[vsnet-grb-info 10052] GRB 101225A: MMT spectroscopy

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  11507
SUBJECT: GRB 101225A: MMT spectroscopy
DATE:    10/12/29 23:09:32 GMT
FROM:    Ryan Chornock at Harvard  <rchornock at cfa.harvard.edu>

R. Chornock, G. H. Marion, G. Narayan, E. Berger, and A. M. Soderberg 
(Harvard/CfA) report:

We obtained spectroscopy of the optical source (Xu et al., GCN 11495; Xu 
et al., GCN 11496; Siegel et al., GCN 11499; Wiersema et al., 11502; 
Thoene et al., 11503; Cenko et al., 11506) associated with GRB 101225A 
(Racusin et al., GCN 11493) using the Blue Channel Spectrograph on the 
6.5-m MMT.  Two 2400 s observations starting on December 29.1 UT covered 
the spectral range 3175-8385 Angstroms.  The source has a smooth blue 
continuum and no clear emission or absorption features associated with a 
host galaxy are detected in our spectra, similar to the findings of 
Wiersema et al. (GCN 11502).  In addition, the continuum has no obvious 
broad undulations or evidence for line blanketing shortward of 4000 
Angstroms, such as would be expected if the spectral features of a 
supernova were emerging.  The spectrum is well fit by a power law of the 
form F_nu ~ constant * nu^(0.4), which is bluer than typical afterglow 
spectra, which typically scale as F_nu ~ nu^(-0.6).