اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدEarly-Phase Spectra of Hypernova SN 2002ap
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The spectral evolution of the peculiar SN Ic 2002ap during the first 40 days is presented. The spectra display very broad absorption features, which are typical of hypernovae. The maximum expansion velocity measured on the earliest spectra exceeds 3 times 10^4 km s^{-1}. The spectrum of SN 2002ap at the epoch of maximum brightness resembles that of SN 1997ef more than that of SN 1998bw. The spectral evolution of SN 2002ap proceeds at about 1.5 times the rate of SN 1997ef. The parameterized supernova spectrum synthesis code SYNOW was used to perform line identification and deduce velocity information from the early-phase spectra, which are heavily affected by line blending. The photospheric velocity, as deduced from the fitting results and from the blueshift of the ion{Si}{2} lambda 6355 absorption minimum, is lower than in previously studied hypernovae. At advanced epochs, the ion{Si}{2} lambda 6355 absorption minimum becomes difficult to distinguish. This may be caused by the growth of [ion{O}{1}] lambda lambda 6300, 6364 emission. Together with the rapid spectral evolution, this suggests that SN 2002ap should enter the nebular phase sooner than previously studied hypernovae.
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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 hy
pernova SN 1997ef. However, its kinetic energy [$sim (4-10) times 10^{51}$ erg] and the mass ejected (2.5-5 $M_{odot}$) are smaller, resulting in a faster-evolving light curve. The SN synthesized $sim 0.07 M_{odot}$ of $^{56}$Ni, 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 a high kinetic energy. The likely main-sequence mass of the progenitor star was 20-25 $M_{odot}$, which is also lower than that of both hypernovae SNe 1997ef and 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 summer 2002, are necessary to confirm these values.
The supernova SN 2002ap was discovered in the outer regions of the nearby spiral M74 on January 29.4 UT. Early photometric and spectroscopic observations indicate the supernova belongs to the class of Ic hypernova. Late time (After JD 2452500) light
curve decay slopes are similar to that of the hypernovae SN 1997ef and SN 1998bw. We present here the $BVRI$ photometric light curves and colour evolutions of SN 2002ap to investigate the late time nature of the light curve.
The nebular spectra of the broad-lined, SN 1998bw-like Type Ic SN 2002ap are studied by means of synthetic spectra. Two different modelling techniques are employed. In one technique, the SN ejecta are treated as a single zone, while in the other a de
nsity and abundance distribution in velocity is used from an explosion model. In both cases, heating caused by gamma-ray and positron deposition is computed (in the latter case using a Monte Carlo technique to describe the propagation of gamma-rays and positrons), as is cooling via forbidden-line emission. The results are compared, and although general agreement is found, the stratified models are shown to reproduce the observed line profiles much more accurately than the single-zone model. The explosion produced ~ 0.1 Msun of 56Ni. The distribution in velocity of the various elements is in agreement with that obtained from the early-time models, which indicated an ejected mass of ~ 2.5 Msun with a kinetic energy of 4 x 10^{51} erg. Nebular spectroscopy confirms that most of the ejected mass (~ 1.2 Msun) was oxygen. The presence of an oxygen-rich inner core, combined with that of 56Ni at high velocities as deduced from early-time models, suggests that the explosion was asymmetric, especially in the inner part.
We present spectropolarimetry of the Type Ic supernova SN 2002ap and give a preliminary analysis: the data were taken at two epochs, close to and one month later than the visual maximum (2002 February 8). In addition we present June 9 spectropolarime
try without analysis. The data show the development of linear polarization. Distinct polarization profiles were seen only in the O I lambda 7773 multiplet/Ca II IR triplet absorption trough at maximum light and in the Ca II IR triplet absorption trough a month later, with the latter showing a peak polarization as high as ~2 %. The intrinsic polarization shows three clear position angles: 80 degs for the February continuum, 120 degs for the February line feature, and 150 degs for the March data. We conclude that there are multiple asymmetric components in the ejecta. We suggest that the supernova has a bulk asymmetry with an axial ratio projected on the sky that is different from 1 by of order 10 %. Furthermore, we suggest very speculatively that a high velocity ejecta component moving faster than ~0.115c (e.g., a jet) contributes to polarization in the February epoch.
Optical and near-infrared photometry and optical spectroscopy are reported for SN 2003bg, starting a few days after explosion and extending for a period of more than 300 days. Our early-time spectra reveal the presence of broad, high-velocity Balmer
lines. The nebular-phase spectra, on the other hand, show a remarkable resemblance to those of Type Ib/c supernovae, without clear evidence for hydrogen. Near maximum brightness SN 2003bg displayed a bolometric luminosity comparable to that of other Type I hypernovae unrelated to gamma-ray bursts, implying a rather normal amount of 56Ni production (0.1-0.2 Msun) compared with other such objects. The bolometric light curve of SN 2003bg, on the other hand, is remarkably broad, thus suggesting a relatively large progenitor mass at the moment of explosion. These observations, together with the large value of the kinetic energy of expansion established in the accompanying paper (Mazzali et al. 2009), suggest that SN 2003bg can be regarded as a Type IIb hypernova.
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