Seppo Mattila

A giant outburst two years before the core-collapse of a massive star

The death of massive stars produces a variety of supernovae, which are linked to the structure of the exploding stars. The detection of several precursor stars of type II supernovae has been reported (see, for example, ref. 3), but we do not yet have direct information on the progenitors of the hydrogen-deficient type Ib and Ic supernovae. Here we report that the peculiar type Ib supernova SN 2006jc is spatially coincident with a bright optical transient that occurred in 2004. Spectroscopic and photometric monitoring of the supernova leads us to suggest that the progenitor was a carbon-oxygen Wolf–Rayet star embedded within a helium-rich circumstellar medium. There are different possible explanations for this pre-explosion transient. It appears similar to the giant outbursts of luminous blue variable stars (LBVs) of 60–100 solar masses, but the progenitor of SN 2006jc was helium- and hydrogen-deficient (unlike LBVs). An LBV-like outburst of a Wolf–Rayet star could be invoked, but this would be the first observational evidence of such a phenomenon. Alternatively, a massive binary system composed of an LBV that erupted in 2004, and a Wolf–Rayet star exploding as SN 2006jc, could explain the observations.

Supernova 2002bo: inadequacy of the single parameter description

We present optical photometry and optical/near-infrared spectra of the type Ia SN 2002bo spanning epochs from -13 days before maximum B-band light to +102 days after. The pre-maximum optical coverage is particularly complete. The extinction de- duced from the observed colour evolution and from interstellar NaID absorption is quite high viz. E(B V ) = 0.43 ± 0.10. On the other hand, model matches to the observed spectra point to a lower reddening (E(B V ) � 0.30). In some respects, SN 2002bo behaves as a typical Branch normal type Ia supernova (SN Ia) at opti- cal and IR wavelengths. We find a B-band risetime of 17.9±0.5 days, am15(B) of 1.13±0.05, and a de-reddened MB = 19.41±0.42. However, comparison with other type Ia supernovae having similarm15(B) values indicates that in other respects SN 2002bo is unusual. While the optical spectra of SN 2002bo are very similar to those of SN 1984A (�m15(B) = 1.19), lower velocities and a generally more structured ap- pearance are found in SNe 1990N, 1994D and 1998bu. For supernovae havingm15(B) > 1.2, we confirm the variation of R(SiII) (Nugent et al. 1995) withm15(B). How- ever, for supernovae such as SN 2002bo, with lower values ofm15(B) the relation breaks down. Moreover, the evolution of R(SiII) for SN 2002bo is strikingly differ- ent from that shown by other type Ia supernovae. The velocities of SN 2002bo and 1984A derived from SII 5640u SiII 6355u and CaII H&K lines are either much higher and/or evolve differently from those seen in other normal SNe Ia events. Thus, while SN 2002bo and SN 1984A appear to be highly similar, they exhibit behaviour which is distinctly different from other SNe Ia having similarm15(B) values. We suggest that the unusually low temperature, the presence of high-velocity intermediate-mass elements and the low abundance of carbon at early times indicates that burning to Si penetrated to much higher layers than in more normal type Ia supernovae. This may be indicative of a delayed-detonation explosion.

Ultra-bright optical transients are linked with type IC supernovae.

Recent searches by unbiased, wide-field surveys have uncovered a group of extremely luminous optical transients. The initial discoveries of SN 2005ap by the Texas Supernova Search and SCP-06F6 in a deep Hubble pencil beam survey were followed by the Palomar Transient Factory confirmation of host redshifts for other similar transients. The transients share the common properties of high optical luminosities (peak magnitudes ~-21 to -23), blue colors, and a lack of H or He spectral features. The physical mechanism that produces the luminosity is uncertain, with suggestions ranging from jet-driven explosion to pulsational pair instability. Here, we report the most detailed photometric and spectral coverage of an ultra-bright transient (SN 2010gx) detected in the Pan-STARRS 1 sky survey. In common with other transients in this family, early-time spectra show a blue continuum and prominent broad absorption lines of O II. However, about 25 days after discovery, the spectra developed type Ic supernova features, showing the characteristic broad Fe II and Si II absorption lines. Detailed, post-maximum follow-up may show that all SN 2005ap and SCP-06F6 type transients are linked to supernovae Ic. This poses problems in understanding the physics of the explosions: there is no indication from late-time photometry that the luminosity is powered by 56Ni, the broad light curves suggest very large ejected masses, and the slow spectral evolution is quite different from typical Ic timescales. The nature of the progenitor stars and the origin of the luminosity are intriguing and open questions.

High-Velocity Features: A Ubiquitous Property of Type Ia Supernovae

Evidence of high-velocity features (HVFs) such as those seen in the near-maximum spectra of some Type Ia supernovae (SNe Ia; e.g., SN 2000cx) has been searched for in the available SN Ia spectra observed earlier than 1 week before B maximum. Recent observational efforts have doubled the number of SNe Ia with very early spectra. Remarkably, all SNe Ia with early data (seven in our Research Training Network sample and 10 from other programs) show signs of such features, to a greater or lesser degree, in Ca II IR and some also in the Si II λ6355 line. HVFs may be interpreted as abundance or density enhancements. Abundance enhancements would imply an outer region dominated by Si and Ca. Density enhancements may result from the sweeping up of circumstellar material (CSM) by the highest velocity SN ejecta. In this scenario, the high incidence of HVFs suggests that a thick disk and/or a high-density companion wind surrounds the exploding white dwarf, as may be the case in single degenerate systems. Large-scale angular fluctuations in the radial density and abundance distribution may also be responsible: this could originate in the explosion and would suggest a deflagration as the more likely explosion mechanism. CSM interaction and surface fluctuations may coexist, possibly leaving different signatures on the spectrum. In some SNe, the HVFs are narrowly confined in velocity, suggesting the ejection of blobs of burned material.

SN 2003du: 480 days in the life of a normal type Ia supernova

Aims. We present a study of the optical and near-infrared (NIR) properties of the Type Ia Supernova (SN Ia) 2003du. Methods. An extensive set of optical and NIR photometry and low-resolution long-slit spectra was obtained using a number of facilities. The observations started 13 days before B -band maximum light and continued for 480 days with exceptionally good time sampling. The optical photometry was calibrated through the S-correction technique. Results. The

A Spitzer Space Telescope study of SN 2003gd: Still no direct evidence that core-collapse supernovae are major dust factories

{it UBVRIJHK}

Early and late time VLT spectroscopy of SN 2001el - progenitor constraints for a type Ia supernova

light curves and the color indices of SN 2003du closely resemble those of normal SNe Ia. SN 2003du reached a B -band maximum of 13.49 ± 0.02 mag on JD2 452 766.38 ± 0.5. We derive a B -band stretch parameter of

Massive Stars Exploding in a He-Rich Circumstellar Medium -- I. Type Ibn (SN 2006jc-Like) Events

0.988 pm0.003

SN 2009jf: A slow-evolving stripped-envelope core-collapse supernova

, which corresponds to

Massive stars exploding in a He-rich circumstellar medium – III. SN 2006jc: infrared echoes from new and old dust in the progenitor CSM

Delta m_{15}=1.02,pm0.05