[en] With a redshift of z ∼ 1.7, SN 1997ff is the most distant type Ia supernova discovered so far. This SN is close to several bright, z = 0.6-0.9 galaxies, and we consider the effects of lensing by those objects on the magnitude of SN 1997ff. We estimate their velocity dispersions using the Tully-Fisher and Faber-Jackson relations corrected for evolution effects, and calculate, applying the multiple-plane lensing formalism, that SN 1997ff is magnified by 0.34±0.12 mag. Due to the spatial configuration of the foreground galaxies, the shear from individual lenses partially cancels out,and the total distortion induced on the host galaxy is considerably smaller than that produced by a single lens having the same magnification. After correction for lensing, the revised distance to SN 1997ff is m-M = 45.49 ± 0.34 mag, which improves the agreement with the (Omega)_M = 0.35, (Omega)Λ = 0.65 cosmology expected from lower-redshift SNe Ia, and is inconsistent at the ∼ 3 sigma confidence level with a uniform gray dust model or a simple evolution model

[en] We have obtained high-quality Keck optical spectra at three epochs of the Type Ia supernova 1997ex, whose redshift z is 0.361. The elapsed calendar time between the first two spectra was 24.88 days, and that between the first and third spectra was 30.95 days. In an expanding universe where 1+z represents the factor by which space has expanded between the emission and detection of light, the amount of aging in the supernova rest frame should be a factor of 1/(1+z) smaller than the observed-frame aging; thus, we expect SN 1997ex to have aged 18.28 and 22.74 days between the first epoch and the second and third epochs, respectively. The quantitative method for determining the spectral-feature age of an SN Ia reveals that the corresponding elapsed times in the supernova rest frame were 16.97+/-2.75 and 18.01+/-3.14 days, respectively. This result is inconsistent with no time dilation with a significance level of 99.0 percent, providing evidence against ''tired light'' and other hypotheses in which no time dilation is expected. Moreover, the observed timescale of spectral evolution is inconsistent with that expected in the ''variable mass theory''. The result is within ∼1 of the aging expected from a universe in which redshift is produced by cosmic expansion

[en] I present an overview of optical observations of Type II, IIb, Ib, and Ic supernovae (SNe), all of which are thought to arise from core collapse in massive progenitors that have previously experienced different amounts of mass loss. SNe Ic appear to have been stripped the most, followed by SNe Ib and SNe IIb. In the case of SNe Iln, part of the hydrogen envelope remains, yet the ejecta interact with unusually dense circumstellar gas, probably a wind from the progenitor star. Some SNe IIn, however, might not be genuine supernovae, but rather 'super-outbursts' of luminous variable stars. Spectropolarimetry of core-collapse SNe reveals that asphericity tends to increase toward the core. It has recently been shown that several long-duration gamma-ray bursts were undeniably associated with peculiar SNe Ic having exceptionally high ejecta velocities

[en] We present a test of the statistical method introduced by Bernard F. Shutz in 1986 using only gravitational waves to infer the Hubble constant (H₀) from GW190814, the first high-probability neutron-star–black hole (NS–BH) merger candidate detected by the Laser Interferometer gravitational-wave Observatory (LIGO) and the Virgo interferometer. We apply a baseline test of this method to the binary neutron star (BNS) merger GW170817 and find ${\mathrm{H}}_0={70}_{-<!--\; ???\; -->18.0}^{+35.0}$ km s⁻¹ Mpc⁻¹ (maximum a posteriori and 68.3% highest density posterior interval) for a galaxy B-band luminosity threshold of $L_B⩾<!--\; ???\; -->0.001L_B^{\ast <!--\; ???\; -->}$ with a correction for catalog incompleteness. Repeating the calculation for GW190814, we obtain ${\mathrm{H}}_0={67}_{-<!--\; ???\; -->26.0}^{+41.0}$ km s⁻¹ Mpc⁻¹ and ${\mathrm{H}}_0={71}_{-<!--\; ???\; -->30.0}^{+34.0}$ km s⁻¹ Mpc⁻¹ for $L_B⩾<!--\; ???\; -->0.001L_B^{\ast <!--\; ???\; -->}$ and $L_B⩾<!--\; ???\; -->0.626L_B^{\ast <!--\; ???\; -->}$, respectively. Combining the posteriors for both events yields ${\mathrm{H}}_0={70}_{-<!--\; ???\; -->18.0}^{+29.0}$ km s⁻¹ Mpc⁻¹, demonstrating the improvement on constraints when using multiple gravitational-wave events. We also confirm the results of other works that adopt this method, showing that increasing the L _B threshold enhances the posterior structure and slightly shifts the distribution’s peak to higher H₀ values.We repeat the joint inference using the low-spin PhenomPNRT and the newly available combined (SEOBNRv4PHM + IMRPhenomPv3HM) posterior samples for GW170817 and GW190814, respectively, achieving a tighter constraint of ${\mathrm{H}}_0={69}_{-<!--\; ???\; -->14.0}^{+29.0}$ km s⁻¹ Mpc⁻¹.

[en] We present a new empirical fitting method for the optical light curves of Type Ia supernovae (SNe Ia). We find that a variant broken-power-law function provides a good fit, with the simple assumption that the optical emission is approximately the blackbody emission of the expanding fireball. This function is mathematically analytic and is derived directly from the photospheric velocity evolution. When deriving the function, we assume that both the blackbody temperature and photospheric velocity are constant, but the final function is able to accommodate these changes during the fitting procedure. Applying it to the case study of SN 2011fe gives a surprisingly good fit that can describe the light curves from the first-light time to a few weeks after peak brightness, as well as over a large range of fluxes (∼5 mag, and even ∼7 mag in the g band). Since SNe Ia share similar light-curve shapes, this fitting method has the potential to fit most other SNe Ia and characterize their properties in large statistical samples such as those already gathered and in the near future as new facilities become available.

[en] A growing number of observations reveal a subset of Type Ia supernovae undergoing circumstellar interaction (SNe Ia-CSM). We present unpublished archival Spitzer Space Telescope data on SNe Ia-CSM 2002ic and 2005gj obtained >1300 and 500 days post-discovery, respectively. Both SNe show evidence for late-time mid-infrared (mid-IR) emission from warm dust. The dust parameters are most consistent with a preexisting dust shell that lies beyond the forward-shock radius, most likely radiatively heated by optical and X-ray emission continuously generated by late-time CSM interaction. In the case of SN 2005gj, the mid-IR luminosity more than doubles after 1 yr post-discovery. While we are not aware of any late-time optical-wavelength observations at these epochs, we attribute this rebrightening to renewed shock interaction with a dense circumstellar shell

[en] The detection of polarized continuum and line emission from the nucleus of NGC 4258 by Wilkes et al. in 1995 provides an intriguing application of the unified model of Seyfert nuclei to a galaxy in which there is known to be an edge-on, rotating disk of molecular gas surrounding the nucleus. Unlike most Seyfert nuclei, however, NGC 4258 has strongly polarized narrow emission lines. To further investigate the origin of the polarized emission, we have obtained spectropolarimetric observations of the NGC 4258 nucleus at the Keck II telescope. The narrow-line polarizations range from 1.0% for [S ii] λ6716 to 13.9% for the [O ii] λλ7319, 7331 blend, and the position angle of polarization is oriented nearly parallel to the projected plane of the masing disk. A correlation between critical density and degree of polarization is detected for the forbidden lines, indicating that the polarized emission arises from relatively dense (n_e (greater-or-similar sign)10⁴ cm-3), radially stratified gas. An archival Hubble Space Telescope narrowband [O iii] image shows that the narrow-line region has a compact, nearly unresolved core, implying a FWHM size of (less-or-similar sign)2.5 pc. We discuss the possibility that the polarized emission might arise from the accretion disk itself and become polarized by scattering within the disk atmosphere. A more likely scenario is an obscuring torus or strongly warped disk surrounding the inner portion of a narrow-line region that is strongly stratified in density. The compact size of the narrow-line region implies that the obscuring structure must be smaller than about 2.5 pc in diameter. (c) (c) 1999. The American Astronomical Society

[en] Type II-plateau supernovae (SNe IIP) are the results of the explosions of red supergiants and are the most common subclass of core-collapse supernovae. Past observations have shown that the outer layers of the ejecta of SNe IIP are largely spherical, but the degree of asphericity increases toward the core. We present evidence for high degrees of asphericity in the inner cores of three recent SNe IIP (SNe 2006my, 2006ov, and 2007aa), as revealed by late-time optical spectropolarimetry. The three objects were all selected to have very low interstellar polarization (ISP), which minimizes the uncertainties in ISP removal and allows us to use the continuum polarization as a tracer of asphericity. The three objects have intrinsic continuum polarizations in the range of 0.83%-1.56% in observations taken after the end of the photometric plateau, with the polarization dropping to almost zero at the wavelengths of strong emission lines. Our observations of SN 2007aa at earlier times, taken on the photometric plateau, show contrastingly smaller continuum polarizations (∼0.1%). The late-time Hα and [O I] line profiles of SN 2006ov provide further evidence for asphericities in the inner ejecta. Such high core polarizations in very ordinary core-collapse supernovae provide further evidence that essentially all core-collapse supernova explosions are highly aspherical, even if the outer parts of the ejecta show only small deviations from spherical symmetry.

[en] We present a detailed analysis of the extremely luminous and long-lasting Type IIn supernova (SN) 2006gy using spectra obtained between days 36 and 237 after explosion. We derive the temporal evolution of the effective temperature, radius, blast-wave and SN-ejecta expansion speeds, and bolometric luminosity, as well as the progenitor wind density and total swept-up mass overtaken by the shock. SN 2006gy can be interpreted in the context of shock interaction with a dense circumstellar medium (CSM), but with quite extreme values for the CSM mass of ∼20 M_sun and SN explosion kinetic energy of at least 5 x 10⁵¹ erg. A key difference between SN 2006gy and other SNe IIn is that, owing to its large amount of swept-up mass, the interaction region remained opaque much longer. At early times, Hα emission-line widths suggest that the photosphere is ahead of the shock, and photons diffuse out through the opaque CSM shell. The pivotal transition to optically thin emission occurs around day 110, when we start to see a decrease in the blackbody radius R_BB and strengthening tracers of the post-shock shell. From the evolution of pre-shock velocities, we deduce that the CSM was ejected by the progenitor star in a ∼>10⁴⁹ erg precursor event ∼8 yr before the explosion. The large CSM mass definitively rules out models involving stars with initial masses of ∼<10 M_sun. If the pre-SN mass budget also includes the likely SN ejecta mass of 10-20 M_sun and the distant >10 M_sun shell inferred from a light echo, then even massive M_ZAMS = 30-40 M_sun progenitor stars are inadequate. At roughly solar metallicity, substantial mass loss probably occurred during the star's life, so SN 2006gy's progenitor is more consistent with sequential giant luminous blue variable eruptions or pulsational pair-instability ejections in extremely massive stars with initial masses above 100 M_sun. This requires significant revision to current paradigms of massive-star evolution.

[en] GRB 130702A is a nearby long-duration gamma-ray burst (LGRB) discovered by the Fermi satellite whose associated afterglow was detected by the Palomar Transient Factory. Subsequent photometric and spectroscopic monitoring has identified a coincident broad-lined Type Ic supernova (SN), and nebular emission detected near the explosion site is consistent with a redshift of z = 0.145. The SN-GRB exploded at an offset of ∼7.''6 from the center of an inclined r = 18.1 mag red disk-dominated galaxy, and ∼0.''6 from the center of a much fainter r = 23 mag object. We obtained Keck-II DEIMOS spectra of the two objects and find a 2σ upper limit on their line-of-sight velocity offset of ∼<60 km s^–1. If we calculate the inclination angle of the massive red galaxy from its axis ratio and assume that its light is dominated by a very thin disk, the explosion would have a ∼60 kpc central offset, or ∼9 times the galaxy's half-light radius. A significant bulge or a thicker disk would imply a higher inclination angle and greater central offset. The substantial offset suggests that the faint source is a separate dwarf galaxy. The star-formation rate of the dwarf galaxy is ∼0.05 M_☉ yr^–1, and we place an upper limit on its oxygen abundance of 12 + log(O/H) < 8.16 dex. The identification of an LGRB in a dwarf satellite of a massive, metal-rich primary galaxy suggests that recent detections of LGRBs spatially coincident with metal-rich galaxies may be, in some cases, superpositions