We study 34 Type Ic supernovae that have broad spectral features (SNe Ic-BL). This is the only SN type found in association with long-duration gamma-ray bursts (GRBs). We obtained our photometric ...data with the Palomar Transient Factory (PTF) and its continuation, the intermediate PTF (iPTF). This is the first large, homogeneous sample of SNe Ic-BL from an untargeted survey. Furthermore, given the high observational cadence of iPTF, most of these SNe Ic-BL were discovered soon after explosion. We present K-corrected Bgriz light curves of these SNe, obtained through photometry on template-subtracted images. We analyzed the shape of the r-band light curves, finding a correlation between the decline parameter Δm15 and the rise parameter Δm−10. We studied the SN colors and, based on g − r, we estimated the host-galaxy extinction for each event. Peak r-band absolute magnitudes have an average of −18.6 ± 0.5 mag. We fit each r-band light curve with that of SN 1998bw (scaled and stretched) to derive the explosion epochs. We computed the bolometric light curves using bolometric corrections, r-band data, and g − r colors. Expansion velocities from Fe II were obtained by fitting spectral templates of SNe Ic. Bolometric light curves and velocities at peak were fitted using the semianalytic Arnett model to estimate ejecta mass Mej, explosion energy EK and 56Ni mass M(56Ni) for each SN. We find average values of Mej = 4 ± 3 M⊙, EK = (7 ± 6)×1051 erg, and M(56Ni)=0.31 ± 0.16 M⊙. The parameter distributions were compared to those presented in the literature and are overall in agreement with them. We also estimated the degree of 56Ni mixing using scaling relations derived from hydrodynamical models and we find that all the SNe are strongly mixed. The derived explosion parameters imply that at least 21% of the progenitors of SNe Ic-BL are compatible with massive (> 28 M⊙), possibly single stars, whereas at least 64% might come from less massive stars in close binary systems.
Photometric classification of supernovae (SNe) is imperative as recent and upcoming optical time-domain surveys, such as the Large Synoptic Survey Telescope (LSST), overwhelm the available resources ...for spectrosopic follow-up. Here we develop a range of light curve (LC) classification pipelines, trained on 513 spectroscopically classified SNe from the Pan-STARRS1 Medium-Deep Survey (PS1-MDS): 357 Type Ia, 93 Type II, 25 Type IIn, 21 Type Ibc, and 17 Type I superluminous SNe (SLSNe). We present a new parametric analytical model that can accommodate a broad range of SN LC morphologies, including those with a plateau, and fit this model to data in four PS1 filters (gP1rP1iP1zP1). We test a number of feature extraction methods, data augmentation strategies, and machine-learning algorithms to predict the class of each SN. Our best pipelines result in 90% average accuracy, 70% average purity, and 80% average completeness for all SN classes, with the highest success rates for SNe Ia and SLSNe and the lowest for SNe Ibc. Despite the greater complexity of our classification scheme, the purity of our SN Ia classification, 95%, is on par with methods developed specifically for Type Ia versus non-Type Ia binary classification. As the first of its kind, this study serves as a guide to developing and training classification algorithms for a wide range of SN types with a purely empirical training set, particularly one that is similar in its characteristics to the expected LSST main survey strategy. Future work will implement this classification pipeline on 3000 PS1/MDS LCs that lack spectroscopic classification.
SN2017egm is the closest (z = 0.03) H-poor superluminous supernova (SLSN-I) detected to date, and a rare example of an SLSN-I in a massive, metal-rich galaxy. We present the HST UV and optical ...spectra covering 1000-5500 , taken at +3 day relative to the peak. Our data reveal two absorption systems at redshifts matching the host galaxy NGC 3191 (z = 0.0307) and its companion galaxy (z = 0.0299) 73″ apart. Weakly damped Ly absorption lines are detected at these two redshifts, with H i column densities of (3.0 0.8) × 1019 and (3.7 0.9) × 1019 cm−2, respectively. This is an order of magnitude smaller than the H i column densities in the disks of nearby galaxies (>1010 M ) and suggests that SN2017egm is on the near side of NGC 3191 and has a low host extinction (E(B − V) ∼ 0.007). Using unsaturated metal absorption lines, we find that the host of SN2017egm probably has a solar or higher metallicity and is unlikely to be a dwarf companion to NGC 3191. Comparison of early-time UV spectra of SN2017egm, Gaia16apd, iPTF13ajg, and PTF12dam finds that the continuum at λ > 2800 is well fit by a blackbody, whereas the continuum at λ < 2800 is considerably below the model. The degree of UV suppression varies from source to source, with the 1400-2800 continuum flux ratio of 1.5 for Gaia16apd and 0.4 for iPTF13ajg. This cannot be explained by the differences in magnetar power or blackbody temperature. Finally, the UV spectra reveal a common set of seven broad absorption features and their equivalent widths are similar (within a factor of 2) among the four events.
Context. The transient iPTF15dtg is a type-Ic supernova (SN) showing a broad light curve around maximum light, consistent with massive ejecta if we assume a radioactive-powering scenario. Aims. We ...aim to study the late-time light curve of iPTF15dtg, which turned out to be extraordinarily luminous for a stripped-envelope (SE) SN, and investigate possible powering mechanisms. Methods. We compare the observed light curves to those of other SE SNe and also to models for the 56Co decay. We analyze and compare the spectra to nebular spectra of other SE SNe. We build a bolometric light curve and fit it with different models, including powering by radioactivity, magnetar powering, and a combination of the two. Results. Between 150 and 750 d post-explosion, the luminosity of iPTF15dtg declined by merely two magnitudes instead of the six magnitudes expected from 56Co decay. This is the first spectroscopically regular SE SN found to show this behavior. The model with both radioactivity and magnetar powering provides the best fit to the light curve and appears to be the most realistic powering mechanism. An alternative mechanism might be circumstellar-medium (CSM) interaction. However, the spectra of iPTF15dtg are very similar to those of other SE SNe, and do not show signs of strong CSM interaction. Conclusions. The object iPTF15dtg is the first spectroscopically regular SE SN whose light curve displays such clear signs of a magnetar contributing to its late-time powering. Given this result, the mass of the ejecta needs to be revised to a lower value, and therefore the progenitor mass could be significantly lower than the previously estimated > 35 M⊙.
Wide-field surveys are discovering a growing number of rare transients whose physical origin is not yet well understood. Here we present optical and UV data and analysis of intermediate Palomar ...Transient Factory (iPTF) 16asu, a luminous, rapidly evolving, high-velocity, stripped-envelope supernova (SN). With a rest-frame rise time of just four days and a peak absolute magnitude of mag, the light curve of iPTF 16asu is faster and more luminous than that of previous rapid transients. The spectra of iPTF 16asu show a featureless blue continuum near peak that develops into an SN Ic-BL spectrum on the decline. We show that while the late-time light curve could plausibly be powered by 56Ni decay, the early emission requires a different energy source. Nondetections in the X-ray and radio strongly constrain the energy coupled to relativistic ejecta to be at most comparable to the class of low-luminosity gamma-ray bursts (GRBs). We suggest that the early emission may have been powered by either a rapidly spinning-down magnetar or by shock breakout in an extended envelope of a very energetic explosion. In either scenario a central engine is required, making iPTF 16asu an intriguing transition object between superluminous SNe, SNe Ic-BL, and low-luminosity GRBs.
Automated classification of supernovae (SNe) based on optical photometric light-curve information is essential in the upcoming era of wide-field time domain surveys, such as the Legacy Survey of ...Space and Time (LSST) conducted by the Rubin Observatory. Photometric classification can enable real-time identification of interesting events for extended multiwavelength follow-up, as well as archival population studies. Here we present the complete sample of 5243 "SN-like" light curves (in gP1rP1iP1zP1) from the Pan-STARRS1 Medium-Deep Survey (PS1-MDS). The PS1-MDS is similar to the planned LSST Wide-Fast-Deep survey in terms of cadence, filters, and depth, making this a useful training set for the community. Using this data set, we train a novel semisupervised machine learning algorithm to photometrically classify 2315 new SN-like light curves with host galaxy spectroscopic redshifts. Our algorithm consists of an RF supervised classification step and a novel unsupervised step in which we introduce a recurrent autoencoder neural network (RAENN). Our final pipeline, dubbed SuperRAENN, has an accuracy of 87% across five SN classes (Type Ia, Ibc, II, IIn, SLSN-I) and macro-averaged purity and completeness of 66% and 69%, respectively. We find the highest accuracy rates for SNe Ia and SLSNe and the lowest for SNe Ibc. Our complete spectroscopically and photometrically classified samples break down into 62.0% Type Ia (1839 objects), 19.8% Type II (553 objects), 4.8% Type IIn (136 objects), 11.7% Type Ibc (291 objects), and 1.6% Type I SLSNe (54 objects).
Abstract
We present analysis of the light curves (LCs) of 77 hydrogen-poor superluminous supernovae (SLSNe I) discovered during the Zwicky Transient Facility Phase I operation. We find that the ...majority (67%) of the sample can be fit equally well by both magnetar and ejecta–circumstellar medium (CSM) interaction plus
56
Ni decay models. This implies that LCs alone cannot unambiguously constrain the physical power sources for an SLSN I. However, 23% of the sample show inverted V-shape, steep-declining LCs or features of long rise and fast post-peak decay, which are better described by the CSM+Ni model. The remaining 10% of the sample favors the magnetar model. Moreover, our analysis shows that the LC undulations are quite common, with a fraction of 18%–44% in our gold sample. Among those strongly undulating events, about 62% of them are found to be CSM-favored, implying that the undulations tend to occur in the CSM-favored events. Undulations show a wide range in energy and duration, with median values (and 1
σ
errors) being as
1.7
%
−
0.7
%
+
1.5
%
E
rad
,
total
and
28.8
−
9.1
+
14.4
days, respectively. Our analysis of the undulation timescales suggests that intrinsic temporal variations of the central engine can explain half of the undulating events, while CSM interaction (CSI) can account for the majority of the sample. Finally, all of the well-observed He-rich SLSNe Ib either have strongly undulating LCs or the LCs are much better fit by the CSM+Ni model. These observations imply that their progenitor stars have not had enough time to lose all of the He-envelopes before supernova explosions, and H-poor CSM are likely to present in these events.
Context.
We present our observations and analysis of SN 2020cxd, a low-luminosity (LL), long-lived Type IIP supernova (SN). This object is a clear outlier in the magnitude-limited SN sample recently ...presented by the Zwicky Transient Facility’s (ZTF) Bright Transient Survey.
Aims.
We demonstrate that SN 2020cxd is an additional member of the group of LL SNe and we discuss the rarity of LL SNe in the context of the ZTF survey. We consider how further studies of these faintest members of the core-collapse (CC) SN family might help improve the general understanding of the underlying initial mass function for stars that explode.
Methods.
We used optical light curves (LCs) from the ZTF in the
gri
bands and several epochs of ultraviolet data from the
Neil Gehrels Swift
observatory as well as a sequence of optical spectra. We constructed the colour curves and a bolometric LC. Then we compared the evolution of the ejecta velocity and black-body temperature for LL SNe as well as for typical Type II SNe. Furthermore, we adopted a Monte Carlo code that fits semi-analytic models to the LC of SN 2020cxd, which allows for the estimation of the physical parameters. Using our late-time nebular spectra, we also make a comparison against SN II spectral synthesis models from the literature to constrain the progenitor properties of SN 2020cxd.
Results.
The LCs of SN 2020cxd show a great similarity with those of LL SNe IIP in terms of luminosity, timescale, and colours. Also, the spectral evolution of SN 2020cxd is that of a Type IIP SN. The spectra show prominent and narrow P-Cygni lines, indicating low expansion velocities. This is one of the faintest LL SNe observed, with an absolute plateau magnitude of
M
r
= −14.5 mag and also one with the longest plateau lengths, with a duration of 118 days. Finally, the velocities measured from the nebular emission lines are among the lowest ever seen in a SN, with an intrinsic full width at half maximum value of 478 km s
−1
. The underluminous late-time exponential LC tail indicates that the mass of
56
Ni ejected during the explosion is much smaller than the average of normal SNe IIP, we estimate
M
56
Ni
= 0.003
M
⊙
. The Monte Carlo fitting of the bolometric LC suggests that the progenitor of SN 2020cxd had a radius of
R
0
= 1.3 × 10
13
cm, kinetic energy of
E
kin
= 4.3 × 10
50
erg, and ejecta mass of
M
ej
= 9.5
M
⊙
. From the bolometric LC, we estimated the total radiated energy
E
rad
= 1.52 × 10
48
erg. Using our late-time nebular spectra, we compared these results against SN II spectral synthesis models to constrain the progenitor zero-age main sequence mass and found that it is likely to be ≲15
M
⊙
.
Conclusions.
SN 2020cxd is a LL Type IIP SN. The inferred progenitor parameters and the features observed in the nebular spectrum favour a low-energy, Ni-poor, iron CC SN from a low-mass (∼12
M
⊙
) red supergiant.
We present results from a systematic selection of tidal disruption events (TDEs) in a wide-area (4800 deg2), 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 (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.
Abstract
We present a comprehensive optical and near-infrared census of the fields of 90 short gamma-ray bursts (GRBs) discovered in 2005–2021, constituting all short GRBs for which host galaxy ...associations are feasible (≈60% of the total Swift short GRB population). We contribute 274 new multi-band imaging observations across 58 distinct GRBs and 26 spectra of their host galaxies. Supplemented by literature and archival survey data, the catalog contains 542 photometric and 42 spectroscopic data sets. The photometric catalog reaches 3
σ
depths of ≳24–27 mag and ≳23–26 mag for the optical and near-infrared bands, respectively. We identify host galaxies for 84 bursts, in which the most robust associations make up 56% (50/90) of events, while only a small fraction, 6.7%, have inconclusive host associations. Based on new spectroscopy, we determine 18 host spectroscopic redshifts with a range of
z
≈ 0.15–1.5 and find that ≈23%–41% of Swift short GRBs originate from
z
> 1. We also present the galactocentric offset catalog for 84 short GRBs. Taking into account the large range of individual measurement uncertainties, we find a median of projected offset of ≈7.7 kpc, for which the bursts with the most robust associations have a smaller median of ≈4.8 kpc. Our catalog captures more high-redshift and low-luminosity hosts, and more highly offset bursts than previously found, thereby diversifying the population of known short GRB hosts and properties. In terms of locations and host luminosities, the populations of short GRBs with and without detectable extended emission are statistically indistinguishable. This suggests that they arise from the same progenitors, or from multiple progenitors, which form and evolve in similar environments. All of the data products are available on the Broadband Repository for Investigating Gamma-Ray Burst Host Traits website.
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