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 [∼ ergs] and 51 (4-10) # 10 the mass ejected (2.5-5) are smaller, resulting in a faster evolving light curve. The SN synthesized M , ∼0.07 of 56 Ni, and its peak luminosity was similar to that of normal SNe. Brightness alone should not be M , 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][21][22][23][24][25] , which is also lower than M , 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.
We present extensive optical (U BV RI), 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 R V = 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 a 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 near-infrared 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 to 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.
The supernova SN 2006aj associated with GRB 060218 is the second-closest GRB-SN observed to date (z = 0.033). We present Very Large Telescope, Liverpool Telescope, and Katzman Automatic Imaging Telescope multi-color photometry of SN 2006aj. This supernova is found to be subluminous and rapidly evolving. Its early light curve includes an additional wavelength-dependent component, which can be interpreted as shock break-out. We compare the photometric evolution of multi-band light curves with the corresponding properties of the present sample of more than 10 GRB-SNe with precisely known redshifts. Using host-galaxy extinction measurements, we derive extinction-corrected GRB-SN luminosities and place SN 2006aj in the context of this GRB-selected supernova sample as well as in the context of local stripped-envelope supernovae.
Observations and modeling for the light curve (LC) and spectra of supernova (SN) 2005bf are reported. This SN showed unique features: the LC had two maxima, and declined rapidly after the second maximum, while the spectra showed strengthening He lines whose velocity increased with time. The double-peaked LC can be reproduced by a double-peaked 56 Ni distribution, with most 56 Ni at low velocity and a small amount at high velocity. The rapid post-maximum decline requires a large fraction of the γ-rays to escape from the 56 Ni-dominated region, possibly because of low-density "holes". The presence of Balmer lines in the spectrum suggests that the He layer of the progenitor was substantially intact. Increasing γ-ray deposition in the He layer due to enhanced γ-ray escape from the 56 Ni-dominated region may explain both the delayed strengthening and the increasing velocity of the He lines. The SN has massive ejecta (∼ 6−7M ⊙ ), normal kinetic energy (∼ 1.0 − 1.5 × 10 51 ergs), high peak bolometric luminosity (∼ 5 × 10 42 erg s −1 ) for an epoch as late as ∼ 40 days, and a large 56 Ni mass (∼ 0.32M ⊙ ). These properties, and the presence of a small amount of H suggest that the progenitor was initially massive (M∼ 25 − 30M ⊙ ) and had lost most of its H envelope, and was possibly a WN star. The double-peaked 56 Ni distribution suggests that the explosion may have formed jets that did not reach the He layer. The properties of SN 2005bf resemble those of the explosion of Cassiopeia A.
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 Ðnd 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 identiÐcations are established through spectrum synthesis. Strong evidence of both Ha and C II j6580 is found. We infer that Ha appears Ðrst, before the time of maximum brightness, and then is blended with and Ðnally overwhelmed by the C II line after maximum ; this favors a thin highvelocity hydrogen skin in this Type Ib supernova.
The net optical light curves and spectra of the supernova (SN) 2003dh are obtained from the published spectra of GRB 030329, covering about 6 days before SN maximum to about 60 days after. The bulk of the U -band flux is subtracted from the observed spectra using earlytime afterglow templates, because strong line blanketing greatly depresses the UV and U -band SN flux in a metal-rich, fast-moving SN atmosphere. The blue-end spectra of the gamma-ray burst (GRB) connected hypernova SN 1998bw is used to determine the amount of subtraction. The subtraction of a host galaxy template affects the late-time results. The derived SN 2003dh light curves are narrower than those of SN 1998bw, rising as fast before maximum, reaching a possibly fainter maximum, and then declining ∼ 1.2 − 1.4 times faster. We then build U V OIR bolometric SN light curve. Allowing for uncertainties, it can be reproduced with a spherical ejecta model of M ej ∼ 7 ± 3 M ⊙ , E K ∼ 3.5 ± 1.5 × 10 52 ergs, with E K /M ej ∼ 5 following previous spectrum modeling, and M ( 56 Ni) ∼ 0.4 +0.15 −0.1 M ⊙ . This suggests a progenitor main-sequence mass of ∼ 25 − 40 M ⊙ , lower than SN 1998bw but significantly higher than normal Type Ic SNe and the GRB-unrelated hypernova SN 2002ap.
We present BV RI photometry and optical spectroscopy of SN 2005bf near light maximum. The maximum phase is broad and occurred around 2005 May 7, about forty days after the shock breakout. SN 2005bf has a peak bolometric magnitude M bol = −18.0±0.2: while this is not particularly bright, it occurred at an epoch significantly later than other SNe Ibc, indicating that the SN possibly ejected ∼ 0.31 M ⊙ of 56 Ni, which is more than the typical amount. The spectra of SN 2005bf around maximum are very similar to those of the Type Ib SNe 1999ex and 1984L about 25-35 days after explosion, displaying prominent He I, Fe II, Ca II H & K and the near-IR triplet P Cygni lines. Except for the strongest lines, He I absorptions are blueshifted by 6500 km s −1 , and Fe II by ∼ 7500 − 8000 km s −1 . No other SNe Ib have been reported to have their Fe II absorptions blueshifted more than their He I absorptions. Relatively weak Hα and very weak Hβ may also exist, blueshifted by ∼ 15, 000 km s −1 . We suggest that SN 2005bf was the explosion of a massive He star, possibly with a trace of a hydrogen envelope. Subject headings: supernovae: general supernovae: individual (SN 2005bf) technique: photometric technique: spectroscopic line: identification 1 gca@iiap.res.in 2 dks@crest.e rnet.in 3 jsdeng@bao.ac.cn
We present a theoretical model for Type Ib supernova (SN) 2006jc. We calculate the evolution of the progenitor star, hydrodynamics and nucleosynthesis of the SN explosion, and the SN bolometric light curve (LC). The synthetic bolometric LC is compared with the observed bolometric LC constructed by integrating the UV, optical, near-infrared (NIR), and mid-infrared (MIR) fluxes. The progenitor is assumed to be as massive as 40M ⊙ on the zero-age main-sequence. The star undergoes extensive mass loss to reduce its mass down to as small as 6.9M ⊙ , thus becoming a WCO Wolf-Rayet star. The WCO star model has a thick carbon-rich layer, in which amorphous carbon grains can be formed. This could explain the NIR brightening and the dust feature seen in the MIR spectrum. We suggest that the progenitor of SN 2006jc is a WCO Wolf-Rayet star having undergone strong mass loss and such massive stars are the important sites of dust formation. We derive the parameters of the explosion model in order to reproduce the bolometric LC of SN 2006jc by the radioactive decays: the ejecta mass 4.9M ⊙ , hypernova-like explosion energy 10 52 ergs, and ejected 56 Ni mass 0.22M ⊙ . We also calculate the circumstellar interaction and find that a CSM with a flat density structure is required to reproduce the X-ray LC of SN 2006jc. This suggests a drastic change of the mass-loss rate and/or the wind velocity that is consistent with the past luminous blue variable (LBV)-like event.
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