Kazuhito Hatano

THE TYPE IC HYPERNOVA SN 2002AP

Photometric and spectroscopic data of the energetic Type Ic supernova (SN) 2002ap are presented, and the properties of the SN are investigated through models of its spectral evolution and its light curve. The SN is spectroscopically similar to the hypernova SN 1997ef. However, its kinetic energy [~(4-10) ? 1051 ergs] and the mass ejected (2.5-5 M?) are smaller, resulting in a faster evolving light curve. The SN synthesized ~0.07 M? of 56Ni, and its peak luminosity was similar to that of normal SNe. Brightness alone should not be used to define a hypernova, whose defining character, namely very broad spectral features, is the result of high kinetic energy. The likely main-sequence mass of the progenitor star was 20-25 M?, which is also lower than that of both hypernovae SN 1997ef and SN 1998bw. SN 2002ap appears to lie at the low-energy and low-mass end of the hypernova sequence as it is known so far. Observations of the nebular spectrum, which is expected to dominate by the summer of 2002, are necessary to confirm these values.

The Luminosity of SN 1999by in NGC 2841 and the Nature of “Peculiar” Type Ia Supernovae

We present UBVRIJHK photometry and optical spectroscopy of the so-called peculiar Type Ia supernova 1999by in NGC 2841. The observations began 1 week before visual maximum light, which is well defined by daily observations. The light curves and spectra are similar to those of the prototypical subluminous event SN 1991bg. We find that maximum light in B occurred on 1999 May 10.3 UT (JD 2,451,308.8 ± 0.3) with B = 13.66 ± 0.02 and a color of Bmax - Vmax = 0.51 ± 0.03. The late-time color implies minimal dust extinction from the host galaxy. Our photometry, when combined with the recent Cepheid distance to NGC 2841, gives a peak absolute magnitude of MB = -17.15 ± 0.23, making SN 1999by one of the least luminous Type Ia events ever observed. We estimate a decline rate parameter of Δm15(B) = 1.90 mag, versus 1.93 for SN 1991bg, for which 1.10 is typical for so-called normal events. We compare SN 1999by with other subluminous events and find that the Bmax - Vmax color correlates strongly with the decline rate and may be a more sensitive indicator of luminosity than the fading rate for these objects. We find a good correlation between luminosity and the depth of the spectral feature at 580 nm, which had been attributed solely to Si II. We show that in cooler photospheres the 580 nm feature is dominated by Ti II, which provides a simple physical explanation for the correlation. Using only subluminous Type Ia supernovae, we derive a Hubble parameter of H0 = 75 km s-1 Mpc-1, consistent with values found from brighter events.

Extinction and Radial Distribution of Supernova Properties in Their Parent Galaxies

We use a Monte Carlo technique and assume spatial distributions of dust and supernova (SN) progenitors in a simple model of a characteristic SN-producing disk galaxy to explore the effects of extinction on the radial distributions of SN properties in their parent galaxies. The model extinction distributions and projected radial number distributions are presented for various SN types. Even though the model has no core-collapse SNe within 3 kpc of the center, a considerable fraction of the core-collapse SNe are projected into the inner regions of inclined parent galaxies owing to their small vertical scale height. The model predicts that because of extinction, SNe that are projected into the central regions should, on average, appear dimmer and have a much larger magnitude scatter than those in the outer regions. In particular, the model predicts a strong deficit of bright core-collapse events inside a projected radius of a few kiloparsec. Such a deficit is found to be present in the observations. It appears to be a natural consequence of the characteristic spatial distributions of dust and core-collapse SNe in galaxies, and it leads us to offer an alternative to the conventional interpretation of the Shaw effect.

Direct Analysis of Spectra of the Type Ic Supernova SN 1994I

Synthetic spectra generated with the parameterized supernova synthetic-spectrum code SYNOW are compared to observed photospheric-phase spectra of the Type Ic supernova SN 1994I. The observed optical spectra can be well matched by synthetic spectra that are based on the assumption of spherical symmetry. We consider the identification of the infrared absorption feature observed near 10250 ?, which previously has been attributed to He I ?10830 and regarded as strong evidence that SN 1994I ejected some helium. We have difficulty accounting for the infrared absorption with He I alone. It could be a blend of He I and C I lines. Alternatively, we find that it can be fitted by Si I lines without compromising the fit in the optical region. In synthetic spectra that match the observed spectra, from 4 days before to 26 days after the time of maximum brightness, the adopted velocity at the photosphere decreases from 17,500 to 7000 km s-1. Simple estimates of the kinetic energy carried by the ejected mass give values that are near the canonical supernova energy of 1051 ergs. The velocities and kinetic energies that we find for SN 1994I in this way are much lower than those that we find elsewhere for the peculiar Type Ic SNe 1997ef and 1998bw, which therefore appear to have been hyperenergetic.

On the High-Velocity Ejecta of the Type Ia Supernova SN 1994D

Synthetic spectra generated with the parameterized supernova synthetic-spectrum code SYNOW are compared with spectra of the Type Ia SN 1994D that were obtained before the time of maximum brightness. Evidence is found for the presence of two-component Fe II and Ca II features, forming in high-velocity (≥20,000 km s-1) and lower velocity (≤16,000 km s-1) matter. Possible interpretations of these spectral splits, and implications for using early-time spectra of Type Ia supernovae to probe the metallicity of the progenitor white dwarf and the nature of the nuclear burning front in the outer layers of the explosion, are discussed.

Optical Spectra of the Type Ia Supernova 1998aq

We present 29 optical spectra of the normal Type Ia SN 1998aq, ranging from 9 days before to 241 days after the time of maximum brightness. This spectrocopic data set, together with photometric data presented elsewhere, makes SN 1998aq one of the best observed Type Ia supernovae at optical wavelengths. We use the parameterized supernova synthetic-spectrum code SYNOW to study line identifications in the early photospheric-phase spectra. The results include evidence for lines of singly ionized carbon, at ejection velocities as low as 11,000 km s-1. Implications for SN Ia explosion models are discussed.

Ion Signatures in Supernova Spectra

A systematic survey of ions that could be responsible for features in the optical spectra of supernovae is carried out. Six different compositions that could be encountered in supernovae are considered. For each composition, the LTE optical depth of one of the strongest optical lines of each ion is plotted against temperature. For each ion that can realistically be considered as a candidate for producing identifiable features in supernova spectra, a sample synthetic spectrum is displayed. The optical depth plots and the synthetic spectra can provide guidance for studies of line identifications in the optical spectra of all types of supernovae during their photospheric phases.

On the spectrum and nature of the peculiar Type Ia supernova 1991T

A parametrized supernova synthetic-spectrum code is used to study line identifications in the photospheric-phase spectra of the peculiar Type Ia SN 1991T, and to extract some constraints on the composition structure of the ejected matter. The inferred composition structure is not like that of any hydrodynamical model for Type Ia supernovae. Evidence that SN 1991T was overluminous for a SN Ia is presented, and it is suggested that this peculiar event was probably a substantially super-Chandrasekhar explosion that resulted from the merger of two white dwarfs.

Spectrum Analysis of the Type Ib Supernova SN 1999dn: Probable Identifications of C II and Hα

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 Hα and C II λ6580 is found. We infer that Hα 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.

Supernova Resonance‐scattering Profiles in the Presence of External Illumination

ABSTRACT We discuss a simple model for the formation of a supernova spectral line by resonance scattering in the presence of external illumination of the line‐forming region by light from circumstellar interaction (toplighting). The simple model provides a clear understanding of the most conspicuous toplighting effect: a rescaling or, as we prefer, a “muting” of the line profile relative to the continuum. This effect would be present in more realistic models, but would be harder to isolate. An analytic expression for a muting factor for a P Cygni line is derived that depends on the ratio E of the toplighting specific intensity to the specific intensity from the supernova photosphere. If \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} ...