We present detailed optical photometry for 25 Type Ibc supernovae (SNe Ibc) within d ≈ 150 Mpc obtained with the robotic Palomar 60-inch telescope in [2004][2005][2006][2007]. This study represents the first uniform, systematic, and statistical sample of multi-band SNe Ibc light curves available to date. We correct the light curves for host galaxy extinction using a new technique based on the photometric color evolution, namely, we show that the (V − R) color of extinction-corrected SNe Ibc at ∆t ≈ 10 d after V −band maximum is tightly distributed, (V − R) V 10 = 0.26 ± 0.06 mag. Using this technique, we find that SNe Ibc typically suffer from significant host galaxy extinction, E(B −V ) ≈ 0.4 mag. A comparison of the extinction-corrected light curves for helium-rich (Type Ib) and helium-poor (Type Ic) SNe reveals that they are statistically indistinguishable, both in luminosity and decline rate. We report peak absolute magnitudes of M R = −17.9 ± 0.9 mag and M R = −18.3 ± 0.6 mag for SNe Ib and Ic, respectively. Focusing on the broad-lined (BL) SNe Ic, we find that they are more luminous than the normal SNe Ibc sample, M R = −19.0 ± 1.1 mag, with a probability of only 1.6% that they are drawn from the same population of explosions. By comparing the peak absolute magnitudes of SNe Ic-BL with those inferred for local engine-driven explosions (GRB-SN 1998bw, XRF-SN 2006aj, and SN 2009bb) we find a 25% probability that relativistic SNe are drawn from the overall SNe Ic-BL population. Finally, we fit analytic models to the light curves to derive typical 56 Ni masses of M Ni ≈ 0.2 and 0.5 M ⊙ for SNe Ibc and SNe Ic-BL, respectively. With reasonable assumptions for the photospheric velocities, we further extract kinetic energy and ejecta mass values of M ej ≈ 2 M ⊙ and E K ≈ 10 51 erg for SNe Ibc, while for SNe Ic-BL we find higher values, M ej ≈ 5 M ⊙ and E K ≈ 10 52 erg. We discuss the implications for the progenitors of SNe Ibc and their relation to those of engine-driven explosions.

Letter

Type Ia supernovae are important cosmological distance indicators. Each of these bright supernovae supposedly results from the thermonuclear explosion of a white dwarf star that, after accreting material from a companion star, exceeds some mass limit, but the true nature of the progenitor star system remains controversial. Here we report the spectroscopic detection of circumstellar material in a normal type Ia supernova explosion. The expansion velocities, densities, and dimensions of the circumstellar envelope indicate that this material was ejected from the progenitor system. In particular, the relatively low expansion velocities suggest that the white dwarf was accreting material from a companion star that was in the red-giant phase at the time of the explosion.

Over the past decade our physical understanding of gamma-ray bursts (GRBs) has progressed rapidly thanks to the discovery and observation of their long-lived afterglow emission. Longduration (T > ∼ 2 s) GRBs are associated with the explosive deaths of massive stars ("collapsars" 1 ), which produce accompanying supernovae, 2-4 while the short-duration (T < ∼ 2 s) GRBs arise from a different origin, which has been argued to be the merger of two compact objects, [5][6][7] either neutron stars or black holes. Here we present observations of GRB 060614, a 100-s long burst discovered by the Swift satellite, 8 which require the invocation of a new explosive process: 2 Gal-Yam et al.either a massive "collapsar" that powers a GRB without any associated supernova, or a new type of engine, as long-lived as the collapsar but without any such massive stellar host. We also discuss the properties of this burst's redshift z = 0.125 host galaxy, which distinguish it from other long-duration GRBs and suggest that an entirely new type of GRB progenitor may be required.On 14 June 2006, 12:43 UT, the burst alert telescope (BAT) on board the Swift satellite detected the γ-Ray Burst (GRB) 060614.8 The BAT detected γ-rays from this event for 120s, and the burst showed strong variability during much of that period, as confirmed by parallel observations by the Konus-Wind satellite. 9 Note that while some evolution in the temporal and spectral properties of this GRB were observed, the emission remained highly variable and relatively hard for tens of seconds, unlike the situation observed for a few short bursts with long, soft "tails". 10,7 This indicates sustained activity of an engine, rather than the early onset of the afterglow. The γ-ray properties of this event are similar to those of other bursts from the long-duration subgroup of GRBs. Swift autonomously slewed to the GRB position and began taking data with the X-ray telescope and UVoptical telescope. 11 We began observing this event ≈ 26 minutes later using the 40 inch telescope at Siding Springs Observatory. The evolution of the optical radiation from this event as traced by our data, augmented by Swift observations and additional data from the literature is shown in Fig. 1. As the optical source decayed, we noticed that it was apparently superposed on a faint dwarf host galaxy. On June 19, 2006 UT We obtained a spectrum of the host using the GMOS-S spectrograph mounted on the Gemini-south 8m telescope at Cerro Pachon, Chile. From this spectrum we derived the redshift of the host galaxy, and by association of the GRB, and found it to be z = 0.125, a low value for long GRBs. We confirmed this redshift with a higher quality spectrum obtained using the same instrument on July 15, 2006 UT (Fig. 2). Previous long GRBs at such low redshifts showed clear signatures of the underlying supernova (SN) explosions at comparable age post-burst. 3,12 However, such signatures were lacking in the case of this long GRB. well-detected in our first-epoch WFPC2 observations, and is apparently gone du...

No abstract

We present optical spectropolarimetry obtained at the Keck-II 10-m telescope on 1998 March 7 UT along with total flux spectra spanning the first 494 days after discovery (1998 March 2 UT) of the peculiar type IIn supernova (SN) 1998S. The SN is found to exhibit a high degree of linear polarization, implying significant asphericity for its continuum-scattering environment. Prior to removal of the interstellar polarization, the polarization spectrum is characterized by a flat continuum (at p ≈ 2%) with distinct changes in polarization associated with both the broad (symmetric, half width near zero intensity 10, 000 km s −1 ) and narrow (unresolved, full width at half maximum < 300 km s −1 ) line emission seen in the total flux spectrum. When analyzed in terms of a polarized continuum with unpolarized broad-line recombination emission, an intrinsic continuum polarization of p ≈ 3% results, suggesting a global asphericity of 45% from the oblate, electron-scattering dominated models of Höflich (1991). The smooth, blue continuum evident at early times is shown to be inconsistent with a reddened, single-temperature blackbody, instead having a color temperature that increases with decreasing wavelength. Broad emission-line profiles with distinct blue and red peaks are seen in the total flux spectra at later times, suggesting a disk-like or ring-like morphology for the dense (n e ≈ 10 7 cm −3 ) circumstellar medium, generically similar to what is seen directly in SN 1987A, although much denser and closer to the progenitor in SN 1998S. Implications of the circumstellar scattering environment for the spectropolarimetry are discussed, as are the effects of uncertainty in the removal of interstellar polarization; the importance of obtaining multiple spectropolarimetric epochs to help constrain the interstellar polarization value is particularly stressed. Using information derived from the spectropolarimetry and the total flux spectra, an evolutionary scenario for SN 1998S and its progenitor are presented.

We present ground-based optical photometric monitoring data for NGC 5548, part of an extended multiwavelength reverberation mapping campaign. The light curves have nearly daily cadence from 2014 January to July in nine filters (BVRI and ugriz). Combined with ultraviolet data from the Hubble Space Telescope and Swift, we confirm significant time delays between the continuum bands as a function of wavelength, extending the wavelength coverage from 1158 Å to the z band (∼ 9160 Å). We find that the lags at wavelengths longer than the V band are equal to or greater than the lags of high-ionization-state emission lines (such as He II λ1640 and λ4686), suggesting that the continuum-emitting source is of a physical size comparable to the inner broad-line region (BLR). The trend of lag with wavelength is broadly consistent with the prediction for continuum reprocessing by an accretion disk with τ ∝ λ 4/3 . However, the lags also imply a disk radius that is 3 times larger than the prediction from standard thin-disk theory, assuming that the bolometric luminosity is 10% of the Eddington luminosity (L = 0.1L Edd ). Using optical spectra from the Large Binocular Telescope, we estimate the bias of the interband continuum lags due to BLR emission observed in the filters. We find that the bias for filters with high levels of BLR contamination (∼ 20%) can be important for the shortest continuum lags, and likely has a significant impact on the u and U bands owing to Balmer continuum emission.

Type IIn Supernovae (SNe IIn) are rare events, constituting only a few percent of all core-collapse SNe, and the current sample of well observed SNe IIn is small. Here, we study the four SNe IIn observed by the Caltech Core-Collapse Project (CCCP). The CCCP SN sample is unbiased to the extent that object selection was not influenced by target SN properties. Therefore, these events are representative of the observed population of SNe IIn. We find that a narrow P-Cygni profile in the hydrogen Balmer lines appears to be a ubiquitous feature of SNe IIn. Our light curves show a relatively long rise time (> 20 days) followed by a slow decline stage (0.01 to 0.15 mag day −1 ), and a typical V -band peak magnitude of M V = −18.4 ± 1.0 mag. We measure the progenitor star wind velocities (600 − 1400 km s −1 ) for the SNe in our sample and derive pre-explosion mass loss rates (0.026 − 0.12 M ⊙ y −1 ). We compile similar data for SNe IIn from the literature, and discuss our results in the context of this larger sample. Our results indicate that typical SNe IIn arise from progenitor stars that undergo LBV-like mass-loss shortly before they explode.