Study of Envelope Velocity Evolution of Type Ib-c Core-Collapse Supernovae from Observations of XRF 080109 / SN 2008D and GRB 060218 / SN 2006aj with BTA

TL;DR

This study models the spectral evolution of two core-collapse supernovae associated with X-ray and gamma-ray transients, revealing envelope velocity patterns and supporting the presence of stellar envelopes through spectral line analysis.

Contribution

It provides new insights into the envelope velocity evolution of Type Ib-c supernovae using spectral modeling of SN 2008D and SN 2006aj.

Findings

Confirmation of envelope presence via velocity agreement of hydrogen and helium lines.

Detection of P Cyg profiles supporting the envelope hypothesis.

Empirical velocity drop law consistent with classic core-collapse supernovae.

Abstract

Results of modeling the spectra of two supernovae SN 2008D and SN 2006aj related to the X-ray flash XRF 080109 and gamma-ray burst GRB / XRF 060218, respectively, are studied. The spectra were obtained with the 6-meter BTA telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences in 6.48 and 27.61 days after the explosion of SN 2008D, and in 2.55 and 3.55 days after the explosion of SN 2006aj. The spectra were interpreted in the Sobolev approximation with the SYNOW code. An assumption about the presence of envelopes around the progenitor stars is confirmed by an agreement between the velocities of lines interpreted as hydrogen and helium, and the empiric power-law velocity drop with time for the envelopes of classic core-collapse supernovae. Detection of a P Cyg profile of the H-beta line in the spectra of optical afterglows of GRBs can be a determinative argument in favor of this hypothesis.