We present space-based ultraviolet/optical photometry and spectroscopy with the Swift Ultra-Violet/Optical Telescope and Hubble Space Telescope (HST), respectively, along with ground-based optical photometry and spectroscopy and near-infrared spectroscopy of supernova SN 2017erp. The optical light curves and spectra are consistent with a normal SN Ia. Compared to previous photometric samples in the near-ultraviolet (NUV), SN 2017erp has UV colors that are redder than NUV-blue SNe Ia corrected to similar optical colors. The chromatic difference between SNe 2011fe and 2017erp is dominated by the intrinsic differences in the UV rather than the expected dust reddening. This chromatic difference is similar to the SALT2 color law, derived from rest-frame ultraviolet photometry of higher redshift SNe Ia. Differentiating between intrinsic UV diversity and dust reddening can have important consequences for determining cosmological distances with rest-frame ultraviolet photometry. This ultraviolet spectroscopic series is the first from HST of a normal, albeit reddened, NUV-red SN Ia and is important for analyzing SNe Ia with intrinsically redder NUV colors. We show model comparisons suggesting that metallicity could be the physical difference between NUV-blue and NUV-red SNe Ia, with emission peaks from reverse fluorescence near 3000 angstrom implying a factor of similar to 10 higher metallicity in the upper layers of SN 2017erp compared to SN 2011fe. Metallicity estimates are very model dependent, however, and there are multiple effects in the UV. Further models and UV spectra of SNe Ia are needed to explore the diversity of SNe Ia, which show seemingly independent differences in the near-UV peaks and mid-UV flux levels.

Our recent work demonstrates a correlation between the high-velocity blue edge, v(ed)(ge), of the iron-peak Fe/Co/Ni H-band emission feature and the optical light-curve (LC) shape of normal, transitional and subluminous SNe Ia. We explain this correlation in terms of SN Ia physics. V-edge corresponds to the sharp transition between the complete and incomplete silicon burning regions in the ejecta. It measures the point in velocity space where the outer Ni-56 mass fraction, X-Ni, falls to the order of 0.03-0.10. For a given Ni-56 mass, M(Ni-56), V-edge is sensitive to the specific kinetic energy E-kin(M(Ni-56)/M-WD) of the corresponding region. Combining V(edge )with LC parameters (i.e., s(BV), Delta m(15)(,s) . in B and V) allows us to distinguish between explosion scenarios. The correlation between V-edge and light-curve shape is consistent with explosion models near the Chandrasekhar limit. However, the available sub-M-Ch WD explosion model based on SN 1999by exhibits velocities that are too large to explain the observations. Finally, the subluminous SN 2015bo exhibits signatures of a dynamical merger of two WDs demonstrating diversity among explosion scenarios at the faint end of the SNe Ia population.

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) and a time of first light of MJD 56629.4(-0.1)(+0.1), which is 1.93(-0.13)(+0.12) days (i.e., <48 h) before the discovery date (2013 December 4.84 UT) and -19.10(-0.13)(+0.12) 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 II lambda 6355 Doppler velocity. Furthermore, discovery photometry and previous nondetection limits enable us to constrain the companion radius down to R-c <= 4 R-circle dot. 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-circle dot. Combined, these limits effectively rule out H-rich nondegenerate companions.

Aims. We present a comprehensive dataset of optical and near-infrared photometry and spectroscopy of type Ia supernova (SN) 2016hnk, combined with integral field spectroscopy (IFS) of its host galaxy, MCG -01-06-070, and nearby environment. Our goal with this complete dataset is to understand the nature of this peculiar object.

Supernova LSQ13abf was discovered soon after explosion by the La Silla-QUEST Survey and then followed by the Carnegie Supernova Project II at its optical and near-IR wavelengths. Our analysis indicates that LSQ13abf was discovered within two days of explosion and its first approximate to 10 days of evolution reveal a B-band light curve with an abrupt drop in luminosity. Contemporaneously, the V-band light curve exhibits a rise towards a first peak and the r- and i-band light curves show no early peak.The early light-curve evolution of LSQ13abf is reminiscent of the post-explosion cooling phase observed in the Type Ib SN 2008D, and the similarity between the two objects extends over weeks. Spectroscopically, LSQ13abf also resembles SN 2008D, with P Cygni Hei features that strengthen over several weeks. Spectral energy distributions are constructed from the broad-bandphotometry, a UVOIR light curve is constructed by fitting black-body (BB) functions, and the underlying BB-temperature and BB-radius profiles are estimated. Explosion parameters are estimated by simultaneously fitting an Arnett model to the UVOIR light curve and the velocity evolution derived from spectral features, and an in addition to a post-shock breakout cooling model to the first two epochs of the bolometric evolution. This combined model suggests an explosion energy of 1.27 +/- 0.23 x 10(51) ergs, in addition to a relatively high ejecta mass of 5.94 +/- 1.10 M-circle dot, a Ni-56 mass of 0.16 +/- 0.02 M-circle dot, and a progenitor-star radius of 28.0 +/- 7.5 R-circle dot. The ejecta mass suggests the origins of LSQ13abf lie with a >25 M-circle dot zero-age-main-sequence mass progenitor and its estimated radius is three times larger compared to the result obtained from the same analysis applied to observations of SN 2008D, and nine times larger compared to SN 1999ex. Alternatively, a comparison of hydrodynamical simulations of greater than or similar to 20-25 M-circle dot zero-age-main-sequence progenitors that evolve to pre-supernova envelope masses of less than or similar to 10 M-circle dot and extended (similar to 100 R-circle dot) envelopes also broadly match the observations of LSQ13abf.

This paper describes the rapidly evolving and unusual supernova LSQ13ddu, discovered by the La Silla-QUEST survey. LSQ13ddu displayed a rapid rise of just 4.8 +/- 0.9 d to reach a peak brightness of -19.70 +/- 0.02 mag in the LSQgr band. Early spectra of LSQ13ddu showed the presence of weak and narrow He I features arising from interaction with circumstellar material (CSM). These interaction signatures weakened quickly, with broad features consistent with those seen in stripped-envelope SNe becoming dominant around two weeks after maximum. The narrow He I velocities are consistent with the wind velocities of luminous blue variables but its spectra lack the typically seen hydrogen features. The fast and bright early light curve is inconsistent with radioactive Ni-56 powering but can be explained through a combination of CSM interaction and an underlying Ni-56 decay component that dominates the later time behaviour of LSQ13ddu. Based on the strength of the underlying broad features, LSQ13ddu appears deficient in He compared to standard SNe Ib.

We present a new method to photometrically delineate between various sub-types of Type Ia supernovae (SNe Ia). Using the color-stretch parameters, s(BV) or s(gr), and the time of i-band primary maximum relative to the B-band (

We present photometric and spectroscopic observations of SN 2013aa and SN 2017cbv, two nearly identical type Ia supernovae (SNe Ia) in the host galaxy NGC 5643. The optical photometry has been obtained using the same telescope and instruments used by the Carnegie Supernova Project. This eliminates most instrumental systematics and provides light curves in a stable and well-understood photometric system. Having the same host galaxy also eliminates systematics due to distance and peculiar velocity, providing an opportunity to directly test the relative precision of SNe Ia as standard candles. The two SNe have nearly identical decline rates, negligible reddenings, and remarkably similar spectra, and, at a distance of similar to 20 Mpc, they are ideal potential calibrators for the absolute distance using primary indicators such as Cepheid variables. We discuss to what extent these two SNe can be considered twins and compare them with other supernova "siblings" in the literature and their likely progenitor scenarios. Using 12 galaxies that hosted two or more SNe Ia, we find that when using SNe Ia, and after accounting for all sources of observational error, one gets consistency in distance to 3%.

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-circle dot 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 (similar to 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 use the spectroscopy and homogeneous photometry of 97 Type Ia supernovae (SNe Ia) obtained by the Carnegie Supernova Project as well as a subset of 36 SNe Ia presented by Zheng et al. to examine maximum-light correlations in a four-dimensional (4D) parameter space: B-band absolute magnitude, M-B, Si II lambda 6355 velocity, vSi II, and Si II pseudo-equivalent widths pEW(Si II lambda 6355) and pEW(Si II lambda 5972). It is shown using Gaussian mixture models (GMMs) that the original four groups in the Branch diagram are well-defined and robust in this parameterization. We find three continuous groups that describe the behavior of our sample in [MB, vSi II] space. Extending the GMM into the full 4D space yields a grouping system that only slightly alters group definitions in the [M-B, v(Si II)] projection, showing that most of the clustering information in [M-B, v(Si II)] is already contained in the 2D GMM groupings. However, the full 4D space does divide group membership for faster objects between corenormal and broad-line objects in the Branch diagram. A significant correlation between M-B and pseudo-equivalent width (Si II lambda 5972) is found, which implies that Branch group membership can be well-constrained by spectroscopic quantities alone. In general, we find that higher-dimensional GMMs reduce the uncertainty of group membership for objects between the originally defined Branch groups. We also find that the broad-line Branch group becomes nearly distinct with the inclusion of v(Si II), indicating that this subclass of SNe Ia may be somehow different from the other groups.