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.
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⊙.
Context.
Type Ic supernovae represent the explosions of the most stripped massive stars, but their progenitors and explosion mechanisms remain unclear. Larger samples of observed supernovae can help ...characterize the population of these transients.
Aims.
We present an analysis of 44 spectroscopically normal Type Ic supernovae, with focus on the light curves. The photometric data were obtained over 7 years with the Palomar Transient Factory and its continuation, the intermediate Palomar Transient Factory. This is the first homogeneous and large sample of SNe Ic from an untargeted survey, and we aim to estimate explosion parameters for the sample.
Methods.
We present K-corrected
Bgriz
light curves of these SNe, obtained through photometry on template-subtracted images. We performed an analysis on the shape of the
r
-band light curves and confirmed the correlation between the rise parameter Δ
m
−10
and the decline parameter Δ
m
15
. Peak
r
-band absolute magnitudes have an average of −17.71 ± 0.85 mag. To derive the explosion epochs, we fit the
r
-band lightcurves to a template derived from a well-sampled light curve. We computed the bolometric light curves using
r
and
g
band data,
g
−
r
colors and bolometric corrections. Bolometric light curves and Fe
II
λ
5169 velocities at peak were used to fit to the Arnett semianalytic model in order to estimate the ejecta mass
M
ej
, the explosion energy
E
K
and the mass of radioactive nickel
M
(
56
Ni) for each SN.
Results.
Including 41 SNe, we find average values of ⟨
M
ej
⟩ = 4.50 ± 0.79
M
⊙
, ⟨
E
K
⟩ = 1.79 ± 0.29 × 10
51
erg, and ⟨
M
56
Ni
⟩ = 0.19 ± 0.03
M
⊙
. The explosion-parameter distributions are comparable to those available in the literature, but our large sample also includes some transients with narrow and very broad light curves leading to more extreme ejecta masses values.
Aims. We study iPTF14hls, a luminous and extraordinary long-lived Type II supernova, which lately has attracted much attention and disparate interpretation. Methods. We have presented new optical ...photometry that extends the light curves up to more than three years past discovery. We also obtained optical spectroscopy over this period, and furthermore present additional space-based observations using Swift and HST. Results. After an almost constant luminosity for hundreds of days, the later light curve of iPTF14hls finally fades and then displays a dramatic drop after about 1000 d, but the supernova is still visible at the latest epochs presented. The spectra have finally turned nebular, and our very last optical spectrum likely displays signatures from the deep and dense interior of the explosion. A high-resolution HST image highlights the complex environment of the explosion in this low-luminosity galaxy. Conclusions. We provide a large number of additional late-time observations of iPTF14hls, which are (and will continue to be) used to assess the many different interpretations for this intriguing object. In particular, the very late (+1000 d) steep decline of the optical light curve is difficult to reconcile with the proposed central engine models. The lack of very strong X-ray emission, and the emergence of intermediate-width emission lines including S II that we propose originate from dense, processed material in the core of the supernova ejecta, are also key observational tests for both existing and future models.
Abstract
The fate of stars in the zero-age main-sequence (ZAMS) range ≈8–12
M
⊙
is unclear. They could evolve to form white dwarfs or explode as electron-capture supernovae (SNe) or iron ...core-collapse SNe (CCSNe). Even though the initial mass function indicates that this mass range should account for over 40% of all CCSN progenitors, few have been observationally confirmed, likely due to the faintness and rapid evolution of some of these transients. In this paper, we present a sample of nine Ca-rich/O-poor Type IIb SNe detected by the Zwicky Transient Facility with progenitors likely in this mass range. These sources have a Ca
ii
λ
λ
7291, 7324/O
i
λ
λ
6300, 6364 flux ratio of ≳2 in their nebular spectra. Comparing the measured O
i
luminosity (≲10
39
erg s
−1
) and derived oxygen mass (≈0.01
M
⊙
) with theoretical models, we infer that the progenitor ZAMS mass for these explosions is less than 12
M
⊙
. The ejecta properties (
M
ej
≲ 1
M
⊙
and
E
kin
∼ 10
50
erg) are also consistent. The low ejecta mass of these sources indicates a class of strongly-stripped SNe that is a transition between the regular stripped-envelope SNe and ultra-stripped SNe. The progenitor could be stripped by a main-sequence companion and result in the formation of a neutron star−main sequence binary. Such binaries have been suggested to be progenitors of neutron star−white dwarf systems that could merge within a Hubble time and be detectable with LISA.
We present photometry and spectroscopy of four hydrogen-poor luminous supernovae discovered during the 2-month long science commissioning and early operations of the Zwicky Transient Facility (ZTF) ...survey. Three of these objects, SN 2018bym (ZTF18aapgrxo), SN 2018avk (ZTF18aaisyyp), and SN 2018bgv (ZTF18aavrmcg), resemble typical SLSN-I spectroscopically, while SN 2018don (ZTF18aajqcue) may be an object similar to SN 2007bi experiencing considerable host galaxy reddening, or an intrinsically long-lived, luminous, and red SN Ic. We analyze the light curves, spectra, and host galaxy properties of these four objects and put them in context of the population of SLSN-I. SN 2018bgv stands out as the fastest-rising SLSN-I observed to date, with a rest-frame g-band rise time of just 10 days from explosion to peak-if it is powered by magnetar spin-down, the implied ejecta mass is only 1 M . SN 2018don also displays unusual properties-in addition to its red colors and comparatively massive host galaxy, the light curve undergoes some of the strongest light-curve undulations postpeak seen in an SLSN-I, which we speculate may be due to interaction with circumstellar material. We discuss the promises and challenges of finding SLSNe in large-scale surveys like ZTF given the observed diversity in the population.
ABSTRACT
We present the data and analysis of SN 2018gjx, an unusual low-luminosity transient with three distinct spectroscopic phases. Phase I shows a hot blue spectrum with signatures of ionized ...circumstellar material (CSM), Phase II has the appearance of broad SN features, consistent with those seen in a Type IIb supernova at maximum light, and Phase III is that of a supernova interacting with helium-rich CSM, similar to a Type Ibn supernova. This event provides an apparently rare opportunity to view the inner workings of an interacting supernova. The observed properties can be explained by the explosion of a star in an aspherical CSM. The initial light is emitted from an extended CSM (∼4000 R⊙), which ionizes the exterior unshocked material. Some days after, the SN photosphere envelops this region, leading to the appearance of a SN IIb. Over time, the photosphere recedes in velocity space, revealing interaction between the supernova ejecta and the CSM that partially obscures the supernova nebular phase. Modelling of the initial spectrum reveals a surface composition consistent with compact H-deficient Wolf–Rayet and Luminous Blue Variable (LBV) stars. Such configurations may not be unusual, with SNe IIb being known to have signs of interaction so at least some SNe IIb and SNe Ibn may be the same phenomena viewed from different angles, or possibly with differing CSM configurations.
We present an analysis of 507 spectra of 173 stripped-envelope (SE) supernovae (SNe) discovered by the untargeted Palomar Transient Factory (PTF) and intermediate PTF (iPTF) surveys. Our sample ...contains 55 Type IIb SNe (SNe IIb), 45 Type Ib SNe (SNe Ib), 56 Type Ic SNe (SNe Ic), and 17 Type Ib/c SNe (SNe Ib/c). We have compared the SE SN subtypes via measurements of the pseudo-equivalent widths (pEWs) and velocities of the He I λλ5876, 7065 and O I λ7774 absorption lines. Consistent with previous work, we find that SNe Ic show higher pEWs and velocities in O I λ7774 compared to SNe IIb and Ib. The pEWs of the He I λλ5876, 7065 lines are similar in SNe Ib and IIb after maximum light. The He I λλ5876, 7065 velocities at maximum light are higher in SNe Ib compared to SNe IIb. We identify an anticorrelation between the He I λ7065 pEW and O I λ7774 velocity among SNe IIb and Ib. This can be interpreted as a continuum in the amount of He present at the time of explosion. It has been suggested that SNe Ib and Ic have similar amounts of He, and that lower mixing could be responsible for hiding He in SNe Ic. However, our data contradict this mixing hypothesis. The observed difference in the expansion rate of the ejecta around maximum light of SNe Ic (Vm = √2Ek/Mej ≈ 15 000 km s−1Vm=2Ek/Mej≈15 000 km s−1${V_{\rm{m}}} = \sqrt {2{E_{\rm{k}}}/{M_{{\rm{ej}}} \approx 1{\rm{5 \, 000 \, km }} \, {{\rm{s}}^{ - 1}}$) and SNe Ib (Vm ≈ 9000 km s−1) would imply an average He mass difference of ∼1.4 M⊙, if the other explosion parameters are assumed to be unchanged between the SE SN subtypes. We conclude that SNe Ic do not hide He but lose He due to envelope stripping.
In this paper, we discuss the outcomes of the follow-up campaign of SN 2018ijp, discovered as part of the Zwicky Transient Facility survey for optical transients. Its first spectrum shows ...similarities to broad-lined Type Ic supernovae around maximum light, whereas later spectra display strong signatures of interaction between rapidly expanding ejecta and a dense H-rich circumstellar medium, coinciding with a second peak in the photometric evolution of the transient. This evolution, along with the results of modeling of the first light-curve peak, suggests a scenario where a stripped star exploded within a dense circumstellar medium. The two main phases in the evolution of the transient could be interpreted as a first phase dominated by radioactive decays, and a later interaction-dominated phase where the ejecta collide with a pre-existing shell. We therefore discuss SN 2018jp within the context of a massive star depleted of its outer layers exploding within a dense H-rich circumstellar medium.
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