TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  2169
SUBJECT: GRB 030329: Spectral Evolution of SN 2003dh
DATE:    03/04/25 02:57:32 GMT
FROM:    Krzysztof Z. Stanek at CfA  <kstanek@cfa.harvard.edu>

D. Zaritsky (U. Arizona), M. Bolte (UCSC), P. M. Garnavich (Notre
Dame), A. Z. Bonanos and K. Z. Stanek (CfA) report:

Spectra of the optical afterglow of GRB 030329 (Peterson & Price, GCN
1985; Torii: GCN 1986) and supernova 2003dh (Garnavich et al.  IAUC
8114) were obtained with the 6.5-m MMT on April 24.15 (UT) and with
the Keck-II telescope and ESI spectrograph on April 24.36. Preliminary
analysis of the spectra show broad peaks at 560 nm, 450 nm and a sharp
break in the continuum at 390 nm (all in the rest frame).

The spectrum continues to closely follow the development of SN~1998bw
(Patat et al. 2001, ApJ, 555, 900). The feature at 450 nm was not
present on spectra of SN 2003dh taken April 6 (Matheson et al. GCN
2107) and suggests a significantly lower photospheric velocity in the
current spectrum. SN 1998bw developed the 450 nm feature around
maximum light and this implies SN 2003dh is now at or past its
maximum.

The continuum of SN 2003dh is bluer than SN 1998bw at a similar phase,
which suggests that the afterglow light still contributes to the total
flux.

The April 24 MMT spectrum is available at:

http://www.nd.edu/~pgarnavi/grb030329_apr24.jpg

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