides. Methods. Our survey was based on multi-epoch J-band observations with the HAWK-I instrument on VLT, with supporting optical data from the Nordic Optical Telescope. Results. Our search resulted in the discovery of five photometrically classified, core-collapse supernovae with high redshifts of 0.671 < z< 1.703 and magnifications in the range Deltam= - 0.31 to -1.58 mag, as calculated from lensing models in the literature. Owing to the power of the lensing cluster, the survey had the sensitivity to detect supernovae up to very high redshifts, z~3, albeit for a limited region of space. We present a study of the core-collapse supernova rates for 0.4 < or = z< 2.9, and find good agreement with previous estimates and predictions from star formation history. During our survey, we also discovered two Type Ia supernovae in A1689 cluster members, which allowed us to determine the cluster Ia rate to be 0.14 super(+0.19) sub(-0.09)+ or -0.01SNuBh super(2)(SNuB=10 super(-12) SNe L super(-1) sub(middot in circle,B) yr super(-1)), where the error bars indicate 1sigma confidence intervals, statistical and systematic, respectively. The cluster rate normalized by the stellar mass is 0.10 super(+0.13) sub(-0.096)+ or -0.02 in SNuMh super(2)(SNuM =10 super(-12) SNe M super(-1) sub(middot in circle) yr super(-1)). Furthermore, we explore the optimal future survey for improving the core-collapse supernova rate measurements at z> = 2 using gravitational telescopes, and for detections with multiply lensed images, and we find that the planned WFIRST space mission has excellent prospects. Conclusions. Massive clusters can be used as gravitational telescopes to significantly expand the survey range of supernova searches, with important implications for the study of the high-z transient Universe.
We present ultraviolet (UV) observations of six nearby Type Ia supernovae (SNe Ia) obtained with the Hubble Space Telescope, three of which were also observed in the near-IR (NIR) with Wide-Field ...Camera 3. UV observations with the Swift satellite, as well as ground-based optical and NIR data provide complementary information. The combined data set covers the wavelength range 0.2-2 ...m. By also including archival data of SN 2014J, we analyse a sample spanning observed colour excesses up to E(B - V) = 1.4 mag. We study the wavelength-dependent extinction of each individual SN and find a diversity of reddening laws when characterized by the total-to-selective extinction ... In particular, we note that for the two SNe with E(B - V) ... 1 mag, for which the colour excess is dominated by dust extinction, we find ... = 1.4 ± 0.1 and ... = 2.8 ± 0.1. Adding UV photometry reduces the uncertainty of fitted ... by ~50 per cent allowing us to also measure ... of individual low-extinction objects which point to a similar diversity, currently not accounted for in the analyses when SNe Ia are used for studying the expansion history of the Universe. (ProQuest: ... denotes formulae/symbols omitted.)
Strong gravitational lensing magnifies the light from a background source, allowing us to study these sources in detail. Here, we study the spectra of a \(z = 1.95\) lensed Type Ia supernova ...SN~Encore for its brightest Image A, taken 39 days apart. We infer the spectral age with template matching using the supernova identification (SNID) software and find the spectra to be at 29.0 \(\pm 5.0\) and 37.4 \(\pm 2.8\) rest-frame days post maximum respectively, consistent with separation in the observer frame after accounting for time-dilation. Since SNe~Ia measure dark energy properties by providing relative distances between low- and high-\(z\) SNe, it is important to test for evolution of spectroscopic properties. Comparing the spectra to composite low-\(z\) SN~Ia spectra, we find strong evidence for similarity between the local sample of SN~Encore. The line velocities of common SN~Ia spectral lines, Si II 6355 and Ca II NIR triplet are consistent with the distribution for the low-\(z\) sample as well as other lensed SNe~Ia, e.g. iPTF16geu (\(z = 0.409\)) and SN~H0pe (\(z = 1.78\)). The consistency in SN~Ia spectra across cosmic time demonstrates the utility of using SNe~Ia in the very high-\(z\) universe for dark energy inference. We also find that the spectra of SN~Encore match the predictions for explosion models very well. With future large samples of lensed SNe~Ia, spectra at such late phases will be important to distinguish between different explosion scenarios.
We present a search for luminous, long-duration ambiguous nuclear transients (ANTs) similar to the unprecedented discovery of the extreme, ambiguous event AT2021lwx with a \(>150\) d rise time and ...luminosity \(10^{45.7}\) erg s\(^{-1}\). We use the Lasair transient broker to search Zwicky Transient Facility (ZTF) data for transients lasting more than one year and exhibiting smooth declines. Our search returns 59 events, seven of which we classify as ANTs assumed to be driven by accretion onto supermassive black holes. We propose the remaining 52 are stochastic variability from regular supermassive black hole accretion rather than distinct transients. We supplement the seven ANTs with three nuclear transients in ZTF that fail the light curve selection but have clear single flares and spectra that do not resemble typical AGN. All but one of these 10 ANTs have a mid-infrared flare from an assumed dust echo, implying the ubiquity of dust around the black holes giving rise to ANTs. No events are more luminous than AT2021lwx, but one (ZTF19aamrjar) has twice the duration and a higher integrated energy release. On the other extreme, ZTF20abodaps reaches a luminosity close to AT2021lwx with a rise time \(<20\) d and that fades smoothly in \(>600\) d. We define a portion of rise-time versus flare amplitude space that selects ANTs with \(\sim50\) per cent purity against variable active galactic nuclei. We calculate a volumetric rate of \(\gtrsim 3\times10^{-11}\) Mpc\(^{-1}\) yr\(^{-1}\), consistent with the events being caused by tidal disruptions of intermediate and high-mass stars.
If high-mass stars (>20-25 Msun) are the progenitors of stripped-envelope (SE) supernovae (SNe), their massive ejecta should lead to broad, long-duration lightcurves (LCs). Instead, literature ...samples of SE~SNe have reported relatively narrow LCs with ejecta masses between 1-4 Msun that favor progenitors <20-25 Msun. Working with the untargeted sample of (i)PTF SNe to better constrain their rates, we search for SE~SNe with broad LCs. Using a simple LC stretch compared to a template to measure broadness, we identified eight significantly broader Type~Ibc SNe after applying quantitative sample selection criteria. The LCs, colors, and spectra of these SNe are found to evolve more slowly relative to typical Type~Ibc SNe, proportional with the stretch. Bolometric LC modeling and their nebular spectra indicate high ejecta and nickel masses, assuming radioactive decay powering. Additionally, these objects are preferentially located in low-metallicity host galaxies with high star-formation rates, which may account for their massive progenitors, as well as their relative absence from the literature. Our study thus supports the link between broad LCs (as measured by stretch) and high-mass progenitor stars in SE~SNe with independent evidence from bolometric LC modeling, nebular spectra, host environment properties, and photometric evolution. In the first systematic search of its kind using an untargeted sample, we use the stretch distribution to identify a higher than previously appreciated fraction of SE~SNe with broad LCs (~13%). Correcting for Malmquist and LC duration observational biases, we conservatively estimate that a minimum of ~6% of SE~SNe are consistent with high-mass progenitors. This result has implications for the progenitor channels of SE~SNe, late stages of massive stellar evolution, oxygen fraction in the universe, and formation channels for stellar-mass black holes.(Abridged)
Supernovae (SNe) that have been multiply-imaged by gravitational lensing are rare and powerful probes for cosmology. Each detection is an opportunity to develop the critical tools and methodologies ...needed as the sample of lensed SNe increases by orders of magnitude with the upcoming Vera C. Rubin Observatory and Nancy Grace Roman Space Telescope. The latest such discovery is of the quadruply-imaged Type Ia SN 2022qmx (aka, "SN Zwicky") at \(z=0.3544\). SN Zwicky was discovered by the Zwicky Transient Facility (ZTF) in spatially unresolved data. Here we present follow-up Hubble Space Telescope observations of SN Zwicky, the first from the multi-cycle "LensWatch" program. We measure photometry for each of the four images of SN Zwicky, which are resolved in three WFC3/UVIS filters (F475W, F625W, F814W) but unresolved with WFC3/IR~F160W, and present an analysis of the lensing system using a variety of independent lens modeling methods. We find consistency between lens model predicted time delays (\(\lesssim1\) day), and delays estimated with the single epoch of HST colors (\(\lesssim3.5\) days), including the uncertainty from chromatic microlensing (\(\sim1\)-\(1.5\) days). Our lens models converge to an Einstein radius of \(\theta_E=(0.168^{+0.009}_{-0.005})\prime\prime\), the smallest yet seen in a lensed SN system. The "standard candle" nature of SN Zwicky provides magnification estimates independent of the lens modeling that are brighter than predicted by \(\sim1.7^{+0.8}_{-0.6}\)mag and \(\sim0.9^{+0.8}_{-0.6}\)mag for two of the four images, suggesting significant microlensing and/or additional substructure beyond the flexibility of our image-position mass models.
A bright (\(m_{\rm F150W,AB}\)=24 mag), \(z=1.95\) supernova (SN) candidate was discovered in JWST/NIRCam imaging acquired on 2023 November 17. The SN is quintuply-imaged as a result of strong ...gravitational lensing by a foreground galaxy cluster, detected in three locations, and remarkably is the second lensed SN found in the same host galaxy. The previous lensed SN was called "Requiem", and therefore the new SN is named "Encore". This makes the MACS J0138.0\(-\)2155 cluster the first known system to produce more than one multiply-imaged SN. Moreover, both SN Requiem and SN Encore are Type Ia SNe (SNe Ia), making this the most distant case of a galaxy hosting two SNe Ia. Using parametric host fitting, we determine the probability of detecting two SNe Ia in this host galaxy over a \(\sim10\) year window to be \(\approx3\%\). These observations have the potential to yield a Hubble Constant (\(H_0\)) measurement with \(\sim10\%\) precision, only the third lensed SN capable of such a result, using the three visible images of the SN. Both SN Requiem and SN Encore have a fourth image that is expected to appear within a few years of \(\sim2030\), providing an unprecedented baseline for time-delay cosmography.
Supernova (SN) H0pe is a gravitationally lensed, triply-imaged, Type Ia SN (SN Ia) discovered in James Webb Space Telescope imaging of the PLCK G165.7+67.0 cluster of galaxies. Well-observed ...multiply-imaged SNe provide a rare opportunity to constrain the Hubble constant (\(H_0\)), by measuring the relative time delay between the images and modeling the foreground mass distribution. SN H0pe is located at \(z=1.783\), and is the first SN Ia with sufficient light curve sampling and long enough time delays for an \(H_0\) inference. Here we present photometric time-delay measurements and SN properties of SN H0pe. Using JWST/NIRCam photometry we measure time delays of \(\Delta t_{ab}=-116.6^{+10.8}_{-9.3}\) and \(\Delta t_{cb}=-48.6^{+3.6}_{-4.0}\) observer-frame days relative to the last image to arrive (image 2b; all uncertainties are \(1\sigma\)), which corresponds to a \(\sim5.6\%\) uncertainty contribution for \(H_0\) assuming \(70 \rm{km s^{-1} Mpc^{-1}}\). We also constrain the absolute magnification of each image to \(\mu_{a}=4.3^{+1.6}_{-1.8}\), \(\mu_{b}=7.6^{+3.6}_{-2.6}\), \(\mu_{c}=6.4^{+1.6}_{-1.5}\) by comparing the observed peak near-IR magnitude of SN H0pe to the non-lensed population of SNe Ia.
Measuring time delays from strongly lensed supernovae (SNe) is emerging as a novel and independent tool for estimating the Hubble constant \((H_0)\). This is very important given the recent discord ...in the value of \(H_0\) from two methods that probe different distance ranges. The success of this technique will rely of our ability to discover strongly lensed SNe with measurable time delays. Here, we present the magnifications and the time delays for the multiply-imaged galaxies behind the Hubble Frontier Fields (HFF) galaxy clusters, by using recently published lensing models. Continuing on our previous work done for Abell 1689 (A1689) and Abell 370, we also show the prospects of observing strongly lensed SNe behind the HFF clusters with the upcoming James Webb Space Telescope (JWST). With four 1-hour visits in one year, the summed expectations of all six HFF clusters are \(\sim0.5\) core-collapse (CC) SNe and \(\sim0.06\) Type Ia SNe (SNe Ia) in F115W band, while with F150W the expectations are higher, \(\sim0.9\) CC SNe and \(\sim0.06\) SNe Ia. These estimates match those expected by only surveying A1689, proving that the performance of A1689 as gravitational telescope is superior. In the five HFF clusters presented here, we find that F150W will be able to detect SNe Ia (SNe IIP) exploding in 93 (80) pairs multiply-imaged galaxies with time delays of less than 5 years.
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