73630268
Observed Fractions of Core-Collapse Supernova Types and Initial Masses of their Single and Binary Progenitor Stars
We analyse the observed fractions of core-collapse supernova (SN) types from the Lick Observatory Supernova Search (LOSS), and we discuss the corresponding implications for massive star evolution. For a standard initial mass function, observed fractions of SN types cannot be reconciled with the expectations of single-star evolution. The mass range of Wolf–Rayet (WR) stars that shed their hydrogen envelopes via their own mass-loss accounts for less than half of the observed fraction of Type Ibc supernovae (SNe Ibc). The true progenitors of SNe Ibc must extend to a much lower range of initial masses than classical WR stars, and we argue that most SN Ibc and SN IIb progenitors must arise from binary Roche lobe overflow. In this scenario, SNe Ic would still trace higher initial mass and metallicity, because line-driven winds in the WR stage remove the helium layer and propel the transition from SN Ib to Ic. Less massive progenitors of SNe Ib and IIb may not be classical WR stars; they may be underluminous with weak winds, possibly hidden by overluminous mass-gainer companions that could appear as B[e] supergiants or related objects having aspherical circumstellar material. The remaining SN types (II-P, II-L and IIn) need to be redistributed across the full range of initial masses, so that even some very massive single stars retain H envelopes until explosion. We consider the possibility of direct collapse to black holes without visible SNe, but find this hypothesis difficult to accommodate in most scenarios. Major areas of remaining uncertainty are (1) the detailed influence of binary separation, rotation and metallicity; (2) mass differences in progenitors of SNe IIn compared to SNe II-L and II-P; and (3) the fraction of SNe Ic arising from single stars with the help of eruptive mass-loss, how this depends on metallicity and how it relates to diversity within the SN Ic subclass. Continued studies of progenitor stars and their environments in nearby galaxies, accounting for SN types, may eventually test these ideas.
14441114
OPTICAL AND NEAR-INFRARED OBSERVATIONS OF THE HIGHLY REDDENED, RAPIDLY EXPANDING TYPE Ia SUPERNOVA SN 2006X IN M100
We present extensive optical (UBVRI), near-infrared (JK) light curves and optical spectroscopy of the Type Ia supernova SN 2006X in the nearby galaxy NGC 4321 (M100). Our observations suggest that either SN 2006X has an intrinsically peculiar color evolution or it is highly reddened [E(B − V)host = 1.42 ± 0.04 mag ] with RV = 1.48 ± 0.06, much lower than the canonical value of 3.1 for the average Galactic dust. SN 2006X also has one of the highest expansion velocities ever published for an SN Ia. Compared with the other SNe Ia we analyzed, SN 2006X has a broader light curve in the U band, a more prominent bump/shoulder feature in the V and R bands, a more pronounced secondary maximum in the I and NIR bands, and a remarkably smaller late-time decline rate in the B band. The B − V color evolution shows an obvious deviation from the Lira-Phillips relation at 1-3 months after maximum brightness. At early times, optical spectra of SN 2006X displayed strong, high-velocity features of both intermediate-mass elements (Si, Ca, and S) and iron peak elements, while at late times they showed a relatively blue continuum, consistent with the blue U − B and B − V colors at similar epochs. A light echo and/or the interaction of the SN ejecta and its circumstellar material may provide a plausible explanation for its late-time photometric and spectroscopic behavior. Using the Cepheid distance of M100, we derive a Hubble constant of 72.8 ± 8.2 km s−1 Mpc−1 (statistical) from the normalized dereddened luminosity of SN 2006X. We briefly discuss whether abnormal dust is a universal signature for all SNe Ia and whether the most rapidly expanding objects form a subclass with distinct photometric and spectroscopic properties.
14733840
Monte Carlo Simulations of Type Ia Supernova Observations in Supernova Surveys
We have performed Monte Carlo simulations of Type Ia supernova (SN Ia) surveys to quantify their efficiency in discovering peculiar overluminous and underluminous SNe Ia. We determined how the type of survey (magnitude-limited, distance-limited, or a hybrid) and its characteristics (observation frequency and detection limit) affect the discovery of peculiar SNe Ia. We find that there are strong biases against the discovery of peculiar SNe Ia introduced by at least four observational effects: the Malmquist bias, the age of the SN Ia at the time of its discovery, the shape of its light curve, and its degree of extinction. Surveys with low observation frequency (less than once per 10 days) tend to discover SNe Ia that are too old for observers to easily recognize their peculiarity. Subluminous SNe Ia are underrepresented in magnitude-limited surveys because they can only be found within a small volume and they remain above the detection limit for less time. Conversely, overluminous SNe Ia are more easily found in magnitude-limited surveys, although their likely association with dusty regions reduces the volume in which they can be discovered. The unbiased rate of peculiar SNe Ia can be recovered only in distance-limited surveys with high observation frequencies and with detection limits that are fainter than the peak magnitude of a subluminous SN Ia in the farthest potential host.
14783547
The Detection of a Light Echo from the Type Ia Supernova 2006X in M100
We report the discovery of a light echo (LE) from the Type Ia supernova (SN) 2006X in the nearby galaxy M100. The presence of the LE is supported by analysis of both the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) images and the Keck optical spectrum that we obtained at ~300 days after maximum brightness. In the image procedure, both the radial-profile analysis and the point-spread function (PSF) subtraction method resolve significant excess emission at 2-5 ACS pixels (~0.05 -->''-0.13 -->'') from the center. In particular, the PSF-subtracted ACS images distinctly appear to have an extended, ringlike echo. Due to limitations of the image resolution, we cannot confirm any structure or flux within 2 ACS pixels from the SN. The late-time spectrum of SN 2006X can be reasonably fit with two components: a nebular spectrum of a normal SN Ia and a synthetic LE spectrum. Both image and spectral analysis show a rather blue color for the emission of the LE, suggestive of a small average grain size for the scattering dust. Using the Cepheid distance to M100 of 15.2 Mpc, we find that the dust illuminated by the resolved LE is ~27-170 pc from the SN. The echo inferred from the nebular spectrum appears to be more luminous than that resolved in the images (at the ~2 σ level), perhaps suggesting the presence of an inner echo at ''). It is not clear, however, whether this possible local echo was produced by a distinct dust component (i.e., the local circumstellar dust) or by a continuous, larger distribution of dust as with the outer component. Nevertheless, our detection of a significant echo in SN 2006X confirms that this supernova was produced in a dusty environment having small dust particles.
119219249
Nearby supernova rates from the Lick Observatory Supernova Search – IV. A recovery method for the delay-time distribution
Recovery of the supernova (SN) delay-time distribution (DTD) – the SN rate versus time that would follow a hypothetical brief burst of star formation – can shed light on SN progenitors and physics, as well as on the time-scales of chemical enrichment. Previous attempts to reconstruct the DTD have been based either on comparison of mean SN rates versus redshift to cosmic star-formation history (SFH), or on the comparison of SN rates among galaxies with different mean ages. Here, we present an approach to recover the SN DTD that avoids the averaging and loss of information of other schemes. We compare the SFHs of individual galaxies to the numbers of SNe discovered by a survey in each galaxy (generally zero, sometimes one SN, rarely a few). We apply the method to a subsample of 3505 galaxies, hosting 82 type-Ia SNe (SNe Ia) and 119 core-collapse supernovae (CC SNe), from the Lick Observatory Supernova Search (LOSS), that have SFHs reconstructed from Sloan Digital Sky Survey (SDSS) spectra. We find a >2σ SN Ia DTD signal in our shortest-delay, ‘prompt’ bin at 99 per cent confidence level. We further find a 4σ indication of SNe Ia that are ‘delayed’ by >2.4 Gyr. Thus, the data support the existence of both prompt and delayed SNe Ia. We measure the time integral over the SN DTD. For CC SNe we find a total yield of 0.010 ± 0.002
1489778
A non-spherical core in the explosion of supernova SN 2004dj
An important and perhaps critical clue to the mechanism driving the explosion of massive stars as supernovae is provided by the accumulating evidence for asymmetry in the explosion. Indirect evidence comes from high pulsar velocities, associations of supernovae with long-soft γ-ray bursts, and asymmetries in late-time emission-line profiles. Spectropolarimetry provides a direct probe of young supernova geometry, with higher polarization generally indicating a greater departure from spherical symmetry. Large polarizations have been measured for ‘stripped-envelope’ (that is, type Ic; ref. 7) supernovae, which confirms their non-spherical morphology; but the explosions of massive stars with intact hydrogen envelopes (type II-P supernovae) have shown only weak polarizations at the early times observed. Here we report multi-epoch spectropolarimetry of a classic type II-P supernova that reveals the abrupt appearance of significant polarization when the inner core is first exposed in the thinning ejecta (∼90 days after explosion). We infer a departure from spherical symmetry of at least 30 per cent for the inner ejecta. Combined with earlier results, this suggests that a strongly non-spherical explosion may be a generic feature of core-collapse supernovae of all types, where the asphericity in type II-P supernovae is cloaked at early times by the massive, opaque, hydrogen envelope.
36928210
The nonlinear effects of fringe fields in HLS
The main body of HLS (Hefei Light Source) is an 800 MeV electron storage ring, whose circumference is about 66 m. As a typical small ring, although the sextupole fields for correction of chromaticities are relatively weak, there still exist strong nonlinear fields coming from fringe fields of dipole and quadrupole magnets. In this paper, the effects of fringe fields on chromaticities and tune shifts with amplitude were discussed and calculated for HLS storage ring. Under the low injection energy, the tune shifts with amplitude coming from fringe fields are one of important sources of transverse Landau damping, which is main stabilizing mechanism for HLS ring.
15020605
The type Ia supernova 1997br in ESO 576-G40
The peculiar type Ia supernova SN 1997br in ESO 576-G40 was extensively observed at Beijing Astronomical Observatory and Lick Observatory. In this paper, we present and discuss the BVRI photometry and the spectra collected over 3 months, beginning 9 days before maximum brightness. The light curves of SN 1997br are similar to those of SN 1991T, with slow decline rates after the B maximum. Well-sampled data before the B maximum show unambiguously that SN 1997br rises more slowly and has a wider peak than normal type Ia supernovae. The optical color evolution of SN 1997br is also similar to that of SN 1991T. We estimate the extinction of SN 1997br to be E(B-V) = 0.35 ± 0.10 mag by comparing its BVRI light curves with those of SN 1991T and by measuring the equivalent width of interstellar Na I D absorption lines. We have conducted a thorough comparison of the spectroscopic evolution of SN 1997br, SN 1991T, and SN 1994D. Although SN 1997br is generally very similar to SN 1991T, it shows some interesting differences at various epochs. Spectra of SN 1997br seem to indicate an earlier transition to the dominant phase of Fe-peak elements after the B maximum. Si II lines in SN 1997br show a very short duration after the B maximum. We discuss the implications of our observations of SN 1997br for models of type Ia supernovae. Specifically, we suggest that some SNe Ia may result from decelerated detonations of white dwarfs.
113828507
Prelimimary Study of the Higher-harmonic Cavity for the Upgrade Project of Hefei Light Source
158654
SUBARU AND KECK OBSERVATIONS OF THE PECULIAR TYPE IA SUPERNOVA 2006GZ AT LATE PHASES
Recently, a few peculiar Type Ia supernovae (SNe Ia) that show exceptionally large peak luminosity have been discovered. Their luminosity requires more than 1 M ? of 56Ni to be ejected during the explosion, suggesting that they might have originated from super-Chandrasekhar mass white dwarfs. However, the nature of these objects is not yet well understood. In particular, no data have been taken at late phases, about one year after the explosion. We report on Subaru and Keck optical spectroscopic and photometric observations of the SN Ia 2006gz, which had been classified as being one of these overluminous SNe Ia. The late-time behavior is distinctly different from that of normal SNe Ia, reinforcing the argument that SN 2006gz belongs to a different subclass than normal SNe Ia. However, the peculiar features found at late times are not readily connected to a large amount of 56Ni; the SN is faint, and it lacks [Fe II] and [Fe III] emissions. If the bulk of the radioactive energy escapes the SN ejecta as visual light, as is the case in normal SNe Ia, the mass of 56Ni does not exceed ~0.3 M ?. We discuss several possibilities to remedy the problem. With the limited observations, however, we are unable to conclusively identify which process is responsible. An interesting possibility is that the bulk of the emission might be shifted to longer wavelengths, unlike the case in other SNe Ia, which might be related to dense C-rich regions as indicated by the early-phase data. Alternatively, it might be the case that SN 2006gz, though peculiar, was actually not substantially overluminous at early times.
118377935
Similarity renormalization group with novel generators
The choice of generator in the Similarity Renormalization Group (SRG) flow equation determines the evolution pattern of the Hamiltonian. The kinetic energy has been used in the generator for most prior applications to nuclear interactions, and other options have been largely unexplored. Here we show how variations of this standard choice can allow the evolution to proceed more efficiently without losing its advantages.