Late Spectral Evolution of the Ejecta and Reverse Shock in SN1987A. (arXiv:1212.5052v1 [astro-ph.HE])

Late Spectral Evolution of the Ejecta and Reverse Shock in SN1987A. (arXiv:1212.5052v1 [astro-ph.HE]):
We present observations with VLT and HST of the broad emission lines from the
inner ejecta and reverse shock of SN 1987A from 1999 until 2012 (days 4381 --
9100 after explosion). We detect broad lines from H-alpha, H-beta, Mg I], Na I,
[O I], [Ca II] and a feature at 9220 A. We identify the latter line with Mg II
9218, 9244,most likely pumped by Ly-alpha fluorescence. H-alpha, and H-beta
both have a centrally peaked component, extending to 4500 km/s and a very broad
component extending to 11,000 km/s, while the other lines have only the central
component. The low velocity component comes from unshocked ejecta, heated
mainly by X-rays from the circumstellar ring collision, whereas the broad
component comes from faster ejecta passing through the reverse shock. The
reverse shock flux in H-alpha has increased by a factor of 4-6 from 2000 to
2007. After that there is a tendency of flattening of the light curve, similar
to what may be seen in soft X-rays and in the optical lines from the shocked
ring. The core component seen in H-alpha, [Ca II] and Mg II has experienced a
similar increase, consistent with that found from HST photometry. The ring-like
morphology of the ejecta is explained as a result of the X-ray illumination,
depositing energy outside of the core of the ejecta. The energy deposition in
the ejecta of the external X-rays illumination is calculated using explosion
models for SN 1987A and we predict that the outer parts of the unshocked ejecta
will continue to brighten because of this. We finally discuss evidence for dust
in the ejecta from line asymmetries.