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Abstract:

Although there is strong support for the collapsar engine as the power source of long-duration gamma-ray bursts (GRBs), we still do not definitively know the progenitor of these explosions. Here we review the current set of progenitor scenarios for long-duration GRBs and the observational constraints on these scenarios. Examining these, we find that single-star models cannot be the only progenitor for long-duration GRBs. Several binary progenitors can match the solid observational constraints and also have the potential to match the trends we are currently seeing in the observations. Type Ib/c supernovae are also likely to be produced primarily in binaries; we discuss the relationship between the progenitors of these explosions and those of the long-duration GRBs.

Abstract:

Context. The nature of the companion stars in type Ia Supernova (SNe) progenitor systems remains unclear. One possible way to discriminate between different scenarios is the presence (or absence) of circumstellar material, the left overs from the progenitor evolution that may be revealed by their interaction with the SN. Aims. A new method to probe the circumstellar environment has been exploited for the normal type Ia SN 2006X, leading for the first time to the direct detection of material which escaped the progenitor system. In this paper we apply the same analysis to the peculiar type Ia SN 2000cx, with the aim of constraining the properties of its progenitor system. Methods. Using multi-epoch, high-resolution spectroscopy we have studied the spectral region where narrow, time-variable Na ID absorption features are expected in case circumstellar material is present along the line of sight. Results. No Na ID absorption is detected in the rest-frame of the host galaxy to a level of a few mÂ, setting a stringent upper limit to the column density of the absorbing material (N(NaI) < 2 × 1010 cm -2). Conclusions. In this respect the peculiar type Ia SN 2000cx is different from the normal Ia SN 2006X. Whether this is to be attributed to a different progenitor system, to viewing-angle effects or to a low metallicity remains to be clarified. © ESO 2007.

Abstract:

The nature of the companion stars in Type Ia Supernova (SNe) progenitor systems remains unclear. One possible way to discriminate between different scenarios is the presence (or absence) of circumstellar material, the left overs from the progenitor evolution that may be revealed by their interaction with the SN. A new method to probe the circumstellar environment has been exploited for the normal Type Ia SN 2006X, leading for the first time to the direct detection of material which escaped the progenitor system. In this paper we apply the same analysis to the peculiar Type Ia SN 2000cx, with the aim of constraining the properties of its progenitor system. Using multi-epoch, high-resolution spectroscopy we have studied the spectral region where narrow, time-variable NaID absorption features are expected in case circumstellar material is present along the line of sight. No NaID absorption is detected in the rest-frame of the host galaxy to a level of a few mA, setting a stringent upper limit to the column density of the absorbing material (N(NaI)<=2 x 10^10 cm-2). In this respect the peculiar Type Ia SN 2000cx is different from the normal Ia SN 2006X. Whether this is to be attributed to a different progenitor system, to viewing-angle effects or to a low metallicity remains to be clarified.

Abstract:

Type Ia supernovae are important cosmological distance indicators. Each of these bright supernovae supposedly results from the thermonuclear explosion of a white dwarf star that, after accreting material from a companion star, exceeds some mass limit, but the true nature of the progenitor star system remains controversial. Here we report the spectroscopic detection of circumstellar material in a normal type Ia supernova explosion. The expansion velocities, densities, and dimensions of the circumstellar envelope indicate that this material was ejected from the progenitor system. In particular, the relatively low expansion velocities suggest that the white dwarf was accreting material from a companion star that was in the red-giant phase at the time of the explosion.