SN 1998A: explosion of a blue supergiant (original) (raw)
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Early time optical spectroscopy of supernova SN 1998S
Astronomy and Astrophysics, 2001
We present medium-resolution optical spectra of the type II supernova SN 1998S obtained during the pre-maximum, maximum and early decline phases. The early decline spectra show complex Balmer line profiles: a narrow P-Cygni emission feature superimposed on a broad emission. The narrow emission has a redshift similar to that of the host galaxy, indicating its origin from a pre-supernova circumstellar material. The Hα luminosity of the broad component implies a shell mass of ∼0.1 M for the supernova ejecta, while the luminosity of the narrow component implies a mass loss rate of 10 −4 M yr −1 for the precursor. The photospheric temperature of the supernova shell decreased from a value of 18 400 ± 2900 K on day 17 to a value of 7500 ± 1200 K on day 44. The observations indicate SN 1998S belongs to type IIn supernovae where the supernova ejecta dynamically interact with a pre-supernova circumstellar material.
The Progenitor of Supernova 1993J Revisited
Publications of the Astronomical Society of the Pacific, 2002
From Hubble Space Telescope images with 0. ′′ 05 resolution we identify four stars brighter than V = 25 mag within 2. ′′ 5 of SN 1993J in M81 which contaminated previous ground-based brightness estimates for the supernova progenitor. Correcting for the contamination, we find that the energy distribution of the progenitor is consistent with that of an early K-type supergiant star with M V ≈ −7.0 ± 0.4 mag and an initial mass of 13-22 M ⊙ . The brightnesses of the nearby stars are sufficient to account for the excess blue light seen from the ground in pre-explosion observations. Therefore, the SN 1993J progenitor did not necessarily have a blue companion, although by 2001, fainter blue stars are seen in close proximity to the supernova. These observations do not strongly limit the mass of a hypothetical companion. A blue dwarf star with a mass up to 30 M ⊙ could have been orbiting the progenitor without being detected in the ground-based images. Explosion models and observations show that the SN 1993J progenitor had a helium-rich envelope. To test whether the helium abundance could influence the energy distribution of the progenitor, we calculated model supergiant atmospheres with a range of plausible helium abundances. The models show that the pre-supernova colors are not strongly affected by the helium abundance longward of 4000Å, and abundances ranging between solar and 90% helium (by number) are all consistent with the observations.
Monthly Notices of the Royal Astronomical Society
Photometric and spectroscopic data for two Low Luminosity Type IIP Supernovae (LL SNe IIP) 2020cxd and 2021aai are presented. SN 2020cxd was discovered 2 d after explosion at an absolute magnitude of Mr = −14.02 ± 0.21 mag, subsequently settling on a plateau which lasts for ∼120 d. Through the luminosity of the late light curve tail, we infer a synthesized 56Ni mass of (1.8 ± 0.5) × 10−3 M⊙. During the early evolutionary phases, optical spectra show a blue continuum ($T\, \gt 8000K)withbroadBalmerlinesdisplayingaPCygniprofile,whileatlaterphases,Caii,Feii,Scii,andBaiilinesdominatethespectra.Hydrodynamicalmodellingoftheobservablesyields8000 K) with broad Balmer lines displaying a P Cygni profile, while at later phases, Ca ii, Fe ii, Sc ii, and Ba ii lines dominate the spectra. Hydrodynamical modelling of the observables yields 8000K)withbroadBalmerlinesdisplayingaPCygniprofile,whileatlaterphases,Caii,Feii,Scii,andBaiilinesdominatethespectra.HydrodynamicalmodellingoftheobservablesyieldsR\, \simeq$ 575 R⊙ for the progenitor star, with Mej = 7.5 M⊙ and E,simeqE\, \simeqE,simeq 0.097 foe emitted during the explosion. This low-energy event originating from a low-mass progenitor star is compatible with both the explosion of a red supergiant (RSG) star and with an Electron Capture Supernova arising from a super asy...
The Type II supernovae 2006V and 2006au: two SN 1987A-like events
Astronomy & Astrophysics, 2012
Context. Supernova 1987A revealed that a blue supergiant (BSG) star can end its life as a core-collapse supernova (SN). SN 1987A and other similar objects exhibit properties that distinguish them from ordinary Type II Plateau (IIP) SNe, whose progenitors are believed to be red supergiants (RSGs). Similarities among 1987A-like events include a long rise to maximum, early luminosity fainter than that of normal Type IIP SNe, and radioactivity acting as the primary source powering the light curves. Aims. We present and analyze two SNe monitored by the Carnegie Supernova Project that are reminiscent of SN 1987A. Methods. Optical and near-infrared (NIR) light curves, and optical spectroscopy of SNe 2006V and 2006au are presented. These observations are compared to those of SN 1987A, and are used to estimate properties of their progenitors. Results. Both objects exhibit a slow rise to maximum and light curve evolution similar to that of SN 1987A. At the earliest epochs, SN 2006au also displays an initial dip which we interpret as the signature of the adiabatic cooling phase that ensues shock breakout. SNe 2006V and 2006au are both found to be bluer, hotter and brighter than SN 1987A. Spectra of SNe 2006V and 2006au are similar to those of SN 1987A and other normal Type II objects, although both consistently exhibit expansion velocities higher than SN 1987A. Semi-analytic models are fit to the UVOIR light curve of each object from which physical properties of the progenitors are estimated. This yields ejecta mass estimates of Mej ≈ 20 M⊙, explosion energies of E ≈ 2 − 3 × 10 51 erg, and progenitor radii of R ≈ 75 − 100 R⊙ for both SNe. Conclusions. The progenitors of SNe 2006V and 2006au were most likely BSGs with a larger explosion energy as compared to that of SN 1987A.
Optical Photometry and Spectroscopy of the SN 1998bw-like Type Ic Supernova 2002ap
Publications of The Astronomical Society of The Pacific, 2003
We present optical photometric and spectral data of the peculiar Type Ic SN 2002ap. Photometric coverage includes UBVRI bands from 2002 January 30, the day after discovery, through 2002 December 12. There are 5 early-time spectra and 8 in the nebular phase. We determine that SN 2002ap is similar to SN 1997ef and the GRB-associated SN 1998bw with respect to spectral and photometric characteristics. The nebular spectra of SN 2002ap present the largest Mg I] \lambda 4571 to [O I] \lambda \lambda 6300, 6364 ratio of any supernova spectra yet published, suggesting that the progenitor of SN 2002ap was a highly stripped star. Comparing the nebular spectra of SN 1985F and SN 2002ap, we notice several similar features, casting the classification of SN 1985F as a normal Type Ib supernova in doubt. We also present nebular modeling of SN 2002ap and find that the object ejected >~ 1.5 M_{sun} of material within the outer velocity shell of the nebula (~5500 km/s) and synthesized ~0.09 M_{sun} of 56Ni.
Spectrum Analysis of Type IIb Supernova 1996cb
We analyze a time series of optical spectra of SN 1993J-like supernova 1996cb, from 14 days before maximum to 86 days after that, with a parameterized supernova synthetic-spectrum code SYNOW. Detailed line identification are made through fitting the synthetic spectra to observed ones. The derived photospheric velocity, decreasing from 11, 000 km s −1 to 3, 000 km s −1 , gives a rough estimate of the ratio of explosion kinetic energy to ejecta mass, i.e. E/M ej ∼ 0.2 − 0.5 × 10 51 ergs/M ej (M ⊙ ). We find that the minimum velocity of hydrogen is ∼ 10, 000 km s −1 , which suggests a small hydrogen envelope mass of ∼ 0.02 − 0.1 M ej , or 0.1 − 0.2 M ⊙ if E is assumed 1 × 10 51 ergs. A possible Ni II absorption feature near 4000Å is identified throughout the epochs studied here and is most likely produced by primordial nickel. Unambiguous Co II features emerge from 16 days after maximum onward, which suggests that freshly synthesized radioactive material has been mixed outward to a velocity of at least 7, 000 km s −1 as a result of hydrodynamical instabilities. Although our synthetic spectra show that the bulk of the blueshift of [O I] λ5577 net emission, as large as ∼ 70Å at 9 days after maximum, is attributed to line blending, a still considerable residual ∼ 20Å remains till the late phase. It may be evidence of clumpy or large-scale asymmetric nature of oxygen emission region.
Spectral evolution of the peculiar Ic Supernova 1998bw
European Journal of Endocrinology, 2000
SN 1998bw holds the record for the most energetic Type Ic explosion, one of the brightest radio supenovae and probably the first supernova associated with a gamma-ray burst. In this paper we present spectral observations of SN 1998bw observed in a cooperative monitoring campaign using the AAT, UKST and the SSO 2.3-m telescope. We investigate the evolution of the spectrum between 7 and 94 days after V_band maximum in comparison to well-studied examples of Type Ic SNe in order to quantify the unusual properties of this supernova event. Though the early spectra differ greatly from the observations of classical Ic SNe, we find that the evolution from the photospheric to the nebular phases is slow but otherwise typical. The spectra differ predominantly in the extensive line blending and blanketing which has been attributed to the high velocity of the ejecta. We find that by day 19, the absorption line minima blueshifts are 10% - 50% higher than other SNe and on day 94 emission lines are 45% broader, as expected if the progenitor had a massive envelope. However, it is difficult to explain the extent of line blanketing entirely by line broadening, and we argue that additional contribution from other species is present, indicating unusual relative abundances or physical conditions in the envelope.
Supernova 1998bw – the final phases
Astronomy and Astrophysics, 2002
The probable association with GRB 980425 immediately put SN 1998bw at the forefront of supernova research. Here, we present revised late-time BV RI light curves of the supernova, based on template images taken at the VLT. To follow the supernova to the very last observable phases we have used HST /STIS. Deep images taken in June and November 2000 are compared to images taken in August 2001. The identification of the supernova is firmly established. This allows us to measure the light curve to ∼1000 days past explosion. The main features are a rapid decline up to more than 500 days after explosion, with no sign of complete positron trapping from the 56 Co decay. Thereafter, the light curve flattens out significantly. One possible explanation is powering by more long lived radioactive isotopes, if they are abundantly formed in this energetic supernova.