Abstract
Tidal disruption events (TDEs) offer a unique way to study dormant black holes. While the number of observed TDEs has grown thanks to the emergence of wide-field surveys in the past few ...decades, questions regarding the nature of the observed optical, UV, and X-ray emission remain. We present a uniformly selected sample of 30 spectroscopically classified TDEs from the Zwicky Transient Facility Phase I survey operations with follow-up Swift UV and X-ray observations. Through our investigation into correlations between light-curve properties, we recover a shallow positive correlation between the peak bolometric luminosity and decay timescales. We introduce a new spectroscopic class of TDE, TDE-featureless, which are characterized by featureless optical spectra. The new TDE-featureless class shows larger peak bolometric luminosities, peak blackbody temperatures, and peak blackbody radii. We examine the differences between the X-ray bright and X-ray faint populations of TDEs in this sample, finding that X-ray bright TDEs show higher peak blackbody luminosities than the X-ray faint subsample. This sample of optically selected TDEs is the largest sample of TDEs from a single survey yet, and the systematic discovery, classification, and follow-up of this sample allows for robust characterization of TDE properties, an important stepping stone looking forward toward the Rubin era.
Abstract
We present preexplosion optical and infrared (IR) imaging at the site of the type II supernova (SN II) 2023ixf in Messier 101 at 6.9 Mpc. We astrometrically registered a ground-based image ...of SN 2023ixf to archival Hubble Space Telescope (HST), Spitzer Space Telescope (Spitzer), and ground-based near-IR images. A single point source is detected at a position consistent with the SN at wavelengths ranging from HST
R
band to Spitzer 4.5
μ
m. Fitting with blackbody and red supergiant (RSG) spectral energy distributions (SEDs), we find that the source is anomalously cool with a significant mid-IR excess. We interpret this SED as reprocessed emission in a 8600
R
⊙
circumstellar shell of dusty material with a mass ∼5 × 10
−5
M
⊙
surrounding a
log
(
L
/
L
⊙
)
=
4.74
±
0.07
and
T
eff
=
3920
−
160
+
200
K RSG. This luminosity is consistent with RSG models of initial mass 11
M
⊙
, depending on assumptions of rotation and overshooting. In addition, the counterpart was significantly variable in preexplosion Spitzer 3.6 and 4.5
μ
m imaging, exhibiting ∼70% variability in both bands correlated across 9 yr and 29 epochs of imaging. The variations appear to have a timescale of 2.8 yr, which is consistent with
κ
-mechanism pulsations observed in RSGs, albeit with a much larger amplitude than RSGs such as
α
Orionis (Betelgeuse).
Unlike ordinary supernovae (SNe), some of which are hydrogen and helium deficient (called Type Ic SNe), broad-lined Type Ic SNe (SNe Ic-bl) are very energetic events, and only SNe Ic-bl are ...coincident with long-duration gamma-ray bursts (GRBs). Understanding the progenitors of SN Ic-bl explosions versus those of their SN Ic cousins is key to understanding the SN-GRB relationship and jet production in massive stars. Here we present the largest existing set of host galaxy spectra of 28 SNe Ic and 14 SNe Ic-bl, all discovered by the same galaxy-untargeted survey, namely, the Palomar Transient Factory (PTF). We carefully measure their gas-phase metallicities, stellar masses (M*), and star formation rates (SFRs). We further reanalyze the hosts of 10 literature SN-GRBs using the same methods and compare them to our PTF SN hosts with the goal of constraining their progenitors from their local environments. We find that the metallicities, SFRs, and M* values of our PTF SN Ic-bl hosts are statistically comparable to those of SN-GRBs but significantly lower than those of the PTF SNe Ic. The mass-metallicity relations as defined by the SNe Ic-bl and SN-GRBs are not significantly different from the same relations as defined by Sloan Digital Sky Survey galaxies, contradicting claims by earlier works. Our findings point toward low metallicity as a crucial ingredient for SN Ic-bl and SN-GRB production since we are able to break the degeneracy between high SFR and low metallicity. We suggest that the PTF SNe Ic-bl may have produced jets that were choked inside the star or were able to break out of the star as unseen low-luminosity or off-axis GRBs.
Abstract
We present nebular spectroscopy of SN 2020hvf, a Type Ia supernova (SN Ia) with an early bump in its light curve. SN 2020hvf shares many spectroscopic and photometric similarities to the ...carbon-rich high-luminosity “03fg-like” SNe Ia. At >240 days after peak brightness, we detect unambiguous emission from Ca
ii
λ
λ
7291, 7324, which is rarely observed in normal SNe Ia and only seen in peculiar subclasses. SN 2020hvf displays “sawtooth” emission profiles near 7300 Å that cannot be explained with single symmetric velocity components of Fe
ii
, Ni
ii
, and Ca
ii
, indicating an asymmetric explosion. The broad Ca
ii
emission is best modeled by two velocity components offset by 1220 km s
−1
, which could be caused by ejecta associated with each star in the progenitor system, separated by their orbital velocity. For the first time in an SN Ia, we identify narrow (FWHM = 180 ± 40 km s
−1
) Ca
ii
emission, which we associate with a wind from a surviving, puffed-up companion star. Few published spectra have sufficient resolution and the signal-to-noise ratio necessary to detect similar narrow Ca
ii
emission; however, we have detected similar line profiles in other 03fg-like SNe Ia. The extremely narrow velocity width of Ca
ii
has only otherwise been observed in SNe Iax at late times. Since this event likely had a double-degenerate “super-Chandrasekhar” mass progenitor system, we suggest that a single white dwarf (WD) was fully disrupted and a wind from a surviving companion WD is producing the observed narrow emission. It is unclear whether this unique progenitor and explosion scenario can explain the diversity of 03fg-like SNe Ia, potentially indicating that multiple progenitor channels contribute to this subclass.
Abstract
Seeing pristine material from the donor star in a type Ia supernova (SN Ia) explosion can reveal the nature of the binary system. In this paper, we present photometric and spectroscopic ...observations of SN 2020esm, one of the best-studied SNe of the class of “super-Chandrasekhar” SNe Ia (SC SNe Ia), with data obtained −12 to +360 days relative to peak brightness, obtained from a variety of ground- and space-based telescopes. Initially misclassified as a type II supernova, SN 2020esm peaked at
M
B
= −19.9 mag, declined slowly (Δ
m
15
(
B
) = 0.92 mag), and had particularly blue UV and optical colors at early times. Photometrically and spectroscopically, SN 2020esm evolved similarly to other SC SNe Ia, showing the usual low ejecta velocities, weak intermediate-mass elements, and the enhanced fading at late times, but its early spectra are unique. Our first few spectra (corresponding to a phase of ≳10 days before peak) reveal a nearly pure carbon/oxygen atmosphere during the first days after explosion. This composition can only be produced by pristine material, relatively unaffected by nuclear burning. The lack of H and He may further indicate that SN 2020esm is the outcome of the merger of two carbon/oxygen white dwarfs. Modeling its bolometric light curve, we find an
56
Ni mass of
1.23
−
0.14
+
0.14
M
☉
and an ejecta mass of
1.75
−
0.20
+
0.32
M
☉
, in excess of the Chandrasekhar mass. Finally, we discuss possible progenitor systems and explosion mechanisms of SN 2020esm and, in general, the SC SNe Ia class.
Abstract
The exact nature of the luminous fast blue optical transient AT 2018cow is still debated. In this first of a two-paper series, we present a detailed analysis of three Hubble Space Telescope ...(HST) observations of AT 2018cow covering ∼50–60 days post-discovery in combination with other observations throughout the first two months and derive significantly improved constraints of the late thermal properties. By modeling the spectral energy distributions (SEDs), we confirm that the UV–optical emission over 50–60 days was still a smooth blackbody (i.e., optically thick) with a high temperature (
T
BB
∼ 15,000 K) and small radius (
R
BB
≲ 1000
R
⊙
). Additionally, we report for the first time a break in the bolometric light curve: the thermal luminosity initially declined at a rate of
L
BB
∝
t
−2.40
but faded much faster at
t
−3.06
after day 13. Reexamining possible late-time power sources, we disfavor significant contributions from radioactive decay based on the required
56
Ni mass and lack of UV line blanketing in the HST SEDs. We argue that the commonly proposed interaction with circumstellar material may face significant challenges in explaining the late thermal properties, particularly the effects of the optical depth. Alternatively, we find that continuous outflow/wind driven by a central engine can still reasonably explain the combination of a receding photosphere, optically thick and rapidly fading emission, and intermediate-width lines. However, the rapid fading may have further implications on the power output and structure of the system. Our findings may support the hypothesis that AT 2018cow and other “Cow-like transients” are powered mainly by accretion onto a central engine.
Abstract
We present observations of a peculiar hydrogen- and helium-poor stripped-envelope (SE) supernova (SN) 2020wnt, primarily in the optical and near-infrared (near-IR). Its peak absolute ...bolometric magnitude of −20.9 mag (
L
bol, peak
= (6.8 ± 0.3) × 10
43
erg s
−1
) and a rise time of 69 days are reminiscent of hydrogen-poor superluminous SNe (SLSNe I), luminous transients potentially powered by spinning-down magnetars. Before the main peak, there is a brief peak lasting <10 days post explosion, likely caused by interaction with circumstellar medium (CSM) ejected ∼years before the SN explosion. The optical spectra near peak lack a hot continuum and O
ii
absorptions, which are signs of heating from a central engine; they quantitatively resemble those of radioactivity-powered hydrogen/helium-poor Type Ic SESNe. At ∼1 yr after peak, nebular spectra reveal a blue pseudo-continuum and narrow O
i
recombination lines associated with magnetar heating. Radio observations rule out strong CSM interactions as the dominant energy source at +266 days post peak. Near-IR observations at +200–300 days reveal carbon monoxide and dust formation, which causes a dramatic optical light-curve dip. Pair-instability explosion models predict slow light curve and spectral features incompatible with observations. SN 2020wnt is best explained as a magnetar-powered core-collapse explosion of a 28
M
⊙
pre-SN star. The explosion kinetic energy is significantly larger than the magnetar energy at peak, effectively concealing the magnetar-heated inner ejecta until well after peak. SN 2020wnt falls into a continuum between normal SNe Ic and SLSNe I, and demonstrates that optical spectra at peak alone cannot rule out the presence of a central engine.
Abstract
We present Young Supernova Experiment
grizy
photometry of SN 2021hpr, the third Type Ia supernova sibling to explode in the Cepheid calibrator galaxy, NGC 3147. Siblings are useful for ...improving SN-host distance estimates and investigating their contributions toward the SN Ia intrinsic scatter (post-standardization residual scatter in distance estimates). We thus develop a principled Bayesian framework for analyzing SN Ia siblings. At its core is the cosmology-independent relative intrinsic scatter parameter,
σ
Rel
: the dispersion of siblings distance estimates relative to one another within a galaxy. It quantifies the contribution toward the total intrinsic scatter,
σ
0
, from within-galaxy variations about the siblings’ common properties. It also affects the combined distance uncertainty. We present analytic formulae for computing a
σ
Rel
posterior from individual siblings distances (estimated using any SN model). Applying a newly trained
BayeSN
model, we fit the light curves of each sibling in NGC 3147 individually, to yield consistent distance estimates. However, the wide
σ
Rel
posterior means
σ
Rel
≈
σ
0
is not ruled out. We thus combine the distances by marginalizing over
σ
Rel
with an informative prior:
σ
Rel
∼
U
(0,
σ
0
). Simultaneously fitting the trio’s light curves improves constraints on distance
and
each sibling’s individual dust parameters, compared to individual fits. Higher correlation also tightens dust parameter constraints. Therefore,
σ
Rel
marginalization yields robust estimates of siblings distances for cosmology, as well as dust parameters for sibling–host correlation studies. Incorporating NGC 3147's Cepheid distance yields
H
0
= 78.4 ± 6.5 km s
−1
Mpc
−1
. Our work motivates analyses of homogeneous siblings samples, to constrain
σ
Rel
and its SN-model dependence.
Abstract
We present the optical photometric and spectroscopic analysis of two Type Iax supernovae (SNe), 2018cni and 2020kyg. SN 2018cni is a bright Type Iax SN (
M
V
,peak
= −17.81 ± 0.21 mag), ...whereas SN 2020kyg (
M
V
,peak
= −14.52 ± 0.21 mag) is a faint one. We derive
56
Ni mass of 0.07 and 0.002
M
⊙
and ejecta mass of 0.48 and 0.14
M
⊙
for SNe 2018cni and 2020kyg, respectively. A combined study of the bright and faint Type Iax SNe in
R
/
r
-band reveals that the brighter objects tend to have a longer rise time. However, the correlation between the peak luminosity and decline rate shows that bright and faint Type Iax SNe exhibit distinct behavior. Comparison with standard deflagration models suggests that SN 2018cni is consistent with the deflagration of a CO white dwarf, whereas the properties of SN 2020kyg can be better explained by the deflagration of a hybrid CONe white dwarf. The spectral features of both the SNe point to the presence of similar chemical species but with different mass fractions. Our spectral modeling indicates stratification at the outer layers and mixed inner ejecta for both of the SNe.
While tidal disruption events (TDEs) have long been heralded as laboratories for the study of quiescent black holes, the small number of known TDEs and uncertainties in their emission mechanism have ...hindered progress toward this promise. Here we present 17 new TDEs that have been detected recently by the Zwicky Transient Facility along with Swift UV and X-ray follow-up observations. Our homogeneous analysis of the optical/UV light curves, including 22 previously known TDEs from the literature, reveals a clean separation of light-curve properties with spectroscopic class. The TDEs with Bowen fluorescence features in their optical spectra have smaller blackbody radii, lower optical luminosities, and higher disruption rates compared to the rest of the sample. The small subset of TDEs that show only helium emission lines in their spectra have the longest rise times, the highest luminosities, and the lowest rates. A high detection rate of Bowen lines in TDEs with small photometric radii could be explained by the high density that is required for this fluorescence mechanism. The stellar debris can provide a source for this dense material. Diffusion of photons through this debris may explain why the rise and fade timescale of the TDEs in our sample are not correlated. We also report, for the first time, the detection of soft X-ray flares from a TDE on ∼day timescales. Based on the fact that the X-ray flares peak at a luminosity similar to the optical/UV blackbody luminosity, we attribute them to brief glimpses through a reprocessing layer that otherwise obscures the inner accretion flow.
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