We present very early, high-cadence photometric observations of the nearby Type Ia SN 2017cbv. The light curve is unique in that it has a blue bump during the first five days of observations in the ...U, B, and g bands, which is clearly resolved given our photometric cadence of 5.7 hr during that time span. We model the light curve as the combination of early shocking of the supernova ejecta against a nondegenerate companion star plus a standard SN Ia component. Our best-fit model suggests the presence of a subgiant star 56 R☉ from the exploding white dwarf, although this number is highly model-dependent. While this model matches the optical light curve well, it overpredicts the observed flux in the ultraviolet bands. This may indicate that the shock is not a blackbody, perhaps because of line blanketing in the UV. Alternatively, it could point to another physical explanation for the optical blue bump, such as interaction with circumstellar material or an unusual nickel distribution. Early optical spectra of SN 2017cbv show strong carbon (C ii λ6580) absorption up through day −13 with respect to maximum light, suggesting that the progenitor system contains a significant amount of unburned material. These early results on SN 2017cbv illustrate the power of early discovery and intense follow-up of nearby supernovae to resolve standing questions about the progenitor systems and explosion mechanisms of SNe Ia.
Abstract
We present a series of high-resolution echelle spectra of SN 2023ixf in M101, obtained nightly during the first week or so after discovery using PEPSI on the Large Binocular Telescope. Na
i
...D absorption in these spectra indicates a host reddening of
E
(
B
−
V
) = 0.031 mag and a systemic velocity of +7 km s
−1
relative to the average redshift of M101. Dramatic changes are seen in the strength and shape of strong emission lines emitted by circumstellar material (CSM), including He
ii
λ
4686, C
iv
λλ
5801,5811, H
α
, and N
iv
λλ
7109,7123. In general, these narrow lines broaden to become intermediate-width lines before disappearing from the spectrum within a few days, indicating a limited extent to the dense CSM of around 20–30 au (or ≲10
14.7
cm). H
α
persists in the spectrum for about a week as an intermediate-width emission line with P Cyg absorption at 700–1300 km s
−1
arising in the post-shock shell of swept-up CSM. Early narrow emission lines are blueshifted and indicate an expansion speed in the pre-shock CSM of about 115 km s
−1
, but with even broader emission in higher-ionization lines. This is faster than the normal winds of red supergiants, suggesting some mode of eruptive mass loss from the progenitor or radiative acceleration of the CSM. A lack of narrow blueshifted absorption suggests that most of the CSM is not along our line of sight. This and several other clues indicate that the CSM of SN 2023ixf is significantly aspherical. We find that CSM lines disappear after a few days because the asymmetric CSM is engulfed by the supernova photosphere.
The Type IIb supernova (SN) 1993J is one of only a few stripped-envelope SNe with a progenitor star identified in pre-explosion images. SN IIb models typically invoke H envelope stripping by mass ...transfer in a binary system. For the case of SN 1993J, the models suggest that the companion grew to 22 M sub(middot in circle) and became a source of ultraviolet (UV) excess. Located in M81, at a distance of only 3.6 Mpc, SN 1993J offers one of the best opportunities to detect the putative companion and test the progenitor model. Previously published near-UV spectra in 2004 showed evidence for absorption lines consistent with a hot (B2 la) star, but the field was crowded and dominated by flux from the SN. Here we present Hubble Space Telescope Cosmic Origins Spectrograph and Wide-Field Camera 3 observations of SN 1993J from 2012, at which point the flux from the SN had faded sufficiently to potentially measure the UV continuum properties from the putative companion. The resulting UV spectrum is consistent with contributions from both a hot B star and the SN, although we cannot rule out line-of-sight coincidences.
Abstract
Current population synthesis modeling suggests that 30%–50% of Type II supernovae originate from binary progenitors; however, the identification of a binary progenitor is challenging. One ...indicator of a binary progenitor is that the surrounding stellar population is too old to contain a massive single star. Measurements of the progenitor mass of SN 2017eaw are starkly divided between observations made temporally close to core collapse, which show a progenitor mass of 13–15
M
⊙
(final helium-core mass
M
He
,
core
=
4.4
–
6.0
M
⊙
—which is a more informative property than initial mass) and those from the stellar population surrounding the SN, which find
M
≤ 10.8
M
⊙
(
M
He
,
core
≤
3.4
M
⊙
). In this paper, we reanalyze the surrounding stellar population with improved astrometry and photometry, finding a median age of
16.8
−
1.0
+
3.2
Myr for all stars younger than 50 Myr (
M
He
,
core
=
4.7
M
⊙
) and
85.9
−
6.5
+
3.2
Myr for stars younger than 150 Myr. 16.8 Myr is now consistent with the helium-core mass range derived from the temporally near-explosion observations for single stars. Applying the combined constraints to population synthesis models, we determine that the probability of the progenitor of SN 2017eaw being an initially single star is 65% compared to 35% for prior binary interaction. 85.9 Myr is inconsistent with any formation scenarios. We demonstrate that combining progenitor age constraints with helium-core mass estimates from red supergiant SED modeling, late-time spectra, and indirectly from light-curve modeling can help to differentiate single and binary progenitor scenarios and provide a framework for the application of this technique to future observations.
Abstract
We analyze pre-explosion near- and mid-infrared (IR) imaging of the site of SN 2023ixf in the nearby spiral galaxy M101 and characterize the candidate progenitor star. The star displays ...compelling evidence of variability with a possible period of ≈1000 days and an amplitude of Δ
m
≈ 0.6 mag in extensive monitoring with the Spitzer Space Telescope since 2004, likely indicative of radial pulsations. Variability consistent with this period is also seen in the near-IR
J
and
K
s
bands between 2010 and 2023, up to just 10 days before the explosion. Beyond the periodic variability, we do not find evidence for any IR-bright pre-supernova outbursts in this time period. The IR brightness (
M
K
s
=
−
10.7
mag) and color (
J
−
K
s
= 1.6 mag) of the star suggest a luminous and dusty red supergiant. Modeling of the phase-averaged spectral energy distribution (SED) yields constraints on the stellar temperature (
T
eff
=
3500
−
1400
+
800
K) and luminosity (
log
L
/
L
⊙
=
5.1
±
0.2
). This places the candidate among the most luminous Type II supernova progenitors with direct imaging constraints, with the caveat that many of these rely only on optical measurements. Comparison with stellar evolution models gives an initial mass of
M
init
= 17 ± 4
M
⊙
. We estimate the pre-supernova mass-loss rate of the star between 3 and 19 yr before explosion from the SED modeling at
M
̇
≈
3
×
10
−
5
to 3 × 10
−4
M
⊙
yr
−1
for an assumed wind velocity of
v
w
= 10 km s
−1
, perhaps pointing to enhanced mass loss in a pulsation-driven wind.
We present HST/WFC3 ultraviolet imaging in the F275W and F336W bands of the Type IIb SN 2001ig at an age of more than 14 years. A clear point source is detected at the site of the explosion, with ...mF275W = 25.39 0.10 and mF336W = 25.88 0.13 mag. Despite weak constraints on both the distance to the host galaxy NGC 7424 and the line-of-sight reddening to the supernova, this source matches the characteristics of an early B-type main-sequence star with 19,000 < Teff < 22,000 K and . A BPASS v2.1 binary evolution model, with primary and secondary masses of 13 M and 9 M , respectively, is found to simultaneously resemble, in the Hertzsprung-Russell diagram, both the observed location of this surviving companion, and the primary star evolutionary endpoints for other Type IIb supernovae. This same model exhibits highly variable late-stage mass loss, as expected from the behavior of the radio light curves. A Gemini/GMOS optical spectrum at an age of 6 years reveals a narrow He ii λ4686 emission line, indicative of continuing interaction with a dense circumstellar medium at large radii from the progenitor. We review our findings on SN 2001ig in the context of binary evolution channels for stripped-envelope supernovae. Owing to the uncrowded nature of its environment in the ultraviolet, this study of SN 2001ig represents one of the cleanest detections to date of a surviving binary companion to a Type IIb supernova.
Abstract
SN 2018ivc is an unusual Type II supernova (SN II). It is a variant of SNe IIL, which might represent a transitional case between SNe IIP with a massive H-rich envelope and SNe IIb with only ...a small amount of the H-rich envelope. However, SN 2018ivc shows an optical light-curve evolution more complicated than that of canonical SNe IIL. In this paper, we present the results of prompt follow-up observations of SN 2018ivc with the Atacama Large Millimeter/submillimeter Array. Its synchrotron emission is similar to that of SN IIb 1993J, suggesting that it is intrinsically an SN IIb–like explosion of an He star with a modest (∼0.5–1
M
⊙
) extended H-rich envelope. Its radio, optical, and X-ray light curves are explained primarily by the interaction between the SN ejecta and the circumstellar material (CSM); we thus suggest that it is a rare example (and the first involving the “canonical” SN IIb ejecta) for which the multiwavelength emission is powered mainly by the SN–CSM interaction. The inner CSM density, reflecting the progenitor activity in the final decade, is comparable to that of SN IIb 2013cu, which shows a flash spectral feature. The outer CSM density, and therefore the mass-loss rate in the final ∼200 yr, is higher than that of SN 1993J by a factor of ∼5. We suggest that SN 2018ivc represents a missing link between SNe IIP and SNe IIb/Ib/Ic in the binary evolution scenario.
Abstract
We perform a comprehensive search for optical precursor emission at the position of SN 2023ixf using data from the DLT40, ZTF, and ATLAS surveys. By comparing the current data set with ...precursor outburst hydrodynamical model light curves, we find that the probability of a significant outburst within 5 yr of explosion is low, and the circumstellar material (CSM) ejected during any possible precursor outburst is likely smaller than ∼0.015
M
⊙
. By comparing to a set of toy models, we find that, if there was a precursor outburst, the duration must have been shorter than ∼100 days for a typical brightness of
M
r
≃ −9 mag or shorter than 200 days for
M
r
≃ −8 mag; brighter, longer outbursts would have been discovered. Precursor activity like that observed in the normal Type II SN 2020tlf (
M
r
≃ −11.5) can be excluded in SN 2023ixf. If the dense CSM inferred by early flash spectroscopy and other studies is related to one or more precursor outbursts, then our observations indicate that any such outburst would have to be faint and only last for days to months, or it occurred more than 5 yr prior to the explosion. Alternatively, any dense, confined CSM may not be due to eruptive mass loss from a single red supergiant progenitor. Taken together, the results of SN 2023ixf and SN 2020tlf indicate that there may be more than one physical mechanism behind the dense CSM inferred around some normal Type II supernovae.
Abstract
We present the discovery of the Type II supernova SN 2023ixf in M101 and follow-up photometric and spectroscopic observations, respectively, in the first month and week of its evolution. Our ...discovery was made within a day of estimated first light, and the following light curve is characterized by a rapid rise (≈5 days) to a luminous peak (
M
V
≈ − 18.2 mag) and plateau (
M
V
≈ − 17.6 mag) extending to 30 days with a fast decline rate of ≈0.03 mag day
−1
. During the rising phase,
U
−
V
color shows blueward evolution, followed by redward evolution in the plateau phase. Prominent flash features of hydrogen, helium, carbon, and nitrogen dominate the spectra up to ≈5 days after first light, with a transition to a higher ionization state in the first ≈2 days. Both the
U
−
V
color and flash ionization states suggest a rise in the temperature, indicative of a delayed shock breakout inside dense circumstellar material (CSM). From the timescales of CSM interaction, we estimate its compact radial extent of ∼(3–7) × 10
14
cm. We then construct numerical light-curve models based on both continuous and eruptive mass-loss scenarios shortly before explosion. For the continuous mass-loss scenario, we infer a range of mass-loss history with 0.1–1.0
M
⊙
yr
−1
in the final 2−1 yr before explosion, with a potentially decreasing mass loss of 0.01–0.1
M
⊙
yr
−1
in ∼0.7–0.4 yr toward the explosion. For the eruptive mass-loss scenario, we favor eruptions releasing 0.3–1
M
⊙
of the envelope at about a year before explosion, which result in CSM with mass and extent similar to the continuous scenario. We discuss the implications of the available multiwavelength constraints obtained thus far on the progenitor candidate and SN 2023ixf to our variable CSM models.
Abstract
We present high-cadence optical and ultraviolet light curves of the normal Type Ia supernova (SN) 2021aefx, which shows an early bump during the first two days of observation. This bump may ...be a signature of interaction between the exploding white dwarf and a nondegenerate binary companion, or it may be intrinsic to the white dwarf explosion mechanism. In the case of the former, the short duration of the bump implies a relatively compact main-sequence companion star, although this conclusion is viewing-angle dependent. Our best-fit companion-shocking and double-detonation models both overpredict the UV luminosity during the bump, and existing nickel-shell models do not match the strength and timescale of the bump. We also present nebular spectra of SN 2021aefx, which do not show the hydrogen or helium emission expected from a nondegenerate companion, as well as a radio nondetection that rules out all symbiotic progenitor systems and most accretion disk winds. Our analysis places strong but conflicting constraints on the progenitor of SN 2021aefx; no current model can explain all of our observations.
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