Spectrum Analysis of the Type Ib Supernova 1999dn: Probable Identifications of C II and H-alpha

Low resolution spectra of SN 1999dn at early times are presented and compared with synthetic spectra generated with the parameterized supernova synthetic-spectrum code SYNOW. We find that the spectra of SN 1999dn strongly resemble those of SN 1997X and SN 1984L, and hence we classify it as a Type Ib event. Line-identifications are established through spectrum synthesis. Strong evidence of both H-alpha and C II 6580 is found. We infer that H-alpha appears first, before the time of maximum brightness, and then is blended with and finally overwhelmed by the C II line after maximum; this favors a thin high-velocity hydrogen skin in this Type Ib supernova.Comment: 15 pages, 3 figures. Accepted for publication in Ap

An asymmetric explosion as the origin of spectral evolution diversity in type Ia supernovae

Type Ia Supernovae (SNe Ia) form an observationally uniform class of stellar explosions, in that more luminous objects have smaller decline-rates. This one-parameter behavior allows SNe Ia to be calibrated as cosmological `standard candles', and led to the discovery of an accelerating Universe. Recent investigations, however, have revealed that the true nature of SNe Ia is more complicated. Theoretically, it has been suggested that the initial thermonuclear sparks are ignited at an offset from the centre of the white-dwarf (WD) progenitor, possibly as a result of convection before the explosion. Observationally, the diversity seen in the spectral evolution of SNe Ia beyond the luminosity decline-rate relation is an unresolved issue. Here we report that the spectral diversity is a consequence of random directions from which an asymmetric explosion is viewed. Our findings suggest that the spectral evolution diversity is no longer a concern in using SNe Ia as cosmological standard candles. Furthermore, this indicates that ignition at an offset from the centre of is a generic feature of SNe Ia.Comment: To appear in Nature, 1st July 2010 issue. 36 pages including supplementary materials. 4 figures, 3 supplementary figures, 1 supplementary tabl

SNLS Spectroscopy: Testing for Evolution in Type Ia Supernovae

Aims: We present a quantitative study of a new data set of high redshift Type Ia supernovae spectra, observed at the Gemini telescopes during the first 34 months of the Supernova Legacy Survey. During this time 123 supernovae candidates were observed, of which 87 have been identified as SNe Ia at a median redshift of z=0.720. Spectra from the entire second year of the survey and part of the third year (59 total SNe candidates with 46 confirmed SNe Ia) are published here for the first time. The spectroscopic measurements made on this data set are used determine if these distant SNe comprise a population similar to those observed locally. Methods: Rest-frame equivalent width and ejection velocity measurements are made on four spectroscopic features. Corresponding measurements are presented for a set of 167 spectra from 24 low-z SNe Ia from the literature. Results: We show that there exists a sample at high redshift with properties similar to nearby SNe. No significant difference was found between the distributions of measurements at low and high redsift for three of the features. The fourth feature displays a possible difference that should be investigated further. Correlations between Type Ia SNe properties and host galaxy morphology were also found to be similar at low and high z, and within each host galaxy class we see no evidence for redshift-evolution in SN properties. A new correlation between SNe Ia peak magnitude and the equivalent width of SiII absorption is presented. We demonstrate that this correlation reduces the scatter in SNe Ia luminosity distances in a manner consistent with the lightcurve shape-luminosity corrections that are used for Type Ia SNe cosmology. Conclusions: We show that this new sample of SNLS SNe Ia has spectroscopic properties similar to nearby objects. (Abridged)Comment: Accepted for publication in Astronomy and Astrophysic

Study of Envelope Velocity Evolution of Type Ib-c Core-Collapse Supernovae from Observations of XRF 080109 / SN 2008D and GRB 060218 / SN 2006aj with BTA

Results of modeling the spectra of two supernovae SN 2008D and SN 2006aj related to the X-ray flash XRF 080109 and gamma-ray burst GRB / XRF 060218, respectively, are studied. The spectra were obtained with the 6-meter BTA telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences in 6.48 and 27.61 days after the explosion of SN 2008D, and in 2.55 and 3.55 days after the explosion of SN 2006aj. The spectra were interpreted in the Sobolev approximation with the SYNOW code. An assumption about the presence of envelopes around the progenitor stars is confirmed by an agreement between the velocities of lines interpreted as hydrogen and helium, and the empiric power-law velocity drop with time for the envelopes of classic core-collapse supernovae. Detection of a P Cyg profile of the H-beta line in the spectra of optical afterglows of GRBs can be a determinative argument in favor of this hypothesis.Comment: 12 pages, 6 figures, accepted for publication in Astrophysical Bulletin

Absolute-Magnitude Distributions and Light Curves of Stripped-Envelope Supernovae

The absolute visual magnitudes of three Type IIb, 11 Type Ib and 13 Type Ic supernovae (collectively known as stripped-envelope supernovae) are studied by collecting data on the apparent magnitude, distance, and interstellar extinction of each event. Weighted and unweighted mean absolute magnitudes of the combined sample as well as various subsets of the sample are reported. The limited sample size and the considerable uncertainties, especially those associated with extinction in the host galaxies, prevent firm conclusions regarding differences between the absolute magnitudes of supernovae of Type Ib and Ic, and regarding the existence of separate groups of overluminous and normal-luminosity stripped-envelope supernovae. The spectroscopic characteristics of the events of the sample are considered. Three of the four overluminous events are known to have had unusual spectra. Most but not all of the normal luminosity events had typical spectra. Light curves of stripped-envelope supernovae are collected and compared. Because SN 1994I in M51 was very well observed it often is regarded as the prototypical Type Ic supernova, but it has the fastest light curve in the sample. Light curves are modeled by means of a simple analytical technique that, combined with a constraint on E/M from spectroscopy, yields internally consistent values of ejected mass, kinetic energy, and nickel mass.Comment: 39 pages, 14 figures, 7 tables; Accepted to A

Superconducting gap of overdoped Tl2Ba2CuO6+d observed by Raman scattering

We report Raman scattering spectra for single crystals of overdoped Tl2Ba2CuO6+d (Tl-2201) at low temperatures. It was observed that the pair-breaking peaks in A1g and B1g spectra radically shift to lower energy with carrier doping. We interpret it as s-wave component mixing into d-wave, although the crystal structure is tetragonal. Since similar phenomena were observed also in YBa2Cu3Oy and Bi2Sr2CaCu2Oz, we conclude that s-wave mixing is a common property for overdoped high-Tc superconductors.Comment: 8 pages, 3 figures, proceedings of SNS200

Spectral Modeling of SNe Ia Near Maximum Light: Probing the Characteristics of Hydro Models

We have performed detailed NLTE spectral synthesis modeling of 2 types of 1-D hydro models: the very highly parameterized deflagration model W7, and two delayed detonation models. We find that overall both models do about equally well at fitting well observed SNe Ia near to maximum light. However, the Si II 6150 feature of W7 is systematically too fast, whereas for the delayed detonation models it is also somewhat too fast, but significantly better than that of W7. We find that a parameterized mixed model does the best job of reproducing the Si II 6150 line near maximum light and we study the differences in the models that lead to better fits to normal SNe Ia. We discuss what is required of a hydro model to fit the spectra of observed SNe Ia near maximum light.Comment: 29 pages, 14 figures, ApJ, in pres

The Nature of SN 1961V

The nature of SN 1961V has been uncertain. Its peculiar optical light curve and slow expansion velocity are similar to those of super-outbursts of luminous blue variables (LBVs), but its nonthermal radio spectral index and declining radio luminosity are consistent with decades-old supernovae (SNe). We have obtained Hubble Space Telescope STIS images and spectra of the stars in the vicinity of SN 1961V, and find Object 7 identified by Filippenko et al. to be the closest to the optical and radio positions of SN 1961V. Object 7 is the only point source detected in our STIS spectra and only its H-alpha emission is detected; it cannot be the SN or its remnant because of the absence of forbidden lines. While the H-alpha line profile of Object 7 is remarkably similar to that of eta Car, the blue color (similar to an A2Ib supergiant) and lack of appreciable variability are unlike known post-outburst LBVs. We have also obtained Very Long Baseline Array (VLBA) observations of SN 1961V at 18 cm. The non-detection of SN 1961V places a lower limit on the size of the radio-emitting region, 7.6 mas or 0.34 pc, which implies an average expansion velocity in excess of 4,400 km/s, much higher than the optical expansion velocity measured in 1961. We conclude the following: (1) A SN occurred in the vicinity of SN 1961V a few decades ago. (2) If the SN 1961V light maximum originates from a giant eruption of a massive star, Object 7 is the most probable candidate for the survivor, but its blue color and lack of significant variability are different from a post-outburst eta Car. (3) The radio SN and Object 7 could be physically associated with each other through a binary system. (4) Object 7 needs to be monitored to determine its nature and relationship to SN 1961V.Comment: 16 pages, 3 figures, accepted by the Astronomical Journal for the 2004 May issu