We present a densely sampled, homogeneous set of light curves of 64 low-redshift (z <, ~ 0.05) stripped-envelope supernovae (SNe of Type IIb, Ib, Ic, and Ic-BL). These data were obtained between 2001 ...and 2009 at the Fred L. Whipple Observatory (FLWO) on Mount Hopkins in Arizona, with the optical FLWO 1.2 m and the near-infrared (NIR) Peters Automated Infrared 1.3 m telescopes. Our data set consists of 4543 optical photometric measurements on 61 SNe, including a combination of U B V R I, U BVr'i', and u'B Vr'i', and 1919 JHK sub(s) NIR measurements on 25 SNe. This sample constitutes the most extensive multi-color data set of stripped-envelope SNe to date. Our photometry is based on template-subtracted images to eliminate any potential host-galaxy light contamination. This work presents these photometric data, compares them with data in the literature, and estimates basic statistical quantities: date of maximum, color, and photometric properties. We identify promising color trends that may permit the identification of stripped-envelope SN subtypes from their photometry alone. Many of these SNe were observed spectroscopically by the Harvard-Smithsonian Center for Astrophysics (CfA) SN group, and the spectra are presented in a companion paper. A thorough exploration that combines the CfA photometry and spectroscopy of stripped-envelope core-collapse SNe will be presented in a follow-up paper.
We present 645 optical spectra of 73 supernovae (SNe) of Types IIb, Ib, Ic, and broad-lined Ic. All of these types are attributed to the core collapse of massive stars, with varying degrees of intact ...H and He envelopes before explosion. The SNe in our sample have a mean redshift left angle bracketczright angle bracket = 4200 km s super(-1). Most of these spectra were gathered at the Harvard-Smithsonian Center for Astrophysics (CfA) between 2004 and 2009. For 53 SNe, these are the first published spectra. The data coverage ranges from mere identification (1-3 spectra) for a few SNe to extensive series of observations (10-30 spectra) that trace the spectral evolution for others, with an average of 9 spectra per SN. For 44 SNe of the 73 SNe presented here, we have well-determined dates of maximum light to determine the phase of each spectrum. Our sample constitutes the most extensive spectral library of stripped-envelope SNe to date. We provide very early coverage (as early as 30 days before V-band max) for photospheric spectra, as well as late-time nebular coverage when the innermost regions of the SN are visible (as late as 2 yr after explosion, while for SN 1993J, we have data as late as 11.6 yr). This data set has homogeneous observations and reductions that allow us to study the spectroscopic diversity of these classes of stripped SNe and to compare these to SNe-gamma-ray bursts. We undertake these matters in follow-up papers.
Spectra and light curves of SN 2006gz show the strongest signature of unburned carbon and one of the slowest fading light curves ever seen in a Type Ia event Delta m sub(15)(B) = 0.69 plus or minus ...0.04. The early-time Si II velocity is low, implying it was slowed by an envelope of unburned material. Our best estimate of the luminosity implies M sub(v) = -19.74 and the production of similar to 1.2 M unk of super(56)Ni. This suggests a super-Chandrasekhar mass progenitor. A double degenerate merger is consistent with these observations.
Empirical models of supernova (SN) spectral energy distributions (SEDs) are widely used for SN survey simulations and photometric classifications. The existing library of SED models has excellent ...optical templates, but limited, poorly constrained coverage of ultraviolet (UV) and infrared (IR) wavelengths. However, both regimes are critical for the design and operation of future SN surveys, particularly at IR wavelengths that will be accessible with the James Webb Space Telescope and the Wide-Field Infrared Survey Telescope. We create a public repository of improved empirical SED templates using a sampling of Type Ia and core-collapse (CC) photometric light curves to extend the Type Ia parameterized SALT2 model and a set of SN Ib, SN Ic, and SN II SED templates into the UV and near-IR. We apply this new repository of extrapolated SN SED models to examine how future surveys can discriminate between CC and Type Ia SNe at UV and IR wavelengths, and present an open-source software package written in Python, SNSEDextend, that enables users to generate their own extrapolated SEDs.
Recent high-resolution spectra of the Type Ia supernova SN 2006X have revealed the presence of time-variable and blueshifted Na I D features, interpreted by Patat et al. as originating in ...circumstellar material within the progenitor system. The variation seen in SN 2006X induces relatively large changes in the total Na I D equivalent width (EW ~ 0.5 A in just over two weeks) that would be detectable at lower resolutions. We have used a large data set comprising 2400 low-resolution spectra of 450 Type Ia supernovae (SNe Ia) obtained by the CfA Supernova Program to search for variable Na I D features. Out of the 31 SNe Ia (including SN 2006X) in which we could have detected similar EW variations, only one other (SN 1999cl) shows variable Na I D features, with an even larger change over a similar ~10 day timescale (EW = 1.66 ± 0.21 A). Interestingly, both SN 1999cl and SN 2006X are the two most highly reddened objects in our sample, raising the possibility that the variability is connected to dusty environments.
We present extensive early photometric (ultraviolet through near-infrared) and spectroscopic (optical and near-infrared) data on supernova (SN) 2008D as well as X-ray data analysis on the associated ...Swift X-ray transient (XRT) 080109. Our data span a time range of 5 hr before the detection of the X-ray transient to 150 days after its detection, and a detailed analysis allowed us to derive constraints on the nature of the SN and its progenitor; throughout we draw comparisons with results presented in the literature and find several key aspects that differ. We show that the X-ray spectrum of XRT 080109 can be fit equally well by an absorbed power law or a superposition of about equal parts of both power law and blackbody. Our data first established that SN 2008D is a spectroscopically normal SN Ib (i.e., showing conspicuous He lines) and showed that SN 2008D had a relatively long rise time of 18 days and a modest optical peak luminosity. The early-time light curves of the SN are dominated by a cooling stellar envelope (for Delta *Dt0.1-4 days, most pronounced in the blue bands) followed by 56Ni decay. We construct a reliable measurement of the bolometric output for this stripped-envelope SN, and, combined with estimates of E K and M ej from the literature, estimate the stellar radius R of its probable Wolf-Rayet progenitor. According to the model of Waxman et al. and Chevalier & Fransson, we derive R W07 = 1.2 +/- 0.7R and R CF08 = 12 +/- 7 R, respectively; the latter being more in line with typical WN stars. Spectra obtained at three and four months after maximum light show double-peaked oxygen lines that we associate with departures from spherical symmetry, as has been suggested for the inner ejecta of a number of SN Ib cores.
We report the successful identification of the type of the supernova (SN) responsible for the supernova remnant SNR 0509-675 in the Large Magellanic Cloud (LMC) using Gemini spectra of surrounding ...light echoes. The ability to classify outbursts associated with centuries-old remnants provides a new window into several aspects of SN research and is likely to be successful in providing new constraints on additional LMC SNe, as well as their historical counterparts in the Milky Way (MW). The combined spectrum of echo light from SNR 0509-675 shows broad emission and absorption lines consistent with a SN spectrum. We create a spectral library consisting of 28 SNe Ia and 6 SNe Ib/c that are time-integrated, dust-scattered by LMC dust, and reddened by the LMC and MW. We fit these SN templates to the observed light echo spectrum using image minimization, as well as correlation techniques, and we find that overluminous 1991T-like SNe Ia with image match the observed spectrum best.
We describe the implementation and optimization of the ESSENCE supernova survey, which we have undertaken to measure the dark energy equation-of-state parameter, w = P/(pc super(2)). We present a ...method for optimizing the survey exposure times and cadence to maximize our sensitivity to w for a given fixed amount of telescope time. For our survey on the CTIO 4 m telescope, measuring the luminosity distances and redshifts for supernovae at modest redshifts (z approximately 0.5 plus or minus 0.2) is optimal for determining w. We describe the data analysis pipeline based on using reliable and robust image subtraction to find supernovae automatically and in nearly real time. Since making cosmological inferences with supernovae relies crucially on accurate measurement of their apparent brightnesses, we describe our efforts to establish a thorough calibration of the CTIO 4 m telescope's natural photometric system. In its first four years, ESSENCE has discovered and spectroscopically confirmed 102 Type Ia supernovae, at redshifts from 0.10 to 0.78, identified through an impartial, effective methodology for spectroscopic classification and redshift determination. We present the resulting light curves for all of the Type Ia supernovae found by ESSENCE and used in our measurement of w, presented in a companion paper by Wood-Vasey and coworkers.
We present early photometric and spectroscopic data on the afterglow of GRB 060218 and report the evolution of the underlying supernova SN 2006aj. Our data span a time range of 4-23 days after the ...GRB and clearly establish that SN 2006aj is a fast-evolving broad-lined Type Ic SN with an extremely short rise time (610 days) and a large optical peak luminosity (M sub(V)= -18.7 mag). The supernova properties are deduced well since the gamma-ray burst (GRB) afterglow does not contribute a significant amount to the total light output. The spectra show broad lines indicative of large expansion velocities but are better matched by those of SN 2002ap and SN 1997ef (not associated with a GRB) than those of the prototypical GRB-related SN 1998bw. We refine the redshift estimate to z = 0.03351 c 0.00007. The host galaxy is a low-metallicity dwarf galaxy (with M sub(V, host) = -16.0 mag), similar to host galaxies of other GRB-associated SNe.
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