Abstract
We present photometric and spectroscopic observations of the 03fg-like Type Ia supernova (SN Ia) ASASSN-15hy from the ultraviolet (UV) to the near-infrared (NIR). ASASSN-15hy shares many of ...the hallmark characteristics of 03fg-like SNe Ia, previously referred to as “super-Chandrasekhar” SNe Ia. It is bright in the UV and NIR, lacks a clear
i
-band secondary maximum, shows a strong and persistent C
ii
feature, and has a low Si
ii
λ
6355 velocity. However, some of its properties are also extreme among the subgroup. ASASSN-15hy is underluminous (
M
B
,peak
=
−
19.14
−
0.16
+
0.11
mag), red (
(
B
−
V
)
B
max
=
0.18
−
0.03
+
0.01
mag), yet slowly declining (Δ
m
15
(
B
) = 0.72 ± 0.04 mag). It has the most delayed onset of the
i
-band maximum of any 03fg-like SN. ASASSN-15hy lacks the prominent
H
-band break emission feature that is typically present during the first month past maximum in normal SNe Ia. Such events may be a potential problem for high-redshift SN Ia cosmology. ASASSN-15hy may be explained in the context of an explosion of a degenerate core inside a nondegenerate envelope. The explosion impacting the nondegenerate envelope with a large mass provides additional luminosity and low ejecta velocities. An initial deflagration burning phase is critical in reproducing the low
56
Ni mass and luminosity, while the large core mass is essential in providing the large diffusion timescales required to produce the broad light curves. The model consists of a rapidly rotating 1.47
M
⊙
degenerate core and a 0.8
M
⊙
nondegenerate envelope. This “deflagration core-degenerate” scenario may result from the merger between a white dwarf and the degenerate core of an asymptotic giant branch star.
We present a comprehensive data set of supernova (SN) 2016adj located within the central dust lane of Centaurus A. SN 2016adj is significantly reddened and after correcting the peak apparent B -band ...magnitude ( m B = 17.48 ± 0.05) for Milky Way reddening and our inferred host-galaxy reddening parameters (i.e., R V host = 5.7±0.7 and A V host = 6.3 ± 0.2 mag), we estimated it reached a peak absolute magnitude of M B ∼ −18. A detailed inspection of the optical and near-infrared (NIR) spectroscopic time series reveals a carbon-rich SN Ic and not a SN Ib/IIb as previously suggested in the literature. The NIR spectra show prevalent carbon-monoxide formation occurring already by +41 days past B -band maximum, which is ≈11 days earlier than previously reported in the literature for this object. Interestingly, around two months past maximum, the NIR spectrum of SN 2016adj begins to exhibit H features, with a +97 days medium resolution spectrum revealing both Paschen and Bracket lines with absorption minima of ∼2000 km s −1 , full-width-half-maximum emission velocities of ∼1000 km s −1 , and emission line ratios consistent with a dense emission region. We speculate that these attributes are due to a circumstellar interaction (CSI) between the rapidly expanding SN ejecta and a H-rich shell of material that formed during the pre-SN phase. A bolometric light curve was constructed and a semi-analytical model fit suggests the SN synthesized 0.5 M ⊙ of 56 Ni and ejected 4.7 M ⊙ of material, though these values should be approached with caution given the large uncertainties associated with the adopted reddening parameters and known light echo emission. Finally, inspection of the Hubble Space Telescope archival data yielded no progenitor detection.
We present an early-phase g-band light curve and visual-wavelength spectra of the normal Type Ia supernova (SN) 2013gy. The light curve is constructed by determining the appropriate S-corrections to ...transform KAIT natural-system B- and V-band photometry and Carnegie Supernova Project natural-system g-band photometry to the Pan-STARRS1 g-band natural photometric system. A Markov chain Monte Carlo calculation provides a best-fit single power-law function to the first ten epochs of photometry described by an exponent of 2.16+0.06−0.06 2 . 16 − 0.06 + 0.06 $ 2.16^{+0.06}_{-0.06} $ and a time of first light of MJD 56629.4+0.1−0.1 56629 . 4 − 0.1 + 0.1 $ 56629.4^{+0.1}_{-0.1} $ , which is 1.93+0.12−0.13 1 . 93 − 0.13 + 0.12 $ 1.93^{+0.12}_{-0.13} $ days (i.e., < 48 h) before the discovery date (2013 December 4.84 UT) and −19.10+0.12−0.13 − 19 . 10 − 0.13 + 0.12 $ -19.10^{+0.12}_{-0.13} $ days before the time of B-band maximum (MJD 56648.5 ± 0.1). The estimate of the time of first light is consistent with the explosion time inferred from the evolution of the Si IIλ6355 Doppler velocity. Furthermore, discovery photometry and previous nondetection limits enable us to constrain the companion radius down to Rc ≤ 4 R⊙. In addition to our early-time constraints, we used a deep +235 day nebular-phase spectrum from Magellan/IMACS to place a stripped H-mass limit of < 0.018 M⊙. Combined, these limits effectively rule out H-rich nondegenerate companions.
The Carnegie Supernova Project II Taddia, F.; Stritzinger, M. D.; Fransson, C. ...
Astronomy and astrophysics (Berlin),
06/2020, Volume:
638
Journal Article
Peer reviewed
Open access
We present ultra-violet (UV) to mid-infrared (MIR) observations of the long-lasting Type IIn supernova (SN) 2013L obtained by the Carnegie Supernova Project II beginning two days after discovery and ...extending until +887 days (d). The SN reached a peak
r
-band absolute magnitude of ≈−19 mag and an even brighter UV peak, and its light curve evolution resembles that of SN 1988Z. The spectra of SN 2013L are dominated by hydrogen emission features, characterized by three components attributed to different emission regions. A unique feature of this Type IIn SN is that, apart from the first epochs, the blue shifted line profile is dominated by the macroscopic velocity of the expanding shock wave of the SN. We are therefore able to trace the evolution of the shock velocity in the dense and partially opaque circumstellar medium (CSM), from ∼4800 km s
−1
at +48 d, decreasing as
t
−0.23
to ∼2700 km s
−1
after a year. We performed spectral modeling of both the broad- and intermediate-velocity components of the H
α
line profile. The high-velocity component is consistent with emission from a radially thin, spherical shell located behind the expanding shock with emission wings broadened by electron scattering. We propose that the intermediate component originates from preionized gas from the unshocked dense CSM with the same velocity as the narrow component, ∼100 km s
−1
, but also that it is broadened by electron scattering. These features provide direct information about the shock structure, which is consistent with model calculations. The spectra exhibit broad O
I
and O
I
lines that emerge at ≳+144 d and broad Ca
II
features. The spectral continua and the spectral energy distributions (SEDs) of SN 2013L after +132 d are well reproduced by a two-component black-body (BB) model; one component represents emitting material with a temperature between 5 × 10
3
and 1.5 × 10
4
K (hot component) and the second component is characterized by a temperature around 1–1.5 × 10
3
K (warm component). The warm component dominates the emission at very late epochs (≳+400 d), as is evident from both the last near infrared (NIR) spectrum and MIR observations obtained with the
Spitzer
Space Telescope. Using the BB fit to the SEDs, we constructed a bolometric light curve that was modeled together with the unshocked CSM velocity and the shock velocity derived from the H
α
line modeling. The circumstellar-interaction model of the bolometric light curve reveals a mass-loss rate history with large values (1.7 × 10
−2
− 0.15
M
⊙
yr
−1
) over the ∼25−40 years before explosion, depending on the radiative efficiency and anisotropies in the CSM. The drop in the light curve at ∼350 days and the presence of electron scattering wings at late epochs indicate an anisotropic CSM. The mass-loss rate values and the unshocked-CSM velocity are consistent with the characteristics of a massive star, such as a luminous blue variable (LBV) undergoing strong eruptions, similar to
η
Carinae. Our analysis also suggests a scenario where pre-existing dust grains have a distribution that is characterized by a small covering factor.
The Carnegie Supernova Project II Stritzinger, M. D.; Taddia, F.; Fraser, M. ...
Astronomy and astrophysics (Berlin),
07/2020, Volume:
639
Journal Article
Peer reviewed
Open access
We present multiwavelength observations of two gap transients that were followed by the Carnegie Supernova Project-II. The observations are supplemented with data obtained by a number of different ...programs. Here in the first of two papers, we focus on the intermediate-luminosity red transient (ILRT) designated SNhunt120, while in a companion paper we examine the luminous red novae AT 2014ej. Our data set for SNhunt120 consists of an early optical discovery, estimated to be within three days after outburst, the subsequent optical and near-infrared broadband followup extending over a period of about two months, two visual and two near-infrared wavelength spectra, and
Spitzer
Space Telescope observations extending from early (+28 d) to late (+1155 d) phases. SNhunt120 resembles other ILRTs such as NGC 300-2008-OT and SN 2008S, and like these other ILRTs, SNhunt120 exhibits prevalent mid-infrared emission at both early and late phases. From the comparison of SNhunt120 and other ILRTs to electron-capture supernova simulations, we find that the current models underestimate the explosion kinetic energy and thereby produce synthetic light curves that overestimate the luminosity. Finally, examination of pre-outburst
Hubble
Space Telescope images yields no progenitor detection.
The Carnegie Supernova Project II Stritzinger, M. D.; Taddia, F.; Fraser, M. ...
Astronomy and astrophysics (Berlin),
07/2020, Volume:
639
Journal Article
Peer reviewed
Open access
We present optical and near-infrared broadband photometry and optical spectra of AT 2014ej from the Carnegie Supernova Project-II. These observations are complemented with data from the CHilean ...Automatic Supernova sEarch, the Public ESO Spectroscopic Survey of Transient Objects, and from the Backyard Observatory Supernova Search. Observational signatures of AT 2014ej reveal that it is similar to other members of the gap-transient subclass known as luminous red novae (LRNe), including the ubiquitous double-hump light curve and spectral properties similar to that of LRN SN 2017jfs. A medium-dispersion visual-wavelength spectrum of AT 2014ej taken with the
Magellan Clay
telescope exhibits a P Cygni H
α
feature characterized by a blue velocity at zero intensity of ≈110 km s
−1
and a P Cygni minimum velocity of ≈70 km s
−1
. We attribute this to emission from a circumstellar wind. Inspection of pre-outbust
Hubble
Space Telescope images yields no conclusive progenitor detection. In comparison with a sample of LRNe from the literature, AT 2014ej lies at the brighter end of the luminosity distribution. Comparison of the ultra-violet, optical, infrared light curves of well-observed LRNe to common-envelope evolution models from the literature indicates that the models underpredict the luminosity of the comparison sample at all phases and also produce inconsistent timescales of the secondary peak. Future efforts to model LRNe should expand upon the current parameter space we explore here and therefore may consider more massive systems and a wider range of dynamical timescales.
The Carnegie Supernova Project II Moriya, T. J.; Stritzinger, M. D.; Taddia, F. ...
Astronomy and astrophysics (Berlin),
09/2020, Volume:
641
Journal Article
Peer reviewed
Open access
We present optical and near-infrared photometry and spectroscopy of the Type IIn supernova, (SN) 2014ab, obtained by the Carnegie Supernova Project II and initiated immediately after its optical ...discovery. We also study public mid-infrared photometry obtained by the Wide-field Infrared Survey Explorer satellite extending from 56 days prior to the optical discovery to over 1600 days. The light curve of SN 2014ab evolves slowly, while the spectra exhibit strong emission features produced from the interaction between rapidly expanding ejecta and dense circumstellar matter. The light curve and spectral properties are very similar to those of SN 2010jl. The estimated mass-loss rate of the progenitor of SN 2014ab is of the order of 0.1
M
⊙
yr
−1
under the assumption of spherically symmetric circumstellar matter and steady mass loss. Although the mid-infrared luminosity increases due to emission from dust, which is characterized by a blackbody temperature close to the dust evaporation temperature (∼2000 K), there were no clear signatures of in situ dust formation observed within the cold dense shell located behind the forward shock in SN 2014ab in the early phases. Mid-infrared emission of SN 2014ab may originate from pre-existing dust located within dense circumstellar matter that is heated by the SN shock or shock-driven radiation. Finally, for the benefit of the community, we also present five near-infrared spectra of SN 2010jl obtained between 450 to 1300 days post-discovery in the appendix.
We present a Hubble diagram of SNe II using corrected magnitudes derived only from photometry, with no input of spectral information. We use a data set from the Carnegie Supernovae Project I for ...which optical and near-infrared light curves were obtained. The apparent magnitude is corrected by two observables, one corresponding to the slope of the plateau in the V band and the second a color term. We obtain a dispersion of 0.44 mag using a combination of the (V − i) color and the r band and we are able to reduce the dispersion to 0.39 mag using our golden sample. A comparison of our photometric color method (PCM) with the standardized candle method (SCM) is also performed. The dispersion obtained for the SCM (which uses both photometric and spectroscopic information) is 0.29 mag, which compares with 0.43 mag from the PCM for the same SN sample. The construction of a photometric Hubble diagram is of high importance in the coming era of large photometric wide-field surveys, which will increase the detection rate of supernovae by orders of magnitude. Such numbers will prohibit spectroscopic follow up in the vast majority of cases, and hence methods must be deployed which can proceed using solely photometric data.
The Carnegie Supernova Project II Moriya, T J; Stritzinger, M D; Taddia, F ...
Astronomy and astrophysics (Berlin),
09/2020, Volume:
641
Journal Article
Peer reviewed
Open access
We present optical and near-infrared photometry and spectroscopy of the Type IIn supernova, (SN) 2014ab, obtained by the Carnegie Supernova Project II and initiated immediately after its optical ...discovery. We also study public mid-infrared photometry obtained by the Wide-field Infrared Survey Explorer satellite extending from 56 days prior to the optical discovery to over 1600 days. The light curve of SN 2014ab evolves slowly, while the spectra exhibit strong emission features produced from the interaction between rapidly expanding ejecta and dense circumstellar matter. The light curve and spectral properties are very similar to those of SN 2010jl. The estimated mass-loss rate of the progenitor of SN 2014ab is of the order of 0.1 M⊙ yr−1 under the assumption of spherically symmetric circumstellar matter and steady mass loss. Although the mid-infrared luminosity increases due to emission from dust, which is characterized by a blackbody temperature close to the dust evaporation temperature (∼2000 K), there were no clear signatures of in situ dust formation observed within the cold dense shell located behind the forward shock in SN 2014ab in the early phases. Mid-infrared emission of SN 2014ab may originate from pre-existing dust located within dense circumstellar matter that is heated by the SN shock or shock-driven radiation. Finally, for the benefit of the community, we also present five near-infrared spectra of SN 2010jl obtained between 450 to 1300 days post-discovery in the appendix.
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