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Register a new userSpectropolarimetry of the Type Ib/c SN 2005bf
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J.R. Maund
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We present spectropolarimetric observations of the peculiar Type Ib/c SN 2005bf, in MCG+00-27-005, from 3600-8550AA. The SN was observed on 2005 April 30.9, 18 days after the first B-band light-curve maximum and 6 days before the second B-band light-curve maximum. The degree of the Interstellar Polarization, determined from depolarized emission lines in the spectrum, is found to be large with $p_{max}(ISP)=1.6%$ and $theta(ISP)=149$fdg$7pm4.0$, but this may be an upper limit on the real value of the ISP. After ISP subtraction, significant polarization is observed over large wavelength regions, indicating a significant degree of global asymmetry, $gtrsim 10%$. Polarizations of 3.5% and 4% are observed for absorption components of Ca II H&K and IR triplet, and 1.3% for He I 5876AA and Fe II. On the $Q-U$ plane clear velocity-dependent loop structure is observed for the He I 5876AA line, suggestive of departures from an axial symmetry and possible clumping of the SN ejecta. Weak High Velocity components of $mathrm{Halpha}$, $mathrm{Hbeta}$ and $mathrm{Hgamma}$ are observed, with velocities of -15 000kms. The low degree of polarization observed at H$beta$ suggests that the polarization observed for the other Balmer lines ($sim 0.4%$ above the background polarization) may rather be due to blending of $mathrm{Halpha}$ and $mathrm{Hgamma}$ with polarized Si II and Fe II lines, respectively. We suggest a model in which a jet of material, that is rich in $mathrm{^{56}Ni}$, has penetrated the C-O core, but not the He mantle. The jet axis is tilted with respect to the axis of the photosphere. This accounts for the lack of significant polarization of O I 7774AA, the delayed excitation and, hence, observability of He I and, potentially, the varied geometries of He and Ca.
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Aims: To gain better insight on the physics of stripped-envelope core-collapse supernovae through studying their environments. Methods: We obtained low-resolution optical spectroscopy with the New Technology Telescope (+ EFOSC2) at the locations of 20 Type Ib/c supernovae. We measure the flux of emission lines in the stellar-continuum-subtracted spectra from which local metallicities are computed. For the supernova regions we estimate both the mean stellar age, interpreting the stellar absorption with population synthesis models, and the age of the youngest stellar populations using the H-alpha equivalent width as an age indicator. These estimates are compared with the lifetimes of single massive stars. Results: Based on our sample, we detect a tentative indication that Type Ic supernovae might explode in environments that are more metal-rich than those of Type Ib supernovae (average difference of 0.08 dex), but this is not a statistically significant result. The lower limits placed on the ages of the supernova birthplaces are overall young, although there are several cases where these appear older than what is expected for the evolution of single stars more massive than 25-30 M_{sun}. This is only true, however, assuming that the supernova progenitors were born during an instantaneous (not continuous) episode of star formation. Conclusions: These results do not conclusively favor any of the two evolutionary paths (single or binary) leading to stripped supernovae. We do note a fraction of events for which binary evolution is more likely, due to their associated age limits. The fact, however, that the supernova environments contain areas of recent (< 15 Myr) star formation and that the environmental metallicities are, at least, not against the single evolutionary scenario, suggest that this channel is also broadly consistent with the observations.
The supernovae of Type Ibc are rare and the detailed characteristics of these explosions have been studied only for a few events. Unlike Type II SNe, the progenitors of Type Ibc have never been detected in pre-explosion images. So, to understand the nature of their progenitors and the characteristics of the explosions, investigation of proximate events are necessary. Here we present the results of multi-wavelength observations of Type Ib SN 2007uy in the nearby ($sim$ 29.5 Mpc) galaxy NGC 2770. Analysis of the photometric observations revealed this explosion as an energetic event with peak absolute R band magnitude $-18.5pm0.16$, which is about one mag brighter than the mean value ($-17.6pm0.6$) derived for well observed Type Ibc events. The SN is highly extinguished, E(B-V) = 0.63$pm$0.15 mag, mainly due to foreground material present in the host galaxy. From optical light curve modeling we determine that about 0.3 M$_{odot}$ radioactive $^{56}$Ni is produced and roughly 4.4 M$_{odot}$ material is ejected during this explosion with liberated energy $sim 15times10^{51}$ erg, indicating the event to be an energetic one. Through optical spectroscopy, we have noticed a clear aspheric evolution of several line forming regions, but no dependency of asymmetry is seen on the distribution of $^{56}$Ni inside the ejecta. The SN shock interaction with the circumburst material is clearly noticeable in radio follow-up, presenting a Synchrotron Self Absorption (SSA) dominated light curve with a contribution of Free Free Absorption (FFA) during the early phases. Assuming a WR star, with wind velocity $ga 10^3 {rm km s}^{-1}$, as a progenitor, we derive a lower limit to the mass loss rate inferred from the radio data as $dot{M} ga 2.4times10^{-5}$ M$_{odot}$, yr$^{-1}$, which is consistent with the results obtained for other Type Ibc SNe bright at radio frequencies.
We present the photometric and spectroscopic evolution of supernova (SN) 2019cad during the first $sim100$ days from explosion. Based on the light curve morphology, we find that SN 2019cad resembles the double-peaked type Ib/c SN 2005bf and the type Ic PTF11mnb. Unlike those two objects, SN 2019cad also shows the initial peak in the redder bands. Inspection of the g-band light curve indicates the initial peak is reached in $sim8$ days, while the r band peak occurred $sim15$ days post-explosion. A second and more prominent peak is reached in all bands at $sim45$ days past explosion, followed by and fast decline from $sim60$ days. During the first 30 days, the spectra of SN 2019cad show the typical features of a type Ic SN, however, after 40 days, a blue continuum with prominent lines of Si II ${lambda}6355$ and C II ${lambda}6580$ is observed again. Comparing the bolometric light curve to hydrodynamical models, we find that SN 2019cad is consistent with a pre-SN mass of 11 M$_{odot}$, and an explosion energy of $3.5times 10^{51}$ erg. The light curve morphology can be reproduced either by a double-peaked $^{56}$Ni distribution with an external component of 0.041 M$_{odot}$ and an internal component of 0.3 M$_{odot}$ or a double-peaked $^{56}$Ni distribution plus magnetar model (P $sim11$ ms and B $sim26times 10^{14}$ G). If SN 2019cad were to suffer from significant host reddening (which cannot be ruled out), the $^{56}$Ni model would require extreme values, while the magnetar model would still be feasible.
We present BVRI 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}=-18.0pm 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_{sun} of 56Ni, 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, and Fe II by ~7500-8000 km/s. No other SNe Ib have been reported to have their Fe II absorptions blueshifted more than their He I absorptions. Relatively weak H-alpha and very weak H-beta may also exist, blueshifted by ~15,000 km/s. We suggest that SN 2005bf was the explosion of a massive He star, possibly with a trace of a hydrogen envelope.
We present the photometric and spectroscopic studies of a Type Ib SN 2015ap and a Type Ic SN 2016P. SN 2015ap is one of the bright (M$_{V}$ = $-$18.04 mag) Type Ib while SN 2016P lies at an average value among the Type Ic SNe (M$_{V}$ = $-$17.53 mag). Bolometric light curve modelling of SNe 2015ap and 2016P indicates that both the SNe are powered by $^{56}$Ni + magnetar model with $^{56}$Ni masses of 0.01 M$_{odot}$ and 0.002 M$_{odot}$, ejecta masses of 3.75 M$_{odot}$ and 4.66 M$_{odot}$, spin period P$_{0}$ of 25.8 ms and 36.5 ms and magnetic field B$_{p}$ of 28.39 $times$ 10$^{14}$ Gauss and 35.3 $times$ 10$^{14}$ Gauss respectively. The early spectra of SN 2015ap shows prominent lines of He with a W feature due to Fe complexes while other lines of Mg II, Na I and Si II are present in both SNe 2015ap and 2016P. Nebular phase [O I] profile indicates an asymmetric profile in SN 2015ap. The [O I]/[Ca II] ratio and nebular spectral modelling of SN 2015ap hints towards a progenitor mass between 12 $-$ 20 M$_{odot}$.
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