[vsnet-grb-info 2972] GRB 060218: emergence of the underlying SN spectrum

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4809
SUBJECT: GRB 060218: emergence of the underlying SN spectrum
DATE:    06/02/22 01:06:34 GMT
FROM:    Alberto Castro-Tirado at Inst.de Astro. de Andalucia  <ajct at iaa.es>

T. A. Fatkhullin, V. V. Sokolov, A. V. Moiseev (SAO-RAS Nizhnij Arkhyz),
S. Guziy and A. J. Castro-Tirado (IAA-CSIC Granada), on behalf
of a larger collaboration, report:

"We have obtained optical spectroscopy of the GRB 060218 optical
counterpart (Cusumano et al. GCNC 4775) with the 6.0m BTA telescope
of SAO-RAS in Zelenchuk, equipped with SCORPIO. First epoch
spectroscopy in the 3500-7500 A range was obtained on Feb 20.65 UT,
confirming z = 0.033 (Mirabal and Halpern GCNC 4792). Second epoch
data was gathered on Feb 21.65 UT.  Comparison between the two datasets
clearly reveals continuum variations that we interpret as the emergence
of the underlying type-Ic SN spectrum, strengthening the SN-GRB 060218
relationship first suggested by Masetti et al. (GCNC 4803).  In
particular, an "emission peak" at ~4500 A is showing up, possibly as
a result of the blending of the Fe lines redward of this feature,
giving rise to a broad absorption trough, as it was seen in the type
Ic SNe 1997ef (Iwamoto et al. 2000, ApJ 534, 660) and 2002ap (Foley
et al. 2003,  PASP 115, 1220). Further spectroscopic observations are
encouraged."